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r t r n r f r r an d r r nlijk

l raar ij d r t l r d h ik nd n h i h d k alit it r f r r ff l raar a - n nkr id l i r ti i i r f r r an r n a nin n ni r it it r f r ill r a nin n ni r it it r r r i - fri a r a k r nt lli r ran i t an t n Proefschrift t r rkrij in an d raad an d t r a an d r t r a nifi an a nin n ni r it it r f r r l an in h t n aar t rd di n rijda t r d na idda t r in d la an t n il q alit and ri r d ti it r l in ah lian irri ati n h h h i a nin n ni r it a nin n - ith r f r n - ith ari in n li h t h and r n h - - - rd z alkalini ati n n tri nt d fi i n i r ana nt far r kn l d a ritania rkina a ali n irri ati n h in th ah l ri i ld and r in int n it ar till far fr th ir t ntial and f th ar ld irri ati n h ri n d linin i ld h lar in t nt in irri ati n infra tr t r ad t i r f d rit t n rat in and t r d ri i rt ar rr ntl at tak an far r and r ar h r t d that th ri r d ti it r l i ht artl d t alt r lat d il d radati n ah lian irri ati n at r ntain littl alt t ar r lati l ri h in ar nat l n th h t and dr ah lian li at irri ati n ith h at r ld l ad t th f r ati n f an alkalin hi h and di hi h di nt nt il hi h ha a l r d ti it in ti at d th a f d linin ri r d ti it in th irri ati n h f l ita a ritania and th r all rkina a f nd that ri r d ti it r l in l ita r ri aril a d and d fi i n hil n d fi i n r ail d in th r all h n tri nt d fi i n i r a d n r in ffi i nt a li ati n f and n f rtili r in inati n ith l lant a aila l and n in th il h alkalin - al ar nat r f th t di d il lik l ntri t d t th l a aila ilit f thr h latili ati n and l a aila ilit f and n thr h r i itati n f r ad r ti n nt ar nat in ral li ati n f a l and n f rtili r in r a d i ld at th t d it fr t ha t t ha r th r q ir d h i al f rtili r ar ft n n i r n t a aila l n th l al ark t hi h ha r ad ti n f i r d f rtili r r ndati n th r r - r ah lian ri far r li ati n f r ani a nd nt a ri tra at a rat f t ha ft n i r d i ld at th t d it t ha n l ita th i ld in r a in ff t a attri t d t i r d a aila ilit hil in th r all r ani att r a nd nt i r d n tak lth h ri r d ti it r l rr lat d ith th alkalin - al ar nat r f th il f nd n id n that irri at d r in in r a d th alkalinit f th il n th ntrar thi t d and lit rat r r indi at that alkalinit r l r inh rit d fr th ar nt at rial and r fr th r l n d lti ati n f n n fl d d r t th t d it in a ritania and rkina a n ntrati n fa t r f irri ati n at r ar all r r d tail d t d in l ita h d that la ri il t ha a lar ff r a a it a ain t alkalini ati n d r d a at th han l i d r d ith in r a in alt n ntrati n in th il l ti n hi h l ad t a d r a in il l ti n alkalinit thr h r i itati n f al it n additi n irri at d ri lar l r nt th ild- f alkalin alt in th il r t n thr h r t n r ti n n a il l n trial in il fr l ita and th ffi d i r ali f nd that irri at d ri r in an d t r lai alkalin - di il r id d nat ral draina i i l h findin ar in lin ith r nt lit rat r n han in il nd r fl d d r in ali and i r i tra a nd nt a l rat d th r la ati n r n il that ntain d al it na r i d iti n f tra in r a d di l ti n f al it and n q ntl a in th il l ti n h a han d ith ad r d a and th latt r a l a h d t th r ith i - ar nat d ti n f ir n h dr id ld th r ti all l ad t f rr l i and a idifi ati n f th r h ri n t f nd that th r a f littl i rtan t th h rt t r alkalinit han f th t di d il CONTENTS ha t r I ha t r e e - e e e e - e e e e e e e ha t r e e e e e e e e e ha t r e e e e e e e - e e e e - e e e e e ha t r e - e e e e e e e e e z e ha t r e e e e e e e e e e ha t r f r n ar a n attin kn ld nt rri l ita Chapter 1 General introduction 1.1 Irrigated rice cropping in the Sahel i i a r ith a l n hi t r in t- fri a raditi nal ri r in in fri an ri z e t d dat a k ar hi traditi nal ri r in a rainf d and a ra ti d in th danian and in an li at n r i itati n r in th land and l land nditi n t r nt th traditi nal ri - r in ar a till a nt f r t f th ri r d d in t fri a t th fri an ri ari ti ha n lar l r la d ian ri ari ti z hi h ha a hi h r i ld t ntial and ar al d f r irri at d ri r in rri at d ri in t- fri a ha a h n r hi t r and i ainl li it d t th ah l r and dan ah lian n r rri at d ri r in a id r ad th aft r d a tatin dr ht l ad t r fail r and a i l f attl in th ah lian ntri ith th a i tan f int rnati nal d n r a i in t nt r ad t ta li h lar irri ati n h ha al n th rd r f th ain ah lian ri r and th ir tri tari and in th h a ft n di id d a n th l al lati n t far r tain d t n ha d ndin n fa il i h j ti f th irri ati n h r i t i r f d rit d rin ri d f dr ht and ii t t th r in d and f r ri in th ah lian ntri h in r a in ri d and a arti larl n d d d t a ra id r in r an lati n till th aj rit f th ah lian ntri ha t i rt t f th ir ri la in r r n th li it d f r i n han r r ard n t al rri at d ri r d ti n in th ah l a nt f r a r lati l lar har f th t tal ri r d ti n in t fri a n a r lati l all fra ti n f t tal ri lti at d ar a h t ntial i ld f r irri at d ri in th ah l i t ha d ndin n a n and it in k hn r i t al a f l hi hi h t ntial i d t th ah lian li at hi h i id al f r ri r in th ini al l d r all f r hi h radiati n and th dr li at r d th r n f t and di a r tr t rat r r an r lt in ld r h at r lat d ik l t t rilit and l ad t t rain and i ld l t in k hn t al a id ld- r h at-r lat d t rilit far r in th ah l ha t f ll a tri t r in al ndar rri at d ri in th ah l an r n in th t l - r and dr a n an ar n r t far r r f r th t a n ith th ti n f i r nl a all in rit f ah lian ri far r ra ti d l r in an tt hi r lt in l r in int n iti th at fi ld h and r i nal l l h r i n t nl a l r in int n it at fi ld t al at a r i n P.J. A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes l l r a l in th n al i r all ha ha n d l d f r irri at d a ri lt r f hi h ld d i diat l ith t aj r r ha ilitati n t a f l t al r nl t n and ha ar rr ntl in d n an ann al a i nd r- tili ati n f th irri ati n h i attri t d t ral r a n h a r ial h i n t n far r ithin a h thni diff r n a t t finan ial fra d f a ri lt ral ntra t r f r il tilla and aint nan a nal ri fl t ati n f r add ri diffi lti r i r in and tainin r dit and titi n ith th r in n ratin a ti iti fl d-r i a ri lt r all in i rati n art fr nd r- tili ati n f th irri ati n h t tal ri r d ti n in th ah l ha fall n h rt f tati n d t l i ld n an t al ra i ld ar ar nd t ha a f l t al h r lati l lar i ld a i t ntial in a t al i ld ha ft n n r lat d t - ti al r ana nt h a a n f il tilla lat in lat tran lantin l f rtili r d lat ti in f f rtili r a li ati n in ffi i nt din th a n f draina t k aft r fl rin and lat and r l n d har t r i t al iall t al a f l t al and in and i in in t al a f l t al and h d that i r d f rtili r and d ana nt an in r a i ld t ha t a t t ha iall t al in d i r d r in ra ti at th fi ld l l ith a tt r at r r ani ati n at h l l and f nd that a ra i ld in r a d fr t t ha an r ar h r r i t al iall t al a f l t al and in and i in in t al t d that - ti al r ana nt a a d la k f t hni al kn l d li it d a t r dit and in t r d q alit lat har t f th r i a n diffi lti llin th har t f th r i a n lat a nt f th at r f la k f fa il la r r f n ti nin f far r rati and r rdinati n f at r ana nt at th h l l h and i an h d that th t nt t hi h far r ar a l t ad t i r d r ana nt ti n i dir tl r lat d t th d r f r r nd nt ri r t th n tr ti n f th irri ati n h t far r did n t ha an ri n ith irri at d ri r in an f th r attl h ld r hil th r ra ti d rainf d r fl d-r i a ri lt r h aj rit f th lar irri ati n h in th ah l r i d t hni al a k t in fr nati nal t n i n r i n th fir t ar aft r n tr ti n f th h t f th t n i n r i al r ani d in t r dit illin and ark tin f th ri and aint nan f th h hi a r a h a rath r t d n ith littl d i i n fr d at th ra r t l l q in t al rin th la t ar th int rnati nal d n r nit ha in r a d r r n tat a th riti t rad all di n a th l fr th dail ana nt f th h and t tran f r it t far r r ani ati n hi tran iti n did n t ft n rin th in r a in l n -t r r d ti it that a h d f r ar r r ani ati n ft n d n t a nt f r aint nan f th h r ltin in d radati n f infra tr t r and ti a and n nt f th Chapter 1 General introduction h il t al h la k f aint nan ha ft n n attri t d t th fa t that th land f th irri ati n h i tat - n d hi h ak far r h itant t in t in l n -t r aint nan i ia n t al lth h irri at d ri r d ti n in th ah l did n t li t th hi h tati n f d n r and ah lian rn nt th r littl alt rnati f r th h ndr d th and ah lian fa ili that dir tl d nd n irri at d ri f r th ir in and f d rit h d n i that in t ah lian h i ld ha in r a d r th la t f d ad d t i r d r ana nt ra ti r a l in th n al i r all i ld in r a d fr an a ra t ha in th t t ha in th la i t d'a na nt t d' n adr nt d lta d la all d fl n al - - n li h d n ali i ld in r a d fr ar nd t ha in th id- i hti t ar nd t t ha n ada t n ta l d t a tran f r fr dir t- d d t tran lant d ri hi h r d d d titi n at arl r r th ta in and i in r d rin th la t ar il alinit and alkalinit r l r in r a in l r rt d in an f th ah lian irri ati n h h thr at f alt-r lat d il d radati n a ra idl rr in far r r ar h r and li ak r a it ld j ardi th f t r f th ah lian irri ati n h n r i f alt-r lat d il d radati n r l in th ah l i i n in ti n t fir t ill r nt a n ral r i f alt-r lat d il d radati n r and th ir int ra ti n ith irri at d ri r in in ti n and r ti l 1.2 Salt-related soil degradation processes hr t f alt-r lat d il d radati n r in th ah l th ar i alini ati n ii alkalini ati n and iii di ati n ll r ar th r lt f t rar a lati n f alt in th il at ral a lati n f alt r ainl in dr li at h r a tran irati n d r i itati n in inati n ith r tri t d draina n th ah l t ntial a tran irati n d r ith a r i itati n f l than r an-ind d alt a lati n an r in irri ati n h h n r q alit irri ati n at r i d r h n a illar ri fr r q alit r nd at r r a a r lt f an irri ati n-ind d ri f th r nd at r ta l alini ati n r f r t th ild f n tral alt n i tin ainl f a l and i n il i la ifi d alin f ll in la ifi ati n if th at rat d il a t ha an l tri al nd ti it f d i hard h il ar na d l n hak in th la ifi ati n ri n and dal h ad r ff t f hi h a- alt nt nt n lant r th i r lat d t ti tr and a t i it alin il an ra idl f r i in a f nth t ar if irri ati n at r q alit i r r if alin r nd at r an r a h th r t n thr h a illar ri h r la ati n f h il i a d n th l a hin f alt ith l alin P.J. A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes irri ati n at r r id d that nat ral r artifi ial draina i i l d alini ati n f th r t n an a ra id r i in a f k t nth lkalini ati n r f r t th ild f ar nat alt and in inati n ith r lati hi h l l f a h alkalinit f a l ti n i q i al nt t th a id n trali in a a it d t r in d titrati n ith a id d n t a f a t t an n rall n id r d q al t th f and in q i al nt r lit r l ti n l l h a lati n f ar nat alt r lt in th r i itati n f al it f th alkalinit f a l ti n d th a n ntrati n than h a l ti n ha a iti al it r id al alkalinit l = lkalinit a in l l all t al rtrand t al h n ntrati n f a l iti l ti n nt all l ad t a d l ti n f a and an a lati n f a and h a l ti n ha a hi h and a hi h a n ntrati n in inati n ith a l a n ntrati n hi h l ad t a hi h han a l di r nta iall in th -h ri n h in r a in i ft n r f rr d t a alkalini ati n hil th in r a in i ft n r f rr d t a di ati n il ith an lar r than i la ifi d di r alkali f ll in la ifi ati n i hard h il ar na d l n t in th la ifi ati n ri n and dal lkalini ati n nt all l ad t th f r ati n f a di il r di il an al d l in il ith l ar nat nt nt h n a n ntrati n ar t raril hi h n h n h t raril alin - di il ar l a h d ith a l ti n ntainin r littl alt th an r ain hi h an ff l n r hi h an l ad t th lla f th il tr t r thr h di r i n f la arti l iall if th il l ti n ntain littl alt h a di il ha r lant r th d t it l r a ilit and a i il tr t r r l t al hi h r lt in n triti nal i alan ainl f and n r l t al h f r ati n f alkalin - di il i l i t n f ar and diffi lt t r th far r la ati n f alkalin - di il i i l t r diffi lt and ti n in t i a d n th l a hin f han a l di and i ar nat i n r th l a hin i ft n r l a at r nt thr h th il i r atl inhi it d th d rad d il tr t r adir t al r id d an t n i lit rat r r i f n r la ati n ra ti h in l d l a hin ith t a nd nt a li ati n t a li rat if r di il l a hin ith hi h l tr l t at r ntainin di al nt ati n in h i al a nd nt in r ani a nd nt dif in th il r fil thr h tilla rfa fl hin f l - r a ilit il h r rti al l a hin i n t ffi i nt a in l tri al rr nt thr h il and r in alt-r i tant r t a li rat al ar di il thr h h t r diati n n th th d h i al a nd nt al i hl rid a id ar n id r d r ff ti in t nditi n and ar th r f r t n i l d rld id r h i al a nd nt ar ft n n i and th hi h initial in t nt n d d i ft n r hi iti adir t al hi a ar iall tr f r irri at d ri r in Chapter 1 General introduction in th ah l h r r fit ar ft n all n an t al and h i al a nd nt n t r adil a aila l r th ah lian far r h t r diati n in inati n ith i r d at r and r ani att r ana nt t th nl a t r lai alkalin - di il r th t trat i r a l t d l r and land ana nt ra ti that ld r nt alkalini ati n and di ati n fr rrin in th fir t la 1.3 Rice cropping on saline and alkaline-sodic soils lth h ri i n t r t l rant t alinit it i ft n d t r lai alin il h n irri ati n at r ith a l alt nt nt an d r l t al rri ati n ith h at r ra idl l ad t th l a hin f alt fr th fir t nti t r f th il hi d alini d n i ffi i nt f r th ri r t r ith t alt tr d t it hall r tin d th h ntin fl din fa r th l a hin f alt fr th il r fil iall if draina i a aila l n alkalin - di il irri at d ri r in ff r niq ad anta r n n fl d d r i i d rat l t hi hl t l rant f r r in in di il ith an t t ar n t it li it d r tin d th th ri lant a id h f th ad r h i al r rti f th di -h ri n r n n-fl d d r th r n f a di -h ri n r nt ad q at d r tin and lar l r d at r a aila ilit f r th lant r at r a aila ilit f r ri r in in a nd d at r la r i n r a r l h r f r if ri rf r rl n alkalin - di il thi i t lik l a d alkalinit -ind d and n n tri nt d fi i n i and n t th di it -ind d d t ri rati n f th il tr t r h l r a ilit f di il i n n id r d an ad anta t ri a at r l d t d r lati n ar r tri t d r l t al al t al f nd that ri lti ati n indir tl fa ilitat th r al f han a l di thr h l a hin in r a in th r - ti nal ar a f nd tin r r ltin in in r a d r a ilit h dr in i f rth r nhan d th ana r i nditi n in th fl d d il n fl din th r r in r a r ltin in a d r a f th t ar nd nna r a t al r t n r ti n lant al h l t a idif th r t n ar i r t al h d r a in nhan th di l ti n f nati al it if r nt th r in r a in th a n ntrati n in th il l ti n hha ra and r l h di l d a han ith a ad r d n th han l th r d r a in th h d r a in al i r th a aila ilit f and n r l t al n l d d that it r lati hall and rfi ial r t t it hi h alkalinit - di it t l ran and it r la ati a ti n ak ri an id al r d rin r la ati n f di il P.J. A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes 1.4 Salt-related soil degradation in the Sahel alin il ar f nd in th ah l a tal ar a t n ta l in th n al i r d lta i r h di nt f th n al i r d lta r d it d d rin a q n f r r i n and tran r i n f th tlanti an h arin ri in f th d it r nd r d th r nd at r alin r rin th t a n at r ta l ri t at an it r ltin in t ntiall hi h ard fl f alt n t al n th id-nin ti irri at d-ri far r in th n al i r d lta in r a in l lain d a t il alinit h a and n nt f rl d i n d h ith t draina fa iliti t d that irri at d ri ntri t d t th alini ati n f th il r n t al and n and r i h d that th il alinit l l d r a d ith in r a in ri r in int n it h r n f draina fa iliti f rth r ntri t d t a l rin in il alinit l l h iti ff t f ri r in i r lat d t th l alt n ntrati n d a f l f th irri ati n at r lkalin - di il ar f nd thr h t th ah lian n arli t r rt f alkalin di il a fr th ffi d i r in ali rtrand t al rin it ar f i t n th r nd at r l l in th inland ri r d lta r fr d th initiall t l than d th dia a nitiall tt n a th aj r r r n t it lar - al lti ati n a a and n d in th arral rr ntl f th ha ar d f r ri lti ati n a illar ri fr th alkalin di r nd at r a d alkalini ati n f th initiall li htl a idi il dia a n th arl a lar art f th h a r t r d and draina fa iliti in r a d arl t a a r lt alkalinit f th la il d f r ri r in d r a d li htl t in r a d in th adja nt ar -t t r d il that r tl d f r ta l r in arl t a n i r alkalin Chapter 1 General introduction di il r f nd n th t rra f th ri r i r in arti larl in th a irri ati n h and art f th na irri ati n h rtrand t al ar i r and an li t- an f nd that th alkalini ati n and di ati n a n l n r rrin and that th alt ri inat d fr th nd rl in dr k far littl i kn n n th r lati n hi t n il alkalinit il f rtilit and ri i ld l in th a nti n d h r kl r arl t r rt d that i ld r r i l d r a d h n al in r a d a a thr h ld al in th ffi d i r h h t d that it i ht r lat d t in r a d latili ati n l it th littl id n f a t al i ld d r a a d n in alkalini ati n th d nari f a i d radati n f th ah l irri at d ri h ain d ra id larit d rin th id-nin ti ati nal and int rnati nal i nti t in n al a ritania ali and i r nd in r a in l r ti n th q antifi ati n f th alkalini ati n thr at lar art f th r ar h a nd t d th r n h a k d- n t rk l t rri ithin thi n t rk a t tal f t- fri an and r n h i nti t rk d n th il d radati n i fr t il h ir rk ainl f d n th ffi d i r in ali th n al i r all in n al and th a h in i r n if th ir aj r findin a that r th la t ar irri at d ri r in ha n t l ad t an i nifi ant in r a in il r in all f th t di d h arl t a nl h r n n-fl d d r r lti at d n r and il i n f n in alkalini ati n and di ati n r r d arl t a n l d d that r ati n f alt ffl r n in th ffi d i r ali initiall l d t i alar in a at r n th alt ffl r n r d t a d f il n tral alt and n t n in alkalini ati n a a r lt f n ntratin irri ati n at r 1.5 Scope and outline it th la k f tantial id n f n in alkalini ati n and di ati n f irri at d ri il in th ah l it i till nl li d that th iti l f th ah lian irri ati n at r a thr at t th taina ilit f th ah lian irri ati n h i in t al dia h r f r ar ha t tak n h n r d ti it and il q alit r l ar r rt d in th ah lian irri ati n h that i ht indi at n in alkalini ati n and di ati n ar r f t ah lian irri ati n h r rt d r l ith alt-r lat d il d radati n nl fi t t n ar aft r n tr ti n f th h n l ita a ritania a ra t a n i ld dr d fr t ha in th arl ar t t ha t n and i t ati nal d l nt ral - - n li h d data i ilarl a ra ann al i ld in th ld t ti n f th r all h in rkina a dr d fr t ha in t i ld t n and t ha fr n ard t rit d i n al r d la all P.J. A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes Socio-economic settings:

