Sang Yoon Kim

Contribution of winter cover crop amendments on global warming potential in rice paddy soil during cultivation

Background and aimsWinter cover crop cultivation during the fallow season has been strongly recommended in mono-rice paddy soil to improve soil quality, but its impact in increasing the greenhouse gases (GHGs) emissions during rice cultivation when applied as green manure has not been extensively studied. In order to recommend a preferable cover crop which can increase soil productivity and suppress GHG emission impact in paddy soil, the effect of winter cover crop addition on rice yield and total global warming potential (GWP) was studied during rice cultivation.MethodsTwo cover crops (Chinese milk vetch, Astragalus sinicus L., hereafter vetch, and rye, Secale cerealis) having different carbon/nitrogen (C/N) ratios were cultivated during the rice fallow season. The fresh above-ground biomasses of vetch [25xa0Mg fresh weight (FW) ha−1, moisture content (MC) 86.9xa0%, C/N ratio 14.8] and rye (29xa0Mg rye FW ha−1, MC 78.0xa0%, C/N ratio 64.3) were incorporated as green manure 1xa0week before rice transplanting (NPK + vetch, and NPK + rye). The NPK treatment was installed for comparison as the control. During the rice cultivation, methane (CH4) and nitrous oxide (N2O) gases were collected simultaneously once a week using the closed-chamber method, and carbon dioxide (CO2) flux was estimated using the soil C balance analysis. Total GWP impact was calculated as CO2 equivalents by multiplying the seasonal CH4, CO2, and N2O fluxes by 25, 1, and 298, respectively.ResultsMethane mainly covered 79–81xa0% of the total GWP, followed by CO2 (14–17xa0%), but the N2O contribution was very small (2–5xa0%) regardless of the treatment. Seasonal CH4 fluxes significantly increased to 61 and 122xa0% by vetch and rye additions, respectively, compared to that of the NPK treatment. Similarly, the estimated seasonal CO2 fluxes increased at about 197 and 266xa0% in the vetch and rye treatments, respectively, compared with the NPK control plots. Based on these results, the total GWP increased to 163 and 221xa0% with vetch and rye applications, respectively, over the control treatment. Rice productivity was significantly increased with the application of green manure due to nutrient supply; however, vetch was more effective. Total GWP per grain yield was similar with the vetch (low C/N ratio) and NPK treatments, but significantly increased with the rye (high C/N ratio) application, mainly due to its higher CH4 emission characteristic and lower rice productivity increase.ConclusionsA low C/N ratio cover crop, such as vetch, may be a more desirable green manure to reduce total GWP per grain yield and to improve rice productivity.

Methane emission and dynamics of methanotrophic and methanogenic communities in a flooded rice field ecosystem

Methane emissions, along with methanotrophs and methanogens and soil chemical properties, were investigated in a flooded rice ecosystem. Methane emission increased after rice transplantation (from 7.2 to 552 mg day(-1) m(-2) ) and was positively and significantly correlated with transcripts of pmoA and mcrA genes, transcript/gene ratios of mcrA, temperature and total organic carbon. Methane flux was negatively correlated with sulfate concentration. Methanotrophs represented only a small proportion (0.79-1.75%) of the total bacterial 16S rRNA gene reads: Methylocystis (type II methanotroph) decreased rapidly after rice transplantation, while Methylosinus and unclassified Methylocystaceae (type II) were relatively constant throughout rice cultivation. Methylocaldum, Methylobacter, Methylomonas and Methylosarcina (type I) were sparse during the early period, but they increased after 60 days, and their maximum abundances were observed at 90-120 days. Of 33 218 archaeal reads, 68.3-86.6% were classified as methanogens. Methanosaeta, Methanocella, Methanosarcina and Methanobacterium were dominant methanogens, and their maximum abundances were observed at days 60-90. Only four reads were characteristic of anaerobic methanotrophs, suggesting that anaerobic methane metabolism is negligible in this rice paddy system. After completing a multivariate canonical correspondence analysis of our integrated data set, we found normalized mcrA/pmoA transcript ratios to be a promising parameter for predicting net methane fluxes emitted from rice paddy soils.

