Measurement and modelling of NO fluxes over maize and wheat crops during their growing seasons: effect of crop management

Fertilized agricultural soils are a significant source of NO, a gas involved in tropospheric ozone formation. The aims of the research reported here were to measure NO fluxes over the length of the growing season of wheat and maize crops, and to build a model of soil NO emissions from arable land. Field experiments were carried out on a 1-ha field divided into two parts. The first one was cropped with wheat and harvested in late July, 2002, whereas the second part was sown with maize and harvested in October. The wheat and maize received 130 kg N ha−1 and 140 kg N ha−1, respectively. For each crop, NO fluxes were measured during 10 months every 2 weeks using manual closed chambers, and continuously with a wind tunnel immediately after nitrogen fertilization. Fertilizer application significantly affected NO emissions: the largest NO emissions were recorded a few days after nitrogen application. This delay depended on the kinetics of nitrogen incorporation in the soil, as influenced by rainfall. The emissions measured on the maize field (2.6% of the fertilizer amount applied) were more important than those on the wheat field (1.0% of the fertilizer amount applied), owing to differences in timing of nitrogen application, with respect to climate and crop growth. Relationships between soil nitrification rate and NO emission obtained from laboratory incubations, and experimental data appeared useful and relevant to predict NO emissions at the field-scale