March 5, 2021

With many fields yet to be drilled this spring, there is still time to check soil nutrient status to give crops the best possible start. Spring crops have much shorter uptake periods than winter crops, so for rapid establishment it’s essential to provide adequate phosphate, potash and magnesium. This is particularly important for spring sown legumes, so if the soil status is below target, spring fertilizer applications have to make up the shortfall.
The availability of all mineral nutrients is significantly affected by pH. If you have acid patches, then now is the time to correct them. The application of granulated lime at rates of up to 500 kg/ha will correct soil pH quickly and effectively.
All spring-planted crops depend on a good uptake of fresh phosphate as soon as roots start to develop. The smaller the seed to be planted, the smaller the phosphate reserve in the seed. There is very little phosphate in soil solution, and most is immobile in the soil, so roots have to grow through the soil to access it. The best way to provide crops with adequate phosphate during establishment is to apply water soluble phosphate in either compounds or ammonium phosphates at recommended rates, adjusted for soil status.

All our crops have very large requirements for potash during their main growth phase. Whilst much of this will return to the soil as crops ripen, those crops harvested green will remove much more potash, reducing reserves more rapidly. Although significant levels of available potash can be in soil solution, the small root structures depend on a good soil potash status to optimise uptake. Results from soil analysis will help the selection of the appropriate ratio of phosphate and potash in fertilizer.
The third major nutrient required by crops is magnesium and this can be overlooked when the focus is on phosphate and potash. Magnesium is a key component of chlorophyll which is required for photosynthesis, and therefore has a significant influence on yield. In root crops, demand is disproportionately higher and a lack of magnesium will jeopardise crop performance. For potatoes and sugar beet, a minimum soil index of 2 is needed and for cereals index 1. To maintain soil magnesium levels, magnesium should be applied every four to five years. For brassica crops, a soil index of 2 is ideal and below this 100 kg of MgO should be applied at index 1 and 150 kg MgO at index 0.

Contact your agronomist, advisor or soil sampling provider or call NRM direct to arrange for soil samples to be tested for pH, phosphate, potash and magnesium, especially where soils have not been analysed in the last four years.