Continuous milk vetch amendment in rice-fallow rotation improves soil fertility and maintains rice yield without increasing CH4 emissions: Evidence from a long-term experiment

doi:10.1016/j.agee.2021.107774

Agriculture, Ecosystems & Environment

Volume 325, 28 February 2022, 107774

https://doi.org/10.1016/j.agee.2021.107774 Get rights and content

Highlights

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Continuous green manure amendment could increase soil organic carbon (SOC).
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Grain yield remains unaffected by green manure and N-application rate.
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Green manure was the main factor mediating paddy CH₄ emission.
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Ryegrass enhanced CH₄ emissions on the contrary to milk vetch amendments.
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SOC and mcrA gene were the key factors to CH₄ emissions in ryegrass amended plots.

Abstract

Catch crop (green manure) planting is considered an efficient strategy to improve soil fertility in agro-ecosystems. Methane (CH₄) emissions from paddies subjected to continuous green manure amendment though is a topic that remains unexplored. To clarify the impact of continuous green manure amendment on rice yield and CH₄ emissions, a long-term trial (established in 2003, Yixing, China) was designed with the field observations conducted between 2019 and 2020. Two green manure crops (milk vetch, ryegrass) were selected as the catch crop with fallow as the control, all trialed at two N application rates i) low N dosage deriving from the optimum effect between yield-N fertilizer (LN, 200 kg ha^-1), and ii) a higher N dose as the empirical farmer's dose (HN, 270 kg ha^-1). The results showed that continuous green manure amendment notably increased soil organic carbon (SOC) compared to that of the control, while HN significantly increased the dissolved organic nitrogen compared to LN. The rice yield among treatments remained similar, ranging from 8.6 t ha^-1 to 9.4 t ha^-1 (two years’ average). CH₄ emissions were notably related to green manure, and remained unaffected by N application rate. Ryegrass amendment after 18 years remarkably stimulated the CH₄ emissions compared to other treatments, while the difference between milk vetch-amended and fallow treatments was found insignificant. Ryegrass increased soil mcrA gene with the abundance becoming the highest under HN. Methanogens abundance and SOC content were the main factors affecting CH₄ emissions under ryegrass addition. Moreover, the CH₄ emission intensity was aligned with CH₄ emissions mainly due to the similar rice yield. Overall, continuous milk vetch planting is a recommended catch crop strategy that increases soil fertility and maintains rice yield without increasing CH₄ emissions.

Introduction

Methane (CH₄) is one of the critical greenhouse gases responsible for climate change when emitted uncontrollably (IPCC, 2013). In particular, the contribution of agricultural farmlands to CH₄ emissions must be seriously considered as it accounts for ~52% of the global methane emissions (Smith et al., 2008). Paddy fields specifically are the highest anthropogenic CH₄ emitting cropland, contributing to ~48% of the overall agricultural emissions (Carlson et al., 2016). Meanwhile, paddy fields ensure global nutrition security since the human population worldwide continuously grow (Arora, 2018, Prosekov and Ivanova, 2018, Seck et al., 2012). Thus, it is crucial to mitigate the CH₄ emissions from paddies while maintaining satisfactory rice yield per unit of land.

Catch crop planting (green manure) during the fallow season in rice cropping systems has been proved to be a strategy that improves soil fertility while ensuring satisfactory cereal yield (Housman et al., 2021, Xie et al., 2016, Yang et al., 2019, Zhou et al., 2020a). As a response, the CH₄ emission from paddies often varies as per the decomposition of green manure and/or the subsequent changes in soil fertility. Based on an incubation experiment, Xiao (2017) indicated that milk vetch addition increased CH₄ emissions compared to the emissions formed from other amendments (ryegrass, winter wheat, and rape), likely due to the accelerated decomposition at a narrower C:N ratio. However, Kim et al. (2012) found that milk vetch can reduce the CH₄ emissions from paddies in comparison with non-leguminous ryegrass. In a double rice cropping system, Zhong et al. (2021) also reported that green manure (milk vetch) addition reduced the CH₄ emissions due to a reduction in the methanogenic cell abundance with soil C:N ratio and an increase in soil permeability. Additionally, Zhou et al. (2020b) indicated that leguminous green manure could decrease the CH₄ emissions by manipulating the abundances of both methanogens and methanotrophs. Overall, these observations show that it is likely that i) green manure (catch crop) is able to mitigate CH₄ emissions from paddies subjected to rice cropping systems; whilst ii) the variety/type of green manure, the trialed conditions, as well as soil factors (e.g., soil pH, nutrient level, functional microbial abundance, etc.) together add complexity to the CH₄ emission process and its mitigation from paddies.

