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Anhydrous ammonia injection depth does not affect N2O emissions in a silt loam over two growing seasons

Maharjan, Bijesh, Venterea, Rodney T.
Journal of environmental quality 2014 v.43 pp. 1527-1535
Zea mays, anhydrous ammonia, clay, clay soils, climatic factors, conventional tillage, crop yield, emissions, equipment, field experimentation, growing season, long term experiments, nitrogen fertilizers, nitrous oxide, no-tillage, reduced tillage, silt, silt loam soils, soil water content, Minnesota
Anhydrous ammonia (AA) is a major fertilizer source in North America and can promote greater emissions of nitrous oxide (N2O) compared to other N fertilizer sources. Equipment for applying AA at shallower depths has become commercially available, but impacts of shallow versus deep AA application on N2O emissions are not well characterized across different soil types. Reduced tillage has been promoted for its benefits but its effects on N2O emissions have varied widely. We conducted a two-yr field study to compare effects of AA placement depth and contrasting tillage practices on soil N2O emissions and crop (Zea mays L.) performance in a silt loam soil in Minnesota. In contrast to two previous studies, N2O emissions were not affected by AA placement depth. Analysis of current and previous results showed a strong correlation (r2=0.989) between soil clay content and AA placement depth effects on N2O, with increasing clay content corresponding to increased N2O with deeper placement. Tillage affected N2O emissions only in the drier of two seasons in which N2O emissions under no-till (NT) exceeded those under conventional tillage (CT) by 55%. Soil moisture content was enhanced to a greater extent under NT in the drier season. These results highlight how management practices interact with soil and climate factors in regulating N2O emissions, and point out that strategies for N2O mitigation need to be evaluated with regard to site-specific factors and their effectiveness has the potential for significant inter-annual variation.