Author
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Harper, Lowry |
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Sharpe, Ronald |
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Submitted to: Atmospheric Environment
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/4/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Isotopes of nitrogen (N) have been used for many years by soil and plant scientists to evaluate fertilizer efficiency and N cycling within soil-plant systems. In this paper, N isotopes were used to evaluate N transport within soil and plant systems while simultaneously measuring net atmospheric ammonia (NH3) transport using micrometeorological techniques. These simultaneous measurements have shown that isotopes can evaluate NH3 loss from soils to the atmosphere when there was no active plant growth. However, in the presence of plant growth, background (non-isotopic) N from the atmosphere is substituted for isotopic N in the plant. Consequently, N losses to the atmosphere measured by micrometeorological techniques by two to six times. Because of atmospheric NH3-N substitution for isotope N in the plant, caution must be exercised in the use of isotopes where isotope exchange between the plant and atmosphere has not been taken into consideration. Previous isotope studies of fertilizer efficiency and plant use have not evaluated the phenomenon of isotope N exchange for atmospheric N, possibly leading to serious errors in evaluation of N relationships. Technical Abstract: Isotopes of nitrogen (14N and 15N) have been used to evaluate N transport in soil-plant systems but these studies generally ignore the atmospheric component of N balance. The purpose of this presentation is to review measurements of atmospheric N cycling and investigate how atmospheric transport may influence isotopic N studies. soil and plant N transport were studied using 15N while simultaneously measuring net atmospheric NH3 transport using micrometeorological techniques. Simultaneous 15N and micrometeorological studies have shown large gaseous NH3 losses and absorption in soil-plant systems. Transport measured by the two techniques agreed closely when there was no plant activity. With plant activity, and the associated substitution of 15N in the plant by 14N from the atmospheric NH3, NH3 losses measured by 15N were from 2 to 6 times greater than NH3 net losses measured by micrometeorological techniques. Although 15N studies are valuable for comparison of treatments, caution must be exercised in the use of isotopes where isotope exchange between the plant and atmosphere has not been taken into consideration. |
