Prof. Richard Bell1, Dr Miaomiao Cheng1, Dr Craig Scanlan1,2
1SoilsWest, Centre for Sustainable Farming Systems, Murdoch University, 2Department of Primary Industries and Regional Development
Biography:
Professor of Land Management since 2007. Research on crop nutrition and soil management in Australia, and on Conservation agriculture, nutrient management, salinity management and farming systems in SE and S Asia. Prescott medallist, awarded by Soil Science Australia in 2022
Abstract:
Negative K balances (averaging 5.5 ± 0.4 kg/ha for wheat to 10.1 ± 0.9 kg/ha for canola) are common in the grain-growing regions of Western Australia. Although growers routinely apply K in cropping programmes in deep sands and duplex soils, the rates are generally below the replacement rates. Recently, attention has turned to emerging K deficiencies on loamy soils where negative K balances have depleted K reserves and K availability to the point where K supply is no longer sufficient for the K requirements of crops. Notably, the critical K concentration on loamy soils appears to be higher than on sandy soils. However, loamy soils have limited capacity to buffer the rundown of available K due to the low content and availability of non-exchangeable K in soils. Additionally, the rundown in K due to negative balances is more pronounced in subsoils than in topsoils that receive K replenishment from recycled crop residues. Therefore, for improved prediction of K deficiency, soils should be sampled to a depth of 30 cm, especially in the loamy soils. Currently, K balance calculations based only in fertiliser input and grain outputs may be quite inaccurate due to uncertainty about the extent of K leaching. With increased emphasis on K nutrition in crop programmes, further research should target increased K-use efficiency by strategies such as banding of fertiliser K and split applications of K.