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From J K senior & sons:
Straw Valuation app for Farmers This is a guide to the value of phosphate & potash removed from the soil when straw is removed from the field. Cereals straw can vary in value ie Oat straw is worth considerably more than wheat straw The cost of baling ,carting and replacement fertiliser are not included in this calculation When inputting Phosphate & Potash values the app works in all currencies. These figures are a guidence only as phosphates & potash contents can vary depending on rainfall, crop maturity & previous chemical applications This app also has the facility to e mail your answer