Abstract
Soil loss and surface runoff from farmland under coffee trees with different weed managements were investigated in Lampung, South Sumatra, Indonesia during rainy seasons from 1996 to 1999. Three treatment practices investigated were as follows : coffee without cover crop ; coffee with Paspalum conjugatum sp. as cover crop, and coffee with natural weeds. Weed management was done every two week by clearing all the weeds in coffee plot, and cutting the weeds around the coffee trees with diameter 1 m for the weedy plots. The results showed that the maximum daily rainfall and intensity based on 10 minutes observation were 82 mm/day and 120mm/h, however, only 14.2% of rainfall intensities was greater than 25 mm/h (classified as erosive rainfall intensity). A relationship between erosivity index (R) and daily rainfall(X) was found as follows : R =1.624 (X-10.9), where R : daily erosivity index (m2-t/ha/h) and X : daily rainfall (mm/day). The runoff ratio for clean-weeded coffee ranged from 7.0 to 15.9%, and decreased after the second year because of the coffee canopy growth. The presence of Paspalum conjugatum had reduced runoff until zero after the third year, whereas in natural weeds plot, runoff became zero after the fourth year. The highest soil loss was found in clean-weeded coffee which reached 22.7 t/ha in the second year of experiment. The use of cover crop could suppress soil loss until zero after the third year in Paspalum plot and after the fourth year in natural weeds plot. However the good management of weeds as cover crops is necessary due to the bad performance of coffee growth at both weedy plots. The average soil loss from clean-weeded coffee plot was 1.24 mm per year which was below the soil formation rate in Indonesia.
