An evaluation of the tactical use of lucerne phase farming to reduce deep drainage

[摘要] Executive Summary:Lucerne phase farming has been suggested as a way to reduce deep drainage in southern Australia. It is based on the concept that lucerne (Medicago sativa L.), a perennial pasture with a deep root system, creates a soil water storage buffer below the root zone of the annual crops, which will gradually fill during the subsequent cropping phase and temporarily reduce the risk of deep drainage. The rate of refilling is variable because it is affected by the amount and distribution of rainfall as well as management of the crop and the summer fallow. There is, therefore, uncertainty about the optimum phase durations that will maximise the impact of the lucerne phase. Computer simulations were applied to evaluate the use of a soil water measurement below the root zone of annual crops to schedule the phase changes, referred to as tactical phase farming. The results confirmed the concept behind phase farming. In general, phase farming showed clear benefits by reducing average annual deep drainage significantly, but at the cost of lower average annual gross margin. Tactical phase farming improved the trade-off between deep drainage and gross margin relative to fixed duration phases; for a given amount of average annual deep drainage the average annual gross margin was larger, and for a given gross margin the drainage was smaller. These benefits were small, however.The average gross margins for the tactical systems were lower than those of fixed phase systems with the same percentage of time under cropping. This was especially the case when the tactical solutions resulted in short lucerne phases and contributed to the small benefits from tactical phase farming. Enforcing a minimum duration for the lucerne phase afforded improved benefits. Climate and soil type influenced the results in that the benefits of tactical phase systems were largest compared with fixed phase systems in soils with a large available water holding capacity (resulting in a larger buffer) and when the variability of the refilling rate was high. For soils with a small available water capacity, resulting in a small soil storage buffer, and with a climate that caused rapid refilling, the reduction in drainage as a result of incorporating a lucerne phase (fixed duration or tactical) was offset by the increased deep drainage that occurred during the first year of the lucerne phase. In these cases the deep drainage outcome of a phase system was a function primarily of the percentage of time under cropping and lucerne, and soil water measurements (tactical phase farming) did not result in any benefits over fixed duration phases.

[发布机构] CSIRO

[学科分类] 地球科学(综合)