PREVIOUS LEGUMES AND N-FERTILIZER EFFECTS ON MINERAL CONCENTRATION AND UPTAKE BY FORAGE CORN

The beneficial effects of legumes grown in rotation with cereal crops can, in part, be attributed to soil N increments through the fixation of atmospheric N2 and conservation of soil N. Other rotation effects h ave been suspected, but have not all been characterized. The objective s of the present study were to determine the impact of faba bean (Vici a faba L.) and soybean (Glycine max [ L. ] Merr.) on the mineral compo sition and uptake of a subsequent forage-corn (Zea mays L.) crop. Fiel d experiments were conducted in 1987 and 1988 on a Riviere-du-Loup gra velly sandy loam (Ferro Humic Podzol) at St-Anselme and on a Chaloupe silty loam (Orthic Humic Gleysol) at Deschambault in eastern Quebec. I n continuous cropping or following soybean Maple Amber or faba bean Ou tlook, N rates applied to com Pioneer 3979 were 0, 50, 100 or 150 kg N ha-1. In 1987, generally, the com mineral composition and uptake were not significantly affected by N treatments. Soil mineral concentratio ns were measured in spring 1988 at both sites, but only a few differen ces were observed among treatments. In 1988, at St-Anselme, the K conc entration of stover and whole plants increased following legumes at al l N levels applied, but decreased at Deschambault as the N level incre ased up to 100 kg N ha-1 for all previous crops. At St-Anselme, the Ca uptake of the com stover following faba bean was higher than that fol lowing com. At the same location, the K uptake by stover was higher fo llowing legumes than following com. The Mg uptake by subsequent corn a t St-Anselme was higher following faba bean than following com and soy bean, while at Deschambault, it generally increased with N application following all previous crops. At both sites, the stover and the whole -plant P uptake varied with N application that also affected Fe and Mn concentrations and uptake.