Potassium added to frost management toolkit

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Potassium fertiliser can provide extra protection for cereal crops against stresses such as frost.

This is a key finding from six years of field trials carried out in Western Australia’s central and southern grainbelt through the GRDC’s More Profit from Crop Nutrition (MPCN) program and the National Frost Initiative (NFI) and led by Murdoch University researcher Dr Richard Bell.

Dr Bell told the GRDC Update in Perth that sampling showed 10 to 50 per cent of WA’s cropping soils are potassium deficient and annual losses in harvested grain are typically higher than what is put back into the system in fertilisers.

Based on results from 190 MPCN trials across the grainbelt, the minimum ‘safe’ (or critical) range of soil potassium levels at a depth of zero to 10 centimetres is about 39 to 45 milligrams Colwell potassium per kilogram. If levels are low at this depth, they are likely to be lower at 30cm.

Potassium-deficient crops have decreased photosynthesis, potentially suppressing grain production and yields and leading to higher screenings at processing.

Dr Bell says MPCN and NFI trials from 2011 to 2016 found cereal crop responses to potassium are more likely in years when there is frost, as plants need more potassium to overcome this stress.

“In 2015, we showed for the first time in field conditions that improved potassium nutrition for wheat crops reduced the level of damage from frost by up to 18 to 20 per cent (in less frost-induced sterility, or FIS),” he says.

In frost conditions at trial sites near Aldersyde in 2015 and Dale in 2016, on frost-prone potassium-deficient soils, wheat yields increased by 0.2 to 0.4 tonnes per hectare and FIS dropped by up to 20 per cent with an extra 80kg of potassium per hectare and 40kg/ha applied – compared with control crops with no added potassium.

Dr Bell says yield gains were achieved with extra potassium when frost coincided with pollen development, as long as the frost effect was not too severe.

“There are a lot of factors growers need to carefully consider, including whether there is frost, when it hits and how much of the farm is affected, to estimate the economic gain from adding potassium,” he says. “At all sites across the six years of research, there were yield responses to added potassium in the absence of frost if soil and plant potassium levels were below the safe range.”

Dr Bell says about 10 to 20kg of potassium per hectare is typically lost each year in grain and leaching (based on a 2 to 4t/ha wheat crop) and to replace that loss, about 20 to 50kg/ha of muriate of potash – or equivalent potassium – is needed.

“From my experience, it appears current rates of potassium fertiliser being used in WA are below replacement levels and too low to replace or build up soil levels,” he says.

Dr Bell suggests growers monitor soil and crop potassium levels by soil sampling to a depth of 30cm pre-season, as well as conducting plant tissue testing in-season to detect any deficiencies – particularly in frost-prone areas – and then apply adequate amounts of this nutrient to help protect cereal crops against stresses such as frost.

He says foliar sprays can be effective during the growing season to reduce potassium deficiency but, so far, researchers have not been able to achieve the same reduction in FIS as with soil application of potassium at higher rates.

Dr Bell emphasises that potassium nutrition should be a part of a comprehensive frost management strategy that should be reviewed regularly.

More information:

Dr Richard Bell,
0405 131 429,
r.bell@murdoch.edu.au

Useful resources:

'K fertiliser to help alleviate abiotic stress' – GRDC Update video
GRDC Update 2017 papers – GIWA
GRDC western Wheat GrowNotes™:
Making Better Fertiliser Decisions for Cropping Systems in Australia (BFDC) database

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End of GroundCover issue #128 (Western edition)

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GRDC Project Code UMU00041, UMU00042, UMU00045

Region West