Curbing Soil Organic Matter Reduction through Integrated Soil Fertility Management in Smallholder Farming Systems in Sub-Saharan Africa.

It is well recognized that soil organic matter is critical for various soil functions that ensure crop productivity and other ecosystems services. Soil organic matter has been declining under smallholder farming system in sub-Saharan Africa, contributing to land degradation. The limited availability of organic input sources, particularly in densely populated regions, coupled with the continuous low crop productivity, exacerbates the degradation. Decades of research have focused on developing technologies with ability to produce significant quantities of organic inputs for building-up soil organic matter, including cover crops, fallows, and agroforestry-based strategies. While these technologies were promising at a research point of view, the applicability by smallholder farming communities encountered various limitations, including limited land to spare for the technologies and the lack of incentives. In view of the non-adoptability of the above options, the development of approaches that address previous constraints became a focus. Integrated soil fertility management (ISFM), which aims at optimizing crop productivity through maximizing resource efficiency by better interactions between inputs (fertilizers, organic inputs, and improved germplasm), is promoted as a promising approach in increasing crop productivity while gradually reversing the soil degradation trend, including building soil organic matter. ISFM contributes to SOM in 2 ways: firstly, the use of organic input in combination with mineral fertilizers is a core component of ISFM, the organic inputs contributing in increasing the use efficiency of the fertilizers; secondly, the increased crop productivity through ISFM practices, is accompanied by an increase in crop residues biomass, becoming a valuable source of organic inputs to the soil. Not only a judicious selection of crop germplasms and nutrient sources is important, but also the considerations of the heterogeneity both in terms of farmer types and biophysical conditions in which the farmers operate, are critical components of the ISFM approach.