A compartmental model to simulate temporal changes in soil structure under two cropping systems with annual mouldboard ploughing in a silt loam

A practical model of the soil structure dynamics in ploughed fields can be a powerful aid to farmers attempting to optimise their management practices. This paper describes a compartmental model that simulates the changes over several years in an indicator of the effects of cropping systems on soil structure. This indicator, the proportion of severely compacted clods in the ploughed layer, was measured in two plots at the INRA Experimental Centre at Grignon (Yvelines, France), where two cropping systems produced very different compaction conditions in a silt loam. The ploughed layer was considered to be a set of elementary compartments delimited by the wheel tracks and actions of tillage tools. The percentage of severely compacted clods in each elementary volume changed with time due to transfer between compartments during mouldboard ploughing, compaction and fragmentation. The proportion of severely compacted clods changed exponentially until it reached a plateau, after about 8 years. The equilibrium values of the indicator were very similar to those measured in the experimental plots. The model was very sensitive to the rate at which severely compacted clods were lost, probably because the vertical distribution of these clods in the soil profile was not taken into account in this compartmental model. The model in its present state can be used to compare the effects on soil structure of various technical changes.