SOIL FERTILITY UNDER FOUR TREE SPECIES IN THE SEMI-ARID CLIMATE OF NIGER

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1 Lnd Restortion Trining Progrmme Keldnholt, 112 Reykjvik, Icelnd Finl project 2016 SOIL FERTILITY UNDER FOUR TREE SPECIES IN THE SEMI-ARID CLIMATE OF NIGER Mrim Bouou Dillo Oumrou Ntionl Institute of Agronomic Reserch in Niger (INRAN) Deprtement of Nturl Resource Mngement (AGRN) Box: 412 Nimey-Niger Supervisor Úlfur Óskrsson Agriculturl University of Icelnd (AUI) ABSTRACT A field study ws conducted to investigte the impct of four tree species (Acci lid, Acci seneglensis, Comretum culetum nd Piliostigm reticultum) on soil fertility in semi-rid Niger. The species re common trees in frmers fields used for restortion of soil fertility. Soil composite smples were collected long four trnsects t different distnces from the tree trunk, t five levels of soil depth (0-10, 10-20, 20-30, nd cm) nd two ge clsses of trees (young nd mture) to ssess the effects of trees on the chemicl properties of the soil (ph, orgnic cron, mmonium-n, P, N, K, C nd Mg). The verticl distriution of ll prmeters, except for P, were significnt, nd decresed with depth. The results lso showed tht tree species influenced differently the distriution of the soil prmeters nlyzed. Soil ssocited with C. culetum ws more cidic thn for the other species. The orgnic cron ws higher eneth leguminous trees (A. lid nd P. reticultum) thn non-leguminous trees (A. seneglensis nd C. culetum). The concentrtion of mmonium-n, P nd K were generlly lower for C. culetum thn other tree species. However, N, C nd Mg concentrtions were generlly lower with A. seneglensis thn for the other tree species. Under A. lid, phosphorus concentrtion decresed with incresing distnce from the tree trunk. And under P. reticultum, phosphorus concentrtion nd ph incresed with tree ge. Bsed on the present project, ll the four tree species under study cn e recommended for use in frmers fields, oth for reforesttion nd for improving soil fertility in the semi-rid zone of Niger. Frmers cn lso e dvised to mintin more mture trees in their fields for improving crop production. Nevertheless, further reserch is needed to understnd etter the effect of distnce from tree trunk nd impct of tree ge on soil chemicl properties nd crop yields.

2 UNU Lnd Restortion Trining Progrmme This pper should e cited s: Oumrou M B D (2016) Soil fertility under four tree species in the semi-rid climte of Niger. United Ntions University Lnd Restortion Trining Progrmme [finl project] ii

3 UNU Lnd Restortion Trining Progrmme TABLE OF CONTENTS 1. INTRODUCTION LITERATURE REVIEW Woody species nd soil fertility Gender nd livelihoods Bckground of lnd degrdtion nd rights to tree utiliztion METHODOLOGY Description of study re Study design nd dt collection Dt nlysis Lortory nlysis Sttisticl nlysis RESULTS Influence of tree species on soil fertility ph Orgnic Cron (OC) Ammonium-N (NH 4) Phosphorus (P) Sodium (N) Potssium (K) Clcium (C) Mgnesium (Mg) Effect of soil smpling distnce from A. lid tree trunk on soil prmeters Impct of P. reticultum tree ge on soil prmeters DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES... Error! Bookmrk not defined. iii

4 UNU Lnd Restortion Trining Progrmme 1. INTRODUCTION The semi-rid su-shrn zone is chrcterized y low soil fertility, especilly with regrds to the low nitrogen nd phosphorus content of soils, low nd unpredictle rinfll, recurrent drought nd high soil temperture which limits crop production (Btiono nd Buerkert 2001; Sivkumr 1993). To enhnce soil fertility, frmers hve trditionlly used fllow griculturl system, ut the growing popultion hs incresed the demnd for griculturl products, which hs induced frmers to reduce the period of fllow or to ndon the prctice ltogether in some res. Soil degrdtion hs incresed due to deforesttion to extend frmers fields over time. When soils re exposed to wind nd wter, erosion increses nd the yield decreses (Wezel 2000; World Resource Institute 2013). In Niger, food production is generlly sed on rin-fed griculture nd soils used for crop production re sndy, degrded nd low in nitrogen nd phosphorus (Btiono nd Buerkert 2001; Kiri et l. 2014). To increse crop production for popultion needs, mny techniques re eing implemented y reserchers to improve soil fertility nd household income, prticulrly in West Afric. Litter nd household wste, orgnic iomss from crop residues nd mulching re mong the methods used to void soil prticle trnsport y wind, reduce wter splsh on soil, increse soil moisture nd improve soil fertility (Wezel 2000). Corrlling livestock on croplnd, crop rottion, intercropping nd micro-dosing re lso utilized to improve soil fertility (Byl et l. 2011). In Niger, mny studies show tht smll doses of inorgnic fertilizers t sowing improve crop production (ICRISAT 2009) nd the use of orgnic mnure nd crop residues increses soil orgnic mtter (Btiono et l. 1993; Buerkert et l. 1996; Ftondji et l. 2006). However, the socioeconomic conditions limit frmers cpcity to uy nd pply inorgnic fertilizers in ll their fields nd lso the costs of trnsporting household wste or orgnic fertilizer to the field limit their use (Kiri et l. 2014). The use of crop residue for construction, fuels nd fodder for livestock during the dry seson (Btiono nd Mokwunye 1991; Wezel 2000) lso limit their use for fertility mngement. Another method for fertility mngement is the integrtion of nturl woody vegettion. This method improves soil fertility y enling recycling of iomss produced y woody vegettion (Sidou et l. 2012). The popultion in the Sudno-shelin zone of west Afric is the poorest in the world nd the integrtion of woody species with crop production requires no monetry input to improve soil fertility (Btiono nd Buerkert 2001; Wezel 2000). Woody species re trditionlly used y smll frmers to limit the climtic risk nd to improve soil fertility. In Niger, most nturl vegettion consists of shrus mixed with few trees in some fields (Hiernux nd Le Houérou 2006; Fll et l. 2010; Byl et l. 2010; Dirr 2011). In southern Niger, the most common shrus nd trees re Acci lid, Annon seneglensis, Comretum cueltum, Guier seneglensis nd Piliostigm reticultum. Millet is the most common crop cultivted in Niger nd its integrtion with woody vegettion increses the yield of grin nd strw (Byl et l. 2011; Ass et l. 2013). The soil eneth shrus nd trees forms fertile islnds which re more productive thn open ground (Wezel et l. 2000). Therefore, frmers put more millet seedlings in these fertile islnds ecuse the yields re higher thn in the re etween woody cnopies (Wezel et l. 2000). 1

