Abstract
Improving fertilizer recommendations for farmers is essential to increase food security in smallholder landscapes. Currently, blanket recommendations are provided across agro-ecological zones, although fertilizer response and nutrient use efficiency by maize crop are spatially variable. We aimed to identify factors that could help to refine fertilizer recommendation by analyzing the variability in fertilizer response (FR) and the agronomic nitrogen use efficiency (N-AE). A literature search for on-farm studies across Kenya and Sub-Sahara Africa (SSA), excluding Kenya, yielded 71 publications. The variability in FR was studied using a meta-analysis whereas key factors that influence FR and N-AE were studied with linear regression models. On average, the FR was 2, but it varied considerably from 1 to 28.5 (excluding outliers). In SSA, 18% of the plots were non-responsive plots with an FR < 1. The main factors affecting N-AE for Kenya were P-Olsen, silt content, soil pH, clay and rainfall, whereas only soil pH, exchangeable K and texture were important for SSA. However, our study indicates that available data on soil, climate and management factors could explain only a small part (< 33%) of the variation in FR and N-AE. Soil pH, P-Olsen, silt content, and rainfall had significant but low levels of power in explaining variation in FR and N-AE. Our findings indicate that strategies to refine fertilizer recommendation should include information on soil types and soil properties.
Highlights
The population of Sub-Saharan Africa (SSA) is projected to increase up to 1.2 billion by 2050 (United Nations Population Division 2009; Ray et al 2013)
There was no obvious relationship between fertilizer response (FR) and N application rate (Fig. 1c, d) the maximum attainable FR in Kenya tended to decrease with N application rate (Fig. 1d)
Our results indicate that both FR and N-AE vary largely within Kenya, which supports the claim that fertilizer recommendations need to be refined to a higher spatial resolution
Summary
The population of Sub-Saharan Africa (SSA) is projected to increase up to 1.2 billion by 2050 (United Nations Population Division 2009; Ray et al 2013). The increasing food demand of this growing population requires agricultural intensification with efficient fertilizer use. Current fertilizer recommendations in SSA are often only specified to the level of a region, for instance, an agro-ecological zone (AEZ) or administrative district (e.g., Mowo and Mlingano 1993; FURP 1994; Schnier et al 1996). The fertilizer recommendations for these larger regions are commonly referred to as blanket fertilizer recommendations. Environmental and management factors vary at short distances in the smallholder landscapes of SSA (Tittonell et al 2005; Vanlauwe et al 2011; Zingore et al 2007; Stoorvogel and Smaling 1998; Tittonell et al 2008).
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