Hyeoun-Suk Cho

Evaluation of regional climate scenario data for impact assessment of climate change on rice productivity in Korea

Spatial evaluation of the uncertainty associated with climate data would allow reliable interpretation of simulation results for regional crop yield using gridded climate data as input to a crop growth model. The objective of this study was to examine the spatial uncertainty of regional climate model data through determining optimal seeding date with the ORYZA2000 model for assessment of climate change impact on rice productivity in Korea. The optimal seeding date was determined at each grid point using regional climate model outputs under the RCP 8.5 scenarios. In major rice production areas such as inland plain regions, where temperatures of regional climate data were relatively accurate, the optimal seeding date determined using those gridded data were reasonable. However, areas with complex terrains including areas near bodies of water, e.g. coastal areas, riverbasins, lakes, and mountainous areas, had a relatively large uncertainty of the optimal seeding date determined using the regional climate data. These results indicated that the uncertainty of regional climate data at a high spatial resolution of 12.5 km should be taken into account in the regional impact assessment based on crop growth simulations in Korea. In addition, further studies would be merited to assess the impact of climate change on rice yield at an ultra-high spatial resolution of 1 km in Korea. Crop yields were projected to decrease after the 2020s when crop yield simulations from inland plain areas were considered, which suggested that adaptation strategies should be established and implemented in the near future.

Changes in Carbon Amount of Soil and Rice Plant as Influenced by the Cultivation of Different Green Manure Crops

A green manure crop were used in many ways, such as for reducing chemical fertilizer, improving physical and chemical properties of soils, protecting soil loss, and creating landscape when its grown in agricultural land. Experiments were conducted to find out carbon emitted with applying green manure crops in paddy field. Amounts of carbon absorbed in the green manure crops during the winter were 1.22 ton in hairy vetch, 1,24 ton in barley, and 1.54 ton in hairy vetch/barley. The soil carbon content was the highest at days before transplanting of rice and decreased after days after harvesting the plant. Soil carbon contents were higher with hairy vetch or barley treatment than with hairy vetch/barley treatment. The content of emitted methane () was the highest at 7 days after transplanting rice plant, and was 17 ~ 25 times higher with green manure treatments than with chemical fertilizer application. The emission was the highest with hairy vetch treatment and than followed by hairy vetch/barley and barley treatments. The content of carbon absorbed in rice plant increased during the cultivation period but was not different with the applications of different green manure crops. The yield amounts of rough rice and rice strow were 5 ~ 13% higher with the green manure treatments than the chemical fertilizer application. In particular, they were the highest with hairy vetch/barley treatment as 14.07 ton .

The Characteristics of Growth and Green Manure Yield by Different Kinds of Landscape Crops Cultivated in Summer in Upland Soil

Landscape crops have decorated its surrounding landscape by being cultivated from spring to late fall. Recently, landscape crops are starting to get the limelight as crops that can be cultivated in large area farmlands. Therefore, we examined the growth characteristics of landscape crops, green manure yield and nitrogen production of crops that are cultivated during summer, which are sunflower, cosmos, sunnhemp and sesbania, in order to select crops that can be utilized as landscape crops and green manure crops. The height of landscape crops increased when the harvest time was later. Especially, sunnhemp, cosmos, sunflower and sorghum grew over 100cm. The days to flowering of sunnhemp and cosmos were 50 and 53 days each, and their flowering period of more than 50 days were long. The days to flowering of sunflower, which was 52 days, was short, and its flowering period, which was 21 days, was also short. When the harvest time was later, the green manure yield and nitrogen production of all crops increased. Individually, the green manure yield was higher in sunnhemp, sorghum, sunflower, with 7.2~7.5 Mg ha -1 , and was lowest in sesbania. The nitrogen production was higher in sunnhemp, with 168.1 kg ha -1 Therefore, as seen in its flowering characteristics, green manure yield and nitrogen production, sunnhemp had the best green manure and landscape effects among the landscape crops for summer.

Yield of Green Manure and Nitrogen of Cornflower (Centaurea cyanus L.) in Different Upland Soil Textures

Experiments were conducted to find out the landscape effects and green manure production at the same time in farmland. Cornflower was grown in different soil texture with sand, sandy loam, loam, clay loam, and was sowing with autumn and spring respectively. The overwintering rate of cornflower was at 58.7% in average, and the treatment at sand soil showed 62.1% that was highest among other soils, which cornflower is possible to winter landscape crop. After flowering of cornflower, the contents of total nitrogen (T-N) and total carbon (T-C) in plant were 15.0 and , respectively, and the carbon-nitrogen ratio (C/N) was 28.6. The yield of cornflower biomass, which will be returned to soil as green manure, recorded at the spring seeding higher than the autumn seeding as , and the biomass treated by soil texture were showed that the treatments at the clay loam had been the largest yields both spring and autumn seeding among at other treatment of soil. The heights of cornflower regardless of soil treatments were 52.8 to 73.6 cm at the autumn seeding and 35.5 to 79.2 cm at the spring seeding although it was more significant variation at the soil textures than the seeding periods. The flowering periods of cornflower ranged from to in May at the autumn seeding and from to in June at the spring seeding, which was faster 30 days approximately at the autumn seeding than the spring seeding. In a view of the cornflower application as green manure after flowering, the autumn seeding, when considered to combine with following crops, was more suitable and various than the spring seeding, even though the yield at spring seeding was higher than one at autumn seeding.

