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 nutrient removals for selected vegetable crops, and on the nutrient contents of the soil have been analysed for the last nineteen harvests of a forty year fertilizer trial at Osnabruck in Germany. It was concluded that: 1. The effects of phosphorus were generally small, with yields without P fertiliser averaging about 90 % Of the maximum. Responses to potassium were much larger, with unfertilised treatments giving 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, fennel, and bean showed strong responses to P, whereas spinach and celery were more responsive to K. In most cases cabbage showed only weak responses to P and K. 5. Annual amounts of nutrients removed by the edible plant parts were on average 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 soil, 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 crops should include soil analysis, nutrient removal by edible plant parts, nutrient supply from organic amendments and the specific responses of different vegetable crops to P and K. Existing computer programs for predicting nutrient requirements can be used to advise on scientifically based fertilizer strategies at a farm level.