Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: March 1, 1996
Publication Date: N/A
Technical Abstract: Livestock utilize only 5 to 30% of the nitrogen (N) ingested to produce meat, milk, and wool, with dairy cows being among the most efficient. The remainder of the ingested N is excreted in urine and feces to only 20% of the pasture area, which can result in poor N use efficiency by pasture plants. Nitrogen losses usually increase with grazing intensity, but there eare few data on N cycling in pastures in the USA. Urine-N output reflects changes in animal diet more than dung-N. Urine is applied at high rates and results in inorganic N supplies far in excess of plant need. Ammonia volatilization, denitrification, and nitrate leaching are higher in urine spots than in dung, and both exceed the N losses in areas of the pasture where animals did not deposit excreta. All three pathways of N loss impair the environment. Recommendations to improve N use efficiency include: use of moderate, split applications of fertilizer N rates; avoiding N application during or immediately after drought periods; including moderat populations of legumes to provide symbiotically fixed N and deeply rooted species to limit nitrate leaching; selecting supplemental feeds that improve N use efficiency of the animal but do not increase N loading on the pasture; adjusting stocking rates to match feed availability in herbage and supplements; avoiding grazing in late autumn to reduce overwinter leaching losses; and installing drain tiles only in those sites where substantial plant yield gains will accrue. Longer term solutions may include breeding livestock for optimum performance on pasture. Using these and other ways to improve N cycling in pastures will help ensure viable livestock systems that protect the environment.