Cereal and legume crop responses to deep-placed K with and without P in NE Australian Vertosols

Abstract

Cereal, legume and fibre crops grown on Vertosols formed in-situ on upland slopes in NE Australia have demonstrated greater yield responses to deep-placement (≈ 0.20 m) of K and P together, rather than just K alone. Beginning in 2013, eight sites were established across central and southern Queensland and northern New South Wales. Treatments consisted of an untreated control, four K application rates (0, 25, 50 or 100 kg K/ha) with a basal P application (20 kg P/ha) and two K rates (0, 100 kg K/ha) without the P. Crop responses in this period showed some effect of seasonal conditions. Pulse species (chickpeas particularly) appearing generally more sensitive to K, whilst responses by grass species (wheat, barley, sorghum) varied with growing season conditions. The cumulative response to fertilizer applications has highlighted the importance of making balanced nutrient applications, with the largest yield increases often resulting from a combination of P and K. Single crop grain yield increases in response to a combination of deep-placed nutrients have been as large as 1070 kg/ha (a 56% gain compared to traditional farmer practice) in a sorghum crop. The longevity of treatment response over a rotation cycle is providing insight into potential future nutrient management strategies.