Productivity + Profitability:

S H S Crop + natural S S resource S management:

S S S A S S l S S S S S S Quality of S natural resources:

Bio-physical S S H settings:

S S A S S S S S S, S S, d r - - n li h d data ar r r lat d th ir i ld d lin t alt ffl r n n th il rfa t littl a kn n a t th alinit and alkalinit f th ir il and th a t al r a n f r th r d i ld d lin h far r r ati n r k d th f ll in r ar h q ti n i r d linin i ld in th ah lian h ind d a d alt-r lat d il d radati n a far r t r ar l i ld r lat d t - ti al r and land ana nt ii f il alinit r alkalinit i a r l th n hat i th r and ra hi di tri ti n f th alkalin alt iii hat ar th t ntial han f th il nd r rr nt and alt rnati r ana nt ra ti i an i r d r and nat ral r r ana nt ti n d l d t i r i ld and r r r iti at alt-r lat d il q alit r l that fit th th l al i h i al and i - n i ttin Chapter 1 General introduction h r ar h q ti n r a lar art f th ri r d ti n nt t a h n in i r hi fi r h that far r r and nat ral r r ana nt ar d t r in d th i - n i and i h i al ttin h r and nat ral r r ana nt dir tl aff t th r d ti it and r fita ilit a ll a th q alit f th nat ral r r a hi h a ain ha dir t i a t n i ld n ld a that in n r in a n th fl hart i a d fr l ft t ri ht t th nd f th a n th r d ti it and r fita ilit and han in th q alit f th nat ral r r a aff t th i - n i and i - h i al ttin f r th f ll in a n r r nt d th d tt d arr h fl hart h that far r ri k ndin in a i i ir l h r r r and nat ral r r ana nt la k f f rtili r draina t r lt in l i ld and a d r a f th q alit f th nat ral r r a n tri nt d l ti n alt a lati n hi h r at finan ial diffi lti f r th f ll in a n and f rth r d r a th q alit f r an nat ral r r ana nt ra ti h fir t r ar h q ti n r ri r d ti it r l a d alt-r lat d il d radati n and r - ti al r and land ana nt i di d in ha t r and ha t r f n ri r d ti it r l in l ita a ritania hil ha t r d al ith ri r d ti it r l in th r all rkina a n th t di in d th r lt f rk h far r r far r ana d trial and r ar h r- ana d trial t id ntif th aj r r in n traint and t id ntif h rt-t r l ti n that an ad t d far r n ha t r tak a l l k at th t ntial r l f i r d r ani att r ana nt a a an t i r i ld and n tri nt a aila ilit in l ita h nd n third r ar h q ti n d alin ith th di tri ti n th ri in f alt r lat d il d radati n and han nd r rr nt and alt rnati r and land ana nt ar tr at d in ha t r and ha t r l k in d tail at th a t al di tri ti n f alt in th l ita land a and in it ith a h i al d lin r i ai d at q antif in th t ntial han f th d radati n r n ha t r tak a l l k at th ff t f irri at d ri r in in inati n ith r ani att r a nd nt n th alkalinit f alkalin il in l ita a ritania and in th ffi d i r ali artial an r n th f rth r ar h q ti n an i r d r and nat ral r r ana nt ti n d l d that an ad t d r r - r far r ith t i nifi antl in r a in r d ti n t ar r id d in ha t r and n ral n l i n n th in d r lt f th ha t r ar r id d in ha t r Chapter 2 Explaining yield gaps in a Sahelian irrigated rice scheme ar r in an irri ati n h in th rn ntral a ritania ri n d d linin ri i ld and ithin a d ad aft r it n tr ti n f th h land ha n a and n d t al i ld t ha ar l ar d ith t ntial i ld a t ha and i ld l h r in th ah l t ha ar r r lat d th r d ti it r l t alt ffl r n n th il rfa i i ld n th r and iddl l il r l t ha h n ar d t i ld n il f rth r d n l t ha ar r la ifi d th r and iddl l il a d rad d t th il ld n t la ifi d alin n r di f ll in la ifi ati n i ld n th d rad d il ar r lat d t -li itati n f and d t l il l k ha l il l k ha a i nal l f rtili r d k ha in inati n ith l f rtili r r r ffi i n k k and n n a li ati n f f rtili r n th n n-d rad d il il l k ha i hi h r and -d fi i n r ail d it hi h r il l k ha and f rtili r r r ffi i n k k i h r nt nt f ar nat alt in th d rad d il in r a il and ar th r f r lik l t ntri t t l il l and l f rtili r r r ffi i n P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes 2.1 Introduction r th la t ar irri at d ri r in z ha n intr d d n a lar al in th ah l h j tifi ati n f th a i in t nt in irri ati n infra tr t r a t i r f d rit t rr ntl th f ha hift d r t ard n i taina ilit and in n rati n r a t al ri i ld r ain ll l th anti i at d l l atl n t al and d linin i ld ha n r d in irri ati n h ral a th r r i t al a f l t al i rd t al h d that ti in f ral r in ra ti in tran lantin din f rtili r a li ati n a ft n lat and f rtili r d t l r ltin in lar i ld a t ntial in a t al i ld n additi n il alkalini ati n ha ft n n nti n d a a t ntial r d ti n n traint j ardi in taina l ri i ld in th ah l rtrand t al i in i in t al r t dat th r ha n f t di in ti atin th ff t f il alkalinit n ri i ld in th ah l i r in in th ah l r q ir lar a nt f at r d t th hi h a tran irati n in th h t and dr li at ah lian irri ati n at r ntain littl di l d alt t ft n a iti r id al al it alkalinit l = lkalinit a in l l all t al rtrand t al n ntrati n f h at r in th il r t n a l ad t th f r ati n f an alkalin hi h and di hi h di nt nt il h a il i l r d ti a f th ind d l a aila ilit f ral lant n tri nt n and th r h i al r rti f th di h ri n r l t al n thi t d ill f n th irri ati n h f l ita a ritania hi h i n f th an t i al lar ha ah lian irri ati n h h h r ha and a ilt t n and lan t t nd th irri ati n h t ha ha far n t n at riali d artl a f r d ti it Morocco Al ge ria N Lexceiba Se ne ga l M a li Barrage Kadi l Mbout Chapter 2 Explaining yield gaps in a Sahelian irrigated rice scheme r l h ain r i ri lti at d in th th t and dr a n ra t a n i ld dr d fr t ha in th fir t ar t t ha t n and hil th r d ar a d r a d fr t r a n i ld in r a d fr t ha t t ha d rin th a ri d t th r d ar a r ain d r lati l ni rtant h l ita i ld ar l th t t ha ran r d in t ah lian irri ati n h r i t al a f l t al i rd t al in th in tallati n f th l ita h far r in r a in l lain d a t d linin i ld and a t f th ar a had n a and n d ar r r lat d th ir r d ti n r l t alt ffl r n n th il rfa and n id r d il aff t d thi r l t d rad d h l f l ita irri ati n at r ari t n and l l hi h i t thr ti hi h r than l al r rt d arl t t al and i in t al f r th i r and n al i r r ti l f alkalini ati n thr h n ntrati n f irri ati n at r i an n in r in ah lian irri ati n h th n it i lik l t r ra id in l ita than l h r n th a aran f alkalinit r l at thi it ld an arl arnin f r hat i ht ha n lat r in th r ah lian irri ati n h h j ti f thi t d a t id ntif t hat t nt ri r d ti it r l ar a d il q alit r l ith ha i n il alkalinit n th n hand and - ti al r ana nt n th th r hand nit r d i ld and ana nt ra ti in far r fi ld and ar d th t d l r di ti n n ti al ana nt and t ntial i ld d th ndar lin a r a h t ar th i a t f th il q alit and ana nt ra ti n i ld n additi n r ar h r n tri nt i i n trial r nd t d t a th il f rtilit and i ld t ntial 2.2 Materials and methods it d ri ti n at r ar r tain d hind th l ita da in ntral th rn a ritania i r all in ra i tri irri ati n t ara l land d n tr a h li at in l ita i t i all ah lian ith rrati rainfall a r in th t a n l t r f ll d a h rt l ri d r r ar ith ini dail air t rat r a l a and a h t dr a n ar h n ith dail a i air t rat r t nn al r f r n a rati n i r h land a ar nd l ita i hara t ri d th r n f all r k t r hi t q art it and lar li htl l in arr n lain hi h drain th ir rfa r n ff in all all hall P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes il ha f r d fr th hi t ar nt at rial n th r and iddl l ll ial d it in r a il d th n th l r l d r i n and ri r ank i r and il t t r i ilt la l a t la l a and h littl rti al and h ri ntal ariati n and in th n l n tr t d irri ati n h a di tri t d a n t th l al lati n ar r tain d t n and ha d ndin n fa il i h aj rit f th l r i-n adi attl h ld r and nfa iliar ith ri r in ra ti t ntial i ld and ti al ti in f a r n i ra ti t ntial i ld li it d lar radiati n and t rat r nl r ti at d in th d l in k hn and f r tran lant d ri ari t a a in th t and dr a n h i l nt d l in k hn al lat d th r nta f ik l t t rilit d t ld r h at tr at fl rin rth r r a r di ti n n r th d rati n and ti in f h n l i al ta f th ri r hi h r d t d ri ti al ti in f tran lantin f rtili r a li ati n draina and har t n t ath r data f r th and i lati n r fr l ita and ata l at d k th t f l ita Chapter 2 Explaining yield gaps in a Sahelian irrigated rice scheme Upper and Middle Slopes Lower Slopes and Depressions River Banks ar r r and far r trial i t far r di tri t d thr h t th irri ati n h l nt r d t arti i at in r and trial f r th tart f th t a n arti i ant r a k d t ta li h in th ir fi ld a ial l t that r i d n f rtili ati n t a th r i ana d a al th far r l t h r t f th fi ld a ana d th far r in l din f rtili ati n ar r r r r at d ith an th r r f far r d rin th dr a n t n far r trial r nd t d th lant and il a l r anal d fr th far r trial la l af a l r tak n at h adin f r anal i rain i ld r a r d fr a ar a har t d in a h and l t at at rit rain i ld r rr t d t i t r nt nt ar t ind a d t r in d fr n-dr i t r nt nt tra and rain i ht f a -hill - a l n ntrati n f in rain and tra at at rit r d t r in d in th i r - j ldahl th d r n r lant h h r n ntrati n and r a r d in th th d d ri d hida t al il l a ti at d fr t tal tak in l t r ffi i n f r a li d f rtili r a a d n th diff r n in tak t n and it t il a l a tak n fr a h l t f r th n t f th r in a n h a l r anal d f r and - l in a a t in a a t - l n and ra han a l ati n a a r d t r in d in an at i ad r ti n tr h t t r aft r tra ti n ith a ni hl rid ati n han a a it f th a l a d t r in d a d ri d ha an han a l di r nta a al lat d in han a l a P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes and h alk - la k th d l n and r a d t d t r in tal a d t r in d in a a r r i n f th j ldahl th d difi d t in l d nitrat and nitrit in thi lfat alal t al ri ti tati ti f r th r ana nt and il r rti and rr lati n ffi i nt ar n i ariat rr lati n ith r t t and i ld r al lat d in ft ar f r ind rin a rk h far r indi at d th l ati n f far r-id ntifi d d rad d land n a a f th irri ati n h th land r ainl it at d n th r and iddl l nit f th a aj r il and r ana nt aria l f th far r trial r la ifi d a rdin t t ra hi iti n i i r and iddl l ii l r l and d r i n and iii ri r ank an f r il and r data a rdin t r h l i al la r ar d ith th an- l t t in th ft ar ndar lin anal i f th far r- ana d trial h ndar lin a r a h a d t tain a i-q antitati ti at f th ntri ti n f th r ana nt and il r rti t and i ld a hi a r a h a fir t d ri d h rin i l i that th r li it f int in a att r dia ra d lin at th r n f th d nd nt aria l and i ld t a arti lar ind nd nt aria l il and r ana nt if th r aria l ar n t li itin h a r a h a fir t l d t d t r in riti al al f n tri nt alan in lant dia n ti d l ll r- i l n and rij - i l n ra r and at n al rth t al at r th a r a h a d t d ri th r lati n hi t n il n tri nt n ntrati n and i ld an l and r an l tandardi d tati ti all nd th d f r n tr tin ndar lin ar till la kin h idt t al ha r t al d hand dra n lin a an a t al and h idt t al d an a r a h in hi h th lit th data t int q idi tant r t ti n n th -a i aft r hi h th al lat ndar int a th r r r ntil r r i n lin a th n fitt d thr h th ndar int f a h r n id rin th i-q antitati j ti f r t d and th r lati li it d a nt f a a i l r r d r a d h r h r int r an all l t d in a att r dia ra aft r hi h a r r i n lin lin ar l arith i r l n ial a fitt d nl il and r ana nt aria l that had a rr lati n ffi i nt ith and i ld r tak n int a nt h r ltin ndar f n ti n f r l t d il and r ana nt aria l r d t al lat th a i attaina l and i ld f r a h far r and f r a h aria l hi r d r all d id ntif in th t li itin aria l and th rr ndin a i attaina l i ld f r a h far r ari n f all li itin aria l r lt d in an ti at f th r lati i rtan f Chapter 2 Explaining yield gaps in a Sahelian irrigated rice scheme th il q alit and r ana nt ith r t t r d ti it r l in l ita h diff r n t n t ntial and a t al i ld i i ld a an lar l lain d in th ndar lin a r a h r if th a i attaina l i ld d th a t al i ld th n thi diff r n an all d th n n-id ntifi d i ld a a an a t al h n n-id ntifi d i ld a i an id a f th lanat r al f th a r a h a lar n n-id ntifi d a indi at that th r i rtant aria l ha n t n tak n int a nt ar h r- ana d n tri nt i i n trial ar h r- ana d n tri nt i i n trial r nd t d in th t a n th dr a n and th dr a n at t it that r id ntifi d far r a d rad d and n n-d rad d rdin t th a th trial it i l at d n th r l and th trial it n th l r l h ri ari t - - - - - in a ritania kn n a ah l a d h trial n i t d f th f ll in i f rtili r tr at nt r li at d f r ti n f rtili r add d and n a t n a t n a t n a t n n h t tal f rtili r r a d a k ha di id d in thr lit a li ati n thr k aft r in at ani l initiati n and at h adin and n r a li d f r tran lantin a al a li ati n f rtili r d a k ha in th f r f tri l r h hat f rtili r d a k ha in th f r f l and n f rtili r d a k ha in th f r f n n th and dr a n n n a a li d t an f th tr at nt d t n na aila ilit n th dr a n nl th and f th n tri nt i i n trial r r at d h n r f r li ati n a r d d fr f r t thr ndi id al l t i a ti ati n f i ld and d t r inati n f lant n tri nt tak il n tri nt l and f rtili r r r ffi i n r i ilar t th th d d in th far r trial n ntrati n f n and in th tra r a r d in a l tra t in an hida t al rtili r r ndati n f r and r d l d f r th and il in a t ha tar t i ld and takin int a nt th a ra il and l and a ra r r ffi i n f a li d and f rtili r f th r ar h r n tri nt i i n trial h k ha and tak k ha that rr nd d t a t ha tar t i ld r a d n a ra n tri nt tak in irri at d ri in th ah l and in ia a f l itt t al t il a l f a h l t r tak n f r th tart f th trial and anal d f r in a a t and in a a t an f diff r nt tr at nt r ar d ith th an- l t t in th ft ar P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes 2.3 Results i lat d t ntial i ld h t ntial i ld in th t a n a i lat d ith ari d a r ar t n t ha and t ha ith an a ra f t ha r a n t ntial i ld h d hi h r aria ilit t n t ha and t ha ith an a ra f t ha ith l i ld in a d hi h ik l t t rilit d t h at tr i lat d t ntial i ld f r th r ari ti d in l ita r al t i ilar a a a t ha diff r n ar r r and far r trial nl t f l nt rin far r tart d th t a n a ai n in rdin t far r th ri ar r a n f r n t tartin r in rd r f i rtan n n-a aila ilit f a hin r f r land r arati n far r d la f th t a n r arati n d t lat har t f th r i dr a n f ll d tr n rain far r n irri ati n at r in th ndar anal far r and n n- a nt f th ann al at r f far r ar r n r nti n d il q alit r l a ri ar r a n f r n t tartin th a ai n i f th r ainin fi ld r l d d fr th anal i d t r r da a ird and rat far r r n n-r t f th trial t far r ri ti tati ti f k r and il SD = standard deviation.