Biotic Interactions in Microbial Communities as Modulators of Biogeochemical Processes: Methanotrophy as a Model System

Microbial interaction is an integral component of microbial ecology studies, yet the role, extent, and relevance of microbial interaction in community functioning remains unclear, particularly in the context of global biogeochemical cycles. While many studies have shed light on the physico-chemical cues affecting specific processes, (micro)biotic controls and interactions potentially steering microbial communities leading to altered functioning are less known. Yet, recent accumulating evidence suggests that the concerted actions of a community can be significantly different from the combined effects of individual microorganisms, giving rise to emergent properties. Here, we exemplify the importance of microbial interaction for ecosystem processes by analysis of a reasonably well-understood microbial guild, namely, aerobic methane-oxidizing bacteria (MOB). We reviewed the literature which provided compelling evidence for the relevance of microbial interaction in modulating methane oxidation. Support for microbial associations within methane-fed communities is sought by a re-analysis of literature data derived from stable isotope probing studies of various complex environmental settings. Putative positive interactions between active MOB and other microbes were assessed by a correlation network-based analysis with datasets covering diverse environments where closely interacting members of a consortium can potentially alter the methane oxidation activity. Although, methanotrophy is used as a model system, the fundamentals of our postulations may be applicable to other microbial guilds mediating other biogeochemical processes.

Cattle Manure Enhances Methanogens Diversity and Methane Emissions Compared to Swine Manure under Rice Paddy.

Livestock manures are broadly used in agriculture to improve soil quality. However, manure application can increase the availability of organic carbon, thereby facilitating methane (CH4) production. Cattle and swine manures are expected to have different CH4 emission characteristics in rice paddy soil due to the inherent differences in composition as a result of contrasting diets and digestive physiology between the two livestock types. To compare the effect of ruminant and non-ruminant animal manure applications on CH4 emissions and methanogenic archaeal diversity during rice cultivation (June to September, 2009), fresh cattle and swine manures were applied into experimental pots at 0, 20 and 40 Mg fresh weight (FW) ha−1 in a greenhouse. Applications of manures significantly enhanced total CH4 emissions as compared to chemical fertilization, with cattle manure leading to higher emissions than swine manure. Total organic C contents in cattle (466 g kg−1) and swine (460 g kg−1) manures were of comparable results. Soil organic C (SOC) contents were also similar between the two manure treatments, but dissolved organic C (DOC) was significantly higher in cattle than swine manure. The mcrA gene copy numbers were significantly higher in cattle than swine manure. Diverse groups of methanogens which belong to Methanomicrobiaceae were detected only in cattle-manured but not in swine-manured soil. Methanogens were transferred from cattle manure to rice paddy soils through fresh excrement. In conclusion, cattle manure application can significantly increase CH4 emissions in rice paddy soil during cultivation, and its pretreatment to suppress methanogenic activity without decreasing rice productivity should be considered.

Contribution of greenhouse gas emissions during cropping and fallow seasons on total global warming potential in mono-rice paddy soils

Background and aimsTemperate rice paddy fields are generally flooded for less than 100xa0days a year during the rice cropping season and are kept under dried soil conditions during the fallow season of over 200xa0days. The impacts of rice paddy soil on the global warming potential (GWP) are generally analysed during rice cultivation, without consideration of the fallow season, using only methane (CH4) and nitrous oxide (N2O) fluxes. To compare the impact of greenhouse gas (GHG) emissions during the flooded rice cultivation and the dried fallow seasons on the annual GWP in a mono-rice cultivation system, the emission fluxes of CH4, N2O and carbon dioxide (CO2) were evaluated under two different fertilization systems (NPK and NPK + Cover crop) for two consecutive years.MethodsIn the NPK + Cover crop treatment, a mixture of barley and hairy vetch were cultivated as a winter cover crop without fertilization during the fallow season. The total above-ground biomass (36xa0Mg fresh weight ha−1, moisture content 68.9xa0%, C/N ratio 20.6) was incorporated as a green manure one week before rice transplanting. The same levels of chemical fertilisers were applied for rice cultivation in the NPK and NPK + Cover crop treatments. The emission rates of CH4, CO2, and N2O gases were simultaneously monitored once a week using the closed-chamber method. However, because the CO2 fluxes included only soil respiration and excluded soil C sequestration through cover cropping and its recycling of biomass, the net ecosystem C budget (NECB), which is defined as the difference between total organic C input and output, was estimated to ascertain pure CO2 emission fluxes. Finally, the net global warming potential (GWP), which was calculated as CO2 equivalents by multiplying the seasonal CH4, CO2, and N2O fluxes by 25, 1, and 298, respectively, was compared between the two treatments and the two seasons.ResultsIn the NPK treatment, the annual net GWP value was 10.7–11.7xa0Mg CO2 eq. ha−1, in which approximately 56–62xa0% was affected by the seasonal net GWP value during the fallow season. Cover crop cultivation during the fallow season and its biomass addition as a green manure for rice cultivation significantly increased the total net GWP value to 28.2–31.5xa0Mgxa0ha−1, in which approximately 73–76xa0% was weighted by the seasonal net GWP value during rice cultivation. Carbon dioxide was the most influential GHG on increasing the growth scale of total net GWP during the dried fallow season, but CH4 most strongly influenced the annual net GWP scale during the rice cropping season, irrespective of soil management conditions. The contribution of CH4 to the annual net GWP value significantly increased as a result of cover crops biomass addition from 34–39xa0% in the NPK treatment to 88–91xa0% in the NPK + Cover crop treatment.ConclusionThe dried fallow season contributed to approximately 30–60xa0% of the annual net GWP scale through GHG emissions. Therefore, proper soil management strategies should be developed to decrease GHG emissions during the fallow season in mono-rice paddy fields.

