Lessons for Managing Soil Fertility from Long-Term Trials at the International Center for Tropical Agriculture (CIAT) in Western Kenya.

Sustainable agricultural intensification is one of the major concerns to meet the growing demand for food, while conserving the natural resource basis for future generations. Without doubt, soils provide the fundamental basis for food production. The continued loss of soils and soil fertility is jeopardizing the sustainability of agriculture in many parts of the world, and sub-Saharan Africa (SSA) in particular. Here, limitations in soil organic matter and other key nutrients are major factors constraining agricultural productivity.

The International Center for Tropical Agriculture (CIAT) has been carrying out research on the sustainable management of soil fertility in the tropics for several decades. In Africa, CIAT soil scientists have a long history of close engagement with a wide range of national and international partners, for example within the African Network for Soil Biology and Fertility (AfNet). In Western Kenya, CIAT is maintaining two long-term trials that address various issues of soil health in the context of sustainable agricultural intensification, such as the management of organic matter, minimum tillage, crop rotation and inclusion of green manure cover crops, and adequate levels of organic and inorganic fertilizer application.

The presentation provides some lessons learnt from these two trials. In a nutshell, they underpin the crucial importance of adequate and continuous inputs of organic matter to the soil to maintain its fertility and productivity. However, some tradeoffs still pose a challenge to the wider scale adoption of improved soil management practices by smallholders. These are competition for organic matter/residues, rather slow changes in the productivity of the soil, and increased labor and cash requirements. Therefore, incentive mechanisms may be required, if the pace of adoption of sustainable soil management practices was to be increased.