Yield and soil system changes from conservation tillage in dryland farming: A case study from North Eastern Tanzania

Conservation agriculture (CA) and its related practices of soil cover, cover crops, and reduced-tillage have often been touted as an effective means of in situ water harvesting, which provides stable yields in times of low rainfall. Applications have been especially relevant to semi-arid sub-Saharan Africa, where yields are characteristically low due to decreased water availability during critical crop development periods. In this study, the impact of adopting CA on the soil's capacity for moisture retention (as indicated by productivity) was assessed over six seasons between 2005 and 2008 in Northern Tanzania. Treatments included conventional tillage, conventional tillage with mulch and manure, tillage via ripper, and tillage via ripper with mulch and manure. No changes in physiological properties of the the soil were observed after treatment, but changes in chemical and microbiological components were measured. Additionally, yield increases were seen for ripper plus manure and mulch treatments but not ripper alone compared to control (conventional). However, results question the ability of conservation agriculture practices to stabilize yields in times of abnormally low rainfall, considering yield increases relative to control were primarily observed after times of elevated rainfall. Thus, short-term benefits to farmers would be increased yields during seasons of high rainfall rather than yield stabilization during low rainfall.