The Response of Crops to Potassium Placement Depth and Band Spacing

Northern Australian cropping systems are dominated by Vertosols and crop productivity is largely dependent on stored soil moisture. Cropping systems are a mix of summer crops of sorghum, cotton, maize and mungbeans and winter opportunity cropping with wheat, barley and chickpeas. Crop performance and the efficient use of water relies on access to adequate subsoil nutrient levels, but there are large variations in native soil P and K reserves. Current soil testing protocols and procedures are not effective at assessing these reserves but previous research has identified that the demand for nutrient is increasing as native organic N and S and inorganic P and K reserves are declining.

The overall research undertaken by Dr Bell and his team aims to assess the size of P and K reserves in the main cropping regions, and develop diagnostic criteria to predict the amount of plant available nutrients, and so the need for added P and K fertilizers. Dr Bell and his colleagues have around 20 field sites in the whole project with 4 of these supported by Canptoex. The sites are all in farmers paddocks and once set up, they follow the host farmers crop selections. In this northern grains region, winter or summer crops are selected mainly on stored water in the soil at the potential planting times, and as a result crop sequences can involve the whole range of crops mentioned earlier.

The project also aims to develop the most effective strategies to meet crop fertilizer requirements in soils with low nutrient status. This research is supported by the Grains Research and Development Corporation and the Cotton Research and Development Corporation as well as the Queensland Department of Primary Industries.

For K, the current exchangeable K test is not a good indicator of K reserves, especially in low K soils, and slow release K reserves (determined by a tetra-phenyl borate extraction) are likely very important but highly variable. Field research has shown good responses to deep K and P placement, and there are important N*P*K and P*K*S interactions, so that multi-nutrient interactions need to be considered in these regions.