Abstract
Low fertilizer application rates for several decades have depleted soil nutrients in Sub-Saharan Africa (SSA) and contributed to relatively stagnant maize (Zea mays L.) yields. As maize is a staple crop, nutrient depletion has resulted in major food insecurity. While one potential solution is to apply more nitrogen (N) fertilizer, previous studies in SSA have found maize yield responses to be variable, likely because N is often not the only limiting nutrient. This study aimed to determine the impact of consecutive N fertilizer applications on plant uptake and available soil reserves of non-N nutrients. Maize was grown continuously in 3 sites that were representative of the ecosystem variability found in East/Southern Africa (Embu, Kenya; Kiboko, Kenya; Harare, Zimbabwe) at 4 different N fertilizer rates (0–160 kg N ha−1) from 2010 to 2015. Following the final season, grain, stover, and soil (sampled at different depths to 0.9 m) samples were analyzed for essential plant nutrients. Nitrogen fertilizer increased plant uptake of P, S, Cu, and Zn by up to 280%, 320%, 420%, and 210%, respectively, showing potential for mitigating non-N nutrient deficiencies in 2 of the 3 sites. Cumulatively, however, there was a net negative effect of higher N rates on the P, K, and S soil-plant balances in all sites and on the Mn and Cu soil-plant balance in Kiboko, indicating that applying N fertilizer depletes non-N soil nutrients. While N fertilizer enhances the uptake of non-N nutrients, a balanced application of multiple essential nutrients is needed to sustainably increase yields in SSA.
Highlights
Sub-Saharan Africa (SSA) is facing a major food security crisis as crop yields fail to meet the needs of its growing population in part due to poor soil fertility (Denning et al 2009; Lal 2009; Tully et al 2015)
Soil pH differed among the sites: pH was lower in Embu than in Harare and pH was much lower in both of these sites than in Kiboko (P \ 0.0001; Table 1)
As a result of 20 kg P ha-1 being applied in all three sites and the return of 1/3 of stover residue in Kiboko, the plantfertilizer P balance was only negative in Kiboko at 80
Summary
Sub-Saharan Africa (SSA) is facing a major food security crisis as crop yields fail to meet the needs of its growing population in part due to poor soil fertility (Denning et al 2009; Lal 2009; Tully et al 2015). Estimates have placed maize’s yield gap in SSA at 200% and have projected that the average yield needs to increase at an annual rate of 2% by 2050 in order to feed the growing population (Fischer et al 2009; Cassman and Grassini 2013; Ten Berge et al 2019). SSA demand for more cereals is disproportionally growing at approximately 5 times the global rate (Van Ittersum et al 2016). Previous studies have found that the yield response to N fertilizer is inconsistent, likely because low N is not the only stress in the system (Sileshi et al 2010)
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