Effects of grass fallow treatments in restoring fertility of Buganda clay loam in South Uganda

Abstract

Between 1924 and 1934 Uganda, in common with many other African territories, tested arable rotations incorporating legumo green manures to maintain soil fertility (Martin, 1944; Uganda Dept., 1931–32) and it was concluded that the green manures failed to maintain fertility and were not worth the trouble involved. The Uganda Department of Agriculture accordingly changed its official rotations to modified forms of the indigenous shifting cultivation, namely 3 years of elephant grass rest alternating with 3 years of cropping. This same failure of green manures, combined with the apparent lack of correlation between crop yields and soil nutrient contents and the obvious deterioration of soil structure under crops, led Martin (1944) to the view that it was the physical not chemical condition of the soil which was important. Using his wet sieving technique he showed that, provided soils contained enough clay, all grass increased the water-stable crumbs over ½ mm diameter in the top soil and that 3 years under elephant grass was about optimal for restoring crumb structure.