Location: Plant Science ResearchTitle: Alfalfa nitrogen credit to first-year corn: potassium, regrowth, and tillage timing effects Author
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2012
Publication Date: 5/1/2012
Publication URL: http://hdl.handle.net/10113/54148
Citation: Yost, M.A., Coulter, J.A., Russelle, M.P., Sheaffer, C.C., Kaiser, D.E. 2012. Alfalfa nitrogen credit to first-year corn: potassium, regrowth, and tillage timing effects. Agronomy Journal. 104(4):953-962. Interpretive Summary: Farmers need to manage purchased inputs, like fertilizer, judiciously so that they can maximize profit and reduce unanticipated environmental damage. Because of changing management systems, corn hybrid yield potential, and weather patterns, it is crucial to develop and improve estimates of fertilizer need in different cropping systems. One of the main advantages of growing the perennial legume, alfalfa, is the nitrogen alfalfa supplies to the following corn crop. In research conducted on 16 Minnesota farms, we found that no additional nitrogen was needed for the corn grain crop that followed alfalfa, except in one case. This supports what others have found in the past, substantiating and extending the current recommendations by universities in the Corn Belt. We also found that enough N was present for the corn, regardless of whether the farmers plowed down alfalfa herbage and whether they tilled the land in the fall or in the spring. This important finding means they have more flexibility in deciding how and when to terminate the alfalfa. At today's prices, farmers that withhold nitrogen fertilizer in the first corn crop after alfalfa will save about $65 per acre, while producing the same high yield of corn.
Technical Abstract: Compared to corn (Zea mays L.) following corn, N guidelines for corn following alfalfa (Medicago sativa L.) in the U.S. Corn Belt suggest that N rates for first-year corn after alfalfa be reduced by about 168 kg N/ha when 43 to 53 alfalfa plants per square meter are present at termination; however, these guidelines have been questioned as corn grain yields have increased. Experiments were conducted at 16 locations in Minnesota to address questions regarding N availability to first-year corn after alfalfa relating to the amount and timing of alfalfa regrowth incorporation and to the effect of carryover K from alfalfa. Corn grain and silage yield and fertilizer N uptake were not affected by amount or timing of regrowth incorporation or by carryover K. Maximum corn grain yield ranged from 12.1 to 16.0 Mg/ha among locations but responded to fertilizer N at only one. At that location, which had inadequate soil drainage, the economic optimum N rate (EONR) was 85 kg N/ha, assuming prices of $0.87/kg N and $132/Mg grain. Assuming the same N price and $39/Mg silage, the EONR for silage yield across six locations in 2010 was 31 kg N/ha. These results demonstrate that on highly productive medium- to fine-textured soils in the Upper Midwest with 43 alfalfa or more plants per square meter at termination, first-year corn grain yield is often maximized without fertilizer N, regardless of alfalfa regrowth management or timing of incorporation, but small N applications may be needed to maximize silage yield.