Variable Rate Lime for cropping systems in the HRZ: an economic analysis

Soil acidity affects 50% of Australia’s agricultural landand significantly affects crop production. Results from grid soil sampling (0-10 cm) for pHCa across hundreds of cropping paddocks in the high rainfall zone(HRZ) in Victoria highlight the variability in soil pH across a paddock, where the coefficient of variation averaged 4.7% and ranged from 0.7 up to 16%. The range in soil pH and the coefficient of variation from the field data were used to develop eight hypothetical paddocks.

A discounted cash flow model was used to investigate the economics of grid soil mapping and variable rate lime application to ameliorate surface soilacidity. Both variable rate and fixed rate lime addition had a positive net present value (NPV) across thehypothetical scenarios,with the inclusion of a pH-sensitive pulse crop increasing the NPV. With a pulse crop in the rotation, variable rate lime had a greater NPV in six of the eight hypothetical paddocks, while in the remaining two paddocks, variable rate and fixed rate applications produced similar NPV results.