Topping up potash this autumn on grass

Potash is vital for regulating water supply and cell turgidity and, like nitrogen, is required during phases of rapid growth. Potash is a key input for high grass yields. It increases individual leaf area and the leaf to stem ratio. 

Regular, annual applications are required to maintain soil K levels at index 2+ or 3 and to maintain yields. Grazing removes small amounts of K as most is recycled back into the soil. Grass silage can remove 125-150 kg/ha of K with an average yielding 1st cut. The RB209 recommendation for K on 1st cut is 80 kg/ha, because we want to minimise the luxury uptake of K in 1st cut grass. Apply K this autumn to replenish soil K reserves after silage. By doing so, you will prevent any slippage in soil K indices and yield. 

Economically, manures are excellent sources of K and it is sensible to apply these on silage fields. K is not leached easily but organic manures especially cattle slurry contain significant amounts of available nitrogen. Therefore it’s important to apply cattle slurry earlier in the autumn when there is demand by grass for nitrogen, and FYM later in the autumn after grazing. The RB209 guideline value for K in FYM is 9.4 kg/tonne at 25% dry matter and cattle slurry 2.5 kg/tonne at 6% dry matter. Low K soils will produce lower K silage which will in turn produce slurry that contains less K than the guideline value of 2.5 kg/tonne. 

Find more information on soil and manure testing.