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Abstract

Variable rate nutrient application (VRA) has the potential to improve farm profitability by improving the overall use of fertiliser inputs on-farm. In addition, VRA nutrient application is potentially a viable option for the reduction of dissolved inorganic nitrogen (DIN) in farm water runoff as a consequence of the associated reduction in overall nitrogen application. Agricultural runoff, in particular DIN from sugarcane production in the Mackay Whitsunday region, enters into the Great Barrier Reef lagoon affecting water quality. In this study we investigate the impact on the economics of the farm business due to a shift from the conventional sugarcane farming practice, using the industry’s ‘Six Easy Steps’ (6ES) nutrient application rate, to variable rate within block. The conventional 6ES rate is based on the district yield potential in conjunction with the soil mineralisation index and organic carbon content of soils on a particular block in a given region. VRA of nutrients aims to match the nutrient application rate to the historical block yield potential and the physical and chemical properties of the soil. Where there is significant variation within-block in terms of yield or crop variation, topography, climate and soil characteristics, nutrients can be varied to match zone yield targets. We find that the VRA system has the capacity to improve farm gross margins and reduce the overall nutrient application on one trial farm (by 14 percent). However, after the capital outlay required for the system was accounted for, we find that the VRA system reduced the profitability of the overall farming enterprise. Consequently, we explore the conditions under which the VRA system adds value to the trial farm, and also the minimum farm size (on land with similar yield variation to the trial property) needed for the capital outlay to breakeven.

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