Patricia Laville

Modeling of nitric oxide emissions from temperate agricultural soils

Arable soils are a significant source of nitric oxide (NO), most of which is derived from nitrogen fertilizers. Accurate estimates of NO emissions from these soils are essential to devise strategies to mitigate the impact of agriculture on tropospheric ozone production and destruction. This paper presents the implementation of a soil NO emissions submodel within the environmentally-orientated soil-crop model, CERES-EGC. The submodel simulates NO production via the nitrification pathway, as modulated by soil environmental drivers. The resulting model was tested with data from 4 field experiments on wheat- and maize-cropped soils representative of two agricultural regions of France, over three years, and encompassing various climatic conditions. Overall, the model provided accurate predictions of NO emissions, but shortcomings arose from an inadequate vertical distribution of N fertilizer in the soil surface. Inclusion of a 2-cm thick topsoil layer in a ‘micro-layer’ version of CERES-EGC gave more realistic simulations of NO emissions and under-lying microbiological process. From a statistical point of view, both versions of the model achieved a similar fit to the experimental data, with respectively a MD and a RMSE ranging from 1.8 to 6.2xa0g N–NOxa0ha−1d−1, and from 22.8 to 25.2xa0g N–NOxa0ha−1d−1 across the 4 experiments. The cumulative NO losses represented 1–2% of NH4+ fertilizer applied in the case of maize crops, and about 1% in the case of wheat crops. The ‘micro-layer’ version may be used for spatialized inventories of NO emissions to improve air quality prediction.

Potential of denitrification and nitrous oxide production from agricultural soil profiles (Seine Basin, France)

The denitrification process and the associated nitrous oxide (N2O) production in soils have been poorly documented, especially in terms of soil profiles; most work on denitrification has concentrated on the upper layer (first 20xa0cm). The objectives of this study were to examine the origin of N2O emission and the effects of in situ controlling factors on soil denitrification and N2O production, also allowing the (N2O production)/(NO3−–N reduction) ratio to be determined through (1) the position on a slope reaching a river and (2) the depth (soil horizons: 10–30 and 90–110xa0cm). In 2009 and 2010, slurry batch experiments combined with molecular investigations of bacterial communities were conducted in a corn field and an adjacent riparian buffer strip. Denitrification rates, ranging from 0.30xa0μg NO3−–Nxa0g−1 dry soil h−1 to 1.44xa0μg NO3−–Nxa0g−1 dry soil h−1, showed no significant variation along the slope and depth. N2O production assessed simultaneously differed considerably over the depth and ranged from 0.4xa0ng N2O–Nxa0g−1 dry soil h−1 in subsoils (the 90–110-cm layer) to 155.1xa0ng N2O–Nxa0g−1 dry soil h−1 in the topsoils (the 10–30-cm layer). In the topsoils, N2O–N production accounted for 8.5–48.0% of the total denitrified NO3−–N, but for less than 1% in the subsoils. Similarly, N2O-consuming bacterial communities from the subsoils greatly differed from those of the topsoils, as revealed by their nosZ DGGE fingerprints. High N2O-SPPR (nitrous oxide semi potential production rates) in comparison to NO3-SPDR (nitrate semi potential reduction rates) for the topsoils indicated significant potential greenhouse N2O gas production, whereas lower horizons could play a role in fully removing nitrate into inert atmospheric N2. In terms of landscape management, these results call for caution in rehabilitating or constructing buffer zones for agricultural nitrate removal.

29 % N2O emission reduction from a modelled low-greenhouse gas cropping system during 2009–2011

Atmospheric concentration of nitrous oxide (N2O), a greenhouse gas (GHG), is rising largely due to agriculture. At the plot scale, N2O emissions from crops are known to be controlled by local agricultural practices such as fertilisation, tillage and residue management. However, knowledge of greenhouse gas emissions at the scale of the cropping system is scarce, notably because N2O monitoring is time consuming. Strategies to reduce impact of farming on climate should therefore be sought at the cropping system level. Agro-ecosystem models are simple alternative means to estimate N2O emissions. Here, we combined ecosystem modelling and field measurements to assess the effect of agronomic management on N2O emissions. The model was tested with series of daily to monthly N2O emission data. It was then used to evaluate the N2O abatement potential of a low-emission system designed to halve greenhouse gas emissions in comparison with a system with high productivity and environmental performance. We found a 29xa0% N2O abatement potential for the low-emission system compared with the high-productivity system. Among N2O abatement options, reduction in mineral fertiliser inputs was the most effective.

High-resolution inventory of NO emissions from agricultural soils over the Ile-de-France region.

Arable soils are a significant source of nitric oxide (NO), a precursor of tropospheric ozone, and thereby contribute to ozone pollution. However, their actual impact on ozone formation is strongly related to their spatial and temporal emission patterns, which warrant high-resolution estimates. Here, we combined an agro-ecosystem model and geo-referenced databases to map these sources over the 12,000 km2 administrative region surrounding Paris, France, with a kilometric level resolution. The six most frequent arable crop species were simulated, with emission rates ranging from 1.4 kg N-NO ha(-1) yr(-1) to 11.1 kg N-NO ha(-1) yr(-1). The overall emission factor for fertilizer-derived NO emissions was 1.7%, while background emissions contributed half of the total NO efflux. Emissions were strongly seasonal, being highest in spring due to fertilizer inputs. They were mostly sensitive to soil type, crops growing season and fertilizer N rates.