Modeling the impact of partial surface mulch on soil heat and water flow

Surface residue is an integral part of many cropping systems, and there are opportunities to optimise its value as mulch by improving our understanding of how it affects the near surface soil physical environment. In this study we use field measurements and a coupled soil heat and water how model to demonstrate the effects of partial surface mulch on the near surface soil physical environment. The model is based on general physical laws and allows analysis of general system behaviour in response to changes in both inputs and systems variables. The field measurements were obtained on both a clay and a sand soil from experiments carried out in the semi-arid tropics. The treatments included a bare soil surface and 0 (completely mulched), 5 cm and 15 cm bare row zones. Both measurements and simulations showed that partial surface mulch cover can have dramatic effects on the soil physical environment near the soil surface, with the development of very strong horizontal gradients across bare soil-mulched soil boundaries. They also show that bare row zones are able to act as either a source or sink for heat and water, and that the resultant soil environmental conditions will exert strong control of soil biological activity. Although model simulations did not always match exactly with the specific measurements, they did capture the major trends given by the field data. While this suggests a certain robustness about the way the processes are modeled, there are several areas in which the model needs improvement and these are highlighted in the paper.