Soil organic carbon and nitrogen in agroforestry systems in sub-Saharan Africa: A review

Abstract

Effective nutrient management is a key to sustainable agroforestry systems, chiefly in the current context of changing and variable climate along with increasing uncertainties of production systems to meet the needs for food security. The diversity of agroforestry systems throughout Sub-Saharan Africa results in a diverse nutrient management models with specific underlying mechanisms. Over the past decades several studies have been conducted on nutrient dynamics in agroforestry practices in various farming systems across a large range of agro-ecological conditions. We conducted a meta-analysis of the published data of four of these practices (alley cropping, improved fallow, mulching and parkland) for sub-Saharan region to examine their contribution to soil organic carbon and nitrogen content. The results of this analysis revealed an increase in both SOC and N contents of these practices over their corresponding treeless control plots. C to N ratios showed the higher values in the mulching and parkland practice as opposed to the alley cropping, which is nitrogen fixing species-based agroforestry technology. It has therefore been hypothesized that increase SOC may contribute to the provision of important supporting ecosystem services (nutrient inputs, the enhancement of internal flows, the decrease of nutrient losses, etc.). Therefore, agroforestry as a science hold promising solutions for alleviating soil fertility problems and achieving sustainable land management provided (1) resources sharing between components are better understood and (2) pathways for sustainable nutrient management are context-oriented and made available for users and policy makers.