Operational aspects of ley farming systems in the semi-arid tropics of northern Australia: A review

The ley farming systems proposed for the Australian semi-arid tropics involve rotating an annual pasture (usually legume) with crops sown using no-tillage. These systems were developed to overcome many of the climatic constraints that beset previous attempts at cropping in the region. However, difficulties in the timing of farm operations also contributed to past failures. No analysis of the operational aspects of ley farming had been made; this was the objective of this paper. During the transition between wet and dry seasons rainfall is extremely variable. These periods were shown to be the most critical time for operations in ley farming systems. During the dry-wet transition, management of ley pastures is very difficult because pastures must provide grazing for livestock as well as sufficient soil cover for timely sowing of a following crop. Legume pastures have reduced grazing value at this time due to spoilage by early rain. Similarly, during the wet-dry transition annual pastures must be allowed to set seed at a time when crops are yet to be harvested and stubbles are not available for grazing. It was suggested that including separate paddocks of perennial pasture could reduce the demand on annual pastures during the seasonal transitions. A limited number of days to sow a crop combined with severe yield penalties for late sowing restrict the area that can be sown in any season. Sowing opportunities were determined for 3 locations in the Northern Territory. No-tillage was shown to increase the potential number of sowing days. However, the time available to apply glyphosate before sowing using no-tillage was confined to the morning due to risk of afternoon rainshowers reducing efficacy. The number of seasons where a particular crop or cultivar could not be sown was independent of the method of tillage. The wet-dry transition was shown to be important for harvest operations. Our analysis of 3 sites in the Northern Territory suggests that for mungbean and sorghum, later maturity combined with prompt harvest will reduce the risk of poor seed quality due to weathering and could permit earlier sowing. However, for sorghum, an economic assessment of these practices required research that can quantify the interaction between sowing date, time-to-maturity and grain yield.