Location: Dairy Forage ResearchTitle: Substitutions of corn silage, alfalfa silage and corn grain in cow rations impact N use and N loss from dairy farms
Submitted to: International Nitrogen Conference
Publication Type: Proceedings
Publication Acceptance Date: 9/9/2016
Publication Date: N/A
Interpretive Summary: Two emerging feeding strategies may impact nitrogen (N) use and loss from dairy farms: 1) more corn for silage and less alfalfa for silage is being grown and fed to reduce feed costs; and 2) more corn grain-based concentrates are recommended to reduce enteric methane production, a potent greenhouse gas. Whole farm computer simulations illustrate that growing more corn silage and less alfalfa silage reduces the land requirement for feed production up to 27%, maintains milk production, increases animal nitrogen use efficiency (from 20 to 25%), and decreases manure nitrogen excretion by 22%. Growing more corn silage however, requires more fertilizer nitrogen (46 lbs N/acre) and increases nitrogen losses from the field. Feeding more corn grain does not impact milk production or animal nitrogen use efficiency, but requires up to 40% more corn grain land area and more fertilizer nitrogen (18 lbs N/acre); and it increases nitrate leaching. When manure was applied to the land, the subsequent crop was able to take up more nitrogen from the manure produced by cows being fed alfalfa silage or corn grain compared to the cows being fed corn silage. This information shows that trade-offs in nitrogen use and loss need to be more fully considered by producers, consultants and policy makers when considering more corn silage and corn grain in dairy cow rations.
Technical Abstract: Many dairy farms in the USA are growing and feeding more corn silage (CS) and less alfalfa silage (AS) to reduce feed costs. More corn grain (CG)-based concentrates are also being promoted to reduce enteric methane, a potent greenhouse gas. Whole farm simulations illustrate that growing more CS and less AS reduces the land requirement for feed production by 27%, maintains milk production, increases animal N use efficiency (from 20 to 25%), and decreases manure N excretion (from 7.6 to 5.9 g N/kg milk). Growing more CS however, requires more fertilizer N (40 kg N/ha) and increases N losses (35 kg N/ha). Feeding more CG does not impact milk production or animal N use efficiency, but requires 40% more CG land area, more fertilizer N (20 kg N/ha), and increases nitrate leaching (9 kg N/ha). CS, AS and CG were labeled with stable isotope 15N and fed to dairy cows. Relatively more of the 15N contained in CS (CS-N) was transformed into milk N than urine N compared to the N in AS (AS-N). Consumed CS-N and AS-N were distributed similarly into milk N and fecal N. Relatively more of the N contained in CG (CG-N) was secreted as milk N compared to AS-N and CS-N. After land application, more manure N from AS-N or CG-N was taken up by corn silage than manure N from CS-N. Trade-offs in N use and loss need to be more fully considered when recommending more CS and CG in dairy cow rations.