The Response of Crops to Potassium Placement Depth and Band Spacing

The right place for K in summer dominant rainfall areas of northern Australia.


24 Mar 2015

2014 Annual Interpretive Summary

The aim of the project is to explore responses to different K application strategies (i.e., place, rate and with other nutrients) for a range of crops grown in central Queensland in modern no-till opportunity cropping systems. In this region, subsoil P, K and S are often co-limiting, although critical soil test values for P and K are poorly defined. While nutrients could be deep placed each year, the amount of soil disturbance required to do this has a high risk of soil erosion and the window of time to undertake those operations is very narrow. The hypothesis being tested was that on low soil nutrient sites, providing high application rates (200 kg K/ha) of banded K at a depth of 20 cm would overcome K limitations for several crop cycles, providing that low P, S or micronutrient concentrations were not limiting.

In year 1 (a moisture good year), there was a positive 20% grain yield response in both sorghum and chickpea to deep P, but there were no responses to deep-placed S or K. In year 2 (a drier year) the effects of deep P were clearly beneficial at the two sites. Additive effects of K over P were also seen and at one site with chickpea, banded K resulted in a 51% yield increase provided adequate P was also present. In year 3 (also a drier year) there were positive yield responses in wheat and chickpea of around 20% to added K where P and S were also supplied.

Deep-placed K fertilizer can show significant yield responses for several years over a range of summer and winter crops, but the response depends on adequate supply of other nutrients, especially P. An economic analysis showed additional crop returns of AU$320/ha to AU$380/ha where P and K were supplied.