It is noteworthy that continuous green manure amendment will inevitably alter soil fertility and re-shape the functional microbial communities over time. For example, Yang et al. (2014) showed that long-term green manure amendments could alter soil C:N ratio and the distribution/storage of carbon and nitrogen could significantly differ depending on green manure type. As per the soil microbial community, it has been proven that continuous green manure addition could alter the soil microbial community and re-shape it, especially within the area close to the rhizosphere (Elfstrand et al., 2007, Gao et al., 2015, Zhang et al., 2017). Particularly, Liu et al. (2016) found that green manure addition increased the abundance of methanotrophs in paddies, an increment disproportional with C:N ratio. Generally, paddy CH₄ emission is a complex by-product affected by nutrients input, soil functional microbial taxa, as well as soil physicochemical properties (Malyan et al., 2016, Mer and Roger, 2001, Yan et al., 2005). Combined analyses on the above factors raised the following questions i) what is the impact of the continuous green manure amendment on the CH₄ emissions from rice cropping systems, especially when different green manure types are applied; ii) what are the main control factors affecting CH₄ emissions under continuous green manure addition? Also, reduction on the chemical N input in the context of green manure addition is a highly recommended strategy (Xie et al., 2016). It is a common knowledge that chemical N fertilizer can affect CH₄ emissions. However the response of CH₄ emissions to N fertilizer remains controversial (Banger et al., 2012). The combined impact of continuous green manure addition and N application rate on CH₄ emissions in paddies is not yet well defined, similarly the sustainable crop productivity at these complex conditions.

Therefore, we hypothesized that catch crop with different C:N ratio may have an effect on CH₄ emissions in rice season by altering soil physicochemical properties and/or functional microbial abundance, especially in combination with different N application rate. To test the hypothesis, this study determined the effects of long term leguminous milk vetch (narrow C:N ratio) and non-leguminous ryegrass (wide C:N ratio) amendments on CH₄ emissions from paddies under two N fertilizer doses. The experiment was established in 2003 in Yixing City, China; the field observations were conducted on the 17th (2019) and the 18th (2020) year. This study is expected to introduce a concept of green manure (catch crop) amendment strategy to ensure crop productivity and mitigation of CH₄ emissions, subsequently limit climate change.

Section snippets

Experimental description

The experimental field plots were located at Weidu Village, Dapu Town, Yixing City, China (31º17.49′N, 119º54.02′E) with a subtropical monsoon climate. Daily ambient temperature and precipitation data were collected and presented (2019 and 2020) in Fig. 1. The trialed soil is classified as Gleyi-Stagnic Anthrosol (CRGCST 2001). Post-harvest data in 2020 were collected to express the soil physicochemical properties (topsoil).

The experimental setup/design has been provided by Lu et al. (2006) and

Soil fertility

The results showed that soil organic carbon (SOC) was significantly affected by green manure, but not by N application rate (Table 1). Compared with the fallow control, continuous green manure amendment resulted in SOC increase. The combined effect of green manure and N application rate though had a statistically significant effect. The SOC under HN treatment was higher than that under LN treatment in ryegrass addition plots. Conversely, the SOC with HN treatment was lower than that with LN

Soil fertility and crop yield

Green manure amendment in agro-ecosystems has been proved to be an efficiency strategy for the improvement of soil fertility (Xie et al., 2016, Yang et al., 2019, Zhou et al., 2020a). The results from this study confirmed that an increase in green manure amendment results in increased soil organic carbon. Notably, the combined effect of green manure and N application rate was found significant effect. Specifically, for the same green manure, the SOC under HN was found higher in ryegrass plots

Conclusions

This study assesses the impact of continuous catch crop planting (green manure addition), under different N application rate, on rice yield and the corresponding CH₄ emissions from paddies; it also delineates the main factors related to CH₄ emissions. Although CH₄ emissions were mainly related to the type of the green manure amendments used, rice yields under different green manure amendments and N application rates remained unchanged. Milk vetch addition for over 18 years at a low N

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (42077092; 41877087), the National Key Research and Development Program, Ministry of Science and Technology, China (2017YFD0300104), and Jiangsu Agriculture Science and Technology Independent Innovation Fund (CX(19)1007).

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Continuous milk vetch amendment in rice-fallow rotation improves soil fertility and maintains rice yield without increasing CH4 emissions: Evidence from a long-term experiment

Highlights

Abstract

Introduction

Section snippets

Experimental description

Soil fertility

Soil fertility and crop yield

Conclusions

Declaration of Competing Interest

Acknowledgements

Soil Biol. Biochem.

Appl. Soil Ecol.

J. Integr. Agric.

Sci. Total Environ.

Agric. Ecosyst. Environ.

Field Crops Res.

Agric. Ecosyst. Environ.

Agric. Ecosyst. Environ.

J. Integr. Agric.

Sci. Total Environ.

Org. Geochem.

Agric. Ecosyst. Environ.

Geoforum

Agric. Ecosyst. Environ.

Soil Biol. Biochem.

Sci. Total Environ.

Field Crops Res.

J. Integr. Agric.

Soil Biol. Biochem.

Environ. Pollut.

Continuous milk vetch amendment in rice-fallow rotation improves soil fertility and maintains rice yield without increasing CH₄ emissions: Evidence from a long-term experiment