Pearson bivariate correlation coefficient.

* = significant at P < 0.05;

** = significant at p < 0.01.

DAT = days after transplanting.

n.a. = not applicable.

Chapter 2 Explaining yield gaps in a Sahelian irrigated rice scheme SD = standard deviation.

Pearson bivariate correlation coefficient.

DAT = days after transplanting.

* = significant at p < 0.05.

No data available for 5 fields.

n.a. = not applicable.

SD = standard deviation.

Pearson bivariate correlation coefficient.

*= significant at 5 < 0.05;

= significant at p < 0.01.

Values higher than 100 are due to dissolved CaCO.

P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes CEC, K, Na, C%, N and P for TF and T0 are not significantly different (p<0.10) NewmanKeuls test. Values in the same row followed by the same letter are not statistically different at the level indicated in the last column. n.s. = not significant.

N recovery efficiency (kg uptake kg fertilizer applied) ana nt aria l at l ita ar i n in a l in far r l ti n in th dr a n nl tart d at th n t f th a n all l nt rin far r r d th ir fi ld h r lt f th dr a n r ar ari d in a l th ta l h lar diff r n in r ana nt ra ti a n t far r and rr lati n f r ana nt aria l ith i ld ran lantin f rtili r a li ati n and har t r d la d h n ar d ith th r ndati n i r a i tati ti n th h i al hara t ri ti f t il a l fr th far r r ar i n in a l h anal i f th atial di tri ti n f i ld il r rti and r aria l fr th far r ana d trial 27- 29- 27- 29- 28- 30- 28- transplanting transplanting 30- 1st urea appl 1st urea appl 29- 2nd urea appl 2nd urea appl harvest 31- 30-7 harvest 30- 1- 30-6 30-7 29-8 28-9 28-10 27-11 27- 1-3 31-3 30-4 30-5 29-6 29- Recommended date Recommended date Exec ted d te P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes in th t a n r al d th i t n f tr n atial r lati n hi a l i ld - l n and - ra in r a in fr th r and iddl l d n t th ri r ank h r nta f far r n t tartin th a ai n a and n d h th r r tr nd i ilarl and a all d r a in fr th t t th tt f th t q n h tra and n ntrati n and in r a in fr th t t th tt f th t q n t f r in th tr at nt that h th r r tr nd alth h n t i nifi ant lant anal r al d that lant n ntrati n ar l third f th n ntrati n in th tra a l r than k indi atin d fi i n anar a at at rit n f th fla l af a l n ntrati n r l k indi atin d fi i n d rin tati r th r ann and airh r t nal i f th far r trial h aria l tak n int a nt in th ndar lin anal i rr lati n ffi i nt r in d n it - l a - ra and - l n h aria l d in th ndar lin anal i r in d n it fir t r a i l te te ti l iel i e tifie iel i e tifie iel T TF 0 1 2 3 4 5 6 7 r ed ic t ed yield (t ha ) Chapter 2 Explaining yield gaps in a Sahelian irrigated rice scheme a li ati n r a- nd r a a li ati n r a- t tal r a a li ati n r a t - l a a - l n and - ra h aria l li itin a i attaina l i ld r in rd r f i rtan - l n = t f far r a - ra - l and in d n it h aria l li itin a i attaina l i ld r - l n a - l in d n it r a t r a- r a- and i r h th al lat d r di t d and i ld l tt d a ain t a t al and i ld in ar r r i n t n a i attaina l and a t al i ld lin n t h n lain d and f th ri i ld ariati n f r and r ti l ar h r- ana d n tri nt i i n trial il a l f th n tri nt i i n trial h d that th n th il a di tin tl hi h r than n th il il d th at th it a and at th it t th it nl and h n in d ith f rtili r had a i ld in r a in ff t ra add i ld and n tri nt r r ffi i n i f r diff r nt a n and tr at nt t ar ari d in a l i ld tak and tak f r and ar n t h n t r i ilar a in t th it a li ati n did n t aff t i ld and n ntrati n in th tra k r ind nd nt f tr at nt and d d th riti al l l f r d fi i n k r ann and airh r t i i n f n f rtili r r d d n n ntrati n in th fla l af at ani l initiati n fr k t k n th il r a li ati n f n did n t SD = standard deviation.

Means in the same row followed by a the same letter are not statistically different (NewmanKeuls;

p < 0.05).

