First noticed four years ago, pink straw at harvest has again been identified at a number of grain field sites across the UK in 2022.
And, no, this is not a figment of overworked and exhausted farmers’ imaginations.
This is another example of just how responsive nature can be to extremes of weather – in this case a combination of long, hot days and record soil moisture deficits.
Pink straw
The phenomenon has been highlighted by the Potash Development Association (PDA).
A spokesperson for that organisation said: “In 2018, the prolonged dry spell during the build-up to harvest meant many crops senesced prematurely. In these situations, some of the natural plant processes are not fully completed.
“Where the grain fill period is shortened, elevated potash levels may remain in the straw at harvest. As the crop matures and senesces the cells of plants crack, allowing some of the potash they contain to be washed back into the soil.
“Where there is little or no rainfall prior to straw being removed from the field, it will result in elevated nutrient concentrations as less potassium is washed from the harvested straw back to the soil.
“So, this may help explain the higher levels of potash found, but it does not show where the change in colour came from.”
According to the PDA, the answer may lie with the plant’s response to stress. Anthocyanins are plant pigments which can give flowers, fruits, and seeds a red/purple colour.
They naturally occur in late summer from the breakdown of sugars as leaves senesce and phosphate levels fall, resulting in the red and purple colours seen in autumn leaves.
While they are not normally present in actively growing leaf tissue, they can be induced in response to abiotic stresses such as drought, high salinity, phosphorus deficiency, excess light and cold.
The PDA representative continued: “The build-up to the 2018 harvest saw two of these abiotic stresses in elevated levels to normal: Drought and light.
“Once again, the pink straw is back this harvest, and once again we have had a particularly dry spell, with high light intensity and high heat, which is likely to have stressed plants, leading to increased levels of anthocyanins, giving off the pink colour in straw.
“Although the colour and the elevated potash levels are not unrelated, the high potash is not the cause, but a symptom, along with the colour, of other factors at play within plants.”
There are also a number of agronomy-related lessons to be learnt from the pink straw phenomenon. Analysis of cereal straw and grain carried out in 2018 confirmed some very low levels of phosphate.
This, along with the changes in potash levels this year, would suggest taking analysis for grain – and straw – could be worthwhile.
The approach will ensure more accurate values are used when planning for the new cropping season.
