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

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 fields 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.