Impacts of heterogeneity in soil fertility on legume-finger millet productivity, farmers’ targeting and economic benefits

Abstract

Targeting of integrated management practices for smallholder agriculture in sub-Saharan Africa is necessary due to the great heterogeneity in soil fertility. Experiments were conducted to evaluate the impacts of landscape position and field type on the biomass yield, N accumulation and N 2 -fixation by six legumes (cowpea, green gram, groundnut, mucuna, pigeonpea and soyabean) established with and without P during the short rain season of 2005. Residual effects of the legumes on the productivity of finger millet were assessed for two subsequent seasons in 2006 in two villages in Pallisa district, eastern Uganda. Legume biomass and N accumulation differed significantly (P \ 0.001) between villages, landscape position, field type and P application rate. Mucuna accumulated the most biomass (4.8-10.9 Mg ha -1 ) and groundnut the least (1.0-3.4 Mg ha -1 ) on both good and poor fields in the upper and middle landscape positions. N accumulation and amounts of N 2 -fixed by the legumes followed a similar trend as biomass, and was increased significantly by application of P. Grain yields of finger millet were significantly (P \ 0.001) higher in the first season after incorporation of legume biomass than in the second season after incorporation. Finger millet also produced significantly more grain in good fields (0.62-2.15 Mg ha -1 ) compared with poor fields (0.29-1.49 Mg ha -1 ) across the two villages. Participatory evaluation of options showed that farmers preferred growing groundnut and were not interested in growing pigeonpea and mucuna. They preferentially targeted grain legumes to good fields except for mucuna and pigeonpea which they said they would grow only in poor fields. Benefit-cost ratios indicated that legumemillet rotations without P application were only profitable on good fields in both villages. We suggest that green gram, cowpea and soyabean without P can be targeted to good fields on both upper and middle landscape positions in both villages. All legumes grown with P fertiliser on poor fields provided larger benefits than continuous cropping of millet.

A Review of Nutrient Management Studies Involving Finger Millet in the Semi-Arid Tropics of Asia and Africa

“…This highlights the importance of applying FYM along with inorganic fertilizer to improve P availability for finger millet. With respect to lessons learned from crop rotations, in Eastern Uganda, Ebanyat et al [53] found that application of P to legume crops generally enhanced the yield of the subsequent finger millet crop; six different legumes were tested in parallel including cowpea, pigeonpea, and groundnut (peanut). Addition of P increased the amount of N fixed by legume crops, resulting in a positive effect on yield of the subsequent finger millet crop.…”

“…The authors also found that P supplied to the previous legume crops increased the N use efficiency in finger millet, but the results were not consistent across the different legume species or soil fertility types tested. Although the application of P to legumes increased the yield of the subsequent finger millet crop, it may not be profitable due to the extra cost associated with P fertilizer [53].…”

“…It was observed that finger millet benefits more from residual fertilizer from the previous crop when the fertilizer is supplied as organic fertilizer compared to inorganic fertilizer [38,40,58] (Table 2). Based on a well-planned study conducted in eastern Uganda, Ebanyat et al [53] found that finger millet yields following legume crops (cowpea, green gram, groundnut, mucuna, pigeonpea, and soybean) were higher compared to continuous finger millet cropping. However, the N benefits derived from the legume crop residues decreased as the season progressed [53].…”

“…Based on a well-planned study conducted in eastern Uganda, Ebanyat et al [53] found that finger millet yields following legume crops (cowpea, green gram, groundnut, mucuna, pigeonpea, and soybean) were higher compared to continuous finger millet cropping. However, the N benefits derived from the legume crop residues decreased as the season progressed [53]. Although, there are N benefits to finger millet following legume crops, farmers were reluctant to use some of the legumes in their crop rotations, as they were not aware of their potential marketability or usefulness as fodder (mucuna) [53].…”

“…However, the N benefits derived from the legume crop residues decreased as the season progressed [53]. Although, there are N benefits to finger millet following legume crops, farmers were reluctant to use some of the legumes in their crop rotations, as they were not aware of their potential marketability or usefulness as fodder (mucuna) [53]. However, the residual N benefit to finger millet was shown to be low when the previous crop was a non-legume [39].…”