A study has confirmed that potassium applied early in the growing season can boost wheat yields during drought, and has provided further evidence of the need to maintain adequate levels of this nutrient.
The recently published Western Australian research also showed that while there may be reduced plant demand for potassium on mildly saline/sodic land, potassium fertiliser can improve barley plant growth on more moderately saline, potassium deficient soils.
“Results from the study have highlighted the importance of applying adequate rates of potassium early in the season which can result in significant benefits including protecting crops against drought,” Murdoch University researcher Richard Bell said.
“Growers are encouraged to use soil tests to help identify which soils will respond to potassium fertiliser.”
The study results were among information presented to researchers and consultants at recent potassium seminars.
The events, held at Northam, Katanning and Albany, were supported by the Grains Research and Development Corporation (GRDC) and the Belgium-based Sulfate of Potash Information Board.
Dr Bell said the WA study, conducted in recent seasons, assessed if more potassium was required for optimal growth and yield of cereal crops under dry and saline conditions.
The work was conducted by Murdoch University and Department of Agriculture and Food (DAFWA) researchers as part of the GRDC’s ‘More Profit from Crop Nutrition’ program.
Dr Bell said one of the trials produced the unexpected result of applied potassium fertiliser boosting wheat yields only at the dry trial site (Dowerin), but not at the wetter sites (Bolgart and Borden).
This was despite soils at all three locations being deficient in potassium.
“At Bolgart and Borden, where good growing season rainfall was received, we expected but did not achieve a yield increase from potassium fertiliser,” Dr Bell said.
“This was most likely because a continuously moist soil profile during the year allowed for greater root uptake of potassium, which is a highly mobile nutrient.
“These results suggest that while a grower might not incur a yield penalty from low potassium levels when rainfall is evenly spread during the growing season, sufficient potassium levels under drought conditions are very important.
“In wheat, potassium deficiency during drought can reduce root growth in particular, which decreases access to soil potassium and is likely to increase the severity of deficiency symptoms.”
The research also indicated yield benefits from applying potassium fertiliser early to cereal crops – within four weeks of sowing.
Dr Bell said another trial conducted as part of the study found that adequate potassium helped barley plants tolerate moderate levels of salinity.
“On these moderately saline soils, yields were improved by increasing the potassium rate through applying sulphate of potash rather than muriate of potash (chloride toxicity from higher muriate of potash rates was possibly detrimental),” he said.
Dr Bell said potassium deficiencies were increasingly common on WA’s sandplain soils and sandy duplex soils due to greater removal of the nutrient through increased hay, grain and straw production.
“Growers are realising that they need to maintain levels of this nutrient in their soils and are applying potassium fertiliser early in the growing season, sometimes before sowing,” he said.
Dr Bell said other recent research suggested that growers could often achieve increased profits by subsoil testing for potassium at depth (to 30cm).
“Potassium fertiliser applied to soils with marginal potassium levels (40-50 mg/kg) in the 0-10cm layer of the soil may not achieve increased yields if higher potassium levels are available at depth,” he said.
Dr Bell said consultants attending the potassium seminars were interested to find out maximum safe levels of banded potassium that could be applied at sowing in medium to low rainfall areas.
“James Easton, of CSBP, said field trials indicated that 15kg of potassium per hectare could be safely applied and even higher rates were generally safe, provided that seed and fertiliser were separated in the drill row,” Dr Bell said.
More potassium research is being conducted in WA this year, including trials to help determine if extra potassium can alleviate frost damage in wheat.
For more information about wheat nutrition and fertiliser, access the GRDC Wheat GrowNotes.
Richard Bell, Murdoch University
08 9360 2370, 0405 131 429
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
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