Defining critical soil nutrient concentrations in soils supporting grains and cotton in Northern NSW and Queensland

Abstract

This project focussed on the phosphorus (P) and potassium (K) status of northern cropping soils. Stores of P and K
have been depleted by crop removal and limited fertiliser application, with depletion most significant in the subsoil.
Soil testing strategies are confounded by slowly available mineral reserves with uncertain availability. The utility of
new soil tests was assessed to measure these reserves, their availability to plants quantified and a regional sampling
strategy undertaken to identify areas of greatest P and K deficit. Fertiliser application strategies for P and K have
been tested and the interactions between these and other nutrients have been determined in a large field program.