SIDASS project: Part 3. The optimum and the range of water content for tillage – further developments

The SIDASS project “A spatially distributed simulation model predicting the dynamics of agro-physical soil state within Eastern and Western Europe countries for the selection of management practices to prevent soil erosion based on sustainable soil–water interactions” required a method for estimating the dates (or soil water conditions) under which soil tillage operations could be performed. For this purpose, methods were developed for estimating the optimum and the range of soil water contents for tillage. These methods are based on the soil water retention curve. In this paper, we further develop the method in two ways. First, we take account of the fact that the soil properties: clay content, organic matter content and bulk density are not independent. This is done through the use of simple pedo-transfer functions which are based on measurements on many soils. Second, we present a simplified and more rapid method for estimating the lower (dry) limit for tillage. This enables this lower limit to be calculated using a computer spreadsheet instead of through tedious iterative calculations which were previously obtained with a special computer program. Examples are given for the tillage limits which take account of the interdependencies between the contents of clay, the content of organic matter and the bulk density. Estimated typical values of the tillage limits are presented for all the soil texture classes in the FAO/USDA classification system. Additionally, it is shown that the range of water contents for tillage is expected to decrease with decreasing soil physical quality as measured by S.