P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes ha an ff t n i ld lant anal f th t a n and dr a n trial h d that n th it a ra n ntrati n r l k f r r tr at nt and and r l k f r tr at nt and n th il a hi h r t ari d id l k f r all tr at nt lant tak and r r ffi i n f a li d f rtili r ar hi h r n th il h n ar d ith th il a l n ntrati n in tra r al l r at th than at th it t th it ari d t n k and k ind nd nt f f rtili r tr at nt t th it ari d t n k and k ith l t n ntrati n a r d in tr at nt ith t a li ati n and lant tak and r di tin tl hi h r n th than n th it a l h l il l = tak in il l = tak in and i nifi antl in r a f rtili r n d n th il h n ar d ith th il tain th tar t i ld f t ha far r n th il n d t a l k ha and k ha ar d ith k ha and k ha n th il 2.4 Discussion ra i lat d t ntial i ld in l ita ar hi h in th t t ha and dr a n t ha ar r i ld in th t a n t ha and Chapter 2 Explaining yield gaps in a Sahelian irrigated rice scheme dr a n t ha r l t th lar aria ilit a n t far r i ld and th i rtant i ld a h that th r i n id ra l f r i r nt h ndar lin anal i r al d that th il q alit - l a a - l n and - ra and r ana nt in d n it r a- r a- and r a- t ntri t d t th r d ti it r l in l ita lth h i ld r n ati l rr lat d t a a and it i nlik l that th il aria l f r a dir t r d ti n n traint n id rin th ir rr nt l al i t il in l ita r n t alin d d n r di f ll in la ifi ati n i hard r th a lati n f alkalin alt i ltan l in r a a a and h in r a in d r a a aila ilit d t latili ati n dd and atri k and d r a a aila ilit d t h i r ti n f n al it and th f r ati n f rl l l a in ral i n and r a adi and ilk a a and i ht th r f r indir tl r lat d t and d fi i n r l q alitati anal i f r ana nt ra ti r al d that th r ft n ti al h n ar d ith r ndati n far r tran lant d t k lat n th a n a k d la in th nd r a a li ati n a r d h n ar d ith r ndati n at ti in f r a a li ati n d r a it ffi i n i ilarl har t a ft n d la d and har t ri d a ft n r l n d data n t h n h a ra r a a li ati n in th t a n k r a ha a l t l al r ndati n k r a ha t q antiti a li d in th dr a n a ra k ha r di tin tl l r d t n n-a aila ilit n th l al ark t tal f rtili r d in th dr a n h d i nifi ant lin ar rr lati n ith i ld indi atin that l d lar l ntri t d t th r d i ld a f rtili r a n t a li d a it did n t f r art f l al r ndati n r - l n al a ra k il f r irri at d ri ar l r ann and airh r t - l n a th ri ar n traint li itin far r and i ld a rdin t th ndar lin anal i hi rr nd t th lar r nta f fla l af a l and tra a l ith n ntrati n l th d fi i n li it h ndar lin anal i l d t a d r di ti n f a t al i ld th r r i n d l f r and i ld lain d and f th ri i ld ariati n hi h i i ilar t findin f th r t di h r il r rti r d t lain irri at d ri i ld ariati n a an a t al and r ann n th l t riti al r ark an ad ith r t t th f ndar lin anal i in thi t f t d ir tl at fi ld a lar art f th i ld a r ain nid ntifi d hi h a r lat d t a r nt rr r th d l i al rr r r aria l h a ird da a and d r r that ha n t n tak n int a nt ndl i i n f f rtili r in th l t ld n t id ntifi d a a r d ti n n traint hi h indi at that i i n f an i rtant aria l fr th anal i d n t n aril l ad t a lar nid ntifi d i ld a if th arti lar aria l d n t ar a n t far r i n ndar f n ti n an ta li h d P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes and i ld th h a tr n atial di tri ti n i ld in r a h n in fr th r and iddl l d n t th ri r ank id th r nta f far r l a in th ir fi ld n lti at d d r a d in fr th r and iddl l t th ri r ank alth h n ith r il q alit r l n r t ra hi iti n r nti n d a a ri ar n traint f r n t tartin th a ri lt ral a ai n t that l r i ld in th a t r lt d in a it ati n h r far r l had r r l findin th finan ial r r and ti ati n n ar t tart th a ai n h q alitati anal i and ndar lin anal i f th far r trial l arl hi hli ht d - ti al ana nt and n n-a li ati n f f rtili r a aj r r in n traint r in r in ra ti did n t i nifi antl diff r thr h t th t q n diff r n in i ld t r lat d t diff r n in il q alit il q alit aria l that infl n th a aila ilit f and all h d a tr n atial di tri ti n n th r and iddl l il and a r i nifi antl hi h r and - l n and - ra r i nifi antl l r h n ar d ith il f rth r d n l h r ati n rr nd t th l n ntrati n k in th tra f far r fi ld n th r and iddl l i ilarl n ntrati n in th tra f th n tri nt i i n trial n th il r r l k and a ra i ld d r a d fr t ha t t ha h n f rtili r a itt d ll f th a r ati n indi at that d fi i n i a aj r r in n traint n th r and iddl l h n k f rtili r ha i a li d tain a i ld f t ha an f rtili r d f k ha in t ad f k ha ld ha n ffi i nt i n th a ra il l k ha and n th il hi d rr nd t far r ra ti n -li itati n f and i lik l in far r fi ld at th r and iddl l i n th rr nt f rtili r ra ti h l tra n ntrati n in far r fi ld n th r and iddl l tr n th n th h th i f li itati n n th il f th l r l and d r i n and f th ri r ank i r l in th l t indi atin that ha n dil t d at a i d fi i n at l f rtili r d i lik l t th aj r n traint li itin i ld in far r fi ld n th il f rtili r a li ati n nl had a iti ff t at hi h i ld l l t ha and n f rtili r a li ati n had n ff t n i ld t l n n ntrati n n th il in tr at nt ith th and t ith t n f rtili r a li ati n indi at d a lik l n d fi i n hida hi h a a r l if hi h i ld ar tain d r a l n r ri d n d fi i n in irri at d ri i ft n r d n alkalin al ar il r ann and airh r t r th far r and n tri nt i i n trial it f ll that i ld l l and n tri nt a aila ilit ar i nifi antl l r n th than n th il n th far r la ifi ati n t r d rad d and n n-d rad d r fl t ll r d ti n n traint in th irri ati n h t d n t r f r t int rnati nal tandard n alinit r di it i i ld ar n t dir tl infl n d a a and t r l r fl t an alkalinit ind d n tri nt n traint Chapter 2 Explaining yield gaps in a Sahelian irrigated rice scheme n th il l a ra il l il l and r lt d in hi h f rtili r k ha and f rtili r k ha r ndati n h n tar t i ld i t ha n th il a ra il l and r h hi h r r ltin in d rat f rtili r r ndati n k ha f r a tar t i ld f t ha t r nt f rtili r n th il i n t n d d in il l k ha till d tak k ha at t ha h f rtili r r ndati n f r th il ar nlik l t ad t d far r a th ill n t a l t rt th hi h t h r nd d f rtili r d ld all r i ilar t in th r ar h r n tri nt i i n trial if a i dil ti n f and in th ri lant a tak n int a nt lt rnati l f rtili r r ndati n an l r d h n tar t i ld i all r and r h n r r ffi i n f a li d f rtili r in r a thr h i r d r ani att r ana nt ha t r n th l th f rtili r r ndati n al lati n ar in tr ntal a th r al a tr n ntra t in f rtili r n d f and il 2.5 Conclusions ar i ld a t n a t al far r i ld and i lat d i ld r d that th r i n id ra l f r i r nt in ri i ld and r d ti it in l ita d and lat ti in f f rtili r a li ati n and n n-a li ati n f f rtili r r id ntifi d a th ain a r n i n traint h h r a aila ilit and alkalinit r th ain il q alit aria l ntri tin t th r d r d ti it r l h il q alit aria l h d tr n r lati n t t ra hi iti n lainin l r i ld and r a and n nt f land n th r and iddl l i h t i ld tain d in n tri nt i i n trial n th far r-id ntifi d d rad d il r n t i nifi antl l r than n il f rth r d n l t and r t that l and ar r lat d t latili ati n f and i ili ati n f r that ill r i rtant n th r alkalin il f th r and iddl l t th l and tak - ti al f rtili r ana nt ill r a il tran lat d int i ld l n th il nd d and f rtili r d t tain a t ha tar t i ld ar h hi h r n th than n th il hi t d h d that anal i f r ana nt ra ti h ld int rat d in t di that r lat i ld a t il q alit r l n inati n ith far r r and n tri nt i i n trial th ndar lin anal i r d t an ll nt t l t tain a i-q antitati id a n th i rtan f diff r nt r d ti n fa t r h ndar lin anal i had a d r di ti a a ilit ara l t th f nd in i ilar t di hi t d i n f th fir t ah lian t di t r lat a t al i ld a in irri at d ri t il alkalinit a r lati n hi that ha ft n n nti n d in ah lian t di t a littl in ti at d lth h n l d that il alkalinit ntri t t l i ld in l ita ann t dra an n l i n n th ri in f th alkalin alt r th t ntial han in il P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes alinit tail d r ar h n th alt and at r alan ill n d d in rd r t nd r tand th han f th il nd r th r nt land ana nt and in rd r t nd r tand t hat t nt l ita ld f n ti n a an arl arnin t f r th r ah lian irri ati n h Chapter 3 Using farmer knowledge to combat low productive spots n th ld t ti n f rkina a lar t irri ati n h in th r all ri z i ld dr d fr a t t t ha in th arl h rtl aft r ta li h nt f th h t t t ha fr n ard ar r la d thi i ld d lin n th a aran f t dia t r l r d ti t rdin t far r and fi ld a r nt th l r d ti t d r a d i ld h l r d ti t ar a d n d fi i n n a aila ilit i r lat d t r l - tra ta l n nt nt f th il k th alkalin - al ar hara t r f th il th n n a li ati n f n f rtili r and a r lati l lar f rtili r d k ha ar r r rr t in r latin th al ar nat r f th il t th r n f th l r d ti t h r in tr ntal in id ntif in a li ati n f d d r ani r r ri tra at t ha a a h rt t r l ti n that in r a i ld t t ha li ati n f n f rtili r k n ha in far r fi ld in th dr a n radi at d th l r d ti t and in r a d i ld fr t t ha li ati n f n f rtili r i th r f r tr n l r nd d r n f rtili r i n t a aila l in rkina a at r nt it th r lati r nt intr d ti n f irri at d ri r in t far r h d a d nd r tandin f r in n traint and i l l ti n th far r and r ar h r t all n fit d fr a h th r kn l d and r ati n Keywords z n d fi i n rkina a r ani att r ana nt P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes 3.1 Introduction n r a in d and f r ri z arti larl in r an nt r i f r in th aj rit f ah lian ntri t i rt ri drainin ar f r i n han r r ard n t al n rkina a ann al add r d ti n d rin r nt ar t a a t t r ith i rt ran in fr t t r rid thi lar a t n ri d and and l al r d ti n in t nt r ad in irri ati n infra tr t r in rkina a fr th id- n ard r ri i ld in irri ati n h ft n fall h rt f tati n rai in q ti n a t th ia ilit f th tl irri ati n h li r t al rkina a lar t irri ati n h i l at d in th r all hi h a nt f r t f nati nal ri r d ti n h rr nt ha h ha n rad all d l d fr th id- n ard lan i t t t nd th irri ati n h t a t tal f ha ra r rri at d ri i a t t third f th irri at d ar a r n d rin th t a n an ar a and d rin th dr a n n r ra d r th t a n i ld in th ld r ti n f th h ntin l in r a d fr t ha in t t ha in f ll d a t ad d lin t i ld ran in fr t t ha fr n ard n li h d data i h i ld ar all ar d t th i lat d t ntial i ld t t ha and a t al i ld in t th r ah lian h t t ha a f l t al r far r in th r all t ak a r fit a ra ri i ld r a n n d t at l a t ran fr t t ha i rd t al ar r and th l al irri ati n and t n i n a th rit na nt t i n al r d la all d r la d th i ld d lin t an in r a in a aran f l r d ti t in th ri fi ld far r r lat d th l r d ti it f h t t alinit r l intin at th rr n f hit ffl r n and n d l at th il rfa di t hi h il alinit and alkalinit l l r arli r r d in art f irri ati n h in ali a ritania and n al t far th r ha n littl id n that alinit r alkalinit a i nifi ant dir t i ld l in ah lian h ha t r n th r all irri ati n at r ntain r littl alt d and n ntrati n fa t r ar all tin that alkalini ati n i n t an n in r arr t al r n tri nt d fi i n r l and i l n r arli r r d n th r alkalin - al ar il in th ah l ha t r and ld a i l r a n f r th a aran f th l r d ti t ral a th r r i t al a f l t al in and i in in t al i rd t al ha t r r d that all ri i ld in ah lian irri ati n h r ft n r lat d t - ti al r and il ana nt ra ti h a th r r lat d - ti al ana nt t a ltit d f i - n i and i h i al n traint th at l t and h l l a f l t al h d that i r d il f rtilit and d ana nt rai d Chapter 3 Using farmer knowledge to combat low productive spots far r i ld a t t ha in th n al i r all ith t i nifi ant in r a in r d ti n t h t d that i r d ri t hn l i ar till n d d t t ri r d ti n hi i nt t d in and i in h li that t hn l i ar alr ad a aila l and that - ti al r ana nt i ri aril d t r ll ti r ani ati n and d i i n akin at th h l l r all a th r a r that tt r a t inf r ati n a ri lt ral in t and d i i n akin ill lar l in r a irri at d ri r d ti n in th ah l ar r in th r all r i d t hni al a k t in fr th l al irri ati n and t n i n a th rit and th r ra ial r la rit li ntair f th nit d ati n l nt r ra r ri r t th n tr ti n f th h far r had n kn l d f irri at d ri r in h q ti n ri t hat t nt far r an r rl id ntif fa t r ntri tin t th all i ld and th r n f th l r d ti t an r ar h r ha r d arli r that t fri an far r ha th r h kn l d f th ir r in t and that thi kn l d i d na i rath r than tati n and h n ha r t al rth r r th r ar ral a l f h r ar h r d far r kn l d f traditi nal r in t t id i ntifi r ar h and d l l ti n that ld tt r fit far r n d ldh i n t al t in r an ah t al f r t al ha h n that ithin th fra rk f int rat d il f rtilit ana nt inin t f arti i at r a ti n r ar h and q antitati anal i an n fi ial f r all tak h ld r in l d in l din far r t n i n a nt r ar h r and li ak r r it i t nkn n t hat t nt far r rr tl r i r d ti n r l in r lati l n irri at d ri r in t and h th r th ir kn l d r ati n and ri n an d t id i ntifi r ar h h j ti f thi t d r t i a th i a t f th l r d ti t n i ld ii nd r tand th ri in and d na i f th ir a aran iii al at far r r ti n f th r l and i id ntif and t t t ntial l ti n inin far r kn l d and i ntifi id n r a h th j ti nd t d far r r and in d th ith r ar h r trial h a th d tail d nit rin f l r d ti t and r ani att r trial nal f data fr th trial r al d i ilariti ith n d fi i nt ri lant a r rt d arli r in ia t t th h th i f n d fi i n nd t d trial in far r fi ld 3.2 Materials and methods it d ri ti n h r all i it at d in th rth- t rn art f rkina a h r i r i a tri tar t th h n i r f r r la k lta and it at r l l i artifi iall aintain d a da k f rth r d n tr a all in irri ati n all ar r nd h li at i t i all ah lian ith rrati rainfall P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes r in th t a n a t r f ll d a h rt l ri d r r ar ith ini dail t rat r a l a and a h t dr a n ar h ril ith a i dail t rat r t h aj rit f th il in th r all ha f r d in thi k all ial al ar -ri h d it and an la ifi d rti l and l l a h ir hi h la nt nt and d rat l hi h l k ak th r ita l f r ri lti ati n r n hi ha t r f n th ha and ha ti n f th h that r th fir t t d f r ntin ri r in h ti n r n tr t d t n and h r all a ri inall i d th arka and th a l t ith th n tr ti n f th h l fr th r thni r i lh fr ithin rkina and ali d int th ar a ar hal t thni r had n ri n ith ri r in and in th n l n tr t d irri ati n h a di tri t d a n t th lati n ar r n rall tain d t n and ha ar r r ti n and ra ti n l a tin a r ani d rin in t th r far r t n i n rk r and i nti t t id ntif r in n traint and t r ar h ri riti a d n th t f th rk h nd t d int r i ith far r in a r d i n d q ti nnair d n q ti n t a far r r ti n f th i a t and d na i f th l r d ti t al a k d far r t q antif th i a t and ff ti n f indi n a r t at th l r d ti t in a r -d t r in d t f la r a l far r r a k d t rat th ir r ti n f th i a t f l r d ti t n i ld in fi l l f ratin i ld l ar r r al a k d t j d th ff ti n f i l int r nti n th d in f r l l f ratin n t ff ti littl ff ti ff ti and r ff ti rth r r r ana nt ra ti i dat f in tran lantin har t and d a and ti in f f rtili r and h r i id a li ati n r l l nit r d l al t n i n rk r thr h t dr a n far r and t a n far r i i ld r ti at d n th a i f th n r f a har t d lti li d th a ra a i ht ar r r in ra ti r ar d t l al r ndati n a l tail d nit rin f l r d ti t t th n t f th dr a n t fi ld and in th ti n r l t d that r aff t d l r d ti t a rdin t th far r n l r d ti t r fi ld a nit r d fr tran lantin n ard h t that r nit r d r n t l at d n ar th nd f th fi ld in rd r t a id rd r ff t lant d l nt h t i a h i ht till r n r and d l nt ta a nit r d thr h t th a n at f a aran t and int n it f lant Chapter 3 Using farmer knowledge to combat low productive spots di a r nit r d h t a l r tak n at diff r nt d l nt ta i h rtl f r ani l initiati n at fl rin and at at rit lant a l a r nd ri i a r tak n at f r int al n tran t at int r al fr th nt r t t id th l r d ti t i r a l tak n at th a di tan f th nt r f th l r d ti t r lk d r ltin in f r it lant a l r t and r d l nt ta t at rit lant r t and th t t il r a l d a ll f ll in th a a lin and lkin r d r lant a l r dri d and and n r tra t d ith a l tra ti n hida t al n a anal d in an a t ati a r ti n tr h t t r and a d t r in d l ri tri all il a l r dri d and i d and anal d f r l tri al nd ti it in a tra t a ra i tri l f alk and la k han a l a and a aft r l- tra ti n ha an and il t t r i tt th d aila l h h r - l n and - ra a anal d in a tr h t t r tal n aq a r ia di ti n and a aila l n ind a and r ll r d t r in d in an at i i i n tr h t t r n additi n t th il a l tak n at at rit in th nit r d t t il a l - r tak n in i th r fi ld th in id and t id l r d ti t P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes ar h r- ana d trial a d n th t f th far r int r i r ar h r- ana d r ani a nd nt trial r nd t d in t far r fi ld and in th dr and t a n h trial it r l at d in fi ld f th ti n h r l r d ti t had a ar d in th r i a n h di d rati n da ri lti ar a d hi h a nl d far r and l all kn n a hr diff r nt r ani a nd nt r a li d r ltin in th f ll in f r tr at nt = ntr l = fr h ri tra = t = attl an r r at nt r r li at d f r ti in a rand i d l k d i n ini i f th indi id al l t a h r ani att r a li ati n a t dr i ht ha h fr h tra ri inat d fr th r i har t t in r di nt r ri tra and attl an r r ani a nd nt r an all in r rat d int th t il t k f r tran lantin in a h h ti in f r ani a nd nt in r rati n a in lian ith il tilla ra ti d far r in ral f rtili r a li ati n r l t n far r ra ti t ri d k ha a al a li ati n f it tt n f rtili r h rtl f r tran lantin and t dr in f k ha r a f rtili r a t k ha di id d in t lit a li ati n thr k aft r in and at ani l initiati n add i ld r ti at d fr a har t ar a in th nt r f a h l t ar t ind a d t r in d fr n-dr i t r nt nt tra and rain i ht f a -hill - a l tra i ld a d ri d fr th har t ind and th rain i ld h r lati rfa ar a aff t d th l r d ti t a d t r in d thr h t th r in a n i at ani l initiati n h adin and fl rin f r all tr at nt lt f th fi ld and a n r a ra d and tandard rr r a al lat d fr th a n fi ld a ra ar r- ana d trial a d n lant r ati n in th l r d ti t h th i d that th t r a d n d fi i n n th t a n r -t t d n f rtili r a li ati n f liar ra and a al a li ati n at a rat f k n ha in t far r fi ld ith l r d ti t th far r and r ar h r a r iat d th r iti i al ff t f a al a li ati n f n f rtili r n lant r th h r f r d id d t ntin t tin a al a li ati n f n f rtili r in far r fi ld n a lar r al n th dr a n far r l nt r d t arti i at in th far r ana d trial h far r r l at d in th and ti n and r n t n aril th a a nit r d in th dr and t a n arti i ant r a k d t ta li h thr ini- l t in th ir fi ld r i in k n ha k n ha and t ha f d d tra r ti l h r aind r f th fi ld r i d n ith r n f rtili r n r r ani a nd nt n f rtili r n a a li d h rtl f r tran lantin a a al a li ati n h a li ati n f d d tra rr nd d t far r ra ti f Chapter 3 Using farmer knowledge to combat low productive spots l a in fr h tra d rin n r in a n in a h a in th ri fi ld f r d iti n f r r adin it r th fi ld at th n t f th f ll in a n ll l t r th r i ana d a al th far r in l din f rtili ati n f and i ari t and far r r ana nt dat f in tran lantin din and har t and il f rtilit ana nt d and ti in f f rtili r r nit r d a r j t t hni ian in a r f r rain i ld r a r d fr a ar a har t d in th nt r f th l t at at rit ar t ind a d t r in d fr n-dr tra and rain i ht f a -hill - a l n ntrati n f and n in th lant r a r d a d ri d in th d tail d nit rin f l r d ti t ti n lant n ntrati n r d t r in d in th i r - j ldahl th d r n r al ati n f th i a t f arth r n lant r th a d n th f th far r int r i d id d t al at th i a t f arth r lati n n ri r th h rtl aft r tran lantin far r h l d id ntif in t fi ld in th ha ti n that a rdin t th ff r d fr th i r n f arth r in th il r t n n th fi ld far r id ntifi d n h a il inf t d arth r and n ith dl f arth r n a h n hill r a l d at id-till rin ta lant h i ht and till r n r r a r d il a l ith a dia t r f a tak n f th r t n t at a h lant a l it h il a l a rin d and th n r f arth r a nt d tati ti al anal ll tati ti al anal r nd t d in th ft ar a ka f r ind r i n n t t f r h n it f arian a nd t d f r i ld data f r ar h r- ana d and far r- ana d trial r at nt ff t n i ld r anal d in = ith q nt t t f r t-h ari n h a r d r a d t ar an f n and n ntrati n f th far r- ana d in trial h r lati n t n arth r n r and lant till rin a d l d ith a lin ar r r i n aft r l tran f r ati n f th arth r data 3.

