Annick Goossens

Two-year field study on the emission of N2O from coarse and middle-textured Belgian soils with different land use

In the following study N2O emissions from 3 different grasslands and from 3 different arable lands, representing major agriculture areas with different soil textures and normal agricultural practices in Belgium, have been monitored for 1 to 2 years. One undisturbed soil under deciduous forest was also included in the study. Nitrous oxide emission was measured directly in the field from vented closed chambers through photo-acoustic infrared detection. Annual N2O emissions from the arable lands ranged from 0.3 to 1.5 kg N ha−1 y−1 and represent 0.3 to 1.0% of the fertilizer N applied. Annual N2O emissions from the intensively managed grasslands and an arable land sown with grass were significantly larger than those from the cropped arable lands. Emissions ranged from 14 to 32 kg N ha−1 y−1, representing fertilizer N losses between 3 and 11%. At the forest soil a net N2O uptake of 1.3 kg N2O-N ha−1 was recorded over a 2-year period. It seems that the N2O-N loss per unit of fertilizer N applied is larger for intensively managed and heavily fertilized (up to 500 kg N ha−1) grasslands than for arable lands and is substantially larger than the 1.25% figure used for the global emission inventory. Comparison of the annual emission fluxes from the different soils also indicated that land use rather than soil properties influenced the N2O emission. Our results also show once again the importance of year-round measurements for a correct estimate of N2O losses from agricultural soils: 7 to 76% of the total annual N2O was emitted during the winter period (October–February). Disregarding the emission during the off-season period can lead to serious underestimation of the actual annual N2O flux.

Calibration of a Multipoint Sampling System Connected with a Photoacoustic Detector

Abstract Photoacoustic detection of gases in the air phase in combination with a multipoint sampling device transfers about 100 mL of air from each sample location to the next one, causing a considerable disturbance when small systems are sampled. In reactive systems, such as trace gas exchange in soil samples, a correction is required to determine the kinetic behavior of the systems. But this kinetic behavior is required in turn to calculate the correction in a repeated sampling sequence. A model was developed for reaction kinetics (zero-order or first-order) within closed systems and the sample transfer between these systems by a CBISS MK2 multipoint sampling system, connected with a Brüel & Kjær photoacoustic detector. By regression, the reaction kinetics is determined, and by simulation of the system in the absence of sample transfer, corrected data are generated. Comparison of experimental and modeled data revealed that part of the sample is transferred directly two systems further. In addition, a slight memory effect of the detector was revealed. These effects were accounted for in the model. If the correction is not made, biased results are obtained for the reaction kinetics.

Influence of land use on long-term methane uptake

A long-term study was conducted to assess the effect of soil type and land use on the CH4 uptake by arable lands, grasslands and a forest with different textures. Overall, CH4 uptake was low at all sites but larger for the grasslands than for the arable lands. Results indicate that land use and climate rather than soil texture influence the CH4 oxidizing capacity of soils.

N2O flux from a forest soil located in an area of intensive animal breeding in Belgium

A laboratory experiment was conducted with a forest soil to investigate the contribution of the organic and mineral (0–10cm) layer at different moisture contents to the N2O-N emission. Fluxes were in the range of 1–11.5 g N2O-N ha-1 d-1. The effect of WFPS of the mineral layer on the N2O flux was highly significant. The effect of the moisture content of the organic layer and the interaction between both layers were less pronounced.