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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Dairy Forage Research » Research » Publications at this Location » Publication #332954
Title: Nitrogen use efficiencies to grow, feed, and recycle manure from the major diet components fed to dairy cows in the USA

Author
item Powell, Joseph
item BARROS, TIAGO - University Of Wisconsin
item DANES, MARINA - Universidade Federal De Lavras
item AGUERRE, MATIAS - Clemson University
item WATTIAUX, MICHEL - University Of Wisconsin
item Reed, Kristan

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2017
Publication Date: 2/15/2017
Citation: Powell, J.M., Barros, T., Danes, M., Aguerre, M., Wattiaux, M., Reed, K. 2017. Nitrogen use efficiencies to grow, feed, and recycle manure from the major diet components fed to dairy cows in the USA. Agriculture, Ecosystems and Environment. 239:274-282.

Interpretive Summary: Because the nitrogen contained in feeds cycle through the entire dairy farm system, changes made to the diet to address an environmental problem, such as ammonia and methane emissions, might create problems in another part of the nitrogen cycle. The objective of this study was to examine how the nitrogen contained in an ingredient of a dairy cow’s diet behaves in a farm’s nitrogen cycle. Four feed ingredients (alfalfa silage, corn silage, corn grain, and soybean meal) were enriched with the stable nitrogen isotope during plant growth and fed to dairy cows to track nitrogen cycling. More of the nitrogen contained in corn grain and soybean meal was secreted in milk or retained in the cow compared to nitrogen contained in alfalfa silage and corn silage. When applied to fields, the manure nitrogen from the soybean meal was more available for crop uptake than the manure nitrogen from the corn silage. Results of the study support an earlier finding that feeding more corn silage (and less alfalfa) to dairy cows would require not only more fertilizer to grow the corn but also to offset the reduced manure N availability to subsequent crops. A balance between corn, alfalfa and soybeans in dairy cropping systems would be needed to not only enhance overall nitrogen use efficiency and reduce loss, but also to capture many of the benefits of corn-legume rotations.

Technical Abstract: Crops and livestock transform a general range of 20% to 50% of applied N into product N. Most applied N not transformed into agricultural products is lost to the environment. The objective of this study was to quantify soil N input (fertilizer N, biologically fixed-N) incorporation into dairy cow diet components, diet component N transformation into milk N and excretion in manure N, and manure N reuptake back into the feed supply. Alfalfa for silage (AS), corn for silage (CS), corn grain (CG) and soybeans (eventually solvent-extracted into soybean meal, SBM) were enriched in the field with the stable isotope 15N. Each 15N-labeled diet component was fed individually to twelve mid-lactation cows (3 cows per 15N-enriched diet component) as part of a total mixed ration (TMR). Proportions of each component’s 15N intake (15NI) recovered in milk, feces, fecal undigested dietary N, urine, urinary urea and retained were determined during a 4-day 15N feeding period and 4 days thereafter. Diet component 15N manure was applied to field plots and 15N uptake by corn for silage was determined over two succeeding years. The wide range in total 15N recoveries (%15NI), greatest from cows fed AS (84) followed by CS (78), SBM (76) and CG (68) indicates significant diet component differences in 15N retention. Relative 15N recoveries (% of total 15N recovered) in milk were greater (and statistically similar) from cows fed CG and SBM (average of 23.3) than from cows fed AS and CS (also statistically similar, average of 14.6). Relative 15N recoveries in feces were greater (and statistically similar) from cows fed AS and CS (average of 44.2) than from cows fed CG and SBM (also statistically similar, average of 33.3). All four diet components had similar relative 15N recoveries in urine (average of 42.3). Differences in % 15N recovery as fecal undigested dietary 15N (range of <1 to 2.7) indicate potential diet component manure differences in long-term contributions to stable organic matter in manure-amended soils. No statistical differences in % 15N recovery as urinary urea (average 36.3) indicate that each diet component contributes similarly to ammonia (NH3) and nitrous oxide (N2O) emissions from dairy farms. The greatest manure 15NUE (% of applied manure 15N recovered as corn silage 15N) during the first year after diet manure application was from SBM (32.7) followed by CG (28.5), AS (27.4) and CS (25.0). There were no significant differences in manure 15NUE among the four diet component treatments (average of 5.7) during the second year after manure application. Relative manure 15NUE differences year 1+2 mirrored differences obtained year 1 with the greatest manure 15NUE obtained from SBM (38.2), CG (34.7) and AS (33.4) and lowest from CS (30.5). The long term environmental impacts, such as soil erosion and soil health associated with land use changes to grow different diet components, will likely be more important than short-term impacts of dietary components on cow N use and manure N recycling through crops. A balance between corn, alfalfa and soybeans in dairy cropping system would be needed to not only enhance NUE in feed and milk production, but also to capture many of the benefits of corn-legume rotations.