The challenges of the 2018 season have led to considerable discussion about potassium.
Contributors from Platinum Ag Services and ABL Agriculture (Coonalpyn, South Australia)
- Michael Camac, Dip AppSci Agri,
- Brian Lund, BAgSci,
- Matt Howell, BAgri
- Jackie Foster, BAgri
Many more questions are being raised this year,
“Some producers already swear by Potash (potassium) as a fundamental of crop nutrition whereas others are ready to take a closer look at how this macro-element could help them manage the crop through drier growing conditions and the threat of frost”.
This important element typically applied as potash plays a critical backstage role in nearly every facet of crop production. Photosynthesis, control of plant nitrogen, formation of new proteins and tissues, and strength of cell walls and stalk tissues are all reliant on potassium. But most importantly in the context of 2018:
Potassium maintains water efficiency. When potassium is deficient photosynthesis declines and the plant’s respiration increases, leaving the producer with a slower growing crop that is using more water and is more prone to dry conditions.
Potassium can minimize frost damage. Plants try to protect themselves from sub-zero temperatures by storing potassium and sugars in their cells to act as antifreeze, explained Michael, “To provide an idea of the effectiveness of this function, in 2012 CSIRO published results of cold damage to canola that reduced from 62% to 7.5% when potassium was applied.”
Potassium is relatively abundant in Australian soils but the vast majority of this is unavailable to plants. At any one time, most soils contain less than 10kg per hectare of potassium in a form that is available to plants. This low availability is often compounded in sandy soils because of leaching. Despite this Brian pointed out, “an assessment of fertilizer sales last season against nutrient replacement levels suggested that potassium was notably underutilized. This is unfortunate as all the evidence suggests that potassium is at its most valuable when available to crops contending with the sort of conditions we have just seen.”
It is also one to watch because crops require considerably more than is actually removed in grain. A typical wheat crop might remove around 3.4kg of potassium per tonne of grain but it will use up to 24kg in growing roots, leaf and stalk. This distinction is of critical concern for the farmer considering bailing the stubble.
Looking toward next season Jackie made the observation that if you’re still unsure about potash take note of this year’s windrows, “if next season these windrows are marked by stronger green stripes of superior growing crop, it’ll be the potassium released by the decomposing chaff that’s doing the job. By comparison the rest of the crop will likely be weaker and potassium deficient.”
Matt agreed but also flagged that the, “subclinical deficiency symptoms in cereals can also be readily spotted, particularly in the lower canopy leaves where an “arrowhead pattern” forms on the leaf tip, coinciding with low vigour early in the plant growth cycle, poor disease tolerance and low biomass production.
Article supplied by AFSA Board Member, Brian Lund
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