A new chamber design for measuring nitrous oxide emissions in maize crops

Abstract

Nitrous oxide (N2O) emissions from agricultural land are often estimated by measuring changes in N2O concentrations over a given period in the headspace of a gas‐sampling chamber covering a specific soil area. This technique is particularly challenging in tall growing row crops such as maize (Zea mays L.), to which farmers regularly apply fertilizer banded below the seeds to ensure good crop development. Placing chambers in the inter‐row space leads to bias in flux measurements, due to exclusion of fertilized and rhizosphere soil. Chambers for N2O flux measurements should therefore be placed centered over the row. A new split chamber for gas sampling was developed in this study from a closed, rectangular chamber (original chamber: 78 cm × 78 cm, 51 cm height). The new chamber is applicable for use for the complete maize growing cycle until harvest. For each flux measurement, the two parts of the chambers are placed in a gas‐tight seal on a collar previously inserted into soil covering a representative area of land. In a later growth stage, when plant height exceeds chamber height, stalks of developed maize plants can be fixed between the two chamber parts through a rubber‐tightening opening on the top of the chamber. Air tightness of the split chamber was tested in the laboratory and the split chamber was compared with the original chamber in a field experiment with slurry injection under maize seeds. The laboratory test demonstrated similar air tightness of both chamber types. The field test yielded almost identical N2O fluxes for the original chamber (244 µg N2O‐N m−1 h−1) and the split‐chamber (254 µg N2O‐N m−1 h−1). It can be concluded that the split chamber is an adequate gas‐sampling unit, with particular advantages when flux measurements are conducted in tall growing row crops.

Effect of cattle slurry application techniques on N2O and NH3 emissions from a loamy soil

“…Own experiments with lettuce ( Lactuca sativa ) showed that exclusion of plants from the chambers did not affect N 2 O flux rates (unpublished), but for maize we did not test this effect. Adapting closed chambers for trace gas measurements in tall crops as proposed by ( Olfs et al., ) might improve reliability when calculating area‐based emissions.…”

Global Research Alliance N2O chamber methodology guidelines: Recommendations for deployment and accounting for sources of variability

“…(2020) describe methods for quantitatively assessing the impacts of varying chamber height on flux‐calculation accuracy and precision in the context of other important factors. These methods are recommended for site‐specific evaluation, including evaluating the use of larger chamber heights to accommodate growing crops or for paddy crops (Bertora, Peyron, Pelissetti, Grignani, & Sacco, 2018; Olfs et al., 2018; Section 3.4. ; note that for paddy crops, the headspace volume above the water level affects the uncertainty of N 2 O flux measurements and should be recorded).…”

“…Indeed, Olfs et al. (2018) describe a new chamber design to account for both row and inter‐row areas (Clough et al., 2020). On irrigated crops, different irrigation systems can lead to different patterns of water distribution and, accordingly, soil moisture (Supplemental Section 2).…”

Effect of the nitrification inhibitor DMPP on nitrous oxide emissions and the stabilization of ammonium following the injection of dairy slurry and digestate in a soil‐column experiment

“…The initial N 2 O headspace concentration was assumed to be the same as the average ambient air value in the laboratory for which four samples were taken. Gas sampling, using glass vials (IVA Analysentechnik, Meerbusch, Germany), chromatographic analyses and calculations of N 2 O flux rates were carried out as described in Olfs et al (2018), except that simple linear regression was used to calculate gas fluxes.…”