5 UNU Lnd Restortion Trining Progrmme Mny uthors hve shown the enefit of trees nd shrus on soil fertility (Mig 1987, Mi Mouss 1996, Grouzis et l. 2006). Integrtion of crop nd trees improves soil chemicl nd physicl properties, increses crop yield nd improves household income, nd lso conserves soil nd wter for environmentl protection (Boff 1999; Byl et l. 2012). Wezel et l. (2000) hve shown tht shrus (A. seneglensis, C. cueltum nd P. reticultum) increse soil nutrient ccumultion nd mintin soil fertility. Trees nd shrus reduce wind velocity nd trp dust mostly if they hve dense folige (Wezel et l. 2000). Trees nd shrus contriute to food security nd comt poverty; they provide fruits, wood nd fodder for nimls (Boff 2000, Nikiem 2005, Fye et l. 2011, Sidou et l. 2012). In Niger, the government hs developed strtegy of reforesttion nd prticipted in progrm clled Frmer Mnged Nturl Regenertion (FMNR) in collortion with some donors, to improve soil fertility in frmers fields (Asse et l. 2013). The common tree species used to improve soil fertility re A. lid, A. seneglensis, C. cueltum, G. seneglensis nd P. reticultum. Furthermore, frmers select trees nd shrus in their fields, in regrd to the socioeconomic, ecologicl nd culturl functions of the tree species nd to increse the diversity within fields (Fye et l. 2011). A study is needed to improve the knowledge of the contriution of vrious tree nd shru species on soil fertility improvement in the semi-rid su-shrn zone, where climtic conditions re unpredictle nd griculture provides for the min household income. The ojective of the present study ws to provide thorough study of soil fertility under some tree nd shru species in frmers fields to show frmers nd community leders the contriution of ech species in the improvement of soil fertility. Especilly to: Anlyze soil fertility under different tree species Compre soil fertility for tree ge nd distnce from the tree trunk The reserch questions were: Do woody species hve vrile effects on soil fertility? Does distnce from tree trunk ffect soil fertility? Does tree ge hve n impct on soil fertility? 2. LITERATURE REVIEW 2.1 Woody species nd soil fertility Woody species in semi-rid climte form mixture of scttered trees nd shrus (Wezel 2000; Byl et l. 2011). Trees nd shrus re deliertely selected y frmers when they re clering fields or when nturl woodlnd is converted into frmlnd (Wezel 2000). This selection of trees nd shrus is importnt ecuse of their influence on soil physicl nd chemicl properties, on household income, incresing food security nd llevition of poverty t ntionl level (Wezel et l. 2000; Cunninghm nd Asse 2005). The multi-functionl uses of species increse their diversity in frmers fields (Fye et l. 2011). Mny studies show differences etween tree crowns, sed on their species nd ge; n individul tree whose stem dimeter t 1.3 m ove the ground 2

6 UNU Lnd Restortion Trining Progrmme is less thn 5 cm is considered s juvenile (Béchir 2004; Ouédrogo et l. 2005; Ouédrogo 2009; Mounytou 2011). Over the lst twenty yers, mny studies hve descried the effect of trees on soil fertility nd crop productivity in mny countries of the world (Wezel, 2000; Joe 2009). The integrtion of trees with crops is utilized y smll frmers to improve susistence griculture (Bonkoungou et l. 1997; Boff 1999; Byl et l. 2011). Trees provide fodder for livestock during the dry seson. While, they represent significnt supplement for cttle, trees re stle food for smll ruminnts s they constitute over 70% of the dry mtter of the diet during the dry seson (Fll et l. 2002). Also, when ssocited with crop systems, trees cn contriute from 10 to 30% of niml feed (Nikiem 2005). Trees nd shrus provide foods nd medicinl services for the popultion in the dry seson nd even during droughts when cerels ecme scrce (Klingnire et l. 2008; Fye et l. 2010; Byl et l. 2011). Tree-crop integrtion improves soil chemicl nd physicl properties, increses soil porosity nd tree litter, increses orgnic mtter ccumultion nd contriutes to the recycling of N nd P under nd ner the tree trunk (Belsky et l. 1989; Vets 1992). Thus, woody species mintin soil moisture, influence soil wter holding cpcity nd wter infiltrtion (Belsky et l. 1989). In reserch conducted y Udwt et l. (2008) in the Midwest region of the United Sttes ner tree uffer zones, trees improved soil porosity three to five times compred to mize soyen rottion nd lso improved soil stility, soil cron nd nitrogen content. Reserch in semi-rid climte showed tht shrus improved soil nutrient ccumultion, s evidenced y incresed soil orgnic cron (39%), nitrogen (38%) nd phosphorus (51%) (Wezel et l. 2000; Wezel 2000). Augustine nd Joseph (1992) lso reported tht in the nturl Guine svnn of Nigeri, soils under tree cnopy hve higher ph, orgnic cron (OC), clcium (C), mgnesium (Mg), potssium (K), totl exchngele ses nd ction exchnge cpcity (CEC) thn in open grsslnd. Reserch in West Afric hs shown tht the presence of Acci species increses CEC, C nd Mg y 47%, 100% nd 78% respectively, under tree crowns compred to open res (Grouzis & Akpo 2006; Mnsour et l. 2013). In southwestern Niger, Wezel et l. (2000) reported tht higher concentrtions of C (39%), N (38%) nd P (51%) were found under some shrus species (A. seneglensis, C. glutinosum, G. seneglensis nd P. reticultum). Also these uthors found tht under the sme shrus, concentrtion of K + nd rtes of Al 3+ nd H + on effective ction exchnge cpcity (ECEC) re incresed y 22%, 44% nd 55%, respectively. Kho et l. (2001) found gin in Niger tht the vilility of N nd P is more thn 200% nd 30% greter, respectively, under A. lid thn in open res. Reserch under A. lid shde shows tht millet yield is multiplied y 2.5 nd seed protein content under trees is higher (10.68%) thn in open res (8.10%) (Kho et l. 2001; Grouzis & Akpo 2006). Studies y Byl et l. (2002) in Sponé, Burkin Fso, lso show tht mulching with Prki prdox leves increse millet yield y 120% nd dry mtter y 43%. Shrus nd trees reduce wind velocity in semi-rid zones nd increse deposition of top soil prticles y trpping. This process in the presence of crop residues nd shrus leves cretes n islnd fertile (Wezel 2000). In ddition, Cunninghm nd Asse (2005) hve reported in Mrdi (Niger) tht frmer-mnged nturl regenertion techniques cn stilize nd reclim degrded lnd. The rnches nd leves plced on crusted soil or hrdpn res re mixed in the top soil y 3

