Whole farm implications on the application of variable rate technology to every cropped field

In the last 10 years precision agriculture has evolved and it is now possible to manage cropping inputs at the sub field scale. However, the expected return generated by these management practices varies with the amount and predictability of the spatial variation in crop yield across the field and may vary from field to field across the farm. We analysed the spatial variation of crop yield from 20 fields totalling 2832 ha from a 5200 ha farm in Western Australia at the field and the sub field scale to determine the economic value of introducing variable rate management (VRT) strategies to fields across the entire farm. In this case study, 6 out of 20 fields generated an additional economic payoff of AU$15/ha when managed with VRT over uniform management. Sensitivity analysis found that the starting levels of soil fertility were an important driver of the payoff for managing a field with VRT. If starting soil fertility was low and uniform across the field, then no fields generated an economic return of more than AU$7.00/ha when managed with VRT. Other factors, including commodity price, fertiliser price, amount of variation in crop yield within the field moderately increased the value of adopting VRT across fields within farm the value of VRT increased if fertiliser budgets were constrained, particularly if the yield distribution of the field was negatively skewed. While VRT does add value to many fields across the farm, the gains are small and the technology must be implemented cheaply for it to be viable.

Research highlights
► The spatial variation of 20 cropped fields sown in 2008 and covering 2800 ha of cropping land from a 5000 ha farm were assessed.
► Only 6 out of 20 fields generated an additional economic payoff of AU$15/ha when managed with VRT over uniform management.
► The starting level of soil fertility was an important driver of the benefit that VRT could generate.
► Other factors, including commodity price, fertiliser price and the amount of yield variation within the field moderately increased the value of adopting VRT.
► If the farmer had to constrain the fertiliser budget, then the payoff of VRT on a single field increased.