Rates and patterns of tillage and water erosion on terraces and contour strips: evidence from caesium-137 measurements

Despite the widespread use of contour-strips and terraces for soil conserva tion little is known concerning the impact of such measures on rates and pa tterns of tillage erosion and tillage translocation. Caesium-137 (Cs-137) m easurements would appear to offer a rapid means of assembling data relevant to the evaluation of tillage erosion and tillage translocation. However, u se of Cs-137 data in this way requires an approach to the analysis of Cs-13 7 data which accounts for both tillage erosion and tillage translocation. T he latter is particularly significant on short slopes, A method of analysin g Cs-137 data has been developed, that employs a linear, multistore, mass-b alance model of soil and Cs-137 redistribution to permit estimation of the contributions to erosion from both water and tillage erosion. This method i s outlined and results from its application are discussed using case studie s from Yanting, in Sichuan Province, China; Ha Sofonia, in Lesotho; and, Ch inamora, in Zimbabwe. These case studies confirm the viability of the appro ach and provide valuable evidence for the importance of tillage erosion and translocation on terraces and contour-strips subject to cultivation by ani mal traction. Gross rates of tillage erosion were found to be of comparable or greater magnitude than gross rates of water erosion on the fields exami ned. It is, therefore, suggested that any evaluation of on-site impacts of erosion must take account of tillage erosion. Relationships between annual soil fluxes due to tillage and slope tangent were found to be very similar to the relationships established for a single pass of equivalent tillage eq uipment with mechanical traction. Furthermore, because tillage by animal tr action necessitates downslope turning of the soil on every occasion, net do wnslope fluxes of soil associated with animal traction may exceed the level s associated with tillage by mechanised traction, in which the soil is typi cally turned in opposing directions on successive occasions. (C) 1999 Elsev ier Science B.V. All rights reserved.