MODELING THE IMPACT OF PARTIAL SURFACE MULCH ON SOIL HEAT AND WATER-FLOW

Surface residue is an integral part of many cropping systems, and ther e are opportunities to optimise its value as mulch by improving our un derstanding of how it affects the near surface soil physical environme nt. In this study we use field measurements and a coupled soil heat an d water how model to demonstrate the effects of partial surface mulch on the near surface soil physical environment. The model is based on g eneral physical laws and allows analysis of general system behaviour i n response to changes in both inputs and systems variables. The held m easurements were obtained on both a clay and a sand soil from experime nts carried out in the semi-arid tropics. The treatments included a ba re soil surface and 0 (completely mulched), 5 cm and 15 cm bare row zo nes. Both measurements and simulations showed that partial surface mul ch cover can have dramatic effects on the soil physical environment ne ar the soil surface, with the development of very strong horizontal gr adients 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 exer t strong control of soil biological activity. Although model simulatio ns did not always match exactly with the specific measurements, they d id capture the major trends given by the held data. While this suggest s a certain robustness about the way the processes are modeled, there are several areas in which the model needs improvement and these are h ighlighted in the paper.