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Title: An index approach to assess nitrogen losses to the environment

item Delgado, Jorge
item Shaffer, Marvin
item WONG, J
item JOOSSE, P
item LI, X
item Follett, Ronald
item Del Grosso, Stephen - Steve
item COLON, W

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2007
Publication Date: 3/24/2008
Citation: Delgado, J.A., Shaffer, M.J., Hu, C., Lavado, R., Wong, J.C., Joosse, P., Li, X., Rimski-Korasako, H., Follett, R.F., Del Grosso, S.J., Colon, W., Sotomayor, D. 2008. An index approach to assess nitrogen losses to the environment. Journal of Ecological Engineering 32: 108-120.

Interpretive Summary: A nitrogen index tool should be used with caution and awareness of its potential limitations. Computers models such as NLEAP or others mentioned in our introduction can be used to conduct mechanistic evaluations of management practices on sensitive analysis, but even computer models have to be calibrated to regions and or areas. There is the need to consider these limitations. As a general evaluation tool we concluded that our nitrogen index field is a good preliminary assessment tool. For more in depth analysis we recommend using a tier two tools such as a nitrogen model. One alternative could be to calibrate the nitrogen index and put the right coefficients for average NH3 losses and denitrification losses for a specific set of management situations. However, we caution that although this suggested approach can match up the assessment between the new nitrogen index and simulated values, still the nitrogen index is not mechanistic, and we suggest that it will not be as sensitive as a mechanistic model as far as detecting pulses that can generate N fluxes higher than average (e.g. a thunderstorm). We continue to support the previous recommended framework from Shaffer and Delgado (2002) of a tier one and two approach, and tier three if needed.

Technical Abstract: We used the new nitrogen index version as a tier one tool and the NLEAP model as a tier two tool to conduct nitrogen management evaluations according to the framework proposed by Shaffer and Delgado in (2002). Nitrogen Index Version 1.0 tier one NAL was correlated with observed NAL measured after harvest and with NLEAP simulated tier two NAL. Although the Nitrogen Index Version 1.0 NO3-N leached, NH3 volatilization and denitrification values were significantly correlated with the NLEAP model tier two values, our nitrogen index tier one values were lower than those from the NLEAP model. Furthermore, sensitivity analyses showed that our Nitrogen Index Version 1.0 is not sensitive to significant pulse situations such as precipitation larger than 2 inches for Hydrology D group soils and even to a two inch precipitation for Hydrology A soils that can contribute to significant losses. We also proposed that there are other potential scenarios where the current nitrogen index will not work, such a rapid meltdown of snow in the spring, and or large NH3 volatilization or denitrification pulses. We recommend that, in case of expected large event nitrogen pulses, a modeling tier two approach be use to get more accurate values. There is potential to use this nitrogen index tool for nitrogen management to assess NAL and to estimate the trend of these losses for NO3 leaching, NH3 volatilization and denitrification. In general, the new Nitrogen Index Version 1.0 assessment of the Annual Leaching Risk Potential index (ALRP) to assess potential impacts to underground water resources were in close agreement with the NLEAP evaluations of ALRP. We propose that this current nitrogen index can potentially be used as a tier one tool, supported by a tier two model evaluation if needed.