Dont underestimate the effects of potassium and magnesium at mitigating the effects of plant stress, growers are being warned.
The advice, given at the International Fertiliser Societys annual conference held just before Christmas, is to maintain adequate levels to keep crop yields on track.
According to the review of recent research, both nutrients can help reduce damage from drought, strong radiation and severe cold conditions as well as protect against lodging.And, with UK crops facing increasingly volatile swings in climate the need for a correct balance of both magnesium and potassium is seen as critical.
According to the papers co-author, K+S UK & Eire technical manager, Jerry McHoul, during reproductive growth, demand for potassium and magnesium is particularly high.
Trials by a number of European research teams confirm reduced stress particularly due to drought over this key period of growth when both nutrients are well balanced and in good supply.
The effect is to maintain root growth and effective plant metabolism, leading to higher levels of starch accumulation in the leaves and also in the seeds or tubers, he says.
New research also highlights the important role of potassium within the soil to help improve its physical structure and, as a consequence, its water holding capacity during times of drought.
Furthermore, under extreme cold stress, plants with high levels of potassium in the cell sap have a lower freezing point. Thus, the nutrient in effect also acts as anti-freeze reducing the damage to plants in severe winters or when subject to early summer frosts, he says.
Finally, looking back to last season, Mr McHoul suggests that poor grainfill in the wet, dull conditions meant that many cereal crops simply didnt have the weight in the ears to lodge.
In a more normal season, given the rainfall we had, wed have expected to see more evidence of lodging and here, potassium, and magnesium can increase root growth, reducing root lodging.
In addition, good potassium supply increases the lignification and strength of plant stems, again helping reduce the effects of stem-break based lodging.
So, with UK crops facing an increasingly mixed cocktail of stresses, nutrient use has never been more important. Yet the signs are that both potash and magnesium use doesnt get the attention it needs.
Potash use, in particular has declined year on year for the last twenty years in the UK. And in Ireland ,where lodging was an issue last year, Department of Agriculture figures show that the ratio of potassium to nitrogen in plant tissues has halved over the same time period and this is bound to have been a contributory factor.
Of the two nutrients, the paper points out that magnesium is more mobile than potassium and that in light soils under intensive crop production needs regular replenishment. Some crops remove 100kg of magnesium (MgO)/ha every year. In addition, soils high in calcium or potassium can restrict magnesium uptake.
While potassium is generally required at much higher levels than magnesium, it is much less mobile and more readily held in the soil. Both nutrients though need to be in balance as too high a level of potassium can restrict magnesium uptake.
This is where agronomists and farmers have to box clever and ensure that fertiliser use contains a balance that works for each specific soil and crop situation, says Mr McHoul.
Foliar use of available magnesium in the form of magnesium sulphate (Epsom salts or bittersalz) will help alleviate in season crop stress, but in the long term, we need to build adequate supplies in the soil.