3 Results ar r r ti n and ra ti h l tin and th q nt tr t r d int r i r al d that in th arl far r r d f r th fir t ti th a aran f th l r d ti t h i and n r f l r d ti t had in r a d r ti and t ft n a ar d at th a la in th fi ld th f ll in a n t far r P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes ti at d th i ld l t n and a d n th r d ti n in a har t d ar r r lat d th a aran f th t t ith r r draina alini ati n il f rtilit d lin th r n f i a nt f arth r r t a inati n f th fa t r ar r tri d t at th l r d ti t thr h th a li ati n f an r t tra r a inati n f th diff r nt r ani att r r n id ra l n r f far r in d th a li ati n f r ani a nd nt ith th r al f al ar n d l fr th il rfa h aj rit f far r r n t r littl ati fi d ith th r lt f th ir nt r a r a ff t r n ti a l f r n t t r in a n nl it th n ral di ati fa ti n far r r i d i r d il r ani att r ana nt a th ir nl ti n t in r a i ld ar r i ld in th and a ra d and t ha r ti l n an a r in ra ti h d littl r n ariati n a n t far r a l n n ral far r ra ti rr nd d r a na l ll t l al r ndati n t th n t f th r in a n all far r fi ld r hani all till d n th a n n arl all far r d th di d rati n ari t da h th r ari t d a - hi h ha a li htl h rt r r in l da and i l all kn n a ran lantin and fir t r a a li ati n r t n k d la d h n ar d t r ndati n h har t a k lat t n ta l in th dr a n din a n rall d n h rtl f r r a a li ati n a i r nd d h fir t din ft n ri d h i al din nda r r tra and th nd din a tl an al ar r a li d k ha l f rtili r than r nd d k ha ar r a li d r a a t dr in in t q al lit n th dr a n r a d a k ha hi h r and in th t a n k ha l r than th r nd d k ha tail d nit rin f l r d ti t h l r d ti t a ar d h rtl aft r tran lantin lant in id th t did n t r l l r r fr th tran lantin h k i r lant di d and lant i a h i ht and till r n r f th r ainin lant in r a d at a h l r rat in id than t id th t data n t h n lant in id th t r a h d ani l initiati n and fl rin n t f r k lat r than lant t id th t lant h d t nt d r th and a dark- r n l rati n f th ld r l a ft n r d d th hit l rati n f th l af idri hl r i h r ati n ar r i ilar t hat i nl n in n-d fi i nt ri lant r ann and airh r t n th r f th r in a n i n f ri la t and r n l af t r n t a aran f th di a a n t ifi t th l r d ti t rain i ld f lant in th nt r f th l r d ti t a l than f rain i ld t id th l r d ti t i r K K K K K SD = standard deviation DAS = days after sowing DAT = days after transplanting P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes Field Field Zone (1 = centre 4 = outside LPS) ield i dex ( Chapter 3 Using farmer knowledge to combat low productive spots l l SD = standard deviation rain i ld f lant in th nt r f th l r d ti t a l than f rain i ld t id th l r d ti t i r h t a l tak n at th nd f th tati r th ta i da aft r tran lantin ntain d k and n k ind nd nt f a l it t at rit and n n ntrati n in th tra had d r a d t k and k r ti l nal i f th il in id and t id th l r d ti t r al d n i nifi ant diff r n n t h n in il t t r and a i h i al ara t r a l h a li htl alkalin t d and han a l di r nta r th all th in id and t id th l r d ti t f t d rat a nt f al ar n d l r f nd al it a r nt in th i d fra ti n f all il a l t a nt nt a n rall all in th a l d t il ar h r- ana d trial ra d r th t fi ld and a n i ld f t ha and t ha r i nifi antl all r than i ld f and th t ha i r r at nt fi ld a n and fi ld a n int ra ti n all had i nifi ant ff t n i ld ll th r int ra ti n fi ld tr at nt a n tr at nt fi ld tr at nt a n r n t i nifi ant h rfa ar a f th l r d ti t d t d r a in ti f r all tr at nt i r t r in tr at nt and P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes K 100 T1 (control) T2 (straw) T4 (manure) T3 (compost) IP BT FL plant development stage ield (t L s r ce Chapter 3 Using farmer knowledge to combat low productive spots ar r- ana d trial t far r d th ri lti ar and a in rit far r d ari t - ran lantin a n rall thr k d la d h n ar d t r ndati n h r l n d r in l in t ad f da h d that r d l nt a d la d a h n n n that n rall r ith l t rat r n d fi i n r d fi i n rtili r a i ilar f r all far r and a l t l al r ndati n a l r th nd r a a li ati n a hat d la d h a li ati n f k n ha in r a d far r i ld fr t t ha i r l in r n did n t f rth r in r a i ld h a li ati n f d d tra in r a d far r i ld t t ha h a li ati n f n f rtili r in r a d n i nifi antl n a k in th and tr at nt and k in and tr at nt r nd r i ilar f r n ith all n ntrati n k f r and and lar r n ntrati n k f r and tra n ntrati n r i nifi antl hi h r f r k than f r tr at nt k and k n th n tr at nt n ntrati n ar l t d fi i n k anar a itr n n ntrati n in th tra h d i ilar tr nd ith i nifi ant diff r n t n k k and and k h all lant n ntrati n rr nd t dil ti n in th tra and n tr at nt i r n t r r nt d t i ilar t and lant a lati n in far r fi ld T T T T F 10- Z n 20- Z n S - ield (t P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes T Paysan F 10 kg Zn T 10-Zn P a ille T S 0 3 06 09 0 1 - N uptake (kg ha ) al atin th i a t f arth r n r r th ar r rr tl id ntifi d n ntainin f and r lati l lar n r f arth r ra d r th t fi ld arth r r a l r nt d in th inf t d n and r arth r in th n n-inf t d n r it a ar d that ar a that far r rat d arth r inf t d did n t n aril in id ith th r n f l r d ti t f nd that lant h i ht a i ilar in th fi ld and did n t diff r t n inf t d and n n-inf t d n ill r n r h d a iti lin ar r lati n = ith th l -tran f r d arth r n r i till r n r in r a d ith in r a in a nt f arth r ntrar t th fra r h th i 3.4 Discussion h i a t and ri in f th l r d ti t h i ld d lin r d in th arl t id in id ith th a aran f l r d ti t ar r ti at d a i ld r d ti n f t hi h rr nd t th r rt d i ld d lin fr t ha in t i ld - ield (t Chapter 3 Using farmer knowledge to combat low productive spots t n t ha and t ha fr n ard i ilar i ld diff r n r r d in th dr a n far r- ana d trial i ith n f rtili r a li ati n i ld r t ha and ith t t ha h t t f th rfa ar a i r and rain i ld f lant in th l r d ti t i l th n i r f th rain i ld r d t id th l r d ti t h th i that th l r d ti t ar th r lt f in d fi i n n a aila ilit n alkalin and al ar il i ll kn n t al r ann and airh r t and i r lat d t th tr n ad r ti n f n n ar nat in ral and r th r i itati n f n in rl -drain d il nna r a h a ra - tra ta l n nt nt a ti l r than th t tal n indi atin that a aila l n i nl a all fra ti n f th t tal il n nt nt h a ra - tra ta l n n ntrati n k a ll l th riti al l l k f r n d fi i n in l land ri r ann and airh r t h r d ran k at th t d it a al l h n ar d t ar a l h r in th rld h r n d fi i n r k in ld ri il f th a r lta in ndia a ithri t al k in th ar r in f ran ari ian and a r i k in ntari anada han and at k in inni ta ra han t al ntrar t hat ld t f nd n i nifi ant diff r n in il hara t ri ti r - tra ta l n nt nt t id and in id th t r n n lant r th and at h f rl ta li h d hill in th fi ld ar t i al f r in d fi i nt il in irri at d ri r ann and airh r t in n a aila ilit i lar l d t r in d il ar nat nt nt and r d t ntial a that in r nd t ta l diff r n in th ara t r at h rt di tan an a in r diff r n in n a aila ilit tri rin n d fi i n in ar a hil th r ar a naff t d h r lt f th far r- ana d trial and th d tail d nit rin f th l r d ti t tr n th n th h th i that th r n f th t i r lat d t n d fi i n h r lati l i ld f l t that r i d n n f rtili r th r d r l n ati n f th tati ta th a aran f hl r ti l af idri and th r n l rati n f ld r l a t al all indi at that th ri in f th l r d ti t a r lat d t n d fi i n h d la in r d l nt r lt d in a r l n d r in l lat har t and ft n lat a li ati n f r a f rtili r h n ar d t l al r ndati n a l n n ntrati n in ri h t k and tra k r l nfir in that n d fi i n a la i l hida r lant n n ntrati n in id and t id th t did n t i nifi antl diff r t that in r a d lant r th lant t id th t a a hi d dil tin n in th lant t a a i n n ntrati n in th tra and rain f and l t r a t half th n ntrati n f nd in and h a al a li ati n f r k n ha a n l t l radi at d th t n l t that r i d n f rtili r P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes lant n l n r h d a r l n ati n f th tati r th and fl rin and at rit r h n thr h t th l t d rat t hi h and n ntrati n in tra f ar i n f and a lati n in th lant al i r hi h r that th r fa t r than r ar li itin r th h n n ith r n f rtili r n r d d tra ar a li d lth h di a r r nt th r n t ifi t th l r d ti t and ft n a ar d at r th ta h n th t r alr ad l arl i i l in th fi ld lth h far r rat d th r n f i n r f arth r a a r d ti n n traint hi h arth r n r did n t in id ith th a aran f l r d ti t n r did arth r infl n lant r th n ati l n th ntrar lant r th a iti l rr lat d t i f th arth r lati n l ti n and r ndati n li ati n f in f rtili r i rtainl th t n ni nt and ra id l ti n f r in r a in i ld rth r t d ill n ar t d t r in th ti in f rtili r d t lik l in f rtili r d an l r d a r ndati n f r l land ri i n rall l k n ha r ann and airh r t a ithri t al in f rtili r i rr ntl n t a aila l in rkina a and littl i kn n a t it f t r ri in f rtili r d in th trial a i rt d fr r a t ar r rati n and ar rr ntl tr in t n in f rtili r ani t i rt in f rtili r r th ti in th a li ati n f r ani a nd nt i an r t r d d tra th nl r adil a aila l alt rnati t in r a i ld t t ha h a li ati n f r ani a nd nt i lik l t li htl i r n a aila ilit alth h n n ntrati n in tra and rain f tra a nd d l t r ain d at n d fi i nt l l k and k r ti l i th a li ati n f r ani a nd nt in r a d n tak t n n ntrati n r ain d at th d fi i n l l indi atin that a li ati n f n f rtili r ld f rth r in r a i ld h iti ff t f r ani att r a nd nt i r a l r lat d t di l ti n f ar nat - nd n n r a d di l ti n f nati ar nat alt n r ani att r a li ati n ha n r d in th r ah lian irri ati n h ha t r h d r a in th rfa ar a f th l r d ti t d rin th r in a n i r i r a l r lat d t r r r at lat r r th ta a ft n r d n in d fi i nt il r ann and airh r t t r nt far r a l k ha f f rtili r and k r a ha rr ndin t k ha and k ha hi d i r lati l lar and d r lati l all h n ar d t th r ah lian it ith i ilar i ld t ntial r i t al a f l t al r - l n and - ra r th l r ann and airh r t and n ntrati n in th tra d r a d t n ar d fi i n l l in th hi h- i ldin n l t hi indi at that th rr nt f rtili r d i n d d h n i ld l l ar hi h t ha r at i ld l l Chapter 3 Using farmer knowledge to combat low productive spots f t t ha th rr nt f rtili r d i lar and d n t nl r lt in a r t- n fit rati t i lik l t d r a n a aila ilit r ann and airh r t h n n f rtili r a a li d i ld n arl d l d t a dil t d t th a i i r hi indi at that lant in th n tr at d l t r t lik l d fi i nt n if n f rtili r i a li d far r an f rth r i r i ld in r a in r a f rtili r a li ati n ar r kn l d and ra ti ar r r k n arti i ant d rin all ha f th r ar h r j t ar r ad a d q antitati ti at f th i ld l a a r lt f th r n f l r d ti t ar r r rr t in r in a r lati n hi t n th al ar nat r f th il i n d l and hit ffl r n n th il rfa and th r n f th l r d ti t far r nti n d r draina a a a f r th l r d ti t r draina an ind d ntri t t a f rth r l rin f in a aila ilit nna r a ar r rr tl nti n d that th l r d ti t r r lat d t a il- rn r l r th ir r ti n a t th r lati n t n l r d ti it t and arth r ld n t nfir d t ld int r tin t tr t tt r nd r tand far r ri n in thi r t n n ral th ir r ati n ha in r a d r nd r tandin f th nat r and ri in f th l r d ti t d and lat ti in f and f rtili r in inati n ith in ffi i nt din ha ft n n n id r d th ain r in n traint in an ah lian h r i t al a f l t al and r n t ti al and f rtili r and d ana nt t n d fi i n a ar d t th ain n traint li itin i ld at th t d it a li ati n f n f rtili r n arl d l d i ld hil f rtili r and d ana nt r ain d n han d hi rr nd t r n ral i r i n that t r in ra ti r l t th l al r ndati n h nl ti n a f rtili r d hi h far r a li d in l r q antiti k ha than hat r nd d k ha t h r that a l rin in d ld n r nd d at rr nt l i ld l l t t ha and in i f th n ati ff t f n n a aila ilit r ann and airh r t n th r rd rr nt far r f rtili r ana nt i r r fita l than hat i r nd d th at r nt h a li ati n f r ani a nd nt a a rdin t far r th nl t ntial l ti n t th r l nd d th a li ati n f t ha an r t r d d ri tra did r t r n fi ial r a li ati n f r ani r r an nl artl l th r l t a li ati n i la r int n i hi h i a n traint f r an far r that ha a all fa il and r li it d finan ial r r h r ani att r a nd nt d d in th trial ar li htl hi h r than th a ra tra i ld hi h i a r i at l q al t rain i ld ta l r in i an i rtant a ti it in th r all ri r in i lik l t t f r th P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes li it d q antit f r ani a nd nt a aila l iall an r and t rth r r i ld a ntin t d lin ith r ani a nd nt a th il n t k i ht f rth r d l t d th r ar h r and far r a r iat d th r -t tin f n f rtili r a li ati n in t far r fi ld in th t a n ti n - far r- ana d trial h iti i al ff t f n f rtili r a li ati n did n t nl n in r ar h r t r th ir r ar h n n d fi i n t al ti at d far r t arti i at in th far r- ana d trial ar r r a r t find a l ti n ra idl and th r t tin th d all d th id ntifi ati n and di inati n f r i in t hniq ith t ndin ar f nd tin a ital and la r int n i trial at a r ar h tati n 3.5 Conclusions n l d that th a aran f l r d ti t in th r irri ati n h and th q nt i ld d lin in th arl id-nin ti a a d n d fi i n i ld l d t n d fi i n ar t n h lar h t r n it in lant r th at h rt di tan in th fi ld and th all nd t ta l diff r n in il r rti t that ri lant ar rr ntl ar nd th r ak- n int f n d fi i n - ffi i n n a f rth r in r d r a in n a aila ilit ld ha a d a tatin i a t n f t r ri i ld lth h it i nl a t d that lar q antiti f ar nat alt r n a aila ilit it ill i rtant t tt r id ntif th hani that l d t n d fi i n at th t d it a t tal il n nt nt in th r t n i r ti lar r than - tra ta l n and r ti lar r than a n f rtili r d f k ha far littl i kn n a t i rtan f n d fi i n in irri at d ri r in in th ah l t f th ah lian ri il ha an alkalin - al ar hara t r a f nd at th t di d it h n d fi i n ld i l an i rtant r in n traint f r th r ah lian irri ati n h in th n ar f t r ar r r a l t rr tl r lat th al ar nat r f th il t th a