Why maintain soil potash reserves? |
Introduction
Potash is an essential nutrient for all crops and grassland and for livestock. Maintaining soil fertility so as
to produce economically viable yields requires the appropriate use of all inputs including plant nutrients
of which one of the most important is potash, K2O (potassium, K). A current danger is reducing potash
inputs to save money, but this can be very short sighted. This leaflet outlines current issues related to
potash use on arable crops, especially recent very worrying evidence for a decline in the use of potash
fertilisers. This declining use will have an adverse effect on soil fertility and on the production of
economically viable crop yields of acceptable quality.
Crop demand - quantity and rate
Crops take up very different amounts of K during growth but all need a readily available supply in the soil at key times in their growth. For potatoes, two-thirds of the season's requirement is taken up in the six weeks after plant emergence. For winter cereals a small amount is needed for establishment but most is taken up in the short period between tillering and earing. During periods of rapid growth and greatest daily need, crops can take up as much as 10 kg K2O/ha each day from the soil. As crop yields continue to increase as better varieties come on stream and agronomy improves, the total amount of readily available K in the soil must be able to satisfy the demand of the crop.
