Autumn Cereals Don’t Need P&K

There are several factors as to why applying P & K in the spring is the favourable option. Phosphate (P) availability is greatly reduced in cold, wet soils therefore if you’re applying it ahead of winter it is unlikely to be taken up because a) the plants are too small to take much up in autumn and b) soils will “lock up” P quickly. 

Within soil, P quickly becomes unavailable to the plant by bonding with iron or aluminium ions or precipitating out with calcium and so becomes non-labile. This happens over a short space of time, however to reverse the process takes much longer i.e. not in time for spring. 

Another reason for applying P&K in the spring is because that is when the crop demand is highest. Within a 4-8 week period, March – May, the daily demand for P&K rises exponentially. Therefore, to utilise the fertiliser in the most efficient way, apply it when the crop requires it. This will mean less chance of wastage through loss to the environment and the nutrient use efficiency will be improved. 

Once soil temperatures rise above 5°C in spring the plant will start to grow, however at this temperature the soil is still too cold for phosphate to become plant-available. Therefore, applying an NPKS, such as YaraMila ActyvaS or 52S, at that first timing (end of February, weather permitting) will give the crop what it needs to kick-start spring growth without relying on soil temperatures to rise. Then once they do, soil-P will become available as the crop continues to grow.