Experiments comparing the effects on yields of potatoes of three methods of applying three amounts of NPK fertilizer and the residual effects on following winter wheat

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Abstract
1. Seven experiments with main-crop potatoes on heavy soils from 1962–5 measured yields from 0, 5, 10 or 15 cwt/acre of 13–13–20 fertilizer; (1) broadcast and worked into the soil by seed bed preparations; (2) broadcast on the final seed bed; (3) placed in bands 3 in. from the seed centre. Wheat followed the potatoes and was manured with 0, 5, or 10 cwt/acre (of the equivalent) of 13–13–20 fertilizer, in all combinations with the four amounts of, and the three ways of applying, the fertilizer given for the potatoes.2. Fertilizer greatly increased potato yields and 15 cwt/acre of 13–13–20 was justified, provided it was broadcast. Both methods of broadcasting gave similar yields with 5 or 10 cwt/acre, but working the fertilizer into the seed bed was usually the better method with 15 cwt/acre of the fertilizer. Placing in bands beside the seed was the best method in four experiments with 5 cwt, in two with 10 cwt, but never with 15 cwt/acre of fertilizer.3. Yields of green wheat, and of grain and of straw, were increased by residues of fertilizer applied for the potatoes, but were increased much more by freshly applied fertilizer. The residues increased wheat yields by the same amount as one quarter as much freshly applied fertilizer. The residues had smallest effects when the winter rainfall was largest, and were the same however the fertilizer had been applied.