A new crop nutrient management tool aims to address concerns that growers may be restricting yields by ignoring key recommendations set out in The Fertiliser Manual over major and minor nutrients, such as P, K and magnesium.

“Most growers and their advisors have focused on changes to nitrogen use, yet hidden in the detail of RB209 are key amendments on other major and minor nutrients,” said K+S UK & Eire technical manager Jerry McHoul.

The Nutrient Wheel includes advice based on the latest trials data and provides recommendations for cereals, oilseed rape, sugar beet and potatoes.

“Growers simply select a target crop yield and reference their latest soil analysis data, and the wheel provides a recommended application rate for P, K and Mg for each field.”

The calculator suggests additional applications to help build P, K or Mg indices, or alternatively, recommends reduced fertiliser use where nutrients are above optimum values. It also allows for the nutritive value of any manures that may have been applied.

Mr McHoul suggested that some problems seen in drought-affected crops this season were linked to an inadequate understanding of the changes and poor fertiliser use. One key update concerns the use of magnesium in oilseed rape, he noted.

“Previously, growers were advised to apply magnesium only when the soil index had run down to 0 and then apply a large amount of magnesium sufficient for the rest of the rotation,” he said.

“But new guidance recommends around 50kg/ha of magnesium for Index 1 soils, somewhere between the recommended soil level and severe depletion.”

This means that around a quarter of the UK’s oilseed rape crop – some 170,000ha – needs magnesium fertiliser to achieve full yield and quality, said Mr McHoul.

“We’re pretty sure that this year some of the pod abortion problems, especially in conventional oilseed rape varieties, were linked to nutrient stress due to two months of drought during flowering and pod set,” he added.

Both potash and magnesium are crucial for water management because they help transport nutrients around the plant “like oil in an engine”, said Mr McHoul.

Independent trials in the UK and across Europe show that fine-tuning magnesium and potash applications to oilseed rape can help growers achieve an average yield increase of 0.2t/ha, or 0.4t/ha if foliar magnesium was also applied. At current prices, this equates to an increase of £18/ha or £35/ha with the foliar program included, said Mr McHoul.