NITROUS-OXIDE EMISSIONS FROM AGRICULTURAL FIELDS DURING WINTER AND SPRING THAW AS AFFECTED BY MANAGEMENT-PRACTICES

Highest rates of N2O emissions from fertilized as well as natural ecos ystems have often been measured at spring thaw. But, it is not clear i f management practices have an effect on winter and spring thaw emissi ons, or if measurements conducted over several years would reveal diff erent emission patterns depending on winter conditions. In this study, we present N2O fluxes obtained using the flux-gradient approach over four winter and spring thaw periods, spanning from 1993 to 1996, at tw o locations in Ontario, Canada. Several agricultural fields (bare soil , barley, soybean, canola, grass, corn) subjected to various managemen t practices (manure and nitrogen fertilizer addition, alfalfa ploughin g, fallowing) were monitored. Nitrous oxide emissions from these field s from January to April over four years ranged between 0 and 4.8 kg N ha(-1). These thaw emissions are substantial and should be considered in the nitrous oxide budgets in regions where thaw periods occur. Our study indicates that agricultural management can play a role in mitiga ting these emissions. Our data show that fallowing, manure application and alfalfa incorporation in the fall lead to high spring emissions, while the presence of plants (as in the case of alfalfa or grass) can result in negligible emissions during thaw. This presents an opportuni ty for mitigation of N2O emissions through the use of over-wintering c over crops.