Effects of biochar amendment on the net greenhouse gas emission and greenhouse gas intensity in a Chinese double rice cropping system

doi:10.1016/j.ejsobi.2014.09.001

European Journal of Soil Biology

Volume 65, November–December 2014, Pages 30-39

https://doi.org/10.1016/j.ejsobi.2014.09.001 Get rights and content

Highlights

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Biochar amendment in paddy fields reduced CH₄ emissions.
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N₂O emissions increased by biochar amendment.
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Soil Rh increased in a short period by biochar amendment.
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Net GHG emission and GHG intensity reduced by biochar amendment.

Abstract

The impacts of biochar amendment on the net greenhouse gas emission (NGHGE) and greenhouse gas intensity (GHGI) of double rice cropping systems are not well examined. In this study, a field experiment was carried out to investigate the effects of biochar amendment on NGHGE and GHGI emissions in a subtropical double rice cropping system managed with intermittent flooding during two rice-growing seasons and drainage during a fallow season from April 2012 to April 2013. Three biochar treatments were studied, with application rates of 0, 24 and 48 t ha⁻¹ (named CK, LC and HC, respectively). In each treatment, the fluxes of methane (CH₄), nitrous oxide (N₂O) and soil heterotrophic respiration (Rh) were measured using a static chamber/gas chromatography method. Key soil properties related to greenhouse gas (GHG) emissions were also determined throughout an entire double rice cycle. The results showed that biochar amendment significantly reduced annual CH₄ emissions by up to 40% compared with the CK treatment, possibly due to the soil pH increase after biochar amendment other than increased soil aeration. In contrast, annual N₂O emissions significantly increased by 150% and 190% in the two biochar treatments, compared with the CK treatment, which may be related to the increase of soil dissolvable organic C or NH₄⁺ in the biochar treatments. The cumulative Rh significantly increased by 19% in the HC treatment possibly due to the additional carbon dioxide (CO₂) emissions from decomposition of the labile C within biochar, but showed no increase and even a decrease in the LC treatment throughout the study period. Annually, the global warming potential for CH₄ and N₂O emissions, NGHGEs, and GHGIs in the biochar amendment treatments were reduced by 31–36%, 1551–2936% and 1452–2894%, respectively (p < 0.05). Our collective data may suggest that as the rice grain yield was improved by the biochar amendment found in this study, the biochar application in paddy fields may be an effective measure for GHG emission mitigation in the subtropics.

Introduction

Biochar is the carbon (C)-rich solid obtained from biomass pyrolysis [1]. It has high C content and is highly stable due to its conjugated aromatic structures, which make it more recalcitrant to be degraded in the natural environment than the pre-processed feedstock material [2]. Thus, it can be stored for long periods in soil as a measure of carbon sequestration [3]. Biochar amendment can also be used to increase crop yields [1]. As reported by Alburquerque et al. [4], biochar amendment can increase wheat yield by 20–30% compared with an unamended control. Moreover, several studies have shown that biochar amendment contributes to reducing soil greenhouse gas (GHG) emissions [5], [6], [7]. Wu et al. [5] reported that wheat straw-derived biochar amendment dramatically reduced nitrous oxide (N₂O) emissions, but had no significant effect on carbon dioxide (CO₂) and methane (CH₄) emissions, compared with an unamended Chernozemic soil. In an incubation study, Liu et al. [6] found that both the rice straw- and bamboo-derived biochar amendments reduced CH₄ and CO₂ emissions in paddy soils. Karhu et al. [7] reported that the birch derived biochar amendment increased CH₄ uptake by 96%, but showed no significant effect on N₂O and CO₂ emissions in on an upland agricultural soil in Southern Finland. Those studies indicated that except for increasing soil carbon sequestration, biochar amendment to agricultural soils could also reduce CH₄ or N₂O emissions and increase crop yields in some degree.

In previous field studies, the effects of biochar amendment on GHG emissions were primarily analyzed in rice-wheat rotation systems or upland fields [7], [8], [9], [10]. Few studies have examined the impact of biochar in the double rice cropping system (in which the paddy field is cultivated with rice (one for early rice and the other for late rice) twice a year), which constitute a large area in subtropical and tropical regions of Asia (e.g. China, Thailand, Malaysia and Vietnam). In a former study of Liu et al. [11], the wheat straw biochar amendment depressed N₂O emissions in the late rice season of the double rice cropping system at two sites in Southern China. Using the corn stalk biochar to amend to a soil collected from a double rice field, however, Xie et al. [12] found that biochar amendment via an incubation experiment did not influence CH₄ and N₂O emissions. The double rice cropping system is usually submerged during the rice-growing season, with soils under this regime possessing a low Eh and relatively high soil organic C content. These conditions are highly conducive to GHG emissions, especially for CH₄ [13], [14], which is the main greenhouse gas emitted from paddy fields. Biochar amendment could improve soil aeration [15], [16] and thus may increase CH₄ oxidization and therefore reduce CH₄ in the double rice cropping system. In addition, when considering the effects of biochar amendment on GHG emissions, the emissions or net exchanges of the three main greenhouse gases (i.e. CO₂, CH₄, and N₂O) should be considered comprehensively to calculate the net greenhouse gas emissions (NGHGE) [17]. However, the effects of biochar amendment on NGHGE (a full-scale evaluation of the effects of biochar on GHG mitigation) remain rarely quantified in the double rice cropping system.