7 UNU Lnd Restortion Trining Progrmme termites nd this improves soil structure. This technique cn mke unproductive crusted soil fertile (Cunninghm nd Asse 2005). In frmer fields, trees reduce the effect of high rinfll velocity on the ground nd reduce sucnopy solr rdition y 45 to 60% (Belsky et l. 1989) nd lso reduce soil temperture y 20% under the crown (Grouzis & Akpo 2006). Under shde, evpotrnspirtion is reduced nd soil moisture is improved (Akpo 1993). Tree-crop integrtion increses crop yields, nd the presence of trees, leves nd crop residues on the soil increses soil fun ctivity nd nutrient cycling which in turn improves soil fertility (Schlecht et l. 2006). Also, woody species improve overll species iodiversity. In field survey, 79% of frmers reported tht tree species increse the presence of irds nd some predtory insects nd reduce the use of pesticides y frmers (Cunninghm nd Asse 2005). In the sme wy, Ass et l. (2013) show tht the flowers of P. reticultum produce repulsive effect which diminish the ttck of flower eetles on millet production under this species. 2.2 Gender nd livelihoods In most developing countries, griculture is the source of the min household income nd gender inequlity, s well s unequl ccess to nturl resources, contriutes to low productivity nd increses poverty (Kiptot & Frnzel 2011). According to FAO (2011), griculturl production could increse y 20-30% if women hd the sme ccess to nturl resources s men. In developing countries, this increse in griculture production could improve totl griculturl output y 2.5-4% nd the numer of the hungry e reduced y 12-17% (FAO 2011). Most of women s time is devoted to the fmily. While they produce sustntil mounts of crops they hve only ccess to smll portion of the totl lnd (Gldwin 2002; Kiptot & Frnzel 2011). Fields cultivted y women re often isolted, nd in most cses it is degrded field with low soil fertility (Kizz et l. 2012). In Niger, these kinds of fields hve een given to women for fertility restortion ecuse they cultivte leguminous crops like sesme (Sesmum indicum), groundnut (Archis hypoge), Bmr en (Vign suterrne) or cowpe (Vign unguicult), which re importnt for improving soil fertility nd for nitrogen fixtion. Women in Afric spend much of their time collecting medicinl plnts, firewood nd fruits (Boff 2000; Reij et l. 2009). The integrtion of tree species cn improve soil fertility resulting in incresed crop yields nd therey lleviting poverty y directly incresing income for smllholders (World Institute 2013). Also, tree species hve importnt enefits for femle frmers y incresing the vilility of fodder nd fuelwood for cooking otined y pruning trees nd shrus (Kiptot & Frnzel 2011), nd this lso reduces their worklod (World Institute 2013). Cunninghm nd Asse (2005) reported tht the use of Frmers Mnged Nturl Regenertion (FMNR) y Mrdi frmers (Niger) provided frmers with 76% of the wood for cooking nd 48% surplus wood for sle, nd frmers cn ern more thn 150,000 FCFA (pproximtely 280$ per yer). In ddition, Boff (2000) reported tht mny Shel countries received export income from tree products (ric gum from Acci senegl nd she nuts from Vitellri prdox). Also, the uthor found tht tree use in frmers fields hd positive effect on the nutrition of children nd diet diversity ecuse it increses women s income. In the sme wy, Reij et l. (2009) reported 4

8 UNU Lnd Restortion Trining Progrmme tht women in Zinder (Niger) who plnted o trees incresed their income (y up to $210) from the sles of tree leves used to mke suces. However, dopting groforestry prctices is ecoming difficult for women ecuse they do not generlly hve ccess to informtion nd time to prticipte in meetings, nd lso hve indequte ckground to understnd nd implement technicl spects of these prctices (Kiptot & Frnzel 2011). 2.3 Bckground of lnd degrdtion nd rights to tree utiliztion Lck of property rights nd implementtion of policy on nturl resource mngement cn contriute to the degrdtion of nturl resources (Neef 2001). In Niger, the degrdtion of nturl resources (lnd nd trees) strted during the colonil period nd ecme drstic in the postcolonil period (Mouss et l. 2016). In the colonil period, the government encourged frmers to produce export crops nd introduce veterinry nd medicl cre, which incresed the numers of nimls (Stickler 2012). This prctice creted pressure on nturl resources y overgrzing nd overhrvesting of fuelwood. To regulte the use, ll trees ecme government property nd frmers could purchse permits to use nd cut trees for wood. After independence, the Niger dministrtion declred ownership of ll trees tht hve n economic vlue, oth in protected res nd on privte lnd, nd they ecme protected species (Neef 2001; Mouss et l. 2016). Due to the lck of rights to the use of trees nd fering to lose their fields or tht their fields would ecome protected res, frmers who cultivted csh crops decided to cut ll young trees (Ajyi & Plce 2012) to limit competition nd to get more spce. This deforesttion decresed soil cover nd crop yields nd lso exposed soil to erosion nd degrdtion. The severity of the drought of 1974 ws enhnced y the scrcity of trees, resulting in loss of livestock, incresed lnd degrdtion nd migrtion (Mouss et l. 2016). This led to chnges in nturl resource mngement. To comt lnd degrdtion nd to improve soil fertility for good yield production, the officil policy ws to initite tree plnting, provide lnd tenure security nd rights to frmers y converting customry lw to forml lw (Lvigne et l. 2002; Ajyi & Plce 2012). In 2004, forestry lw gve tree tenure to lnd owners, nd the locl community otined legl rights to protect nd conserve nturl resources (Adm et l. 2006; Stickler 2012; Mouss et l. 2016). In collortion with some donors projects, the Niger government strted progrm of disseminting technologicl informtion nd to encourge frmers to mnge trees in their fields (Adm et l. 2006; Neef 2001; Ajyi & Plce 2012). The Niger Independence Dy ecme dy of plnting trees throughout the country. Adoption of tree mngement improves soil fertility nd household income nd re re-greening (Hglund et l. 2011; Boff 2000). 5

9 UNU Lnd Restortion Trining Progrmme Study re (Dntindou) Figure 1. A mp of Western Niger showing the study re in yellow (Source: Hiernux & Ayntunde 2000). 6

