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

Authors: Osterholz, William - Will; RUARK, MATTHEW - University Of Wisconsin; RENZ, MARK - University Of Wisconsin; Grabber, John

Submitted to: Agronomy for Sustainable Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2021
Publication Date: 8/2/2021
Citation: Osterholz, W.R., Ruark, M.D., Renz, M.J., Grabber, J.H. 2021. Interseeding alfalfa into corn silage increases corn N fertilizer demand and increases system yield. Agronomy for Sustainable Development. 41. Article 58. https://doi.org/10.1007/s13593-021-00711-1.
DOI: https://doi.org/10.1007/s13593-021-00711-1

Interpretive Summary: Corn silage and alfalfa are the primary crops grown for dairy forage in temperate regions of the US, so enhancements to this system are important for farm dairy profitability. Recent research suggests that alfalfa can be planted with corn silage (interseeded), thus establishing the alfalfa crop while a corn silage crop is produced. After corn harvest the alfalfa takes over production in future years. This interseeding system has been shown to increase productivity and reduce negative environmental impacts such as soil erosion. However, nitrogen fertility of this system is likely to differ substantially from conventional corn-alfalfa rotations as both corn and alfalfa crops are present simultaneously, and as nitrogen limitation or excess has serious implications for economics and environmental quality, it is important to develop better understanding of the nitrogen requirements of the interseeding system. This study tested the importance of nitrogen fertilizer rate and fertilizer application approach (timing and placement) to both interseeded corn silage yield as well as interseeded alfalfa establishment and yield in the second year. Our results showed that nitrogen fertilizer rate was highly important to obtaining high corn silage yield, and the interseeded corn required additional nitrogen fertilizer compared to conventional solo-seeded corn. However, the nitrogen application approach was not important for determining corn yield. Interseeded alfalfa establishment and yield was acceptable for all the nitrogen fertilizer rates and application approaches, although at the highest nitrogen fertilizer rates we observed reductions in alfalfa establishment. Overall, this study provided important insights into nitrogen fertilizer management in interseeded corn silage/alfalfa, and will help improve the successful implementation of this production system.

Technical Abstract: Interseeding alfalfa into corn silage can increase dairy forage rotation productivity and reduce negative environmental impacts, but the importance of N fertilizer management for successful implementation of the interseeding system remain unexplored. Nitrogen fertilizer application rate and placement/timing effects were explored in two locations in southern WI. 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, particularly at low N rates. Maximum corn silage yields were depressed by 7-16% when alfalfa was interseeded, but interseeded alfalfa yields in the subsequent year were at least 40% greater than spring-seeded alfalfa, resulting in greater total forage yield over the two-year study period. Alfalfa establishment was greatest at low N rates, but all N rates resulted in acceptable alfalfa stands with good yields (9.3 to 11.1 Mg DM ha-1). Split N application plus precision placement, where half of the N rate was banded along the corn row at the V5 corn growth stage, did not significantly influence most corn N responses compared to a single pre-plant broadcast application. Here we demonstrate for the first time that additional N fertilizer can ensure high interseeded corn silage yields without causing major issues with alfalfa establishment, and that side-dressing plus precision placement did not favor corn N uptake.