Soil Organic Carbon and Proper Fertilizer Recommendation

Abstract

Soil carbon in the form of organic matter is a key component of the soil ecosystem structure. In most parts of West Africa agro-ecosystems (except the forest zone), the soils are inherently low in SOC content due to low organic matter additions, and accelerated degradation. The rapid turnover rates of organic material is as a result of high soil temperatures and fauna activity particularly termites. The SOC levels rapidly decline with continuous cultivation. For the sandy soils, average annual losses may be as high as 4.7% whereas with sandy loam soils, losses are lower, with an average of 2.0%. To maintain food production for a rapidly growing population, application of mineral fertilizers and the effective recycling of organic amendments such as crop residues and manures are essential especially in the smallholder farming systems that rely predominantly on organic residues to maintain soil fertility. The efficiency of fertilizer use is likely to be high where the organic matter content of the soil is also high. In unhealthy or depleted soils, crops use fertilizer supplied nutrients inefficiently. Where soils are highly degraded, crops hardly respond to fertilizer applications. When SOM levels are restored, fertilizer can help maintain the revolving fund of nutrients in the soil by increasing crop yields and, consequently, the amount of residues returned to the soil. Crop yields can be increased by 20–70 kg ha−1 for wheat, 10–50 kg ha−1 for rice, and 30–300 kg ha−1 for maize with every 1 Mg ha−1 increase in soil organic carbon pool in the root zone. There is need to increase crop biomass at farm level and future research should therefore focus on improvement of nutrient use efficiency in order to increase crop biomass.