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Much research has been conducted on cereal-legume intercropping as a sustainable intensification (SI) practice in Eastern and Southern Africa (ESA). However, the role of inorganic fertilizers in sustainably intensifying intercropping systems has not been systematically analyzed. Therefore, the objective of the present analysis was to assess the role of inorganic fertilizer use in cereal-pigeonpea (Cajanus cajan) intercropping in terms of SI indicators, namely, yield, production risks, input use efficiency, and economic returns. The data used for this analysis were gathered from over 900 on-farm trials across Kenya, Tanzania, and Mozambique. All SI indicators assessed showed that intercropping combined with application of small amounts of inorganic fertilizers is superior to unfertilized intercrops. Fertilizer application in the intercropping system improved cereal yields by 71–282% and pigeon pea yields by 32–449%, increased benefit–cost ratios by 10–40%, and reduced variability in cereal yields by 40–56% and pigeonpea yields by 5–52% compared with unfertilized intercrops. Improved yields and reduced variability imply lowering farmers’ risk exposure and improved credit rating, which could enhance access to farm inputs. We conclude that the strategic application of small amounts of inorganic fertilizers is essential for the productivity and economic sustainability of cereal-pigeonpea intercropping under smallholder farming in ESA.

Striga hermonthica (striga) weed is a major threat to crop production in sub-Saharan Africa, and short duration improved fallow species have recently been found to reduce the effects of this weed because of their ability to replenish soil nitrogen. The objective of this study was to compare the efficacy and profitability of coppicing improved fallow species (Gliricidia sepium [gliricidia], Leucaena trichandra [leucaena] and Calliandra calothyrsus [calliandra]) and non-coppicing species (Sesbania sesban [sesbania], Mucuna pruriens [mucuna], and Tephrosia vogelii [tephrosia]), in controlling striga.Natural fallow and a sole maize crop were included as control treatments. The fallow treatments were split into two and either fertilized with N or unfertilized. The results showed that coppicing fallows produced higher biomass than non-coppicing fallows. For example, Callindra (coppicing fallow species) produced 19.5 and 41.4 Mg ha -1 of leafy and woody biomass, respectively after four cumulative harvests as compared with Sesbania (non-coppicing species), which produced only 2.3 and 5.9 Mg ha -1 leaf and woody biomass, respectively. Improved fallows reduced striga population in proportion to the amount of leafy biomass incorporated into the soil (r = 0.87). N application increased cumulative maize yield by between 15-28% in improved fallow systems and by as much as 51-83% in the control treatments. Added total costs of the coppicing fallows did not differ significantly from those of the non-coppicing fallows and control treatments. However, the added net benefits of the coppicing fallows were significantly higher (US$ 527 for ?N and 428 for -N subplots; P \ 0.01) than those of the non-coppicing fallows (US$ 374 for ?N and 278 for -N), and the least for the control treatments. The most profitable fallow system was Tephrosia with net added benefits of US$ 453.5 ha -1 season -1 without N, and US$ 586.7 ha -1 season -1 with added N.

A better understanding of the agronomic and economic benefits of integrating organic and inorganic fertilizers is essential for their wide-scale dissemination and adoption in smallholder farming systems in developing countries. Field studies were conducted for 10 cropping seasons (1996)(1997)(1998)(1999)(2000) on a Kandiudalfic Eutrudox soil to compare the effects of Minjingu phosphate rock (MPR) and triple superphosphate (TSP) on the yield of maize (Zea mays), in combination with three nitrogen (N) sources: urea, Tithonia diversifolia and Sesbania sesban leafy biomass. Urea and tithonia were applied to provide 60 kg N ha −1 . Phosphorus (P) from either MPR or TSP was added either once at 250 kg P ha −1 at the beginning of the experiment or annually at 50 kg P ha −1 for five years, the two rates representing two P recapitalization strategies. From the second year, potassium (K) was added to half of each plot to correct for the deficiency that emerged. Over the 10 cropping seasons, the agronomic and economic benefits of the two P recapitalization strategies were similar and were not influenced by the P sources used. With N and K application, both P sources resulted in at least a two-fold maize grain yield increase over the control with no P application that averaged 1.1 tons ha −1 . Comparing the N sources, although urea and tithonia had similar net benefits when P was applied, the total cost associated with tithonia was considerably higher. Without P application, sesbania fallow was the most financially attractive option. Sesbania fallows as an N source were also least sensitive to increases in the price of fertilizers and the cost of labour although the financial benefits of this system remained low in the absence of P and K application.

Summary Although soybean is emerging as an important commercial crop in sub-Saharan Africa (SSA), its productivity on smallholder farms is very low. Soybean requires application of phosphorus (P) fertilizer and inoculation with the right rhizobium strains to achieve optimum biological nitrogen fixation and higher yields. However, subsistence farmers in SSA rarely invest in P fertilizers and inoculants due to lack of knowledge of their use and benefits. Most of the early reports on soybean in SSA have been based on work on research stations; hence, information is lacking on the profitability of fertilizer and inoculant use on smallholder farms in SSA. The main hypothesis of the present study was that the combined application of P and inoculants significantly reduces yield risks and increases P use efficiency and profitability compared with P fertilizer alone under smallholder farm conditions. We analyzed a data set of over 2,800 observations from on-farm demonstrations across Ghana, Kenya, Malawi, Rwanda, Tanzania, Uganda, and Zambia. Soybean yields, the partial factor productivity of P (PFPP), agronomic efficiency of P (AEP), and the value cost ratio (VCR) were significantly improved by the combined application of P fertilizer with inoculants than with P fertilizer alone. Combining P and inoculants increased yields over P alone by 17.3% in Kenya, 21.4% in Zambia, 25.7% in Ghana, 56.4% in Tanzania, and 57.1% in Malawi. However, soil organic matter was an important determinant of yield response and P use efficiency. The VCR increased linearly with increasing AEP in P + inoculant (R2 = 0.829) and less so with P fertilizer alone (R2 = 0.672). Net present values were positive in all countries, indicating that investments in P fertilizer and inoculants will generate profits over time. In order to increase uptake of fertilizers and inoculants among subsistence farmers and make soybean production more profitable, appropriate policies and market incentives need to be created.