Factors affecting nitrogen benefit from soybean [ Glycine max (L.) Merr. cv Lee] to interplanted corn ( Zea mays L. cv Co-op S259)

Abstract

Nitrogen transfer from legumes to non-legumes has been observed and mechanisms have been studied but the effects of environmental factors are not well understood. This work attempts to clarify how N-benefit to corn ( Zea mays L.) from associated soybean [ Glycine max (L.) Merr.] is influenced by factors that interactively affect nodulation, mycorrhizal infection, and biomass and N yields. Pots of corn (cv. Co-op S259)-soybean (cv. Lee) mixtures were arranged in a split-plot design with two main plot light levels (full light and shade). The subplot factorial consisted of two nodulation levels (nodulating and non-nodulating soybean), two N levels (200 and 400 mg N applied at planting, tagged with 15N), and four P levels (12.5, 25, 50 and 100% of normal nutrient concentration). All treatments were inoculated with mycorrhizal fungi. Complications resulted from differences in relative competitiveness for mineral N and from decreasing 15N concentrations in shoots as P levels increased. The lower rate of N maximized nodulation and biomass and N yields in nodulating soybean, and maximized total harvestable N. Conversely, the higher rate of N maximized corn biomass and N yields. Significant, albeit modest, N transfer from soybean to corn occurred with 25% P under: (1) full light and 200 mg N; and (2) shade and 400 mg N.