Response of silage corn and wheat to dairy manure and fertilizers in long-term fertilized and manured trials

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Silage corn (Zea mays L.) and wheat (Triticum aestivum L.) were grown (1987–1991) in trials that had been manured and fertilized since 1978 to evaluate the effects of annual N, P, K and Mg fertilizers and dairy cattle manure on yields and nutrient uptake. Manure as the main factor was applied at 0 and 20 Mg ha−1 on a wet-weight basis. The subplots consisted of six fertilizer treatments: NK, PK, NP, NPK, NPKMg and the unfertilized control. For silage corn, fertilizer rates were 150, 100, 150 and 40 kg ha−1 N, P2O5, K2O and Mg, respectively. Fertilizer rates for wheat were 80, 100, 120 and 40 kg ha−1 N, P2O5, K2O and Mg, respectively. In manured plots, reduced N rates were applied for silage corn (100 kg N ha−1) and wheat (50 kg N ha−1). Silage corn and wheat yields and nutrient uptake were significantly increased by manure, N and K fertilizers whereas P and Mg effects were limited. A N-K synergistic effect on yields and nutrient uptake was observed both for silage corn and wheat. Application of K fertilizer significantly reduced silage corn Mg uptake without limiting yields, while it increased wheat yields and Mg uptake. Reduced N rates applied to silage corn and wheat achieved maximum yields and nutrient uptake in long-term manured treatments. Crop response to fertilizer application varied with crop species and was higher for silage corn than for wheat. Fertilizer adjustment is necessary after a long-term fertilizer or manure application. Key words: Silage corn, wheat, yields, nutrient uptake, manure, fertilizers, long-term, response to fertilizers