10 UNU Lnd Restortion Trining Progrmme 3. METHODOLOGY 3.1 Description of the study re The re in which the study ws conducted is the rurl town of Dntindou, locted in western Niger etween 13 o N nd 2 o E (Fig. 1). Dntindou covers 500 km 2 nd lies 75 km to the west of the cpitl re of Nimey. Soils re clssified s Arenosol or Psmmentic Pleustlf with 90% snd in horizon A (Akponikpe et l. 2014). The soils hve corse texture nd high infiltrtion rte, low orgnic cron (~ 0.2%) nd CEC (~1.2 cmolc kg -1 ). These soils re cidic with ph of out 5.3 nd low totl nitrogen (~ 0.16 g kg -1 ) nd ville phosphorus content (~ 4.1 mg kg -1 ) (Hyshi (2005), s cited in Hyshi et l. 2012). The climte is semi-rid with unpredictle nd monomodl rinfll centered in August nd vrying in spce nd time (Sivkumr 1993). Yerly verge rinfll is out 550 mm. Dntindou hs two sesons: short riny seson of 3 to 4 months (July to Septemer) nd long dry seson of 9 months (Octoer to June). The dry seson is lso divided into two periods: dry humid seson (2 to 3 months) nd dry hot seson (5 to 6 months). In the town of Dntindou, the popultion prctices susistence griculture in integrtion with trees nd shrus. Millet is the min crop nd it is cultivted generlly in ssocition with cowpe. At the edge of millet fields, frmers dd some rows of sesme or sorrel. Agriculture is the min source of household income nd is chllenged y climtic conditions. 3.2 Study design nd dt collection The reserch field is one hectre under prklnd, nd millet is the min crop. The study design ws complete rndomized lock with three replictes per tree species which were divided into two ge clsses, young nd mture. Soil smples were tken under nd outside crowns of trees long trnsects ccording to crdinl points (North, South, Est nd West). The soil ws smpled t five levels of depth t distnce of 1 nd 2 m from the tree trunk for young trees (Fig. 2) nd 1.5, 3, 4.5, 6, 7.5, 9, 10.5 nd 12 m for old trees (Fig. 3) long the 4 trnsects (crdinl points). The crown rdius of young trees ws less thn 2 m nd for mture trees it rnged etween 6 nd 10.5 m. At ech smpling loction long the trnsect, soil cores were tken. The 4 cores from ech of the four crdinl trnsects were mixed to form composite smple for one point. A soil uger (4.7 cm in dimeter) nd smpling shovel were used for tking composites smples in Decemer In this study, the fctors were:. Tree/shru species: 4 Acci lid, Piliostigm reticultum, Annon seneglensis Comretum culetum. 7

11 UNU Lnd Restortion Trining Progrmme. Age: 2 clsses Age 1: shrus with crown rdius less thn 2 m (Fig. 2). In this cse, smpling strted t 1 m from trunk (under crown) nd 2 m (outside crown) (A. seneglensis, C. culetum nd P. reticultum) Age 2: trees with crown rdius more thn 2 m (Fig. 3), smpling strted t 1.5 m from trunk (under crown) nd t 1.5 m intervls until outside crown (A. lid nd P. reticultum). c. Soil depth: smples were tken t 5 levels (Figs. 2B nd 3B show cross-sectionl view) 0 10 cm cm cm cm cm A Tree crown Tree trunk B Smpling loctions Tree crown Tree trunk Figure 2. Soil smpling under young trees in 4 trnsects (crdinl points: Est, West, North nd South) t ll soil depths nd distnces from tree trunk (A: top view nd B: cross-sectionl view). 8

12 UNU Lnd Restortion Trining Progrmme North A West 1.5m 3m Est Tree crown Tree trunk B South Smpling Smples loctions Tree crown Soil Tree trunk 3.3 Dt nlysis Figure 3. Soil smpling under mture trees in 4 trnsects (crdinl points: Est, West, North nd South) t ll soil depths nd distnces from tree trunk (A: top view nd B: cross-sectionl view) Lortory nlysis Soil smples were ir dried nd pssed through 2 mm sieve efore chemicl nlysis. The soil smples were nlyzed in the lortory of the Interntionl Crops Reserch Institute of Semi- Arid Tropics (ICRISAT) nd ll the nlyses were done ccording to Reeuwijk (1993) methods. The following prmeters were nlyzed: ph, orgnic cron (OC), mmonium-n (NH4), phosphorus (P), sodium (N), potssium (K), clcium (C) nd mgnesium (Mg). Soil ph ws determined with ph meter in soil smples mixed with distilled wter (1:2.5). The silver-thioure (AgTu) on 0.01M method ws used for exchngele ses extrction (Reeuwijk 1993). Atomic spectroscopy sorption ws used for C nd Mg determintion, nd flme spectroscopy emission ws used for N nd K determintion. Bry 1 method ws used for phosphorus quntittive determintion, HCl 0.025N nd NH4F 0.03N were used for extrction. The quntittive determintion ws done y colorimetry with molydo-phosphte complex reduced to scoric cid method. The Wlkley nd Blck method ws used for orgnic cron nlysis. Soil orgnic mtter ws oxidized with mixture of H2SO4 nd K2Cr2O7, nd quntittive determintion of orgnic cron in the smple ws chieved y extrcting nd titrting the remining mount of K2Cr2O7 with ferrous sulfte (Reeuwijk 1993). The indophenol lue method, method tht oth detects NH4 + nd NH3 forms of N, ws used for mmonium-n determintion (FAO 2008). For mmonium-n extrction, 2M KCL ws mixed with 1 ml of EDTA nd 2 ml of

