The influence of management and environmental variables on soil N2O emissions in a crop system in Southern Italy

Soil N2O emissions were monitored throughout a 3-year crop rotation including maize, fennel and a ryegrass-clover sward, at Borgo Cioffi NitroEurope site. N2O emission rates were highly variable in time and space and controlled by soil nitrogen and soil water content. The N2O effluxes were low for most of the monitored period. The highest N2O emissions were recorded throughout the 2007 maize cropping season, ranged form 15.2 to 196.2 mu g m(-2) h(-1) whereas the lowest ones ranged form -5 to 10 mu g m(-2) h(-1) during the 2007-2008 ryegrass-clover winter crop. For the maize crops, N2O peaks were detected after fertilization but with a delay of some weeks from applications, probably due to the presence of DMPP nitrification inhibitor in the applied fertilizer. A properly designed ANOVA model was developed to explain the influence of the main chemical-physical factors. This model also allowed the quantification of the delay time in peak emissions following fertilization, which resulted variable over the years and ranged between 2 and 21 days. A dependence of emissions from soil temperature and moisture was found, with significant interactions in some instances. Calculated Emission Factors (maize 2007: 0.48%; ryegrass-clover sward 2007-2008: 0.05%; maize 2008: 0.14%; fennel: 0.28% 2008-2009; maize 2009: 0.015%) resulted well below the values reported in the literature and the 1% reference value indicated by IPCC, probably due to a sub-optimal water regime inducing low Water Filled Pore Space (WFPS) values.