Hyo Suk Gwon

Optimizing the harvesting stage of rye as a green manure to maximize nutrient production and to minimize methane production in mono-rice paddies.

Rye (Secale cerealis) has been widely cultivated to improve soil quality in temperate paddies. However, its biomass incorporation can significantly increase greenhouse gas emissions, particularly the emission of methane (CH4), during rice cultivation. The chemical composition and productivity of cover crop biomass may vary at different growing stages. Therefore, nutrient productivity and CH4 production potential might be controlled by selecting the optimum harvesting stage. To investigate the effect of rye harvesting stage on nutrient productivity and CH4 production potential, rye was harvested at different growing stages, from the flowering stage to the maturing stage, for seven weeks. The chemical composition and biomass productivity of rye were investigated. CH4 production was measured by laboratory incubation, and CH4 production potential was estimated to determine the real impact on CH4 dynamics in rice soils. Rye biomass increased with plant maturation, but nutrient productivities such as N (nitrogen), P2O5, and K2O were maximized at the flowering stage. The contents of cellulose and lignin increased significantly as plants matured, but the total N, labile organic carbon (C), and hot and cold water-extractable organic C clearly decreased. Soils were mixed with 0.3% (wt wt(-1) on dry weight) air-dried biomass and incubated to measure the maximum CH4 productivity at 30 °C under flooded conditions. Maximum CH4 productivity was significantly correlated with increasing labile organic C and protein content, but it was negatively correlated with total organic C, cellulose, and lignin content. CH4 production potentials were significantly increased up to the pre-maturing stage (220 DAS) and remained unchanged thereafter. As a result, CH4 production potential per N productivity was the lowest at the late flowering stage (198-205 DAS), which could be the best harvesting stage as well as the most promising stage for increasing nutrient production and decreasing GHG emissions in temperate mono-rice paddy soils.

Environmental risk assessment of steel-making slags and the potential use of LD slag in mitigating methane emissions and the grain arsenic level in rice (Oryza sativa L.)

Over the past decades, with increasing steel manufacturing, the huge amount of by-products (slags) generated need to be reused in an efficient way not only to reduce landfill slag sites but also for sustainable and eco-friendly agriculture. Our preliminary laboratory study revealed that compared to blast furnace slag, electric arc furnace slag and ladle furnace slag, the Linz-Donawitz converter (LD) slag markedly decreased CH4 production rate and increased microbial activity. In the greenhouse experiment, the LD slag amendment (2.0 Mg ha-1) significantly (p < 0.05) increased grain yield by 10.3-15.2%, reduced CH4 emissions by 17.8-24.0%, and decreased inorganic As concentrations in grain by 18.3-19.6%, compared to the unamended control. The increase in yield is attributed to the increased photosynthetic rates and increased availability of nutrients to the rice plant. Whereas, the decrease in CH4 emissions could be due to the higher Fe availability in the slag amended soil, which acted as an alternate electron acceptor, thereby, suppressed CH4 emissions. The more Fe-plaque formation which could adsorb more As and the competitive inhibition of As uptake with higher availability of Si could be the reason for the decrease in As uptake by rice cultivated with LD slag amendment.

Evaluation of Methane Oxidation Potentials of Alpine Soils Having Different Forestation Structure in Gajwa mountain

Abstract BACKGROUND: Forest soils contain microbes capable of consuming atmospheric methane (CH 4 ), an amount matching the annual increase in CH 4 concentration in the atmosphere. However, the effect of plant residue production by different forest structure on CH 4 oxidation is not studied in Korea. The objective of this study was to evaluate the effect of Korean alpine soils having different forestation structure on CH 4 uptake rates. METHODS AND RESULTS: the CH 4 flux was measured at three sites dominated with pine, chestnut and oak trees in southern Korea. The CH 4 uptake potentials were evaluated by a closed chamber method for a year. The CH 4 uptake rate was the highest in the pine tree soil (1.05 mg/m 2 /day) and then followed by oak (0.930 mg/m 2 /day) and chestnut trees (0.497 mg/m 2 /day). The CH 4 uptake rates were highly correlated to soil organic matter and moisture contents, and total microbial and methanotrophs activities. Different with the general concent, there was no any correlation between CH

Importance of Harvesting Time of Winter Cover Crop Rye as Green Manure on Controlling CH4 Production in Paddy Soil Condition

Winter cover crop cultivation provides high amount of organic matter when applied as green manure in paddy soils but can adversely increase methane (CH4) production during rice cultivation. Main organic components (cellulose, hemicellulose, lignin,) concentrations of cover crops may vary according to the different harvesting dates and might affect differently CH4 production in the paddy soil when applied as green manure. In this study, aboveground biomass of rye (Secale cereale L.) was harvested over a week interval for 9 weeks (April 23 to June 19) and then mixed with dried paddy soil with the rate of 5 Mg ha−1 on dry-weight base for incubation test. The concentration of total C, cellulose, and lignin of rye biomass was steadily increased with crop maturing, but total N and labile C concentrations were reversely decreased. Methane production activity has very high positive correlation with labile C (water-soluble C, hot-water-extractable C) concentration of rye biomass but negative correlation with C/N ratio, total C, and lignin concentrations. Therefore, CH4 production activity was higher in soils treated with early-harvested rye to that of the late-harvested rye treatment. Rye that was harvested on the 2nd–3rd week after the 1st harvesting date had slightly lower labile C but very high amount of total N, which could be the optimum harvesting period to regulate CH4 production without compromising its ability to provide added N supply when used as green manure in paddy soil. Conclusively, selection of the optimum period of rye harvesting is considerable to regulate CH4 production and improve soil fertility during green manure application in paddy soils.