Thursday, August 22, 2019

‘Pink straw’ concern over phosphate and potash levels

February 1, 2019 by  
Filed under Crops

Compound fertilisers which include sulphur could prove invaluable in restoring phosphate and potash levels this spring – following concern over nutrient use in crops in the wake of last year’s exceptionally dry summer.

Agronomists and fertiliser specialist share concerns that the “pink straw” seen at harvest across many regions last year could point to a significant crop nutrition issue for arable producers.

Some tests carried out last autumn showed straw contained three times as much 0otash as the previous year – and higher levels than published values, according to Agrii research and development manager Jim Carswell.

“It’s likely this is a result of the speed at which crops matured before harvest in 2018 combined with the lack of rainfall,” he explained.

Stress conditions

“When the plant senesces – dries out and dies before harvest – the stalk naturally cracks and then when it rains it helps wash some of these nutrients out of the straw. 

Last year, it dried out so quickly it did not have the chance to crack so much and we obviously didn’t have the rain to wash it out, so that potassium was held in the straw itself.”

The amount of potash in the straw in Agrii tests was measured at 2.4kg per tonne compared to 0.8kg the previous year. This meant it was likely the straw removed had taken nutrients out of the soil and these needed to be replaced.

An analysis of grain, straw and soil from a number of Agrii sites suggested the pink colouration may be linked to anthocyanins, said Mr Carswell. “They may have been produced by the plants under stress conditions resulting from sub-optimal phosphate availability,” he said. 

“It is recognised that phosphate plays an important role in promoting rooting and driving energy within the plant in the early establishment phase but phosphate is also important in grain maturation.”

Variable reserves

A relationship between low soil phosphate levels and low straw and grain phosphate levels, was exacerbated by the dry conditions last summer and should act as a ‘wake-up’ call to growers to check their soil phosphate levels and optimise nutrient availability.

CF Fertilisers arable agronomist Allison Grundy says the ‘pink straw’ phenomenon is something the company is keeping a watching brief on and urges all growers to test their soils for P, K Mg and pH, prioritising fields where a pink straw incident has been noticed.

NPKS fertilisers are becoming increasingly popular with growers as they offer simpler management as well as yield benefits, but they could come into their own in 2019, Ms Grundy says.

“Certainly if you saw pink straw last year, you need to get your soils checked out to make sure phosphate and potash indices are where they should be and if they’re low, NPKS compounds might be the solution.

“But even if you didn’t see pink straw, you should talk to your fertiliser specialist about the best options.”