In the present study, a field experiment was performed in a paddy field in subtropical central China with the following ultimate aims: (i) to measure the fluxes of CH₄, N₂O and soil heterotrophic respiration (Rh), (ii) to identify the key soil properties that influence these GHG emissions and (iii) to quantify the annual NGHGE and greenhouse gas intensity (GHGI) in a double rice cropping system with the different biochar amendment rates. The specific hypothesis tested in this study was that the biochar amendment in the double rice cropping systems can: (i) reduce GHG emissions and (ii) decrease the global warming potential for CH₄ and N₂O emissions (GWP), NGHGE and GHGI.

Section snippets

Experimental site and biochar

The plot experiment was performed in a paddy field (113°19′52″E, 28°33′04″N, 80 m a.s.l.), typical of those used for double rice production in Jinjing of Changsha County in Hunan Province in subtropical central China. The soils at the site is classified as Stagnic Anthrosols [18] developed from granite-weathered red soil. The study region is characterized by a subtropical humid monsoon climate. The annual mean precipitation, air temperature, sunshine hours, and frost-period are 1330 mm,

Dynamics of soil properties

Dynamics and mean values of soil major chemical and biological properties (NH₄⁺–N, DOC, MBC, pH and Eh) in different rice seasons are shown in Fig. 1 and Table 2, respectively. Soil NH₄⁺–N contents increased significantly in the biochar amendment treatments (LC and HC) as compared with the control treatment (CK) in the early rice season (p < 0.05), but this increase was not observed (even decreases in soil NH₄⁺–N content were observed) in the biochar treatments in the following late rice season

Effect of biochar amendment on CH₄ emissions

CH₄ is the main GHG emitted from paddy fields [14], [29], [30]. In this study, CH₄ emissions decreased in paddy fields with biochar amendment. The finding was consistent with the results of Feng et al. [31] and Liu et al. [6], but inconsistent with Zhang's [10] study. Reduced CH₄ emissions from paddy soils with biochar amendment have been ascribed to increased methanotrophic proteobacterial abundance [31] or decreased methanogenic activity [6]. In this study, soil pH increased significantly

Conclusions

In this study, we observed the annual dynamics of the fluxes of CH₄, N₂O and Rh for different biochar amendment rates in a double rice cropping system with the intermittent flooding during the rice-growing seasons and the drainage during the fallow season. We found persistent decreased CH₄ emissions in two rice-growing seasons and a fallow season with biochar amendment compared with the control treatment. In contrast, the annual N₂O emissions were increased with the biochar amendment. Rh rates

Acknowledgments

This research was financially supported by the National Basic Research Program of China (2011CB100506 & 2012CB417105), the National Natural Science Foundation of China (41090283 & 41101247) and the Natural Science Foundation of Hunan province (13JJ4114). We also thank the two anonymous reviewers for their suggestions for improving the manuscript.

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Original articleEffects of biochar amendment on the net greenhouse gas emission and greenhouse gas intensity in a Chinese double rice cropping system

Highlights

Abstract

Introduction

Section snippets

Experimental site and biochar

Dynamics of soil properties

Effect of biochar amendment on CH4 emissions

Conclusions

Acknowledgments

Agr. Ecosyst. Environ.

Soil Biol. Biochem.

Soil Biol. Biochem.

Agr. Ecosyst. Environ.

Ecol. Eng.

Field Crop Res.

Agr. Ecosyst. Environ.

Agric. For. Meteorol.

Agr. Ecosyst. Environ.

Agr. Ecosyst. Environ.

Agr. Ecosyst. Environ.

Agr. Ecosyst. Environ.

Soil Biol. Biochem.

Soil Biol. Biochem.

Agr. Ecosyst. Environ.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Original article
Effects of biochar amendment on the net greenhouse gas emission and greenhouse gas intensity in a Chinese double rice cropping system

Effect of biochar amendment on CH₄ emissions