DON”T NEGLECT potash levels if you want to keep high yielding cereals standing, new research suggests.
Potash is essential to avoid lodging in breadmaking varieties needing high N inputs.
That is the initial finding from Rothamsted work, for Kemira GrowHow, comparing standard and managed nitrogen systems.
The key difference between the approaches was that the first N dressing under the managed system was delayed and linked to crop growth stage.
On soils with K index 1 the standard N system left 75% lodged. This fell to 30% at K index 2 and 20% at K index 3, notes Kemira GrowHow agronomist, Allison Grundy.
Where a managed N system was used, the risk of lodging was significantly reduced by better K supply, dropping from 10% at soil K index 1, and to zero at indices 2 and 3.
On soils at a lower K index not only was there was more lodging, because lack of K weakens straw, but yields were lower.
“The dramatic effect of delaying the first N application fits well with the theory that N and K need to be in balance” to promote crop growth and grain quality,” says Miss Grundy.
As well as reducing yield, lodging delays harvesting and hits quality. “Current advice to cereal farmers in RB209 is to maintain soils in the lower half of K index 2 by replacing crop off-take. But there is a danger that soils growing mainly cereals have less soil K than this.
“For nitrogen-hungry varieties like Xi19, where yields in excess of 12t/ha with 13% protein are achievable, growing them successfully on soils with anything less than K index 2 is questionable.
“We have asked Rothamsted to continue looking at this on our behalf, testing the effect of soil K, freshly applied K and N management on winter wheat with a large yield potential.”
Both the level of yield and the shape of the N response curve are altered when K is in short supply, notes Rothamsted”s Johnny Johnston. “We know that K and N are strongly associated in plant growth and that both are needed in large amounts during peak growing periods.”
With adequate K, the optimum N rate is lower and yields are larger because the crop can use available N much more efficiently, he says. “We also know that when K is deficient the complex process by which protein is formed from nitrogen in the plant will be interrupted.
“Logic suggests that the increased demand for nitrogen of modern bread-wheat varieties may well have a knock-on effect on the amount of potassium they need to reach their full potential.”
“This research is continuing for a second year,” says Miss Grundy. “And we will be particularly interested in finding out more about whether freshly applied K is beneficial for Xi19 and Malacca.
“For the time being we can say that maintaining soil K indices and matching crop supply and demand is essential when growing modern varieties like these.”