Effect of Straw Residues in Combination with Reduced Fertilization Rate on Greenhouse Gas Emissions from a Vegetable Field

Abstract

Greenhouse gases mainly come from farmland soils. Re-spreading chaff (straw returning) is an effective ecological management in China. Quantitative analysis of straw residues together with reduced fertilization rates can provide a scientific basis for reducing greenhouse gas emissions. A field experiment with six different fertilizer amounts combined with straw residues was carried out in a vegetable field (lettuce-cabbage-chili rotation), including the control (CK), conventional fertilizing (F), straw returning with 100% conventional fertilizing (100FS), straw returning with 70% conventional fertilizing (70FS), straw returning with 60% conventional fertilizing (60FS),and straw returning with 50% conventional fertilizing (50FS). The dynamic characteristics and emission factors of CO2, CH4 and N2O in the soil were analyzed using an in-situ, closed chamber, gas chromatography-based system, from November 2016 to September 2017. The results showed that the emission of CO2, CH4 and N2O has seasonal variation characteristics. The peak value mainly occurred in April to August, and the gas emission peak would appear after fertilizing and irrigating. Compared with F treatment, straw returning with fertilizing treatments reduced the N2O emission fluxes, cumulative emission and emission factor, especially in the 100FS treatment. The N2O cumulative emission and emission factor was 60.76 kg·hm-2, 0.138 kg·kg-1 (N2O-N/N) respectively in 100FS treatment during planting chili was more than that during planting lettuce and cabbage. Moreover, straw returning with reducing conventional fertilizing could reduce the N2O emission factor compared with 100FS treatment. The CO2 emission fluxes 55.28-1831.62[mg·(m2·h)-1] and cumulative emission (7502.13-25988.55 kg·hm-2) in 70FS treatment were lower than that in CK and F treatments, while other treatments increased the CO2 emission fluxes and cumulative emission, especially in 60FS and 50FS treatments. During planting lettuce and cabbage, the CH4 cumulative emission mainly showed negative values in treatments except for CK, indicating that soil could adsorb CH4. Moreover, straw returning with 30%-50% conventional fertilizing treatment could reduce CH4 emission fluxes and cumulative emission during planting chili, but increased in 100FS. Compared with CK and F treatment, generally, straw retuning with conventional fertilizing could significantly increase the global warming potential (GWP) in the study, except for 70FS treatment. 70FS could reduce the CO2, CH4 emission and the GWP of greenhouse gases, but could not significantly affect N2O emission reduction.