The effect of soil oxygen availability on greenhouse gases emission in a double rice field

Abstract

To investigate the effect of soil oxygen availability (SOA) on greenhouse gas (GHG) emissions from a double- rice cropping field, a two-year observation of greenhouse gas emissions of seven treatments from a rice paddy field was conducted by using the static closed-chamber method. There were seven management practices (or treatments), including CWS (Conventional Tillage+Without Straw Residues+Urea), NWS (No Tillage+Without Straw Residues+Urea), SCU (Conventional Tillage+Without Straw Residues+Controlled-Release Urea), HN (High Stubbles+No Tillage+Urea), HC (High Stubbles+Conventional Tillage+Urea), SN (Straw Cover+No Tillage+Urea) and SNF (Straw Cover+No Tillage+ Urea+Continuous Flooding). Three SOA factors, i.e., soil redox potential (Eh), pH and field water level (H) of each treatment was determined simultaneously. Our results indicated that methane emissions was sensitive to all of the three SOA factors. The critical values at which the higher methane fluxes were observed, for Eh, pH and H was -100-0mV, 5-6 and 1-5cm, respectively, and therefore the proportions of methane emitted from these three ranges were 48.8%, 61.1% and 77.0%, respectively. The determination coefficient of linear or quadratic polynomial regression models of the methane fluxes and the individual three SOA factors ranged from 0.04 to 0.38 (P<0.05). Among of them, H was attributed to the most important influence on methane emissions, explaining 37.8% of the variance of methane emissions from paddy field (P<0.05). While for nitrous oxide (N2O), large amount of negative fluxes occurred, If only positive N2O emissions considered, most of them were observed under conditions of 0mV