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

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 identicalN₂Ofluxes for the original chamber (244 ~kgN₂O-Nm^–1 h^–1) and the splitchamber (254 ~kg 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.