Lucerne phase farming has been suggested as a way of reducing deep drainage in the cereal belt of 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 gradually refills during the subsequent cropping phase, temporarily reducing 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 effect 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 that phase farming reduced average annual deep drainage significantly, but at the cost of lower average annual gross margin. In most cases, 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. The benefits of tactical phase systems were greatest in soils with a large available water-holding capacity and when the variability of the refilling rate was large. Overall, however, the benefits of the tactical approach relative to fixed phase systems were small.