Background: Rice production in low‐input systems of West Africa relies largely on nitrogen supply from the soil. Especially in the dry savanna agro‐ecological zone, soil organic N is mineralized during the transition period between the dry and the wet seasons. In addition, in the inland valley landscape, soil N that is mineralized on slopes may be translocated as nitrate into the lowlands. There, both in‐situ mineralized as well as the laterally translocated nitrate‐N will be exposed to anaerobic conditions and is thus prone to losses. Aim: We determined the dynamics of soil NO3‐N along a valley toposequence during the dry‐to‐wet season transition period and the effects of soil N‐conserving production strategies on the grain yield of rainfed lowland rice grown during the subsequent wet season. Methods: Field experiments in Dano (Burkina Faso) assessed during two consecutive years the temporal dynamics and spatial fluxes of soil nitrate along a toposequence. We applied sequential and depth‐stratified soil nitrate analysis and nitrate absorption in ion exchange resin capsules in lowlands that were open to subsurface interflow and in those where the interflow from the was intercepted. During one year only we also assessed the effect of pre‐rice vegetation on conserving this NO3‐N as well as on N addition by biological N2 fixation in legumes using δ15N isotope dilution. Finally, we determined the impact of soil N fluxes and their differential management during the transition season on growth, yield and N use of rainfed lowland rice. Results: Following the first rainfall event of the season, soil NO3‐N initially accumulated and subsequently decreased gradually in the soil of the valley slope. Much of this nitrate N was translocated by lateral sub‐surface flow into the valley bottom wetland. There, pre‐rice vegetation was able to absorb much of the in‐situ mineralized and the laterally‐translocated soil NO3‐N, reducing its accumulation in the soil from 40–43 kg N ha−1 under a bare fallow to 1–23 kg N ha−1 in soils covered by vegetation. Nitrogen accumulation in the biomass of the transition season crops ranged from 44 to 79 kg N ha−1 with a 36–39% contribution from biological N2 fixation in the case of legumes. Rice agronomic performance improved following the incorporation as green manure of this “nitrate catching” vegetation, with yields increasing up to 3.5 t ha−1 with N2‐fixing transition seasons crops. Conclusion: Thus, integrating transition season legumes during the pre‐rice cropping niche in the prevailing low‐input systems in inland valleys of the dry savanna zone of West Africa can temporarily conserve substantial amounts of soil NO3‐N. It can also add biologically‐fixed N, thus contributing to increase rice yields in the short‐term and, in the long‐term, possibly maintaining or improving soil fertility in the lowland.
RESUMELes sols du Burkina Faso sont caractérisés par leur pauvreté en éléments nutritifs et en matière organique. Plusieurs sources de matière organique ont été étudiées mais très peu d'études se sont intéressées à l'utilisation du tourteau de neem (Azadirachta indica). Un dispositif en blocs de Fisher complètement randomisé comprenant 7 traitements a été mis en place au cours des saisons humide 2017 et 2018. Les traitements sont les fumures T0 : Sans apport de fertilisants ; T1 : NPK+urée 200 kg/ha + 100 kg/ha (dose vulgarisée) ; T2 : (Micro-dose = MD) NPK 4 g/poquet + urée 2 g/poquet (dose vulgarisée) ; T3 : TDN (2 t/ha) + (MD) NPK 4g/poquet + urée 2 g/poquet, ; T4 : TDN (2 t/ha) + (MD) NPK 2 g/poquet + urée 2 g/poquet ; T5 : TDN (4 t/ha) + (MD) NPK 4 g/poquet + urée 2 g/poquet ; T6 : TDN (4 t/ha) + (MD) NPK 2 g/poquet + urée 2 g/poquets. Les résultats indiquent des teneurs importantes en matière organiques et éléments nutritifs du TDN. Les meilleurs rendements de maïs ont été obtenus avec les traitements ayant reçu du TDN T5 et T6 avec respectivement 3,01 t/ha et 2,68 t/ha en grains de maïs et 3,73 t/ha et 3,58 t/ha de biomasse. Le TDN associé aux engrais minéraux permet d'améliorer la productivité du maïs au Burkina Faso. ABSTRACTIn Burkina Faso, several sources of organic matter were studied but very few were interested in the use of neem seed cake (Azadirachta indica). A completely randomized Fisher block device of 7 treatments was set up during the wet seasons of 2017 and 2018. Treatments are T0 : Without fertilizer; T1: NPK + urea 200 kg/ha + 100 kg/ha (common dose); T2: (Micro-dose = MD) NPK 4 g/pocket + urea 2 g/pocket (recommended dose); T3: TDN (2 t/ha) + (MD) NPK 4 g/pocket + urea 2 g/pocket,; T4: TDN (2 t/ha) + (MD) NPK 2 g/pocket + urea 2 g/pocket; T5: TDN (4 t/ha) + (MD) NPK 4 g/pocket + urea 2 g/pocket; T6: TDN (4 t/ha) + (MD) NPK 2 g/pocket + urea 2 g/pocket. The results indicate significant levels of organic matter and nutrients in TDN. The best yields of maize are obtained with the treatments that received TDN T5 and T6 with respectively 3.01 t/ha and 2.68 t/ha in maize grains and 3.73 t/ha and 3.58 t/ha respectively of biomass. TDN associated with mineral fertilizers improves maize productivity in Burkina Faso.
Burkina Faso is an agricultural and landlocked country whose agriculture is dependent on climatic hazards. Irrigated agriculture therefore appears as an alternative to secure, intensify and sustainably increase agricultural production. However, irrigation systems in Burkina Faso suffer from numerous technical, organizational, land and structural problems, which strongly undermine their performance. This is the case of the irrigated perimeter of Karfiguéla which since its development in 1977, has experienced insufficient water. This research has contributed to the reflection on the performance and operation of gravity irrigation networks on the irrigated perimeter in Burkina Faso and the contribution of satellite images in the mapping of irrigated perimeters. Then, an approach based on a mapping of hydraulic networks and on four main diagnostic methods were used: 1) mapping of hydraulic networks, 2) a detailed visual inspection of hydraulic infrastructure, 3) estimation of canals' hydraulic efficiency, 4) surveys of the various actors involved in the management of the perimeter. These methods lead to the same results concerning the state of degradation and the functioning of irrigation networks in wet seasons. In terms of results, Karfiguéla perimeter has a net area of 360 ha and is How to cite this paper: Compaore, H.M.M.,
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