Author
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STOUT W L - 1902-05-00 |
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Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/20/1995 Publication Date: N/A Citation: N/A Interpretive Summary: Economic realities are forcing many dairy farmers in northeastern United States to make increased use of pastures as a means of increasing overall profitability. Nitrogen is the most important fertilizer element in pasture production. Thus, it's important that nitrogen be used efficiently if pastures are to increase farm profitability. Nitrogen use efficiency can be measured using stable isotopes or by comparison between fertilized and unfertilized plants. In our work we evaluated the two methods using data from field experiments conducted on seven different soils and three pasture grasses and using two fertilizer nitrogen isotopes (ammonium nitrate and ammonium sulfate). We found that both methods gave similar results for nitrogen use efficiency. However, the ammonium nitrate isotope gave more consistent results than ammonium sulfate. Increased fertilizer nitrogen use efficiency contributes to increased farm profitability and decreased contamination of groundwater. Technical Abstract: In northeastern USA, intensive grazing systems utilizing cool-season grasses are being increasingly adopted by dairy farmers as a way of reducing operating costs. Since N fertilization is a major factor in cool-season grass production in northeastern USA, the accurate determination of N use efficiency is necessary in determining N fluxes in intensive grazing systems. When using isotopic N the added N interaction (ANI), or 'priming' effect, can greatly affect the calculation of N use efficiency of crops and forages. The objective of this paper is to evaluate the magnitude of ANI as it relates to determination of N use efficiency of forage grasses in northeastern USA. Data from experiments on the effects of soils, environment, and N fertilization on the yield and N use efficiency of various forage grasses was used in this study. In these experiments multiple rates of isotopic ammonium nitrate and ammonium sulfate were applied to cool- and warm-season grasses. Nitrogen use efficiency was calculated using the isotopic and difference methods, and ANI was determined as the difference in N uptake as determined by these two methods. In experiments in which the N source was ammonium sulfate, ANI averaged 24.2 and 38.5% of the applied N on cool- and warm-season grasses, respectively. The ANI averaged 7.4% on the applied N on cool- season grass where the N source was ammonium nitrate. The ANI was always greater in the spring growth of cool-season grasses than it was in the fall growth. However, the seasonal difference was greater in the case where the N source was ammonium sulfate than it was where the N source was ammonium nitrate. |