aran f th l r d ti t ar r id ntifi d th a li ati n f d d ri tra a a i l l ti n lth h a li ati n f n f rtili r i l la r t n i and r ff ti than f r ani a nd nt it i n t t a aila l in rkina a it ff rt and far r rati n t tain n f rtili r th a li ati n f d d ri tra th nl l ti n a aila l t far r at r nt it th r lati r nt intr d ti n ar a f irri at d ri r in t far r r d t ha d nd r tandin f r in n traint and i l l ti n hi t d h that far r kn l d an d t id r ar h n ri r in n traint in th ah l f r th t al n fit f th far r and r ar h r Chapter 4 The effect of straw application on rice yields and nutrient availability ik l h r in th ah l a t al ri i ld t ha in an irri ati n h in ntral th rn a ritania ar far l i ld t ntial t ha arli r t di h d that and d fi i n r th ain a r n i n traint ntri tin t th all i ld in ti at d th t ntial f ri tra a li ati n a a an t i r i ld and f rtili r ffi i n n an alkalin al ar il and a n tral il ar r at th t d it la ifi d th alkalin il a 'd rad d' and th n tral il a 'n n-d rad d' li ati n f t tra ha in r a d i ld t ha n a ra ind nd nt f il t and f rtili r d nl at n ar- t ntial i ld t ha a th iti ff t f tra a li ati n n l n r i nifi ant tra a li ati n i r d a aila ilit t n t a aila ilit h i r d a aila ilit a attri t d t in rali d fr th tra fr in r a d in rali ati n f il r ani att r ith a l rati and fr in r a d r r ffi i n f a li d in ral f rtili r r a d d d that i r d f rtili r r r n tra a li ati n a d t r d d nitrifi ati n d nitrifi ati n l h l f rtili r r r n th alkalin il ar d t th n tral il a attri t d t latili ati n l tra a li ati n did n t aff t latili ati n i ilar t di in ia h d littl h rt-t r ff t f tra n i ld and tak h th i that th iti ff t f tra a li ati n at r t d it i r lat d t th il ' l nt nt k and l rati h n ar d t t l land ri il in ia tra i a l - t alt rnati t i r i ld and f rtili r r r ffi i n at th t d it P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes 4.1 Introduction h irri ati n h f l ita in th rn ntral a ritania i n f th an t i al lar ah lian irri ati n h that r d l d t i r f d rit aft r th d a tatin dr ht in th and i z i th d inant r in th irri ati n h t al i ld ar ft n l t ha and far fr t ntial t ha hi h rai q ti n a t th n i ia ilit f th tl irri ati n h in thi r i n li r t al h r i an r nt n d t i r r d ti it hil k in in t t l in ral f rtili r ak a t f th t tal r d ti n t f r ri far r in th ah l n an t al n ha t r n l d d that in ral f rtili r ana nt iti n d and ti in in l ita i ft n far fr ti al ntri tin lar l t th r d i ld a t ntial in a t al i ld i ld l l ar al lar l r lat d t il t in l ita r d ti it r l ar r r n n d n far r-id ntifi d 'd rad d' il than n th - all d 'n n-d rad d' il h il ar al ar hil th il ar n t al ar n ha t r r d that il and l and and f rtili r r r ffi i n r h l r n th il = = than n il = = h th i d that l and n th il r artl d t latili ati n and i ili ati n r that r i rtant ith in r a in ar nat l l n n i a r t i r n tri nt a aila ilit iall n th il ld t in r a in ral f rtili r d lt rnati l th d ld d l d that i r th l r r ffi i n i f th a li d in ral f rtili r d hil k in la r r q ir nt at an a ta l l l i far r in ia ha ri nt d f r a l n ti ith th f tra a a l - t r f n tri nt and a a a t i r il q alit nna r a t ri far r in l ita rr ntl rn th ir tra alth h tra i d at attl f dd r at th nd f th dr a n h ff t f ri tra in r rati n n il q alit n tri nt tak and ri i ld ha n t di d in a id ran f il and li ati nditi n nna r a tat d that th i ld ad anta d t tra in r rati n r tra rnin r r al i a t t ha and it in r a ith ti a il f rtilit ild r ann and airh r t tat d that th r i littl h rt-t r ff t f tra in r rati n n ri i ld t that l n -t r n fit ar i nifi ant r th aj rit f th t di n hi h th a a th r ha a d th ir n l i n r nd t d at n tral t a idi l land il in ia nna r a it d hatt rj t al h f nd that a ra d f r thr nitr n l l and t a n in r rati n f t ha f fr h tra in r a d i ld t ha t t ha n an alkalin la l a il in ndia art fr in a nitr n r tra a li ati n i ht i r th r r ffi i n f a li d in ral f rtili r i r ial r ani that d th tra an a t a a ink i ili ati n h n tra i in r rat d h rtl f r tran lantin in far r fi ld itt t al r thi ff t i t rar and a Chapter 4 The effect of straw application on rice yields and nutrient availability f k t nth lat r i r ial r ani ill a t a a n tri nt r in rali ati n n a a and hida nna r a itt t al lk t al n l d d fr a lit rat r r i that th r f i ili ati n- in rali ati n ff r il in r ani at l l nd i t ad q at lant r th hil r d in i tati r th arl in th a n l a hin and lar d nitrifi ati n l n additi n t r ntin i l a hin and d nitrifi ati n l it ll i l that thi ff rin ff t al d r a th hi h latili ati n l n th il thr h t rar i ili ati n f f th r a- tra a li ati n a al infl n h h r a aila ilit tra i a r f and n d iti n art f thi a a aila l t lant r i r ial r ani that d r ani att r an al t raril i ili a i th a ith h a aila ilit f in r a n fl din ainl a f in r a d l ilit f - nd and in r a d l ilit f a- nd r ann and airh r t h r l a f - nd lar l d nd n th il r d l l h hil th di l ti n f a- nd d nd n th il and h a li ati n f fr h r ani att r nhan th d r a in th h and f r d al ar -alkalin il h r and n a a n tra an al indir tl i r a aila ilit thr h l ili ati n f - and a- nd h r f r h th i that lant a aila l in r a dir tl and indir tl h n tra i a li d r th a it f ll that th tra a nd nt an ha dir t and indir t n fi ial ff t n and a aila ilit r th t nt f th n fi ial ff t and th ir i a t n i ld ill d nd lar l n th i rtan and d rati n f i r ial and i ili ati n n rd r t rif h th r tra an d a a l t a nd nt f r th i r nt f i ld in l ita nd t d a ri f fi ld trial ith tra n th and il n additi n n- tati n t trial r arri d t t f rth r a in th ff t f tra a nd nt n r that d t r in and a aila ilit r ial att nti n a i n t th id ntifi ati n f r that aff t and n th alkalin il 4.2 Materials and methods it d ri ti n l ita i it at d in ntral th rn a ritania h li at in l ita i t i all ah lian ith rrati rainfall r t n l and t r f ll d a h rt l ri d r r ar ith ini air t rat r a l a and a h t dr a n ar h n ith a i air t rat r t h l ita h a ilt in and a lar da all f r ra i tri irri ati n thr h t th ar h irri ati n at r q alit ari P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes thr h t th ar and d a a f n ti n f rainfall and a rati n h il ar f nd n th r and iddl l and ha f r d fr th hi t ar nt at rial h il ntain r littl h h r k h il ar f nd f rth r d n l n th l r l ri r ank and d r i n h il ha a artl all ial ri in and ntain r h h r k ha t r n th il r ani ar n and rati ar l a l FAO (1990) i ld trial ar h r- ana d tra trial r nd t d in th and dr a n n th a and il il n th it = a hi h r than n th it = i ari t - - - - - in a ritania kn n a ah l a d r l l f f rtili r d and t l l f tra a li ati n r lt d in th f ll in i ht tr at nt = ntr l = = = = ntr l = = = r at nt r r at d thr ti in a rand i d l k d i n h t tal f rtili r r a d a k ha di id d in thr lit a li ati n thr k aft r tran lantin at ani l initiati n and at h adin h f rtili r a k ha and th d a k ha ll f rtili r a a li d f r tran lantin a al a li ati n in th f r f tri l r h hat h tra a li d a fr h at a rat f t dr att r ha h tra a in r rat d l l int th t il da f r tran lantin hi h in id d ith il tilla ra ti ndi id al l t i a add i ld r ti at d fr a har t ar a in th nt r f th l t rain i t r nt nt a d t r in d fr a -hill a l rain i ld r rr t d t i t r nt nt ar t ind a d t r in d fr n-dr i t r nt nt tra and rain i ht f th -hill a l tra i ld a d ri d fr th har t ind and th rain i ld n ntrati n f in rain and tra at at rit r d t r in d in th i r j ldahl th d r n r lant h h r n ntrati n r a r d in th th d f hida t al tal and tak r ti at d fr th Chapter 4 The effect of straw application on rice yields and nutrient availability and n ntrati n f tra and rain and tra and rain i ld il l a ti at d fr t tal tak in and il l f ll d fr th t tal tak in tra l a ti at d a th diff r n in tak t n and and tra l a i ilarl al lat d in th diff r n in tak t n and r ti l and r al lat d a th additi nal n tri nt tak t tal n tri nt tak in il and tra n tri nt l f ll in f rtili r a li ati n di id d th in r ani f rtili r d t trial lar q antit f t il a a l d in a ri fi ld rd rin th fi ld trial at th d rad d il = h a l a r ht t th tati n in aint i air-dri d and h ni d f r in tran f rr d t la ti lit r l r l n k t h trial n i t d f tr at nt ar in in f rtili r a li ati n tra a li ati n and th r n f a la ti r a l a h tr at nt a r li at d ti r ltin in a t tal f t hi h r di tri t d rand l r t lar n r t a in t r at rat d ith at r da f r tran lantin hr thirt -da - ld ri dlin f - - - - ah l r tran lant d int a h t t th il i r - n ir n nt f irri at d ri a t n th t a fill d ith arth and a rd r f ri lant a tran lant d ar nd th t t i i li ht titi n at r la r f a t a aintain d in th a in t irri at th rd r ri dlin and t n r th a il and at r t rat r f r all t tal d r a a t k ha and d a t di id d in thr lit a li ati n and at arl till rin ani l initiati n and fl rin r a a di l d in irri ati n at r ri r t a li ati n t n r an n di tri ti n r th il tra d a t t ha and d a t k ha tra a i d ith th t t il thr da f r tran lantin ran l r li d i ltan l h tr at nt t r r d ith tran ar nt la ti dir tl aft r th fir t a li ati n in rd r t r latili ati n l n th iddl f th r d t a hi h t a in rt d int th il d thr h hi h th lant ld r h fl d at r P = Phosphorus application of 26 kg P ha in id th t a r d ith N = Nitrogen application of 175 kg N ha a la r f all l t r n f a all N= Nitrogen application of 87,5 kg N ha in rd r t di ini h a han S = Straw application of 5 t ha and C = Pot cover with transparent plastic and t n th at r rfa and th acidification of the floodwater to a pH < 7. at h r i ilar t r P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes al d in n n- r d t t radi at ia ff t n rd r t all th nit rin f th fl d at r q alit a r nd h l a ad in th la ti r h h l a l d ith a r r t r rth r r th fl d at r in th tr at nt a aintain d l a an additi nal an t d r a latili ati n hi h i r l h n ikk l n ail a idifi ati n f th fl d at r f tr at nt tart d dir tl aft r th fir t a li ati n in l rri ati n at r ri inat d fr th n al i r t alkalinit a in r a d t l l in a in rd r t i i a ra irri ati n at r q alit in l ita t r irri at d dail t aintain n tant at r l l n rd r t a id i alt tr th fl d at r in th t a r n d at and da aft r tran lantin h fl d at r and t rat r r a r d dail at a and at in all t n ntrati n f in th fl d at r f all tr at nt r nit r d at and da aft r a li ati n h a l r tak n at a and t r d at in air-ti ht l r l n ttl l aft r a idifi ati n t ith n ntrat d l n ntrati n f a d t r in d ith th ali lat th d l n l d at r n ntrati n f tr at nt and tr at nt r nit r d aft r th a li ati n in a kalar - ntin -fl anal r lant a aila l in th il a nit r d in r in a l n an a h a l ntain d l f ati n ani n han a a it and had a t tal rfa ar a f h r f a r ti n th r in i n id r d t i i i rtant han l ili ati n and tran rt r rrin in th ri rhi h r r ann t al il a l f th and tr at nt r tak n at and da aft r tran lantin a h a l a lit int thr - a l and tran f rr d int airti ht l r l n ttl r in a l a in rt d int a h - a l and th ttl r t r d f r in ati n at a dark la in a l r r d fr a fir t ri f - a l aft r da f in ati n h a r d r a r at d aft r and da f in ati n a tra t d fr th r in a l in l a an tra tant r ann t al h il at d th a a r d kl in n trati n l tr d ar t a d n at at rit and i ld and i ld n nt r d t r in d lant a l r n dri d lant and n ntrati n n tri nt tak and f rtili r r r rat r d t r in d a in th tra fi ld trial tati ti al anal tati ti al anal r nd t d in th ft ar a ka f r ind r i n i nifi an f fa t r and int ra ti n n i ld and lant n tri nt n ntrati n fr th fi ld trial r anal d f r a h a n in an f r i ld r ar d in l a t q ar diff r n t t an f r f diff r nt tr at nt r ar d ith th t t i nifi an f fa t r and int ra ti n n ak n ntrati n f fl d at r in th t trial aft r th nd and rd r a a li ati n r anal d in n -tail d t d nt t-t t a d t ar n ntrati n in fl d at r f th t trial Chapter 4 The effect of straw application on rice yields and nutrient availability 4.3 Results i ld and in th fi ld trial i ld ar h n f r a h il t a n inati n in i r h trial at th il ff r d fr i ird da a d rin th and n r r i ld data r tain d r lant a r nt h i ht till r n r at id- a n h d that lant r th tr nd r i ilar t hat a f nd in th data n t h n h iti ff t f tra n ri r th a alr ad n ti a l at arl till rin ta th f rtili r d and tra a li ati n h d i nifi ant ff t n i ld at th it in th t th tra ff t a n t i nifi ant = in th h r a n i nifi ant int ra ti n in an f th trial n r a th r an il t int ra ti n in th trial i ND D without straw a without straw a a with straw 8 a ab ab with straw ac bc ab 6 bcd c ce def d f e - - N - N P N P Treatment ND a a without straw a a ab with straw b c d Y ( h ) P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes N NP N P S N S NP S N P S N NP N P S N S NP S N P S th i ld in r a in ff t f tra a ind nd nt f f rtili r d and il t tra a li ati n had a i nifi ant iti ff t n and n ntrati n in all trial rtili r d al had a i nifi ant ff t n in all trial t th il in th trial and int ra ti n had i nifi ant ff t n h and r i nifi antl l r at th il ith al ran in fr Chapter 4 The effect of straw application on rice yields and nutrient availability k and k r ti l n th il and fr k and k r ti l n th il il t and il t int ra ti n f r and r n t i nifi ant itr n tak and ar h n in a l a n a ra k k hi h r n th il h n ar d t i ilar tr at nt n th il n th il th th a li ati n f and tra i r d al tra a li ati n had n i nifi ant ff t n at th il t f rtili r d had n th il a k in tr at nt that r i d in inati n ith n r half th d and k in tr at nt that r i d f ll d r nd r i ilar n th il t a di tin tl hi h r k tak and f r all fi ld trial ar r nt d in a l h n tra a a li d in r a d n th il t d r a d n th il h n n tra a a li d in th trial al r di tin tl hi h r n th il h n ar d t th il n th il a di tin tl hi h r in th h n ar d t th a r id al ff t f a li ati n a n t tak n int a nt in th al lati n f th r r fra ti n.

