Interseeding alfalfa into corn silage increases corn N fertilizer demand and increases system yield

Abstract

Interseeding alfalfa (Medicago sativa L.) into corn (Zea mays L.) harvested as silage can increase rotation productivity and reduce negative environmental impacts, but the importance of N fertilizer management for successful implementation of the interseeding system remains unexplored. Nitrogen fertilizer enhanced leaf chlorophyll content, corn silage yield, and total N content of corn with interseeded alfalfa and conventional solo-seeded corn at two locations in southern Wisconsin. However, greater N rates (additional 83 kg N ha−1 at one location; could not be estimated at second location) were needed to maximize corn silage yield when alfalfa was interseeded, suggesting that alfalfa effectively competed with corn for N. Maximum corn silage yields were depressed by 7–16% when alfalfa was interseeded, but interseeded alfalfa yields in the subsequent year were 40–160% greater than spring-seeded alfalfa, resulting in greater total forage yield over the 2-year study period. Alfalfa plant density after corn silage harvest was greatest at low N rates, but all N rates resulted in acceptable stands with good yields in the second year of the studies. This is the first demonstration that application of additional N fertilizer can ensure high interseeded corn silage yields without causing major issues with alfalfa establishment. Additionally, split N application where half of the N rate was broadcast at planting and the balance banded along the corn row as a side-dressing did not influence most corn or alfalfa N responses compared to a single broadcast application at planting. Results of this work and previous studies suggest near maximal yields of corn silage can be obtained in this interseeding system if N is applied at 224 kg ha−1, but further refinement of fertilizer and other crop management practices is, however, needed to maximize the forage production and environmental stewardship potential of this system.