| heal.abstract |
Tillage displaces large amounts of soil from upper slopes and deposits soil in lower landscape positions, greatly affecting productivity in these areas. The long-term effect of tillage on soil erosion was studied in four field sites growing mainly rainfed wheat. The soil loss from landscape positions with slopes, ranging from 3 to 28%, was estimated by: (a) comparing data of horizon thickness described at the same position at different times; and (b) using soil movement tracers added to the soil. Existing empirical relationships were used for estimating soil loss by tillage and runoff water, and loss in wheat biomass production. The experimental data showed soil losses of 0.4 to 1.4 cm yr-1 depending on slope gradient, plough depth, and tillage direction. In two of the sites, soil depth has been reduced by 24-30 cm in a period of 63 years. The mean soil displacement of the plough layer (30 cm thick), measured by soil movement tracers, ranged from 31 to 95 cm yr-1 depending mainly on slope gradient, corresponding to a rate of soil loss of 0.3 cm to 1.4 cm yr-1. Soil eroded from the upper slopes was deposited on the lower slopes increasing soil thickness by 0.4 cm to 1.4 cm yr-1. The application of empirical relationships, estimating soil loss by tillage and water runoff, showed that soil erosion at the field sites can be mainly attributed to tillage. The loss in wheat biomass production due to erosion was estimated at 26% on upper slopes for a period of 63 years, while a 14.5% increase in wheat production was estimated due to deposition of soil material in the lower landscape. |
en |