Are nutrient deficiencies limiting crop yields?

Deficiencies in major nutrients and trace elements are being detected regularly in a high percentage of crops, says leading analytical laboratory, NRM. Of particular concern are potassium and magnesium levels and the trace elements boron, zinc and copper. Left uncorrected, such deficiencies will limit crop yields.

The findings come from a ten year review of plant tissue data by NRM, which is part of Cawood Scientific, the UK’s largest truly independent provider of accredited analytical laboratory testing services for the land-based sector.

The company’s Duncan Rose explains: ’The data we have pulled together spans ten years from 2000 and covers four major crops ’ wheat, oilseed rape, sugar beet and peas. In wheat over a third of all samples analysed show that potassium (K) is deficient. It’s a similar story in oilseed rape where over 50% of samples were deficient in K.’

Indeed the problem seems to be getting worse. ’When we split the OSR data into two five year periods, it was the later period, 2006 to 2011, where the most K deficiencies were seen.’ This coincides with reductions in K fertiliser applications measured in the British Survey of Fertiliser Practice, where K applications to tillage crops were recorded as dropping from 49 kg/ha in 2006 to 38 kg/ha in 2010 (2009 was even lower at 33 kg/ha). ’With straw prices high and many farmers choosing to sell straw rather than incorporate, K levels are likely to fall further,’ he suggests.

For sugar beet and peas it is magnesium that is most deficient ’ over 70% of sugar beet samples and more than 90% 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,’ adds Mr Rose.

Typically wheat is also low in sodium. However both phosphorous and calcium levels are generally good. As for sulphur the results are more varied with almost as many wheat samples testing high, as deficient and over 10% coming in as excessive.

Looking at the trace elements, in wheat, boron and zinc are the two which are most likely to be deficient, whilst 40% of the peas were also recorded as low or worse.

For sugar beet, copper is the trace element most likely to be lacking, whilst both iron and manganese were very often measured at levels rated as high or excessive ’ 80% 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% 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. ’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 whilst high potassium levels may reduce magnesium uptake,’ explains Mr Rose.

’Plant tissue analysis is a particularly useful tool for detecting ’hidden hunger’,’ he adds. ’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, however 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 concludes.