N S - P.

-.

.

.

.

NP NP.

.

.

.

.

DAT (days after transplanting) l d ter t. P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes N P - - C S S C NP NP DAT (days after transplanting) nit rin il and at r h i tr han in th t trial h r lt f th rnin a fl d at r a r nt ar h n in i r h r lt f th aft rn n a r nt h d a r i ilar att rn t al r a t nit hi h r f r tr at nt ith f rtili r a li ati n and nit hi h r f r tr at nt ith t f rtili r a li ati n n t h n tra a nd nt had littl ff t n th fl d at r and al in all tr at nt r hi h n h t rt tantial latili ati n h han f fl d at r n ntrati n an r d in i r h ak n ntrati n aft r th nd and third a li ati n h d r i ilar tr nd fa t r r all i nifi antl ntri tin t th n ntrati n and th r a i nifi ant int ra ti n f and aft r th nd a li ati n ak n ntrati n in tr at nt that r i d f rtili r d r a d in th f ll in rd r - - -- n ntrati n aft r th r a a li ati n r nl a r d fr da n ard d t t hni al r l n da aft r th a li ati n th tr at nt had di tin tl hi h r n ntrati n ( eq l + - Chapter 4 The effect of straw application on rice yields and nutrient availability 0 DAT.

32 DAT.

92 DAT.

.

N NP NS NPS Treatment H l d at r n ntrati n f r th tr at nt and ari d littl d rin th fir t da aft r th nd a li ati n t a ra n ntrati n in th tr at nt l l a i nifi antl hi h r than in th tr at nt l l h in ati n ti and da had n i nifi ant ff t n th a r d at th r in a l n i r al ar h n f r a l fr and and da in ati n t n diff r n t n th tr at nt r f nd t in th tr at nt a i nifi antl hi h r than in th and tr at nt t in th and tr at nt r i nifi antl hi h r than tr at nt and 4.4 Discussion n th fi ld trial th a li ati n f tra in r a d i ld t ha n a ra ind nd nt f il t r f rtili r d n th a i ilar i ld in r a t ha ld r d t f r th tr at nt that r i d th and f rtili r n th il h i ld f th latt r tr at nt r l t i ld t ntial t ha ha t r n f rth r i ld in r a ld t d n th il a li ati n f k ha i nifi antl in r a d i ld ddin f rtili r f rth r in r a d i ld at th il indi atin th rr n f - li itati n n th i ld l l r i ilar at th il t f r all tr at nt resin (, l c P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes t f r th tr at nt that r i d f rtili r t n f rtili r i ld f r th latt r tr at nt r l r at th il than n th il indi atin that d fi i n a r r n th il h lant n ntrati n and tak nfir that d fi i n i r i rtant n th il n th il a l th d fi i n l l k r ann and airh r t and arti larl l k f r tr at nt that r i d n f rtili r h t f th fi ld trial a i ilar t findin in ha t r h r n l d d that d fi i n a a aj r n traint in l ita iall n th il h n t n f rtili r i a li d n d fi i nt nditi n a li ati n f t n f rtili r tak did n t r hardl in r a h n tra a a li d n th il n n l d that tra ha littl dir t ff t n a aila ilit and a h ann t n id r d an i rtant r ith r r th r an i n that tra in r a d a aila ilit l ili in art f th r a- nd in th il h ff t f tra n a n ati f r th il t li htl iti f r th il r r in a l a r nt in th t trial t d n ati ff t f tra a li ati n n a aila ilit in th il rin th tati r th ri d in tr at nt that r i d f rtili r a ark dl l r h n in d ith tra a li ati n d r a in a aila ilit d rin th fir t k aft r tra a li ati n i lik l d t i r ial i ili ati n n l d that d fi i n i an i rtant i ld-li itin fa t r iall n th il r th r i littl id n that indi at that th a li ati n f tra i r a aila ilit n ith r f th t di d il n in that tra a li ati n had littl iti ff t n a aila ilit hil at th a ti it a li ati n in r a d i ld i nifi antl ha all th r r a n t l l a in th ff t f tra a li ati n n a aila ilit n th il n tr at nt that r i d n f rtili r tra a li ati n in r a d i ld t ha n a ra and tak k ha n a ra f r th il t hi q al a t half th a li d thr h tra a li ati n hi i r lati l hi h h n ar d t lit rat r al n d iti n and n tri nt r l a f ri tra nd r th r ailin nditi n ill a - an a t al h r f r a that th iti ff t f tra n tak in th n n-f rtili d l t i artl d t an additi nal r l a f il h rati f th l ita il i l and in th ran nl f nd f r il i r i ta i hardt t al hi indi at that i r ial r akd n f il r ani att r i ri aril ar n li it d h a li ati n f r r id ith a hi h rati ld r id il i r th n ar n r t in rali art f th -ri h n id it dir t ff t i tra a an - r tra a indir tl i r a aila ilit thr h in rali ati n f -ri h i ld l l f r tr at nt that r i d th and f rtili r r i ilar at th il t lant n ntrati n tak and r all h l r n th Chapter 4 The effect of straw application on rice yields and nutrient availability il h n ar d t th il r th in r a f i ld tak and n tra a li ati n a r i ilar n th il n th tra ff t a ind nd nt f il t n tr at nt that r i d th f ll and d tra a li ati n in r a d tak k ha n a ra hi h lar l d th nt nt f th a li d t tra ha h in r a d tak a al r d in th hi h in r a d k k f r tr at nt at th il latili ati n l ar lik l t hi h n th il d t it hi h and al ar hara t r in h and fl d at r in th t trial a hi h n h t rt tantial latili ati n l dd and atri k h n t al r d hi h r n ntrati n h n fl d at r a a idifi d and attri t d th h n n n t d r a d latili ati n h n i t ntl hi h r n ntrati n in th fl d at r f tr at nt rr nd t h n' r ati n and ar in lin ith th a ti n that latili ati n l ar i rtant n th il n r intr d ti n h th i d that th a li ati n f tra ld d r a latili ati n l thr h t ral i r ial i ili ati n f f thi ff rin ff t f tra h ld hi h t n th il and ld l ad t hi h r in r a in than n th il r did n t r thi h th fi ld trial r id d n id n that rt d th h th i f d r a d latili ati n d t t ral i r ial i ili ati n l d at r a r nt in th t n ith r r id d id n f r r d d latili ati n h n tra a a li d n th ntrar a li ati n f tra in r a d in th fl d at r hil fl d at r in n n- r d tra tr at nt r ain d a hi h a in n n- tra tr at nt hi ld n r lt in in r a d latili ati n rat in tra tr at nt ld n t al alr ad r rt d that in r a d r a h dr l i r lt d in in r a d fl d at r n ntrati n hi h nhan d latili ati n l rth r r if latili ati n d r a d a a r lt f tra a li ati n h ld ha r d n ati int ra ti n f th fa t r n ak n ntrati n t th in r a in ak n ntrati n n tra a li ati n a q al r hi h r in tr at nt h n ar d t th n tr at nt h r f r r j t th h th i that th a li ati n f tra i r a aila ilit thr h a d r a in latili ati n l hi n l i n i in lin ith t di ian t al and ill t al h f nd that a li ati n f ri tra had r ti l n ff t and an in r a in ff t n latili ati n l f tra a li ati n d n t d r a latili ati n l th n hat r i r d n th il h an r a f nd in th fl d at r a r nt f th t trial h han f n ntrati n in th fl d at r aft r th nd and rd a li ati n h d i ilar att rn i th tra and r i nifi antl in r a d ak n ntrati n t da aft r th and a li ati n n ntrati n in tr at nt r n l n r hi h r than th in tr at nt that r i d n attri t th hi h r ak n ntrati n in th tr at nt t in r a d h dr l i f th a li d r a hi iti ff t f r ani att r a li ati n n r a h dr l i a f nd arli r ral a th r attnaik t al P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes ahra at ill t al f nd in in ati n trial that a t f th a li d r a h dr l d ithin da in h at tra and r n an r a nd d il ar d t da f r th na nd d il n d l ti n f th a li d r a t k a h r ra id in ri tra a nd d il r ra id h dr l i ld l ad t hi h r ak n ntrati n initiall t ld l a l r a f r n r i n t lat r n i da h n tran lat thi t th tra and n tra tr at nt it ld an that t d ak n ntrati n t hi h r f r th tra tr at nt t th ak ld f h rt r d rati n h n ar d t th n tra tr at nt n th r rd fl d at r n ntrati n h ld initiall l r t lat r n hi h r in th n tra tr at nt h n ar d t th tra tr at nt r aft r th initial ak n ntrati n da t fl d at r in th tra tr at nt d r a d t l l q i al nt t and n t l r than th n ntrati n in th n n- tra tr at nt da la i l lanati n i that th fl d at r n ntrati n in th tra tr at nt r ain d r lati l hi h d t d r a d nitrifi ati n-d nitrifi ati n l t i n rall a r d that th rat f d nitrifi ati n i ntr ll d th rat f nitrifi ati n in fl d d il a t al itrifi ati n-d nitrifi ati n i an i rtant f rtili r l hani in irri at d ri alth h ti at ar id l t a th r find l f f a li d lakh t al dd t al dd and atri k ha d r a n t li that nitrifi ati n d nitrifi ati n l ar r hi h in l ita ir tl l t d rat indi at that tantial l f a li d r at th and il ndl th il ntain littl r ani ar n k in inati n ith a l rati i r ial a ti it i th r f r -li it d n in ati n trial r d ti n rat a ti l r n th l ita il h n ar d t f ia t- t di d ri il ahaa a an all n i iana and ila an d n li h d r lt a r lt nitrif in a t ria ld ff r littl fr n titi n ith i r i ta that d r ani att r h r f r hi h nitrifi ati n rat ld tain d in th n - tra tr at nt r a li ati n f fr h r ani att r lik l in r a d titi n f r n a t ria that a r i all r akd n r ani att r t t th nitrif in a t ria f r th li it d a nt f n in th fl d d il ht and r tra t n r a d n titi n ld l ad t d r a d nitrifi ati n rat and n q ntl d r a d nitrifi ati n-d nitrifi ati n l dh a t al h d that nitrifi ati n t ntial f a l fr r n- an r a nd d l t a di tin tl l than that f a l fr ntr l l t in a ri il h l r fl d at r n ntrati n in tr at nt ar in lin ith thi h th i alth h th latt r ld al attri t d t hi h r d nitrifi ati n rat a a r lt f ri tra a li ati n h t r and n ta l th il ha i ilar and rati and a that th ara l hara t ri ti lain h th iti ff t f tra n a aila ilit and ar r i ilar n th il Chapter 4 The effect of straw application on rice yields and nutrient availability 4.5 Conclusions n l ita th a li ati n f ri tra ha a tr n iti ff t t ha n ri i ld ind nd nt f f rtili r d and il t hi i in ntra t t t ian ri il that h littl h rt-t r ff t f ri tra a li ati n n i ld h i ld in r a an attri t d t in r a d a aila ilit f n t n r a d a aila ilit i lik l d t in rali d fr th tra and in rali d fr th hi h ha a l rati rth r r th a li ati n f tra in r a d r r ffi i n f a li d r a- h i r d ld n t attri t d t a d r a in latili ati n l alth h f nd tantial id n that indi at that latili ati n l la a aj r r l n th r alkalin al ar il attri t d th i r d t r d d nitrifi ati n-d nitrifi ati n l itrifi ati n i t d t la an i rtant r l in th il ar d t t f ia' aj r ri il th il ha a l and l rati and r lati l littl i r k n d n h n il ar in at d ti at that nitrif in a t ria ri n littl titi n f r n hi h r lt in nditi n that fa r lar nitrifi ati n d nitrifi ati n l h r than in t ian ri il a li ati n f fr h tra ill l ad t a r lati lar in r a f th il' and rati tra a nd nt ill ti lat i r i ta a ti it and in r a n titi n d r a in a aila l n ill l d n nitrifi ati n and q ntl li it nitrifi ati n-d nitrifi ati n l h th i that ri tra ha i ilar ff t n i ld and n th r ri il ith i ilar l and rati rif h th r th iti ff t f tra n a aila ilit i r lat d t th l and l rati f th il f rth r r ar h h ld nd t d in -la l d r a ar r in l ita an ri tra a a h a alt rnati t in r a i ld and r fita ilit n th h rt t r ind nd nt f th ir in ral f rtili r ana nt and il t Chapter 5 Actual and potential salt-related soil degradation in an irrigated rice scheme alt-r lat d il d radati n d t irri ati n a ti iti i n id r d a aj r thr at t th taina ilit f ri r in nd r i-arid nditi n in t fri a i r d ti it r l r lat d t il alinit alkalinit and t ra hi iti n r r d in an irri at d ri h in th rn ntral a ritania tail d t d f il in a t q n r al d that hi h t t il alinit and alkalinit r f nd at th hall il f th iddl and r l r il ha f r d fr th hi t ar nt r k hi h r l a ar nat ri h alt n ath rin ithin th il lar diff r n in alinit and alkalinit l l r at h rt di tan indi atin ini al r nd at r fl and a tr n ariati n in th h i al iti n f th rti all iti n d dr k rth r d n l il ha a artl ll i -all ial ri in r di ntati n d rin ann al fl d in r a d il d th and alinit l l r ain d l d t l a hin l ita irri ati n at r d i a n t th t alkalin in th ah l r n l ar indi ati n f ndar alini ati n r alkalini ati n d t irri ati n a ti iti r r d ari n f hi t ri al data r al d n i nifi ant han f t il alinit and r th la t thirt ar h d l a d t t d a t al and t ntial d l nt f il alinit and alkalinit r l i latin i n ntrati n f th irri ati n at r thr h a rati n h han int a tr n l di alkalin l ti n d t r i itati n f - al it and ili at in ral did n t fit ith rr nt iti n f r nd and rfa at r hi h h d h i al ntr l f alkalinit at hi h n ntrati n n r rati n f ati n han r in a all l dr il t al i at rat d r lt d in a tt r fit ith fi ld data lt indi at that th il ff r a a it t nt ra t alkalini ati n r i lar r th il at r and alt alan n d t q antifi d in rd r t d t r in d l nt rat and q ili ri l l f il alinit and alkalinit f r diff r nt il t at r ana nt inati n hi t d d n ith r r j t th h th i that alt r lat d il d radati n j ardi th taina ilit f ri r in in th ah l n r d it r id id n f r it rifi ati n r r r lt ar in lin ith th r t di in t fri a in that rr nt alt-r lat d r d ti n r l ar inh rit d rath r than in ind d irri at d ri r in P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes 5.1 Introduction n r n t th dr ht hi h d a tat d r and li t k in th ah l in th and a i in t nt r ad int rnati nal d n r and ah lian ntri t ta li h lar irri ati n h that ld i r f d rit rri at d ri z a intr d d a th ain r in th h i r in in th ah l r q ir lar a nt f at r d t th hi h a rati d and f th h t and dr li at lth h t irri ati n at r in th ah l ar f d q alit i l in rali d at r i n ntrati n thr h a rati n an ha ard a th at r ft n a iti al it id al lkalinit l = lkalinit a in l l all t al rtrand t al il d radati n thr h alini ati n and alkalini ati n i n id r d n f th t i rtant thr at j ardi in taina l irri at d ri r in in th ah l rtrand t al i in n t al i in t al i n th hi h in t nt t f irri at d a ri lt r and th hi h t f r r in alkalini ati n r r a ti n ha t tak n h n alt-r lat d r d ti n r l ar f nd in th n ir n nt r r d ti n r l r lat d t il alinit and alkalinit ha n r rt d thr h t th ah lian n i th n al i r d lta r i t al ffi d i r in ali rtrand t al r all in rkina a arr t al a in i r arl t t al a and l ita in a ritania ha t r r th r lt f il t di at th it r n t al a in lin ith th h th i that irri at d ri r in in r a alini ati n r alkalini ati n in th ah l n th ntrar n and r i h d that il alinit in th n al i r d lta ri inatin fr arin d it r r i l d r a d a a f n ti n f ri r in int n it n th ffi d i r ri i ld in r a d i nifi antl r th la t ar a a f n ti n f i r d ana nt ra ti hil il alkalinit d r a d li htl n th la il d f r ri r in t in r a d n th r and il h r ta l r in r ail d arl t a n th r all in d fi i n in ri a f nd hi h d r r lat d t th al ar ri in f th ar nt at rial than t a ti alkalini ati n ind d irri ati n arr t al n th a irri ati n h ar i r and an li t- an f nd that il alkalini ati n a n l n r rrin and ar i r t al r d that alkalin il in a d alkalini d r ra id h n lti atin th l al f dd r r r i nd r r d nditi n i ilar t irri at d ri r in r th a t di it f ll that alt-r lat d il d radati n in irri at d ri h in th ah l n d ar f l t d f r dra in n l i n a t it i rtan it r and it t ntial han n thi t d f n th irri ati n h f l ita th rn ntral a ritania i r n tr t d t n and ith a rfa ar a f ha it i n f th an r nt and t i all lar irri ati n h in th ah l lan t t nd th irri ati n h t h tar ha far n t n at riali d artl d t r d ti it r l th i ld l l and Chapter 5 Actual and potential salt-related soil degradation in an irrigated rice scheme r d ar a tart d t d lin a f ar aft r in tallati n f th h n additi n far r in r a in l lain d a t alinit r l and a t ha f th ar a had n a and n d ar r and t n i n rk r in th ar a f ar that alt- r lat d il d radati n thr at n th i t n f th irri ati n h n ha t r h d that r d ti it r l in l ita r th r lt f th il q alit r l and - ti al r ana nt i i ld in r a d and th r nta f a and n d land d lin d in fr hall t hi t ar nt r k il l t d r il f rth r d n l h t il and al f hall il r i nifi antl hi h r than f r d r il t th ld n t la ifi d a alin n r di f ll in la ifi ati n rth r r th l f th irri ati n at r ari d t n and l l ha t r hi h i t ti hi h r than n ntrati n r rt d rtrand t al arl t t al and i in t al f r th i r and n al i r hi ak l ita irri ati n at r t ntiall r dan r ith r t t alkalini ati n ha ard than th at r f th t aj r ah lian ri r h th i that il alkalini ati n ill d l r ra idl in l ita than l h r in th ah l n th it ld a t a an arl arnin t h j ti f thi t d r i t hara t ri th di tri ti n f alkalin alt in l ita th r f in n th th t ntial r l f th hi t ar nt r k and th irri ati n at r a r f alkalin alt and ii t r at in i ht int th d na i f th il d radati n l kin th a k ard i arin a t al t hi t ri al il data and f r ard i in h i al i lati n t l in ti in rd r t tain a i-q antitati id a n th han f th il nd r th rr nt irri ati n ra ti 5.2 Materials and methods h r ar h it h li at in l ita i t i all ah lian ith rrati rainfall r t n l and t r f ll d a h rt l ri d r r ar ith ini air t rat r a l a and a h t dr a n ar h n ith a i air t rat r t f r n a tran irati n i r h r l ir ri r at r h d tr a f l ita i l at d n th a ritanid l i al r i n n i tin tl f r a rian and ri ar ta r h d r k hi h a f ld d and lift d in th ala hian ra arit h il ha f r d fr a ar nt r k r d at a d th ran in fr l t d n l and n i tin tl f hl rit hi t r n hi t al hl rit hi t i a hi t and q art n th hi t rit and ir n id in ral ar al fr q ntl r d hir n h rti all iti n d hi t ha a n rth th ri ntati n radi all ndar d l rit intr i n an r d in th f r f all r k t r h land a i hara t ri d P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes Rock Outcrop lar li htl l in arr n lain int rr t d r k t r and all tt that ar n rall ark d th r n f hr and all tr r aj r r h l i al nit an di tin i h d in th l ita irri ati n h i r k t r ii th r and iddl l iii l r l and d r i n and i ri r ank i r il f th land a ar hall and ha f r d fr th ath r d ar nt r k rth r d n l th il ar r d ith l al ll ial and all ial d it hi h in r a il d th t il at th ri r ank n i t f alt rnatin and and la d it arall l t th f r r ri r r and il ar t d h r l ri r i a tri tar t th n al i r ri inall th ri r r i a int r itt nt ith ak fl d d rin rain nt h n tr ti n f th da l kin th ri r narr a a thr h th a- a ntain hain r d d ak fl d and a r d a ini di har fl in th dr a n at r fr a k lar at r h d n a lat in a hall t lar artifi ial lak k h n r al r t nti n a a it f th da i lar ar d t i lat d n d t irri ati n at r i i l d hi h ti l ad t d l ti n f t k d n t th ini t ra a a it r q ir d t n r l t irri ati n f th and ar a h n ral it ati n in l ita i n f i at r r anal aint nan i d r th n n-a li ati n f draina ra ti and n n-f n ti nal drain nditi n that ar in r a in th ri k f alkalini ati n a rati d and i r hi h and a nt f r f t tal at r l fr th da a r lt irri ati n at r q alit ari thr h t th ar i = and = d j t aft r th t a n and in r a in t = and = d at th nd f th dr a n an t n n li h d Chapter 5 Actual and potential salt-related soil degradation in an irrigated rice scheme tail d t d f il in a t q n h di tri ti n att rn f alkalin alt a t di d in a t q n in rd r t r at f rth r in i ht int th ri in and han f alkalinit in l ita ll il a lin rr d t n an ar and t r a d n th il a and tat nt f far r and t n i n rk r a l n t q n a l t d f r d tail d t d in th n rth rn art f th irri ati n h irri ati n l k h t q n r d th th r h l i al nit r and iddl l a ll a th l r l and d r i n and an n id r d r r ntati f r th aj rit f th l ita ri il h t q n in l d d f r irri ati n l k l k t ith an a ra idth f i r a h irri ati n l k a d li it d an irri ati n anal l and a draina anal d n l t r aint nan draina anal r hall h a il d inf t d and ral ntain d at r thr h t th ar n d rin fall ri d ar r a and n d ri lti ati n in th r- l irri ati n l k l k nl a f ar aft r n tr ti n f th h rdin t far r il q alit a r and th t il t t n n a h irri ati n l k a l it r h n at nl a d int r al r ltin in a t tal f a l int rin th l t t q n t tal f a l a tak n at d th int r al t th ar nt r k in a hand a r a l r n-dri d and r nd f r anal in in a a t and in a a t lt f th anal r int r lat d in rd r t tain r - ti n a il it r d d n t th ar nt r k at thr diff r nt it in th t q n i r and h il r fil r d ri d f ll in th id lin f r il r fil d ri ti n and il a l r tak n f a h h ri n f r anal i a l r anal d f r and - l in a a t and l tri al nd ti it in a a t han a l a a a r d t r in d in an aft r tra ti n ith a ni hl rid ati n han a a it f th a l a d t r in d a d ri d ha an il t t r a anal d in th i tt th d and la ifi d f ll in th id lin n i ht i t r r in tall d al n th t q n rin irri ati n l k and f th t q n i r and i t r r a h d d n t th ar nt r k r t hard q art la r n t all i t r ntain d at r hi h all d f r i ltan ari n f r nd at r q alit al n th t q n at r a l r tak n at a h i t r and filt r d aft r n it i fi ld d t r inati n f and alkalinit ran ilt r d - a l r a idifi d in n ntrat d and t r d in l r l n ttl f r la rat r anal i ati n r d t r in d in an l a anal d l ri tri all in r r th i anat i n t al a d t r in d l ri tri all in a l and th l l and i n ntrati n r d t r in d f ll in th P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes Block I Block II Block III Block IV O O O O sample point O 2 soil pit O O piezometer O O drainage canal 20 O 2000.

