Abstract
Improved understanding of soil fertility factors limiting crop productivity is important to develop appropriate soil and nutrient management recommendations in sub-Saharan Africa. Diagnostic trials were implemented in Kenya, Malawi, Mali, Nigeria and Tanzania, as part of the African Soils Information Service (AfSIS) project, to identify soil fertility constraints to crop production across various cropping systems and soil fertility conditions. In each country, one to three sites of 10km×10km were included with each site having 12–31 field trials. The treatments tested included a control, an NPK treatment, three treatments in which the N, P and K nutrients were omitted one at a time from the NPK treatment, and three treatments in which secondary and micronutrients (Ca, Mg, S, Zn and B) simply referred here as multi-nutrients, manure and lime were added to the NPK. The field trials were conducted for 1–2 seasons; the test crop was maize except in Mali where sorghum was used. Nitrogen was limiting in all sites and generally the most limiting nutrient except in Sidindi (Kenya) and Kontela (Mali) where P was the most limiting. The general pattern in Kiberashi (Tanzania) shows none of the nutrients were limiting. K is mainly limiting in only one site (Mbinga) although incidences of K limitation were seen in almost all sites. Addition of multi-nutrients and manure further improved the yields of NPK in most sites. Cluster analyses revealed that maize crop in 11% of fields were highly responsive to nitrogen application, 25% (i.e., 21% poor and 4% fertile) ‘non-responsive’ to any nutrient or soil amendment, 28% being ‘low responsive’ and 36% of ‘intermediate response’. This study indicates that constraints to crop production vary considerably even within a site, and that addressing limitations in secondary and micronutrients, and increasing soil carbon can improve response to fertilizers. For sustainable crop production intensification in smallholder farming systems in SSA, there is need to develop management strategies to improve efficiency of fertilizer use and of other inputs, recognizing the site-specific nutrient response patterns at various spatial scales.
Highlights
Achieving food security is a key agenda that is eluding governments in sub-Saharan Africa (SSA) (Shapouri et al, 2010)
The 1–3 sites are predominantly agricultural, measuring an area of 10 km  10 km and were chosen from the sentinel sites used in the African Soils Information Service (AfSIS) land degradation surveillance framework (LDSF), which had been identified using a random selection process
The high prevalence of poor non-responsive and low responsive soils observed in this study indicate major challenges for increasing crop productivity, as attainable yields in more than 50% of these sites were less than the initial yield target of 3 t haÀ1 towards achieving the African Green Revolution in SSA (Sanchez, 2010), even when nutrient and other agronomic inputs are applied in adequate quantities
Summary
Achieving food security is a key agenda that is eluding governments in sub-Saharan Africa (SSA) (Shapouri et al, 2010). Low productivity of food crops due to low nutrient application, in a region that has faced land degradation for several decades, is one of the major contributors to food insecurity in SSA (IFDC, 2006; Shapouri et al, 2010; Muller et al, 2012), besides post-harvest losses and inequitable food distribution. The use of fertilizers remains very low in SSA (IFDC, 2006; Liu et al, 2010) despite the resolution to increase fertilizer use to 50 kg haÀ1 by 2016 by the Africa Fertilizer Summit in 2006.
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