ARS | Publication request: Effects of N fertilization and supplementation strategies on forage intake, dietary selection, and performance of growing beef cattle.

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 9, 2009
Publication Date: August 10, 2009
Citation: Gunter, S.A., Springer, T.L., Bradford, J.A. 2009. Effects of N fertilization and supplementation strategies on forage intake, dietary selection, and performance of growing beef cattle. Journal of Animal Science 87 (E-Supplement 2):320. (Abstract)

Technical Abstract: The N cycle on pasture is the movement of N through several pools found in the pastoral system. Except on a global scale, N cycles are generally not closed; that is, there are inputs to and losses from the pasture system. Nitrogen is the most perplexing of all nutrients; it moves in a variety of pathways-both biological and chemical; it has several oxidative states, can exist as a gas, a dissolved cation or anion, a precipitated salt, or a dissolved or solid organic molecule. There are 6 major pathways of N loss in grazed land: NH3 volatilization, denitrification, wind and water erosion, nitrate leaching, and animal losses (export). Fecal pats of cattle contain the equivalent of 560 to 1,120 kg of N/ha, but plant recoveries of N from these pats rarely exceed 30%. Nitrogen fertilizers have been the tool most easily manipulated to affect herbage quality and availability to grazing ruminants. Recently, the price of N fertilizers increased to a point where graziers are questioning the economics of adding N via chemical fertilizers. Nitrogen fertilizers increase herbage mass production, thereby impacting the optimal stocking rate for maximal net-return per unit of land. The net return of the stocker cattle enterprise is functions of ADG, BW gain/ha, production cost, and revenues. Supplementation practices that decrease herbage DMI can increase the carrying capacity of a pasture without placing greater demand on the herbage mass, except through trampling loss, and accelerate the N cycle. Supplements transport N into the pasture N cycle from an outside source and can make a significant contribution to nutrient pool. Nitrogen in excreta generated from supplemental grain, hay, silage, and product feeds enter the system and increase the quality and quantity of forage produced. Nitrogen in feces is mainly in organic forms, with one-third in microbial biomass. Fecal N degradation in the pat is usually slow, being limited by anaerobic conditions at first, then by dry conditions. There is a need to discover what management will optimize the relationship between plant growth and N cycling in the full range of climatic conditions.