How Much Potash should I Apply to Raise my Soil K Index to Target Index 2 ?
September 2009, ref PDA News - Precision Farming Articles -
Willington Crop Services
This depends on soil type. Heavy soils will require more potash than light soils. When less potash is applied than used, the K index on light soils will fall more quickly than on heavy soils.
Rothamsted Research suggests that on a sandy clay loam of pH 6.5, 10kg/ha of potash needed to raise soil K status by 1mg/l. So to increase soil nutrient status from mid index 1 to mid index 2, an increase of 60mg/l, you need to apply 600kg/ha of potash or 1t/ha of muriate of potash. Heavier soils would need more, maybe 800kg/ha of potash, whilst lighter soils would need less. These values are as well as current crop demand for potash and known soil reserves from soil sampling.
The fertilizer needed to correct a deficiency should not be a financial burden on the current crop. Each crop in each field should pay for the nutrients it removes from the field up till harvest, but not for improvements in soil fertility, raising soil K index in this case. Correcting a potash deficiency in an expense to improve farm assets. If you tackle the deficiency by applying 600kg/ha over 10 years, you may suffer yield losses and profit losses. Best to tackle a deficiency with soil nutrient management to rectify the problem fast. If 600kg/ha of potash is needed, apply it over 2 or 3 years to prevent yield losses and hence losses in profitability.
