Pervasive control of soil pH on N2O and N2 emissions under anaerobic conditions from upland agricultural soils across China

Feifei Zhu1,2, Yunting Fang1,2*, Limei Zhang3, Rong Sheng4, Wenxue Wei4, Jizheng He3,5.

1 Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, China, 110016, [email protected]

2 Qingyuan Forest CERN, Shenyang, China, 110016

3 State Key Laboratory of Urban and Regional Ecology, Research Centre for Eco-environmental Sciences, Chinese Academy of Sciences, Beijing, China, 100085

4 Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, China, 410125

5 Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville, VIC, 3010, Australia.

Abstract

Soil N2 emission is an important pathway of N losses which is difficult to quantify in terms of both the magnitude and the contributions of the processes involved, yielding uncertainty in closing the N budget for agricultural systems. In this study, by adopting 15N labelling and 15N pairing technique under in vitro anaerobic conditions, the potential production rates of N2O and N2, the N2:N2O, and factors controlling denitrification, combined co-denitrification and anaerobic ammonium oxidation (anammox) were investigated for soils from 8 maize-growing regions across China from 26° N to 46° N latitude. The measured potential rates of N2O and N2 productions were 0.1 to 6.5 nmol 15N g-1 h-1 and 8.1 to 41.5 nmol 15N g-1 h-1, respectively. The dominance of N2 over N2O production resulted in N2:N2O ratios from 4 to 372 in these soils. N2O production was high at low pH soils, suggesting possible inhibition on N2O reduction. Denitrification dominated both N2O and N2 production, contributing to 85 ~ 99% of N2O, and 65 ~ 100% of N2 productions, respectively. Correlation analysis suggested that soil pH explained 30% and 46% of the variations in 15N2O and 15N2 production, respectively. Soil pH was the most important factors controlling the ratio of N2 to N2O emissions through denitrification in the studied upland agricultural soils across China, which implies that we may be able to estimate soil N2 losses from upland soils at a regional scale using N2O emission rates and soil pH.