Chinese Milk Vetch as Green Manure Mitigates Nitrous Oxide Emission from Monocropped Rice System in South China.

Zhijian Xie,Changxu Xu,Shuxin Tu,Weidong Cao,Farooq Shah,P Pardha-Saradhi

doi:10.1371/journal.pone.0168134

Abstract

Monocropped rice system is an important intensive cropping system for food security in China. Green manure (GM) as an alternative to fertilizer N (FN) is useful for improving soil quality. However, few studies have examined the effect of Chinese milk vetch (CMV) as GM on nitrous oxide (N2O) emission from monocropped rice field in south China. Therefore, a pot-culture experiment with four treatments (control, no FN and CMV; CMV as GM alone, M; fertilizer N alone, FN; integrating fertilizer N with CMV, NM) was performed to investigate the effect of incorporating CMV as GM on N2O emission using a closed chamber-gas chromatography (GC) technique during the rice growing periods. Under the same N rate, incorporating CMV as GM (the treatments of M and NM) mitigated N2O emission during the growing periods of rice plant, reduced the NO3- content and activities of nitrate and nitrite reductase as well as the population of nitrifying bacteria in top soil at maturity stage of rice plant versus FN pots. The global warming potential (GWP) and greenhouse gas intensity (GHGI) of N2O from monocropped rice field was ranked as M<NM<FN. However, the treatment of NM increased rice grain yield and soil NH4+ content, which were dramatically decreased in the M pots, over the treatment of FN. Hence, it can be concluded that integrating FN with CMV as GM is a feasible tactic for food security and N2O mitigation in the monocropped rice based system.

Highlights

Mitigating climate change and ensuring food security are the two widely acknowledged key challenges of the 21st century
Our findings showed that the incorporation of Chinese milk vetch (CMV) as green manure (GM) (M and N with CMV (NM)) into paddy soil notably inhibited the N2O emission from monocropped rice system over the treatment of fertilizer N (FN) alone (Fig 2 and Table 1)
Our results showed that integrating CMV as GM with FN decreased the activities of nitrate reductase (NaR) and nitrite reductase (NiR) (Fig 5), which presumably decreased the amounts of electron acceptor (NO2-) of denitrification and in turn the N2O fluxes in paddy soil

Summary

Introduction

Mitigating climate change and ensuring food security are the two widely acknowledged key challenges of the 21st century. China will need to produce ~26.9% more rice by 2030 (compared with 2000) to meet the domestic need and ensure food security, if rice consumption per capita stays at the current level [2]. Green Manure Mitigates Nitrous Oxide Emission fertilizer N (FN) in rice production is essential in increasing rice yield, partly due to the limited cultivated area of rice paddies [3]. Since the early 1980s, Chinese agriculture has intensified greatly within a limited land area due to large inputs of chemical fertilizer [4]. Large input of FN and low nitrogen use efficiency (NUE) are causing serious environmental problems [5], include soil and water pollution, loss of biodiversity and greenhouse gases (GHGs) emissions [6]

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Discussion

Conclusion