13 UNU Lnd Restortion Trining Progrmme phenol-nitroprusside used s regent, followed y 4 ml of uffered hypochlorite regent (FAO 2008) Sttisticl nlysis Dt on soil properties for the four tree species were nlysed with three-wy ANOVA for determintion of the influence of tree species, crown nd soil depth on soil nutrient distriution. One-wy ANOVA ws used for determintion of tree ge effect nd impct of distnce of smpling from tree trunk on soil fertility. For tree ge nlysis, P. reticultum ws chosen ecuse it ws the only species tht hd oth young nd mture trees. For distnce from tree trunk nlysis, A. lid ws chosen ecuse it ws the only specie tht hd ig crown. The Student-Newmn-Keuls (SNK) test ws used to compre mens for species, soil depth, crown, ge, nd distnce from tree trunk clssifiction t the 95% of confidence level. SAS 9.4 ws used for ll sttisticl nlyses (SAS 2014). Excel ws used for mking grphics of vriles nd fctors, where sttisticlly significnt differences were found, for visul presenttion nd evlution. 4. RESULTS 4.1 Influence of tree species on soil fertility In ll cses the ANOVA model significntly explined the vrition of the mesured soil vriles in the field (Tle 1). Tle 1. F-vlues form three-wy ANOVA nlysis for Dntindou site (Niger). (df = degrees of freedom, OC = orgnic cron, NH4 = mmonium-n, P = phosphorus, N = sodium, K = potssium, C = clcium, Mg = mgnesium, ns = not significnt, *p<0.05, **p<0.01, ***p<0.001). Source df ph OC NH4 P N K C Mg Model *** 7.70*** 2.03** 1.69* 8.47*** 4.44*** 3.80*** 3.73*** Species *** 9.69*** 3.96** 16.60*** 77.10*** 22.41*** 10.00*** 13.46*** Crown 1 ns ns ns ns ns ns 4.26* ns Soil depth *** 20.56*** 4.22** ns 8.92*** 14.49*** 13.63*** 12.84*** Species*Crown *** ns ns ns 5.12** ns 5.30** ns Species*Soil depth 12 ns 3.35*** ns ns ns ns ns ns Crown*Soil depth 4 ns ns ns ns ns ns ns ns Species*Crown*Soil depth 12 ns ns ns ns ns ns ns ns Three-wy ANOVA results showed tht there were significnt differences etween species for ll the prmeters mesured (ph, OC, NH4, N, K, C nd Mg). Tree crown hd significnt effect only on C, nd soil depth hd significnt effect on ll chemicl properties nlyzed except for 10

14 ph UNU Lnd Restortion Trining Progrmme P. The interction etween species nd crown ws significnt for ph, N nd C nd the interction etween species nd soil depth ws only significnt for OC ph The soil eneth P. reticultum hd higher ph thn for the other tree species, except for A. seneglensis (Fig. 4), ut C. culetum displyed lower ph thn ll other species. The ph vried significntly etween soil depth clsses (Tle 1), where ph ws higher ner the surfce thn elow 20 cm depth (Fig. 5). The interction etween species nd crown ws lso significnt (Tle 1); the ph ws higher under the crown of C. culetum nd P. reticultum thn outside crown. The reverse ws oserved with A. lid (Fig. 6) c 5 A. lid A. seneglensis C. culetum P. reticultum n = Figure 4. Soil ph under the four tree species. Ech column represents the men vlue of ph for ll soil depths nd crown positions nd n represents the numer of oservtions for ech men. The verticl rs show stndrd devition nd different letters indicte significnt differences (p<0.05) etween species. 11

15 ph Soil depth UNU Lnd Restortion Trining Progrmme ph cm cm cm cm c cm c Figure 5. Soil ph for the five soil depths. Ech men includes vlues from ll tree species nd crown positions, with 36 smples ehind ech soil depth. The horizontl rs show stndrd devition nd different column letters show significnt differences (p<0.05) OC UC OC UC OC UC OC UC A. lid A. seneglensis C. culetum P. reticultum n = Figure 6. Soil ph under crown positions (UC = under crown nd OC = open crown) for ech species t ll soil depths. n represents the numer of oservtions for ech men. The verticl rs show stndrd devition nd different letters indicte significnt differences (p<0.05) etween OC nd UC for ech species. 12

16 Soil depth OC (%) UNU Lnd Restortion Trining Progrmme c c A. lid A. seneglensis C. culetum P. reticultum n = Figure 7. Soil orgnic cron (OC) under the four tree species. Ech column represents the men vlue of OC for ll depths nd crown positions nd n represents the numer of oservtions for ech men. The verticl rs show stndrd devition nd different letters indicte significnt differences (p<0.05) etween species Orgnic Cron (OC) The soil OC ws significntly different etween species (Tle 1). A. lid hd the highest men (0.14%) of soil orgnic mtter nd C. culetum nd A. seneglensis hd the lowest men (Fig. 7). As for ph, the percentge of OC decresed with soil depth. The top lyer (0-10 cm) hd the highest vlue nd the lowest vlues were found elow 20 cm (Fig. 8). OC (%) cm cm cm c cm c cm c Figure 8. Soil orgnic cron (OC) for the five soil depths. Ech men includes vlues from ll tree species nd crown positions, with 36 smples ehind ech soil depth. The horizontl rs show stndrd devition nd different letters show significnt differences (p<0.05). 13

17 NH 4 (mg/kg) 0-10 cm cm cm cm cm 0-10 cm cm cm cm cm 0-10 cm cm cm cm cm 0-10 cm cm cm cm cm OC (%) UNU Lnd Restortion Trining Progrmme The interction etween species nd soil depth ws significnt for soil OC (Tle 1) nd the chnge with soil depth evolved in the sme mnner for ech species s descried ove, except for P. reticultum (Fig. 9) c c c c c c c cd d Figure 9. Soil orgnic cron (OC) for the five soil depths under ech tree species. Ech men includes vlues for crowns positions nd n represents the numer of oservtion of ech men. The verticl rs show stndrd devition nd different letters indicte significnt differences etween soil depth for ech species Ammonium-N (NH4) A. lid A. seneglensis C. culetum P. reticultum n = A. lid A. seneglensis C. culetum P. reticultum n = Figure 10. Soil NH4 under the four tree species. Ech column represents the men vlue of NH4 for ll soil depths comined nd crown positions. n represents the numer of oservtions for ech men. The verticl rs show stndrd devition nd different letters illustrte significnt differences etween species (p<0.05). 14

18 P (mg/kg) Soil depth UNU Lnd Restortion Trining Progrmme There ws significnt difference etween species for soil mmonium-n (Tle 1). Men mmonium-n content in soils eneth P. reticultum ws higher thn for C. culetum (Fig. 10). Also, NH4 decresed with soil depth nd the top lyer (0-10 cm) hd higher men thn the other soil depth clsses (Fig. 11). NH 4 (mg/kg) cm cm cm cm cm Figure 11. Soil NH4 for the five soil depths. Ech men includes vlues from ll tree species nd crown positions, with 36 smples t ech soil depth. The horizontl rs show stndrd devition nd different column letters show significnt differences (p<0.05) Phosphorus (P) A. lid A. seneglensis C. culetum P. reticultum n = Figure 12. Soil P under the four tree species. Ech column represents the men vlue of P for ll soil depths nd crown positions, nd n represents the numer of oservtions for ech men. The verticl rs show stndrd devition nd different letters illustrte significnt differences etween species (p<0.05). 15

