Impacts of Chicken Manure Biochar on Nitrous Oxide and Methane Emissions from Vegetable Field in Subtropical China

Abstract Vegetable production in Subtropical China is distinguished by excessive nitrogen (N) fertilization, frequent irrigation, and multiple crop rotations in a single year, making it one of China’s most severely impacted agro-ecosystems. The aforementioned variables are closely related to soil nitrous oxide (N2O) and methane (CH4) emissions. However, not much research has been conducted on the emission characteristics of N2O and CH4 from local farmers’ practices, and the impacts of chicken manure biochar on the emissions of multiple-cropping vegetable fields in south subtropical China. Hence, we conducted a field trial to measure N2O and CH4 emissions using static chamber-gas chromatography. Four treatments were used: control (CK) with no fertilizer, 100% chemical N fertilization (CN), the conventional 30% chicken manure N plus 70%CN (CMN+CN), and 30% chicken manure biochar N plus 70%CN (CMBN+CN). Seven seasons continuous vegetable production showed, the annual cumulative N2O emissions reached to 12.4, 63.5, 111.8 and 44.1 kg N2O-N ha-1 for CK, CN, CMN+CN, and CMBN+CN treatments, respectively. Compared to CN and CMN+CN treatments, CMBN+CN treatment reduced N2O emissions by 35.9% - 65.7%, while it simultaneously increases annual total vegetable yield by 16.1% relative to CN treatment. Seven seasons mean N2O emission factors are 1.3% for CN, 3.8% for CMN+CN, 0.9% for CMBN+CN. The CH4 emission was negligible, fall into 0.07 kg CH4-C ha-1 for CK treatment to 0.8 kg CH4-C ha-1 for CN treatment. Temperature and soil moisture had a strong relationship with N2O emissions. For N2O emissions, the ideal interior chamber temperature was around 31.9 °C and the soil's water-filled pore space (WFPS) was approximately 60%. Our research highlighted that, fertilizer rates and types, soil moisture and temperature were the main controlling factors of N2O emissions in subtropical vegetable field. Future climate change will cause environmental factors to change more dramatically, which will probably result in more N2O emissions from conventional vegetable fields in subtropical areas. Chicken manure biochar can be one of the best substitutes for fresh chicken manure as a soil supplement, because it has a beneficial effect on improving vegetable yield and reducing N2O emissions in subtropical China.