This manuscript presents a multi-disciplinary analysis of the opportunity and economics of double cropping on well-drained loamy soils in the Fitzroy catchment, Western Australia, sourcing water from the undeveloped inter-connected Grant Group and Poole Sandstone regional-scale groundwater system. This study sought to identify those locations in the catchment that are likely to have the lowest cost, lowest risk and soils suitable for double cropping.
A horizontally integrated enterprise was examined using the APSIM agricultural production and NABSA beef systems models, where cotton seed and an irrigated forage are used on station to increase the weight and reproductive rates of an existing beef enterprise. Assuming the existence of a cotton gin at Fitzroy Crossing the ‘effective’ gross margin for a cotton – mungbean - forage rotation would be about $3205/ha, Under a more likely potential development scenario of a cotton gin at Kununurra the effective combined crop-forage gross margin is estimated to be about $2580/ha. These gross margins are about 25% higher than potential returns from a single crop and highlights the opportunity for a more diverse investment strategy in double cropping, which in most years is more likely to better meet the capital costs of development.
Interpolated surfaces of depth to the inter-connected Grant Group and Poole Sandstone aquifers and hydraulic head were used to calculate the capital costs of irrigation infrastructure and the annual operational costs of groundwater pumping respectively.
Under the scenario of the nearest cotton gin at Kununurra, approximately 280,000 and 660,000 ha of suitable land (i.e. ‘lighter’ soils and Class 3 or better) is underlain by the Grant and Poole Sandstone such that it may be possible to achieve an IRR of more than 3% for average yields of 25 and 50 L/s respectively, and 0 and 42,000 ha of suitable land is underlain by the Grant and Poole Sandstone such that it may be possible to achieve an internal rate of return of at least 7% for average yields of 25 and 50 L/s respectively.
Although it may be challenging to find a set of circumstances where it is possible to achieve a high commercial return on an irrigation development (e.g. 7% or greater), the horizontally integrated scenario examined in this study may enable a station to grow out young cattle and provide alternative markets to the live export trade, thereby reducing risk.