Influence of drip irrigation under plastic film mulching on concentrations of CO₂ and CH₄ in soil

A pot experiment was conducted in a greenhouse to compare the influences of flood (F) and drip (D) irrigations on soil concentrations of CO₂ and CH₄ during potato cropping season using the static opaque chamber and gas chromatography technique. Two agronomic measures were evaluated for each irrigation regime under mulched (M) and non-mulched conditions. Three more treatments were set under mulched drip irrigation (MD) based on different wet ratio (P) — P1 (P=25%), P2 (P=33%) and P3 (P=50%). There were six treatments altogether, denoted as DP1, MDP1, MDP2, MDP3, FC and MF. Bare soils with (MBS) and without (BS) plastic film mulching were set as control treatments. Results suggested that mulching treatments increased soil CO₂ concentration by 10.4%~94.5% due to plastic film mulching increasing effect on temperature and moisture, and barrier effects on natural air transmission of the soil-atmosphere system. Mulching treatments decreased soil CH₄ concentration by 5.1%~47.4%. Because of dry-wet alternation under drip-irrigation and decreased soil aeration under flood irrigation, CO₂ concentration was 7.4%~49.7% higher under flood irrigation and CH₄ concentration 6.6%~68.2% lower under drip irrigation. Soil moisture influenced greenhouse gas emission by altering soil aeration and soil dissolved organic matter. The higher the wet ratio under MD, the lower was CO₂ concentration. However, the effect of wet ratio on CH₄ concentration was not clear. Soil temperature was the main driving factor of soil respiration, which also regulated CH₄ oxidation processes. The greenhouse gas concentration in soils after DP1 irrigation showed a significant positive correlation between soil temperature and soil CO₂ concentration. Also after DP1 irrigation, a significant negative correlation existed between soil temperature and soil CH₄ concentration while a significant negative correlation was noted between soil CO₂ and CH₄ concentrations.