Ripe Wheat.jpg


Concerns that ‘pink straw’ seen at harvest across many regions last year could point to a significant crop nutrition issue for arable producers.

NPKS fertilisers could prove invaluable in restoring P and K levels this Spring following widespread concerns over nutrient use in crops as a result of 2018’s exceptionally dry summer.

Agronomists and fertiliser specialist alike 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.

According to Agrii R&D Manager Jim Carswell, some tests carried out last autumn showed straw contained three times as much Potash as the previous year and higher levels than published values.

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

"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 our tests was measured at 2.4kg per tonne compared to 0.8kg the previous year so it’s likely the straw removed has taken nutrients out of the soil and we need to make sure these are replaced.”

An investigation involving grain, straw and soil analyses from a number of Agrii ifarm sites suggested that the pink colouration may have been linked to anthocyanins, Jim Carswell points out.

“They may have been produced by the plants under stress conditions resulting from sub-optimal phosphate availability and the high light intensity during late season. 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.”

From the Agrii results, it was not surprising that there seemed to be a relationship between low soil phosphate levels and low straw and grain phosphate levels, he adds.

“This was exacerbated by low phosphate availability in the dry conditions last summer and should act as a ‘wake-up’ call to growers to not only check their soil phosphate levels but also ensure that nutrient availability to crops is optimised.”


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.

“The legacy of 2018 is something we are just starting to see the impact of for the following crop. Certainly, there are implications as far as N is concerned with some soils likely to have more variable soil reserves and others, with likely high levels.

It all depends on individual circumstances, whether fertilisers were applied on time, whether they were utilised fully and it will vary from region to region. It is likely to be the same in the case of P and K with the drier regions such as East Anglia likely to be affected the most, she says.

“The overall relationship between N, P and K is important. Adequate levels of Phosphate and Potash are essential to avoid growth checks and healthy soil indices, around 2 are needed to ensure optimum N recovery and utilisation. Furthermore, once soil P and K levels are depleted they can be difficult and costly to build back. As well as affecting yield productivity, there are potential impacts on plant health and disease control.

Whilst the traditional method of applying P and K is usually in the autumn as individual straights, trials carried out at the Royal Agricultural University in Gloucestershire suggest this might not always be the best nor the only method, she says.

“These trials suggest applying a crop’s full requirement for P and K as part of an NPKS true granular compound granular fertiliser in the spring can increase wheat yields by 1.0t/ha compared to individual winter applications. CF Heartland Sulphur NPKS 24-8-8 (8SO3) was applied during the spring on some plots whilst others received straight P and K in the autumn followed by just N and S in the spring.

“Those plots that received the P and K as an autumn application with N and S applied in the spring produced 8.6t/ha whilst those that had all nutrients applied as Heartland Sulphur NPKS in the spring produced 9.6t/ha.”

It is thought the approach encourages rapid uptake of nutrients when the plants are actively growing, encouraging the crop to respond and make best use of the applied fertiliser, she says. “The highly soluble Phosphate encourages optimum root development with the Nitrogen and Sulphur improving overall growth. All the nutrients effectively work together to maximise Nitrogen recovery, utilisation and final yield.”

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, Alli Grundy says.

“Certainly if you saw pink straw last year, you need to get your soils checked out to make sure P and K 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. Last year took its toll on soils so you need to get them fully tested, including a CF N-Min test for soil N, and make the correct decision from there.”

The full CF Fertiliser NPKS range is designed to have options available for most farming systems and soil types and includes KayNitro Sulphur 25-0-13 (7SO3), MultiCut Sulphur 23-4-13 (7SO3) and Heartland Sulphur 24-8-8 (8SO3).