Crop yields are being hit by deficiencies in major nutrients and trace elements, according to the leading analytical laboratory, Natural Resource Management (NRM).
In the run-up to the 2011 main grain harvest, NRM reports the shortages are being detected regularly in a high percentage of crops. Of particular concern are potassium and magnesium levels and the trace elements boron, zinc and copper.
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Wheat crop yields could be limited because of the deficiencies
Left uncorrected, such deficiencies will limit crop yields.
The findings come from a 10-year review of plant tissue data by NRM, which is part of Cawood Scientific, an independent provider of accredited analytical laboratory-testing services for the land-based sector.
NRM's Duncan Rose explained: "The data we have pulled together spans 10 years, from 2000, and covers four major crops – wheat, oilseed rape, sugar-beet and peas. In wheat, over a third of all samples analysed showed that potassium was deficient. It was a similar story in oilseed rape where over half of samples were deficient in it."
And the problem seems to be getting worse, he said.
"When we split the OSR data into two five-year periods, it was the later period, 2006 to 2011, where the most potassium deficiencies were seen," he explained.
This coincided with reductions in potassium fertiliser applications measured in the British Survey of Fertiliser Practice, where potassium applications to tillage crops were recorded as dropping from 49kg per hectare in 2006 to 38kg in 2010. "With straw prices high and many farmers choosing to sell straw rather than incorporate, potassium levels are likely to fall further," he forecast.
For sugar-beet and peas it is magnesium that is most deficient – over 70 per cent of sugar-beet samples and more than 90 per cent of pea samples. Magnesium was also measured as low, or deficient, in half of all wheat samples. "With both magnesium and potassium essential for moving amino acids and carbohydrates from the leaf around the plant, these deficiencies will threaten yield unless corrective action is taken," added Mr Rose.
Typically wheat was also low in sodium. However both phosphorous and calcium levels were generally good. As for sulphur, the results were more varied, with almost as many wheat samples testing high, as deficient and over 10 per cent coming in as excessive.
Looking at the trace elements, in wheat, boron and zinc are the two which are most likely to be deficient, while 40 per cent of the peas were also recorded as low or worse.
For sugar-beet, copper is the trace element most likely to be lacking, while both iron and manganese were very often measured at levels rated as high or excessive – 80 per cent of samples in the case of iron and around half of the samples for manganese. In pea crops, both iron and copper were either high or excessive in around 80 per cent of samples.
Plant tissue analysis provides a measure of the nutrient status of the crop at the time of sampling and so reveals whether soil nutrient supplies are adequate.
Mr Rose added: "It is important to know the levels of the different nutrients, because interactions between these can affect overall crop growth and development. For example, zinc uptake may be reduced by high phosphorous applications, while high potassium levels may reduce magnesium uptake.
"Plant tissue analysis is a particularly useful tool for detecting hidden hunger. That's where no visual symptoms are yet apparent, but where the lack of nutrient will already be starting to limit crop growth."
The technique can also be used to confirm diagnosis made from visual symptoms. This is useful since different deficiencies can look very similar, making it difficult to determine precisely which nutrients are causing the problem. Plant tissue analysis is most commonly used as a diagnostic tool for future correction of nutrient problems, but analysis of early season crop growth will allow corrective action to be taken in season, before problems become yield limiting. "Combining plant tissue results with soil analysis data is a powerful tool for solving plant growth problems," he stressed.
