Soil CO2 emissions pulse and water-carbon regulation effect of greenhouse tomato after irrigation under irrigation-biochar combinations application

Post-irrigation soil CO 2 emission pulses contribute substantially to greenhouse soil carbon fluxes under drip irrigation, yet the responses to irrigation-biochar combinations remain poorly characterized. In this study, greenhouse tomato experiment was conducted under three irrigation levels (W1, 60% ET 0 ; W2, 80% ET 0 ; W3, 100% ET 0 ) and three biochar rates (BC1, 7.5 t ha −1 ; BC2, 11.25 t ha −1 ; BC3, 15 t ha −1 ). Based on observations at four key tomato growth stages and within 0 ~ 48 h after irrigation, post-irrigation CO 2 pulse dynamics were analyzed across treatments. Soil CO 2 flux was measured immediately before irrigation and at 3, 24, and 48 h after one representative irrigation event at each of four growth stages. Event pulses were calculated separately for three spatial blocks and analyzed with a repeated measures model based on a split plot design. An auxiliary 2025 dataset of background fluxes and DNDC simulations provided supplementary context only. Soil CO 2 flux generally increased rapidly after irrigation and then declined within 48 h. Average cumulative CO 2 pulse after a single irrigation event ranged from 38.31 to 296.22 kg ha −1 , with a significant irrigation×biochar interaction ( P < 0.05). TOPSIS with entropy weights based on measured fresh fruit yield, irrigation water productivity, and the observed CO 2 pulse ranked BC1W2 first ( C = 0.828). Moderate irrigation combined with the lower tested biochar rate provided the most balanced productivity, irrigation water performance, and CO 2 emission cost at the event scale under the tested site, season, and framework used for indicator weighting.