irrigation canal O O 0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00 400.00 500. 0 300 400 100 Distance ( m) ili l di a id r d r n and r h r at rati n indi f r in ral d fin d in th data a r al lat d in th h i al i lati n d l arkh r t and l hi all d f r th a nt f in ral that ld t ntiall r i itat in thi n ir n nt th r alt rin th il l ti n iti n eig t e se le el ( Chapter 5 Actual and potential salt-related soil degradation in an irrigated rice scheme Block I Block II Block III Block IV 2450. 2400. 2350. 8. 2300. 8. 8. 2250. 7. 2200. 2 7. 7. 2150. sample point 7. 2100. soil pit 7. piezometer 2050.0 6. drainage canal 6. 2000. irrigation canal 6. 0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00 400.00 450.00 500. 0 300 400 100 Distance ( m) i t ri al anal i f il data i t ri al il data r ar d t th r lt f r nt il t di in rd r t rif h th r il q alit d r a d in irri ati n a ti iti tart d h ar a rd rin th r l ir i r d n tr a f th a- a ntain hain ha n th j t f ral il t di r th la t ar h fir t t d in ti atin th il t ntial t tain irri at d a ri lt r a arri d t th t a a r nnai an t d id ntif in th aj r il t t n th f t r da l ati n and i a k f rth r d n tr a t a l f t il eig t ( P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes h ri n ar in in d th fr t r tak n and and r a r d in th at rat d a t tra t nd r d tail d t d a arri d t l a t r f in n ha t ntial irri a l land j t d n tr a f th rr nt da in l din th a t al ha l ita irri ati n h and r d t r in d in a at r tra t f r all t il h ri n f il it rin th t tal ar a n a third il t d a nd t d th r n h r a ntral d t d r l q i nt d tr - r f in nl n th ha f th rr nt h il it thr h t th h r t di d and a l d il a l fr th t h ri n a ra d th r anal d f r and in a tra t f rth il t d n li h d a arri d t in th a ritanian a rat ir ati nal d l t in ti at il d radati n r l in l ita that ti f th irri ati n h land had alr ad n a and n d il h ri n f all a and n d fi ld r a l d and and r anal d in a a t h t r nt il a l r tak n f r thi t d at th n t f th t a n and th t a n il a l r tak n in far r fi ld thr h t th irri ati n h and in l d d th lti at d and n lti at d fi ld h a l r anal d f r in a a t and in a a t an f r t il fr th and il t di r ar d ith th an- l t t in th ft ar lt fr th r il t di r ar d q alitati l a th d l i al diff r n did n t all f r tati ti al ari n i diff r nt a l ar a and tra ti n th d h iti n and han f rfa and r nd at r hr h t th ar irri ati n draina and r nd at r a l r tak n if r nt at ari it ithin th irri ati n h at nth int r al a l r tr at d and anal d a d ri d in th d tail d t d f il in a t q n h han in irri ati n at r iti n n n ntrati n thr h a rati n r d l d in th h dr - h i al i lati n d l and th data a arkh r t and l h initial irri ati n at r iti n d f r d lin a th a ra f al a r d in l in n ntrati n a al lat d a in q ili ri ith ka linit r th d l r i l t d th in ral that r lik l t r i itat in nat ral il n ir n nt ithin th r d alinit ran i - al it i lit illit r i itati n f r al it a n t all d h i al anal i f ar nat n d l a l d d rin th d tail d t q n t d r al d that th ntain n a ra f hi h i i ilar t findin f ar and h ad h r i itati n f a - al it a lid l ti n a all d in th q ili ri n tant f al it [l k = ral a th r - a f r ak ad darri f r h tt l j rid ar i r f r i r irri ati n at r and nd t al f r nja irri ati n at r - t d ntr l f ili a and Chapter 5 Actual and potential salt-related soil degradation in an irrigated rice scheme a n i thr h f r ati n f i lit alth h th r na l t i id n f r th r n f th in ral in th il r r i itati n f i lit i i ll th r i itati n f r l - nt rill nit in ral that an nl d l d if l l in i tak n int a nt all t al a t al and ar i r r d that th han f n ntrati n in th il l ti n ld n t lain d i l n ntratin irri ati n at r in th il l ti n a h r ntr ll d i d r a d r ra idl than hat ld t d fr th d l i lati n h h th i d that i tin i-ri h in ral in th il a t a a i ff r r idin th n ar r at rial f r th f r ati n f -ri h nt rill nit la intr d d thi il i ff r f n ti n all in di l ti n f q art = fr an infinit t k th nt i n ntrati n in th il l ti n r a h th f th r nd at r a l all th r t if th al at hi h r i itati n f a ifi in ral r in rd r t a nt f r th rr n f r at rati n l and t a al f r all in ral that ld t ntiall r i itat r t r t f r - al it hi h r i itat d at = h l a a d n th n ar a i al f th t r nd at r a l at = at ll i lati n r d n at a n tant f at hi h rr nd t th a ra f tr i al il n ir n nt r k t al rat r a aintain d at a n tant n ntrati n f irri ati n at r a rati n a i lat d tra tin r at r fr th initial l ti n t a h i lati n t th at r nt nt f th l ti n a d r a d half k h a f n ntrat d l ti n a than d l d i aft r a h i lati n l th initial a nt f at r a r t r d k a h n ntrati n t a f ll d r i itati n f in ral f r hi h th i n at rati n ind had n d d hi i lati n l a r at d ti r ltin in a final n ntrati n fa t r f h a i lati n r d r a rf r d a nd ti t n ati n han r r in l d d q ili ri ith th han l a al lat d aft r a h n ntrati n r i itati n l h initial iti n f th han l a al lat d a in q ili ri ith th irri ati n at r n th han l a d fin d a th n r f han it r k at r i lati n r nd t d ith al ar in t n k at r and k at r i l dr il and l dr il r ti l h n il lk d n it q al k l and at r nt nt q al k at r l 5.3 Results nal i f il r rti in a t q n lt f th t q n a lin in r lati n t th l ati n f irri ati n l k il it and i t r ar h n in i r and il r hall in irri ati n l k and r lati l d in l k i h t t il and al r r d in th r art f th t q n r aria ilit a lar th h ri ntall a rti all and th r ti n a did n t h a l ar P.J.A. van Asten Soil quality and rice productivity problems in Sahelian irrigation schemes Texture classes according to FAO guidelines for soil description (1990b).

l l SodiumAdsorptio Ration = (Na ) / ((Ca + Mg )/2), concentrations in mmol l at pCO =10 atm.

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