19 N (Cmol + /kg) UNU Lnd Restortion Trining Progrmme The soil phosphorus ws only significntly different etween tree species (Tle 1). C. culetum hd lower men vlue thn the other species (Fig. 12) Sodium (N) The results from the three-wy ANOVA of N (Tle 1) show tht there ws significnt difference for species nd soil depth. P. reticultum hd higher men thn other species nd A. seneglensis hd the lowest men (Fig. 13). The mount of N chnged with soil depth nd the top 20 cm hd higher content thn other soil depth clsses (Fig. 14). In ddition, the deepest soil depth clss (40-50 cm) hd less N thn other clsses. The interction etween species nd crown showed tht there ws significnt difference etween species under nd outside the crown (Tle 1). The men of N under the crown of P. reticultum ws higher thn outside the crown, ut the reverse ws oserved with A. lid (Fig. 15) d c 0 A. lid A. seneglensis C. culetum P. reticultum n = Figure 13. Soil N under the four tree species. Ech column represents the men vlue of N for ll depths nd crown positions nd n represents the numer of oservtions for ech men. The verticl rs show stndrd devition nd different letters illustrte significnt differences etween species (p<0.05). 16

20 N (Cmol + /kg) Soil depth UNU Lnd Restortion Trining Progrmme N (Cmol + /kg) cm cm cm cm cm c Figure 14. Soil N for the five soil depths. Ech men includes vlues from ll tree species nd crown positions, with 36 smples ehind ech soil depth. The horizontl rs show stndrd devition nd different letters show significnt differences (p<0.05) OC UC OC UC OC UC OC UC A. lid A. seneglensis C. culetum P. reticultum Figure 15. Soil N under crown positions (UC = under crown nd OC = open crown) for ech species t ll soil depths nd n represents the numer of oservtions for ech men. The verticl rs show stndrd devition nd different letters show significnt differences (p<0.05) etween OC nd UC for ech species Potssium (K) n = In the sme wy s for some other soil prmeters, the vlue of soil K ws significntly different etween species nd soil depth clsses (Tle 1). There ws no significnt difference etween A. seneglensis, P. reticultum nd A. lid ut C. culetum hd lower men of K thn the other species (Fig. 16). The top 20 cm of the soil were richer in K thn elow 20 cm (Fig. 17). In ddition, the lowest soil depth clss (40-50 cm) hd less K thn other soil depth clsses. 17

21 Soil depth K (Cmol + /kg) UNU Lnd Restortion Trining Progrmme A. lid A. seneglensis C. culetum P. reticultum n = Figure 16. Soil K under the four tree species. Ech column represents the men vlue of K for ll soil depths nd crown positions. n represents the numer of oservtions for ech men. The verticl rs show stndrd devition nd different letters indicte significnt differences etween species (p<0.05). K (Cmol + /kg) cm cm cm cm cm c Figure 17. Soil K for the five soil depths. Ech men includes vlues from ll tree species nd crown positions, with 36 smples ehind ech soil depth. The horizontl rs show stndrd devition nd different letters show significnt differences (p<0.05) Clcium (C) With C, there ws significnt vrition etween tree species nd soil depths (Tle 1). A. lid hd higher men thn other species except for P. reticultum. A. seneglensis hd lowest men thn A. lid nd P. reticultum (Fig. 18). The top 20 cm of the soil hd higher men vlue of C thn other soil depths, nd elow 20 cm ll depth clsses were successively lower thn the next one ove (Fig. 19). 18

22 Soil depth C (Cmol + /kg) UNU Lnd Restortion Trining Progrmme The interction etween species nd crown lso showed tht the mount of C ws higher under thn outside the crown for P. reticultum nd C. culetum ut the reverse ws found with A. lid (Fig. 20) c c 0 A. lid A. seneglensis C. culetum P. reticultum n = Figure 18. Soil C under the four tree species. Ech column represents the men vlue of C for ll depths nd crown positions, nd n represents the numer of oservtions for ech men. The verticl rs show stndrd devition nd different letters indicte significnt differences etween species (p<0.05). C (Cmol + /kg) cm cm cm cm c cm d Figure 19. Soil C for the five soil depths. Ech men includes vlues from ll tree species nd crown positions, with 36 smples ehind ech soil depth. The horizontl rs show stndrd devition nd letters show significnt differences (p<0.05). 19

23 Mg (Cmol + /kg) C (Cmol + /kg) UNU Lnd Restortion Trining Progrmme Figure 20. Soil C under crown positions (UC = under crown nd OC = open crown) for ech species t ll soil depths. n represents the numer of oservtions for ech men. The verticl rs show stndrd devition nd letters show significnt differences (p<0.05) etween OC nd UC for ech species Mgnesium (Mg) 0 OC UC OC UC OC UC OC UC A. lid A. seneglensis C. culetum P. reticultum n = With Mg, there ws significnt vrition etween species nd soil depths (Tle 1). A. lid hd higher men of Mg thn other species except for P. reticultum. Also, A. seneglensis hd the lowest men (Fig. 21). Mg lso significntly decresed with soil depth except elow 30 cm (Fig. 22) c A. lid A. seneglensis C. culetum P. reticultum n = Figure 21. Soil Mg under the four tree species. Ech column represents the men vlue of Mg for ll depths nd crown positions nd n represents the numer of oservtions for ech men. The verticl rs show stndrd devitions nd different letters illustrte significnt differences etween species (p<0.05). 20

24 Soil depth UNU Lnd Restortion Trining Progrmme Mg (Cmol + /kg) cm cm cm c cm d cm d Figure 22. Soil Mg for the five soil depths. Ech men includes vlues from ll tree species nd crown positions, with 36 smples t ech soil depth. The horizontl rs show stndrd devitions nd different letters show significnt differences (p<0.05). 4.2 Effect of soil smpling distnce from A. lid tree trunk on soil prmeters The nlysis of one-wy ANOVA shows tht there ws significnt vrition with distnce for only P (Tle 2). Tle 2. F-vlue from one-wy ANOVA nlysis results for distnce from A. lid tree trunk (df = degrees of freedom, OC = orgnic cron, NH4 = mmonium-n, P = phosphorus, N = sodium, K = potssium, C = clcium, Mg = mgnesium, ns = not significnt, ***p<0.0001). Source df ph OC NH 4 P N K C Mg Model 7 ns ns ns 5.93*** ns ns ns ns Distnce 7 ns ns ns 3.70*** ns ns ns ns Soil P decresed with incresing distnce from A. lid tree trunk. Close to the tree trunk (1.5 nd 3 m) the P vlue ws higher thn outside crown (9, 10.5 nd 12 m) (Fig. 23). 21

