Legume cover crops are more benefi cial than natural fallows in minimally tilled ugandan soils

It is important to establish the various eff ects of legume cover crops on soil physicochemical properties because they have been considered for use as improved fallows (with shorter rest periods) to enhance development and maintenance of soil productivity. Our objectives were to assess: (i) aboveground dry matter yields of legume cover crops; and (ii) cover crop eff ects on weed infestation and soil physicochemical properties in a minimum tillage management system. Trials were conducted for 2 yr at Kawanda Agricultural Research Institute and on farmers' fields in Mbale and Pallisa districts, eastern Uganda. The experiment layout was a Randomized Complete Block Design (RCBD) in a split-plot arrangement with four replications. Natural and improved fallows were established in the second cropping season of 2004. Cover crops used in the improved fallows included mucuna [Mucuna pruriens (L.) DC.var. utiliz], Dolichos lablab (Lablab vulgaris Savi cv. Rongai), canavalia [Canavalia ensiformis (L.) DC.], and crotalaria (Crotalaria paulina Schrank). The fallows were reestablished in the same plots in the second cropping season of 2005 aft er maize (Zea mays L.). Canavalia yielded signifi cantly more dry matter than the other fallows regardless of year or site. With an average yield of 169 kg N ha ^-1 canavalia accumulated signifi cantly more N than the other fallows; all improved fallows produced signifi cantly more N than the natural fallow. Canavalia also accumulated signifi cantly more P than the other fallows; all improved fallows, with the exception of crotalaria, accumulated more P than the natural fallow. There was no signifi cant change in soil physicochemical properties by the improved fallows. All eff ects considered, improved fallows were more benefi cial than natural fallow. A signifi cant improvement in soil physicochemical properties using legume cover crops might be possible, though it may require more than the two cropping cycles used in this study of degraded soils.