Potash implications of baling straw
Last harvest there were quite a lot of last-minute decisions to bale as a result of anticipated straw shortages and higher prices. Baling and removing straw, here there is no specific requirement for other enterprises on the farm, can often be a sensible agronomic and economic decision.
These include high level of residue on the surface which may reduce the establishment of the following crop, or straw prices that are sufficient to cover the costs of baling and replacement of nutrients and organic matter. This last calculation is often not considered in enough detail and will depend on the price of phosphate and potash required to replace what is removed, and being able to allocate a cost to organic matter. Whatever the reasoning for the decision, where straw is removed it is important to fully account for everything that is being taken off the field, which can be a large quantity of potash. Removing winter cereal straw nearly doubles the amount of potash taken off, compared with removing the grain alone. Potash recommendations do not mirror that of nitrogen, where applications are required annually to meet the economic optimum yield. They can be dealt with rotationally, but any large discrepancies between planned actions and what actually happens at harvest, need accounting for to ensure soil levels do not drop too low.
Last year, the dry conditions meant that average offtake values for K in straw significantly underestimated the amount of potash being removed. This year, the higher straw yields may do similar if basing offtake on grain yield alone. Where straw yield is known, RB209 gives average values for P&K removed per tonne of straw. Whichever method is used it should be remembered that potash content of straw can vary greatly. Drier than average conditions between crop maturity and baling straw will increase straw potash content, whereas higher than average rainfall is likely to have the opposite impact.