As spring approaches it is important to think about your phosphate and potassium soil status to know what rates to apply. However irrespective of your indices some fresh P&K in the spring will benefit your crops with early availability.
With soil temperatures generally being low in mid-end of February the availability of nutrients from the soil is limited, particularly phosphate. An application of an NPKS grade at this first nitrogen timing is perfect for the plant as it starts growing before soils are warm enough for it to be able to utilise what nutrients might be there.
Phosphate is important in the spring and is necessary for energy transfer in the plant as well as root production; which is also essential during the rapid phase of growth in spring. Phosphate is almost completely immobile in the soil (P needs to be less than 1mm from the root before uptake can occur) and most of it is unavailable to the plant.
In this same spring period there is a high demand for potassium too, especially on cereals and oilseed. The demand for potash may be in excess of 10-12kg/ha/day (depending on the crop) with a total requirement of 250-300kg by the end of flowering.
With growers taking P& K holidays they are depleting the soil without adding a maintenance dressing to ensure that the P&K the previous crops have removed has been replaced. Unless you are confident of the P&K availability in your soils this is a risky business as crop requirement is high.
In trials conducted on behalf of Yara, a fresh application of P&K in the spring gives a yield benefit. Use of a compound NPKS fertiliser, such as YaraMila Actyva S (16:15:15 + 6.5% SO3), supplies a uniform application of N, P and K as well as sulphur.