Water Conservation by Fallowing In Semiarid Tropical East Africa

Abstract

Crop yields and soil-moisture changes to 6-ft. depth were measured in two cycles of five 2-year groundnut rotations. Fallows kept bare, sown with protective grass cover, and allowed to regenerate volunteer weeds and grasses were compared with maize and with sorghum in alternate-year cropping with groundnuts. Soil moisture- tension changes were following by gypsum blocks and quantitative changes were measured by soil sampling Measurements were made of the root ranges at different growth stages of groundnuts, maize, sorghum, and teff; all lay within the 6-ft. depth. Annual rainfall totals for the four years of the experiments were 22, 8t, 13, 13 in. respectively. The volunteer cover removed all available water from 6 ft: and used more water than maize, sorghum, or groundnuts. Bare fallow conserved water and increased subsequent yields of groundnuts, but no fully satisfactory soil conservation measures were achieved. Protection of fallow by a heavy sowing of 'teff' grass provided efficient soil conservation and, with a seed-rate of 20 lb. of viable seed per acre, suppressed weeds and stored subsoil moisture. Groundnut yields of over 400 lb. kernels per acre were thus secured in a year of 8'5 in. total annual rainfall.