Manure and Soil Organic C Effects on Yield and Response to Fertilizer in Tropical Africa.

Manure is a valuable resource of integrated soil fertility management for soils typically with soil organic C (SOC) of < 10 mg kg^-1 in the Sahel and Sudan Savanna of West Africa. Manure application effects on yield and response to fertilizer were not well established. On-farm and on-station trials were conducted during 2014 and 2015 in Niger to evaluate effects of 2.5 Mg ha-1 manure with eight trials each for sorghum, pearl millet and cowpea and four trials for groundnut. Fourteen 14 trials were conducted in Burkina Faso to determine the effect of 5 Mg ha-1 manure, and an additional 12 trials were conducted to evaluate the residual effect during the following year. Yield of pearl millet and cowpea with no fertilizer applied was increased in Niger by manure application but sorghum and groundnut yield were not affected. Response to fertilizer was about 300% greater for manure application including for N applied to sorghum and pearl millet, P applied to all crops, and K applied to cowpea. In Burkina Faso, the mean yield increase over all crops was 33 and 42% following application of 5 Mg ha^-1 manure and with the residual effect, respectively. Crop response to applied P and K was increased with manure application but the residual effect was not important to response to applied nutrients. In addition, results of >1000 comparisons derived from research conducted in 12 African nations relating SOC to crop productivity and to response to applied N, P and K will be reported.