25 P (mg/kg) UNU Lnd Restortion Trining Progrmme m 3 m 4.5 m 6 m 7.5 m 9 m 10.5 m 12 m n = Figure 23. Soil P under A. lid for distnce from tree trunk (n = numer of soil smples). Verticl rs show stndrd devition of mens nd different letters show significnt differences etween distnces. 4.3 Impct of P. reticultum tree ge on soil prmeters The one-wy ANOVA nlysis showed tht there ws only significnt difference etween ges for ph nd P. Tle 3. F-vlue from One-wy ANOVA nlysis results for P. reticultum tree ge (df = degrees of freedom, OC = orgnic cron, NH4 = mmonium-n, P = phosphorus, N = sodium, K = potssium, C = clcium, Mg = mgnesium, ns = not significnt, **p<0.001, ***p<0.0001). Source df ph OC NH4 P N K C Mg Model *** ns ns 11.91** ns ns ns ns Ages *** ns ns 11.17** ns ns ns ns The ph ws significntly different etween ge clsses nd the mture trees hd higher soil ph thn young trees of P. reticultum. Also for P, the men ws higher eneth mture trees thn young trees (Fig. 24). 22

26 Mens UNU Lnd Restortion Trining Progrmme Young trees Mture trees Young trees Mture trees ph Figure 24. Soil ph nd soil P for P. reticultum young nd mture tree (numer of smples = 20 for young trees nd 20 for mture trees). Verticl rs show stndrd devitions nd different letters show differences etween tree ges. P (mg/kg) 5. DISCUSSION Tree species influenced differently the distriution of soil nutrients in the present study. Lower ph nd higher concentrtion of elements were generlly found under tree crowns rther thn outside crowns, except for A. lid. Under this species, concentrtions of ph, N nd C were lower under crowns thn outside crowns. A. lid hs reverse cycle compred to other species (A. seneglensis, C. culetum nd P. reticultum): in the riny seson, this species does not produce more folige (Jonsson et l. 1999). Under A. lid trees, there is n ccumultion of oth rk nd lef litter. According to Zinke (1962), the rk is very cid nd low in ses, wheres lef litter is high in ses nd nitrogen content (Zinke 1962). Due to the fct tht A. lid is ig tree, it produces more rk litter. Therefore, the cidity of rk litter cn reduce the concentrtions of N nd C under the A. lid crown (Zinke 1962). The influence of the tree crown decreses with incresing distnce from the tree trunk ecuse of the ccumultion of orgnic mtter ner the tree trunk. Leves of trees re rich in cron nd the ccumultion of lef litter under trees increses microiologicl ctivities nd soil orgnic mtter (Isc et l. 2011; Mnsour et l. 2013). The minerliztion of soil OC under trees nd the root symiosis with mycorrhizl fungi increse the concentrtion of soil nutrients under tree crowns (Mnsour et l. 2013). The sme result ws reported y Vets (1992) in dry svnns. According to this uthor, the interction etween trees, the contriution of symiotic micro-orgnisms, nd understory plnts increse the nutrient recycling ner the tree trunk. Also, there is some ttrction of nimls who cn contriute nutrients y mnure (Vets 1992). The higher concentrtion of soil nutrients ner the tree trunk is therefore due to the ccumultion of orgnic mtter ner the tree trunk, positively influenced y cooler microclimte nd micro-funl ctivity (Buerkert et l. 1989; Vets 1992). This phenomenon diminishes when the input of orgnic mtter is reduced with incresing distnce from tree trunk (Vets 1992; Mnsour et l. 2013). As result, mny reserchers investigting the influence of trees on soil fertility considered three zones: the first 23

27 UNU Lnd Restortion Trining Progrmme zone is the rdius of the crown in which there is reltively high concentrtion of rk nd lef litter, the second zone is the prt under the crown which hs less lef litter, nd the third zone is outside the crown where there is no litter ccumultion (Zinke 1962). Rhodes (1997) reported tht the soil ner the tree trunk is richer in nutrients ecuse of the leching of dust from the lef surfce, scrps of ded insects, nd nutrients from the tree trunk crried y flowing wter or rinfll which concentrtes t the tree trunk se. Also, Wezel et l. (2000) hs shown tht in the presence of shrus, soil nutrients (N, P nd K) were significntly higher within 50 cm rdius from the tree trunk nd ecme less outside 150 cm rdius. Zinke & Crocker (1962) showed tht for old Sequoidendron gignteum with 6 to 9 m of crown dimeter, the influence zone cn rech 3 m from the tree trunk, which ws similr to our result of A. lid with crown dimeter etween 6 to 10.5 m. In the sme wy, tree crown size nd soil nutrients increse with tree ge ecuse they produce nd ccumulte more orgnic mtter thn young trees. The work of Zhong & Zho (2003) in the north of Chin with Crgn microphyll in sequence ge of 0, 5, 13 nd 28 yers old showed tht soil cron nd nitrogen ccumultion increses with ge of plnttion. In Indi, under sequence of Prosopis juliflor plnttion of ges 0, 5, 7 nd 30 yers, Bhojvid & Timmer (1998) showed tht the soil fertility increses with the plnttion ge. In their study, the first yers (0 to 5 yers) were chrcterized y high soil temperture nd initil chnges in soil properties (Bhojvid & Timmer 1998). The trnsitionl phse with closure of the tree cnopy strted etween 5 to 7 yers; in this period litter production, nutrient cycling nd soil fertility incresed, nd the tree root system expnded. The lst phse ws fllow enrichment in which there ws stiliztion of soil development with incresed verticl soil formtion with time (Bhojvid & Timmer 1998). Also, Augustine nd Joseph (1992) hve shown tht trees with more thn 7 m of crown dimeter hve higher OC, CEC, C, Mg nd P under their cnopy thn trees with less thn 7 m of crown dimeter. The effect of tree ge reduces ttck on crops y insects, s showed y Ass et l. (2013) in the region of Aguié (Niger). The uthors found tht, under three ge groups of P. reticultum (0-2 yers, 3-5 yers nd more thn 6 yers), the old trees (more thn 6 yers) produced more flowers thn the young trees. The flowers produce repulsive odor on flower eetles which ttck the crops, thus resulting in incresed yield under old trees compred to young trees (Ass et l. 2013). In the present study, soil nutrient concentrtions decresed with incresing soil depth irrespective of tree species, distnce from the tree trunk or tree ge. The orgnic mtter ws lso concentrted ner the soil surfce etween 0 nd 20 cm ut elow this lyer nutrient concentrtions chnged. Bhojvid & Timmer (1998) got similr result under Prosopis juliflor. Soil smples tken t 15, 30, 60, 90 nd 135 cm depth showed tht the level of N nd C declined with depth fter 30 cm. This ws due to high litter ccumultion nd decomposition nd higher fine root turnover ner the soil surfce which incresed nutrient recycling (Bhojvid & Timmer 1998). Zhong & Zho (2003) lso got similr results for Crgn microphyll in the north of Chin. The smples were tken t two depths (0-5 cm nd 5-20 cm) in n ge sequence of 0, 5, 13, 21 nd 28 yers. C nd N decresed with soil depth for ll the ges ecuse tree estlishment nd development initilly influenced mostly soil properties in the surfce horizon, strting with n increse in soil orgnic mtter ccumultion nd decomposition. In order to explin the verticl distriution of soil nutrients Jogy nd Jckson (2001) took soil smples t 5 depths (0-20, 20-40, 40-60, nd cm) nd found tht the iologicl cycling y plnts nd trees incresed the movement of 24

