Long-term trial with increasing amounts of phosphorus, potassium and magnesium applied to vegetable crops

The effects of different rates of P, K and Mg fertilizer on the yield and n utrient removals for selected vegetable crops, and on the nutrient contents of the soil have been analysed for the last nineteen harvests of a forty y ear fertilizer trial at Osnabruck in Germany. It was concluded that: 1. The effects of phosphorus were generally small, with yields without P fe rtiliser averaging about 90 % Of the maximum. Responses to potassium were much larger, with unfertilised treatments givin g an average of only 74 % of maximum yield. 3. Mg had no effect on yield. 4. Different crops showed different responses to P and K. Lettuce, onion, f ennel, and bean showed strong responses to P, whereas spinach and celery we re more responsive to K. In most cases cabbage showed only weak responses t o P and K. 5. Annual amounts of nutrients removed by the edible plant parts were on av erage 22 kg P ha(-1), 190 kg K ha(-1) and 10 kg Mg ha(-1). 6. Average nutrient removals in edible plant parts were 0.4 kg P t(-1), 3.7 kg K t(-1) and 0.22 kg Mg t(-1). 7. On average, soil nutrient contents of between 8 and 12 mg P per 100 g so il, 8 and 16 mg K per 100 g soil and 5 mg Mg per 100 g soil can be regarded as sufficient for maximum yield. 8. Important factors in deciding the fertiliser requirements of vegetable c rops should include soil analysis, nutrient removal by edible plant parts, nutrient supply from organic amendments and the specific responses of diffe rent vegetable crops to P and K. Existing computer programs for predicting nutrient requirements can be used to advise on scientifically based fertili zer strategies at a farm level.