Contribution of dairy ration components to nitrogen in milk, manure, crops, and environmental nitrogen loss

Authors: Powell, Joseph; BARROS, T - University Of Wisconsin; DANES, M - University Of Wisconsin; WATTIAUX, M - University Of Wisconsin

Submitted to: Nitrogen Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/18/2014
Publication Date: 6/30/2014
Citation: Powell, J.M., Barros, T., Danes, M., Wattiaux, M.A. 2014. Contribution of dairy ration components to nitrogen in milk, manure, crops, and environmental nitrogen loss. In: Cordovil, C.M.d.S. (ed.). The Nitrogen Challenge: Building a Blueprint for Nitrogen Use Efficiency and Food Security. 18th Nitrogen Workshop, June 30 –July 3, 2014, Lisbon, Portugal. p. 177-178.

Interpretive Summary: To better understand the integrated nature of nitrogen use and loss from dairy production systems, a series of experiments was designed to quantify the nitrogen contribution of individual ration components to milk and manure production, crop nitrogen requirements after manure application to soil, and environmental nitrogen loss. Alfalfa silage (AS), corn silage (CS), corn grain (CG), and soybeans (SB) were grown in the field with applications of fertilizer enriched in 15N. The stable isotope 15N is commonly used as a tracer to monitor the uptake and utilization of nitrogen in plant and animal systems. 15N-enriched AS, CS, CG and SB (as SB meal) were then fed individually (as components of total mixed rations) to 12 lactating cows. Production of milk and manure were recorded, and samples of each were collected from these 12 cows. The manure produced by each 15N enriched ration component will be applied to barn floors and soils to determine nitrogen losses and incorporation into crops. This research will provide unique information on relative contribution of individual dairy ration components to milk and manure production and environmental nitrogen loss.

Technical Abstract: Of the total nitrogen (N) consumed by dairy cows, a general range of 20 to 35% is secreted in milk, and the remaining N is excreted in manure, which is subject to environmental loss. For many dairy herds, improved feed management, including feeding rations balanced in energy and crude protein, can enhance milk production and reduce manure N excretion and N loss. To better understand the integrated nature of N use and N loss in dairy production systems, a series of experiments was designed to quantify the relative amounts of N from individual ration components secreted in milk, excreted in urine and feces, available to crops after manure application to soil, and lost as ammonia, nitrate and nitrous oxide. Alfalfa silage (AS), corn silage (CS), corn grain (CG), and soybeans (SB) were grown in the field with applications of 15N-enriched fertilizer. Each 15N-enriched feed was then fed individually (as components of total mixed rations) to 12 mid-lactation cows (3 cows per ration component). The mass of milk, urine, and feces produced by each cow were recorded and sampled the day before and 3 days after the 4-day 15N feeding period. Highest 15N incorporation in the field was achieved with CS and CG, and lowest with AS and SB due to 15N dilution by the atmospherically-fixed N by these legumes. The experimental methods used to ensile the 15N-enriched corn and alfalfa, the milling of 15N-enriched corn grain, and the extraction of 15N-enriched soybean grain to produce soybean meal did not impact ration intake, milk production, or N excretion by the 12 dairy cows, as indicated by similar cow responses to unlabeled feed components. Feces and urine from each 15N-enriched ration component will be applied to emission chambers that simulate barn floor and field soil surfaces, and 15N concentrations in ammonia, ammonium, nitrate and nitrous oxide will be measured. Manure-soil incubations, greenhouse and field trials will be conducted to determine each ration N component contribution to crop N uptake.