Optimum application level of winter cover crop biomass as green manure under considering methane emission and rice productivity in paddy soil

The combined seeding and cropping of non-leguminous and leguminous cover crops during the cold fallow season is recommended as an important agronomic practice to improve total biomass productivity and soil fertility in mono-rice (Oryza sativa L.) cultivation system. However, application of plant residues as green manure can increase methane (CH4) emission during rice cultivation and affect rice quality and productivity, but its effects are not well examined. In this field study, the mixture of barley (Hordeum vulgare R.) and hairy vetch (Vicia villosa R., hereafter, vetch) seeds with 75xa0% recommended dose (RD 140xa0kg ha−1) and 25xa0% RD (90xa0kg ha−1), respectively, were seeded after rice harvesting in late November, 2010, and harvested before rice transplanting in early June 2011. Total aboveground biomass was 36xa0Mg ha−1 (fresh weight basis with 68xa0% moisture content), which was composed with 12xa0Mg ha−1 of barley and 24xa0Mg ha−1 of vetch. In order to determine the optimum recycling ratio of biomass application that can minimize CH4 emission without affecting rice productivity, different recycling ratios of 0, 25, 50, 75, and 100xa0% of the total harvested biomass were incorporated as green manure 1xa0week before rice transplanting in a typical temperate paddy soil. The same rates of chemical fertilizers (N–P2O5–K2Ou2009=u200990–45–58xa0kg ha−1) were applied in all treatments. Daily mean CH4 emission rates and total CH4 fluxes were significantly (pu2009<u20090.05) increased with increasing application rates of cover crop biomass. Rice productivity also significantly (pu2009<u20090.05) increased with biomass application, but the highest grain yield (53xa0% increase over the control) was observed for 25xa0% recycling. However, grain quality significantly (pu2009<u20090.05) decreased with increasing cover crop application rates above 25xa0% recycling ratio, mainly due to extended vegetative growth periods of rice plants. Total CH4 flux per unit grain yield, an indicator used to simultaneously compare CH4 emission impact with rice production, was not statistically different between 25xa0% biomass recycling ratio and the control but significantly increased with increasing application rates. Conclusively, the biomass recycling ratio at 25xa0% of combined barley and vetch cover crops as green manure might be suitable to sustain rice productivity without increasing CH4 emission impact in mono-rice cultivation system.

Effect of industrial by-products containing electron acceptors on mitigating methane emission during rice cultivation.

Three industrial by-products (fly ash, phosphogypsum and blast furnace slag), were evaluated for their potential re-use as soil amendments to reduce methane (CH(4)) emission resulting from rice cultivation. In laboratory incubations, CH(4) production rates from anoxic soil slurries were significantly reduced at amendment levels of 0.5%, 1%, 2% and 5% (wt wt(-1)), while observed CO(2) production rates were enhanced. The level of suppression in methane production was the highest for phosphogypsum, followed by blast slag and then fly ash. In the greenhouse experiment, CH(4) emission rates from the rice planted potted soils significantly decreased with the increasing levels (2-20 Mg ha(-1)) of the selected amendments applied, while rice yield simultaneously increased compared to the control treatment. At 10 Mg ha(-1) application level of the amendments, total seasonal CH(4) emissions were reduced by 20%, 27% and 25%, while rice grain yields were increased by 17%, 15% and 23% over the control with fly ash, phosphogypsum, and blast slag amendments, respectively. The suppression of CH(4) production rates as well as total seasonal CH(4) flux could be due to the increased concentrations of active iron, free iron, manganese oxides, and sulfate in the amended soil, which acted as electron acceptors and controlled methanogens activity by limiting substrates availability. Among the amendments, blast furnace slag and fly ash contributed mainly to improve the soil nutrients balance and increased the soil pH level towards neutral point, but soil acidity was developed with phosphogypsum application. Conclusively, blast slag among the selected amendments would be a suitable soil amendment for reducing CH(4) emissions as well as sustaining rice productivity.