28 UNU Lnd Restortion Trining Progrmme the most importnt nutrients (N, P nd K). Some nutrients re trnsported oveground y trees nd plnts, nd recycling in the topsoil mixes nutrients in lef litter nd those rought y rinfll (Jogy nd Jckson 2001). This phenomenon increses the nutrient ccumultion in the soil surfce (Jogy nd Jckson 2001). In ddition, Ekelund et l. (2001) mesured the numers nd iomss of protozo, cteri nd fungi t different depths ( cm). They found generl decrese of iomss for ll the groups with incresing soil depth. This ws ecuse the orgnic mtter nd micro-orgnism ctivities were more concentrted in the top soil nd this incresed the nutrient content in the shllowest more thn in the deepest soil profile (Ekelund et l. 2001). 6. CONCLUSION Woody species re importnt for the restortion of soil fertility, prticulrly in semi-rid zone like in Niger where the low soil fertility is the min rrier to crop production. The tree species improve soil fertility in different wys nd they cn e integrted into crop production nd soil restortion. The nutrients re more concentrted ner the tree trunk nd the ge of trees increses their ccumultion over time. A recommendtion for soil fertility mngement nd soil restortion is to sensitize frmers to mintin more mture trees in their fields nd to put more crops ner the tree trunks. However, further reserch cn e done in the sme wy to explin etter the influence of tree ge nd distnce from tree trunk on soil fertility improvement. 25

29 UNU Lnd Restortion Trining Progrmme ACKNOWLEDGEMENTS I would like to thnk the Director of the UNU-LRT Progrm nd ll stff for this opportunity to e one of the fellows in 2016 from Niger. I thnk Berglind Orrdóttir, deputy of this progrm to mke this project success with her ludle remrks. I wnt to cknowledge the project CerLiveTrees (CLT) for funding the field work nd the ICRISAT Shelin Center, especilly Dr. Ftondji, for seeing to funding the soil nlysis. My thnks go to Boukry Adou (INRAN, Niger) for technicl support nd the frmers of Korto (Dntchndou) for mking their fields ville. Further thnks to ll my supervisors,especilly Úlfur Óskrsson who went through the mnuscript with vlule remrks, Dr. Asse Toudjni (INRAN, Niger), Dr. Pierre Akponikpe (University of Prkou, Benin), nd Pr. Agossou Euloge (University of Aomey-Clvi, Benin). I wnt to thnk ll the lecturers of the Agriculturl University of Icelnd nd Soil Conservtion Service for shring their knowledge nd experience with us. I would lso like to thnk the UNU-LRT fellows of 2016 for spending their time together nd shring their knowledge nd experience. 26

30 UNU Lnd Restortion Trining Progrmme LITERATURE CITED Ass T, Guero C, Rinudo T (2009) Community moiliztion for improved livelihoods through tree crop mngement in Niger. Geojournl 74: Ass T, Aisstou Y, Zkri AB, Admou AI, Adm T (2013) Effet de Piliostigm reticultum sur l infesttion des prcelles de mil pr les insectes floricoles et Coniest ignefuslis (foreur du mil) dns l zone d Aguie u Niger. [Effect of Piliostigm reticultum on millet plots infesttion y flowers insects nd Coniest ignefuslis in Niger] Journl of Applied Biosciences 66: (In French) Adm T, Reij C, Adoulye T, Lrwnou M, Tppn G (2006) Impcts des investissements dns l Gestion des Resources Nturlles (GRN) u Niger : Rpport de Synthèse Nimey, Niger : Centre Régionl d Enseignement Spécilisé en Agriculture [Investment impcts in Nturl Resource Mngement (NRM) : Synthesis Report Nimey, Niger] (In French) Akpo LE (1993) Influence du couvert ligneux sur l structure et le fonctionnement de l strte hercée en milieu shélien [Influence of woody species cover on the structure nd functioning of the herceous lyer in Shel]. TDM 93 Frnce, Pris: ORSTOM Editions (In French) Akponikpe PBI, Gerrd B nd Bielders CL (2010) Soil wter nd crop modeling for decision support in millet sed systems in the Shel: A chllenge. Africn Journl of Agriculturl Reserch 9: Ajyi OC nd Plce F (2012) Policy support for lrge-scle doption of groforestry prctices: Experience from Afric nd Asi. Pp In: Agroforestry - The Future of Glol Lnd Use Augustine OI, Joseph IM (1992) The effect of trees cnopy cover on soil fertility in Nigerin svnn. Journl of Tropicl Ecology 8: Btiono A, Buerkert A (2001) Soil orgnic cron mngement for sustinle lnd use in Sudno- Shelin West Afric. Nutrient Cycling in Agroecosystems 61: Btiono A, Christinson BC & Klij MC (1993) The effect of crop residue nd fertiliser use on perl millet yields in Niger. Fertilizer Reserch 349(3): Btiono A, Mokwunye AU (1991) Alleviting soil fertility constrints to incresed crop production in West Afric: The experience in the Shel. Fertilizer Reserch 29: Byl J, Klingnire A, Tchoundjeu Z, Sinclir F, Grrity D (2011) Conservtion griculture with trees in the West Africn Shel A review. ICRAF Occsionl Pper No. 14. Niroi: World Agroforestry Centre Byl J, Kindt R, Belem M, Klingnire A (2011) Fctors ffecting the dynmics of tree diversity in groforestry prklnds of cerel nd cotton frming systems in Burkin Fso. New Forest 41: