Nutrient use efficiency and crop yield response to the combined application of cattle manure and inorganic fertilizer in sub-Saharan Africa
The combined application of cattle manure and inorganic fertilizer has been widely recommended in the context of integrated soil fertility management (ISFM) on smallholder farms in sub-Saharan Africa (SSA). However, the conditions under which this combination (hereafter ISFM) improves nutrient and water use efficiency and crop yields have not been systematically studied. Therefore, we undertook a meta-analysis of studies conducted in rain-fed maize production systems across SSA with the objective of (1) quantifying the magnitude of improvement in grain yield, rain use efficiency (RUE), agronomic efficiency of nitrogen (AEN) and phosphorus (AEP) due to ISFM; (2) determining conditions under which ISFM achieves greater yield response, RUE, AEN and AEP; and (3) compare yield responses to the substitutive and additive approaches of ISFM with sole application of cattle manure. Application of high rates of cattle manure in combination with high N fertilizer rates increased yield response only by 27.5%, but it achieved 47% lower AEN and 27% lower AEP relative to a combination of low manure and low N fertilizer rate. The substitutive approach of ISFM achieved 54% greater AEN and 16% greater AEP than the additive ISFM approach. Yield response and AEN also significantly varied with soil type. On most soil types, AEN was 2–195% lower under sole manure than under ISFM or sole fertilizer. We recommend application of moderate rates of cattle manure (5–10 t ha−1) combined with moderate doses of N fertilizer (< 50 kg N ha−1) on responsive soils to optimize AEN and maize yield response.