Comparison of oyster shell and calcium hydroxide as liming materials for immobilizing cadmium in upland soil

Cadmium is both readily available and highly toxic to plants and animals. Our objectives were to evaluate the effect of oyster shell as a liming material on reducing plant cadmium (Cd) uptake and to compare oyster shell and Ca(OH)2, a common liming material in Korea. Ground oyster shell and Ca(OH)2 were applied at 0, 2, 4, and 8xa0Mg Ca per hectare to an upland soil contaminated manually with CdSO4 (total Cd 8.96xa0mg kg−1). Radish (Raphanus sativa L.) was sown on the contaminated soil. Oyster shell was less effective at increasing soil pH and net negative charge than Ca(OH)2, but more effective at suppressing radish Cd uptake in both roots and shoots. The portion of Cd that is strongly bound to soil (fraction 5) increased more with oyster shell than with Ca(OH)2. Radish plant Cd concentration was positively correlated with 0.1xa0N HCl-extractable Cd and negatively correlated with the residual Cd fraction (F5), indicating that an increase in the strongly bound Cd fraction played an important role in reducing radish Cd uptake in soil to which oyster shell was applied. The greater potential of oyster shell to decrease Cd extractability in soil and plant Cd uptake compared to Ca(OH)2 might be attributed to the layered morphology of oyster shells. Based on these results, oyster shell could be a very good alternative liming material to reduce Cd phytoavailability in Cd-contaminated soil.

Unexpected stimulation of soil methane uptake as emergent property of agricultural soils following bio‐based residue application

Intensification of agriculture to meet the global food, feed, and bioenergy demand entail increasing re-investment of carbon compounds (residues) into agro-systems to prevent decline of soil quality and fertility. However, agricultural intensification decreases soil methane uptake, reducing, and even causing the loss of the methane sink function. In contrast to wetland agricultural soils (rice paddies), the methanotrophic potential in well-aerated agricultural soils have received little attention, presumably due to the anticipated low or negligible methane uptake capacity in these soils. Consequently, a detailed study verifying or refuting this assumption is still lacking. Exemplifying a typical agricultural practice, we determined the impact of bio-based residue application on soil methane flux, and determined the methanotrophic potential, including a qualitative (diagnostic microarray) and quantitative (group-specific qPCR assays) analysis of the methanotrophic community after residue amendments over 2xa0months. Unexpectedly, after amendments with specific residues, we detected a significant transient stimulation of methane uptake confirmed by both the methane flux measurements and methane oxidation assay. This stimulation was apparently a result of induced cell-specific activity, rather than growth of the methanotroph population. Although transient, the heightened methane uptake offsets up to 16% of total gaseous CO2 emitted during the incubation. The methanotrophic community, predominantly comprised of Methylosinus may facilitate methane oxidation in the agricultural soils. While agricultural soils are generally regarded as a net methane source or a relatively weak methane sink, our results show that methane oxidation rate can be stimulated, leading to higher soil methane uptake. Hence, even if agriculture exerts an adverse impact on soil methane uptake, implementing carefully designed management strategies (e.g. repeated application of specific residues) may compensate for the loss of the methane sink function following land-use change.

Manure-associated stimulation of soil-borne methanogenic activity in agricultural soils

The growing human population and scarcity of arable land necessitate agriculture intensification to meet the global food demand. Intensification of agricultural land entails manure input into agrosystems which have been associated to increased methane emission. We investigated the immediate short-term response of methane production and the methanogens after manure amendments in agricultural soils and determined the relevance of the manure-derived methanogenic population in its contribution to soil methane production. We followed methane production in a series of unamended and manure-amended batch incubations: (i) manure and soil, (ii) sterilized manure and soil, and (iii) manure and sterilized soil. Moreover, we determined the methanogenic abundance using a quantitative PCR targeting the mcrA gene. Results show that the soil-borne methanogenic community was significantly stimulated by manure amendment, resulting in increased methane production and mcrA gene abundance; manure-derived methanogenic activity contributed only marginally to overall methane production. Accordingly, our results highlighted the importance of the resident methanogenic community and physiochemical properties of a residue when considering methane mitigation strategies in agricultural soils.