At a recent GRDC Regional Cropping Solutions Network open forum at Morawa in Western Australia, Dr Richard Bell from Murdoch University spoke of the importance of potassium (K) for optimal plant growth and alleviating crop stress.
Low soil K is common in the sand and duplex soils of WA cropping regions. Soil test analysis shows 20-32% of soils in these regions have Colwell K levels of less than 60 mg/kg in 0-10 cm depth.
Typical K fertiliser inputs for cropping and hay production do not replace the soil K removed by these processes. Up to 20 kg/ha K can be removed when a 4 t/ha cereal crop is harvested, and by a 2 t/ha canola or lupin crop. Extra K may also be lost by leaching.
Research has shown the critical soil Colwell K range for wheat at 0-10 cm depth across all soil types in WA is 39-45 mg/kg. This is the most critical depth for predicting a grain response to K, but doesn’t give the full picture of soil K reserves. Soil test down to 30 cm to check subsoil K stocks.
K levels play a role in helping crops cope with many stressors, including sodic and saline soils, frost and drought conditions and disease.
Drought-stressed plants show an increased response to K. Applying K at rates of at least 10-15 kg/ha may maintain topsoil K levels. Higher rates are needed to maintain subsoil K levels and alleviate crop stress in dry times.
Higher levels of internal K concentrations in plants will also increase tolerance to frost damage and reduce frost-induced sterility in wheat.