Determining the minimum threshold temperature for normal maturation of temperate rice in South Korea

[Introduction] The late marginal heading date for normal maturation is essential to determine the range of late transplanting date. A minimum threshold temperature for normal maturation has been used to determine the late marginal heading date. In this study, a statistical procedure was developed to determine the threshold temperature for new Korean varieties for 40 days of grain filling period. [Material and Method] The threshold temperature was chosen to be the minimum temperature at which grain filling ratio and weight are minimally affected. To identify the threshold temperature, grain filling ratio and weight, which were observed at Suwon and Iksan with four transplanting date (25th Jun, 2nd Jan, 9th Jan, 16th Jan) for two years in Korea, were compared with a cumulative temperature during 40 days of grain filling stage. [Results] The accumulated temperature between 800 and 840 oC would be the point of inflection, which could be used as the threshold temperature in relative grain filling ratio (Fig 1). In contrast, the relative 1000 grain weight decreased significantly only when the accumulated temperature was lower than 760oC (Fig 2). Compared with the relative grain filling ratio, the relative 1000 grain weight would not decrease at lower temperature during grain filling period. Still, it would be preferable to choose conservative criteria for determination of the threshold temperature for normal maturation. Therefore, it would be suitable to choose 800oC as the threshold temperature for normal maturation

Responses of Soybean Yield to High Temperature Stress during Growing Season: A Case Study of the Korean Soybean

In soybeans, responses of high temperature according to shift of sowing dates during the growing season was explored using the crop model, CROPGRO-soybean. In addition, it analyzed impact on change of sowing dates affects yield potential of soybean under future climate scenario (2041-2070). In Jeonju and Miryang during 1981-2010, if sowing at 15 or ten days ahead from 10 June, namely in shorten of the sowing day (i.e. when sown on 25 or 30 May), the yield potential reduced. However, the yield potential increased when sown 5 June. In the case of delay of sowing day (i.e. when sown on 15 or 20 June), reduction of yield potential in the average -5% was higher than increase in the average +2%. In particular, the relative changes for shorten of the sowing day or delay of the sowing day do not be shown in normal years which high temperatures did not abnormally occur during the growing season from 2003 to 2010 except when sown on 25 May. In abnormal years which high temperatures occurred during the critical period, especially R5 to R7, shorten of the sowing day affected to the increase of yield potential in Miryang, while the yield potential decreased in Jeonju except when sown on 5 June. However, delay of the sowing day influenced on the reduction of yield potential both in two sites. In future climate scenario of Representative Concentration Pathway (RCP) 8.5 during from 2041 to 2070, the increase and decrease of yield potential for shorten of the sowing day were +10/-9% for RCP 8.5 of Jeonju, and +14/-9% for RCP 8.5 of Miryang, respectively. Additionally, it showed +10/-17% for RCP 8.5 in Jeonju, and +10/-29% for RCP 8.5 in Miryang, respectively in the increase and decrease of yield potential for delay of the sowing day.

Influence of Upland Soil Texture on Dry Weight and Growth of Yellow Mustard as a Landscape and Green Manure Crop

Although it is not a landscape crop according to MIFAFF(ministry of agriculture, food and rural affairs), yellow mustard is considered a superb landscape crop because of its growth and flower characteristics. We sowed yellow mustard as a landscape and green manure crop in upland soil (four types of soil texture) in spring. And we studied its flowering characteristics, dry weight, and nitrogen yield. The growths of yellow mustard were possible in every soil ranging from sandy soil to clay loam. Its height was 54.1 ~ 76.1cm and the number of node per hill was 11.3 ~ 17.0. Its flowers had a light yellow. It took about 44 ~ 50 days to flower, and flowered for 22~25 days. The dry weight of yellow mustard was 2.27 ~ 3.60 ton ha -1 with highest in sandy loam and loam. Among the nutrients of yellow mustard, nitrogen(T-N) was 12.6~20.8 g kg -1 , and C/N ratio was 21.6~37.7. The nitrogen yield of yellow mustard was 35 ~ 62 kg ha -1 . In conclusion, because of its flowering characteristics and dry weight, yellow mustard was considered appropriate for both green manure and landscape crop uses.

Effect of seeding rate of Crotalaria (Crotalaria juncea L.) on Green Manure Yield and Nitrogen Prodution in Upland Soil

We researched nitrogen and green manure yield of crotalaria by seeding rate; 50, 60, 70, 80, 90 kg ha -1 in upland soil to find out crotalarias optimal seeding rate. Crotalarias plant height and number of leaves increased when the harvest time was later regardless of its seeding rate. Its nitrogen content of above-ground part was 19.8 g ha -1 , and C/N ratio was 22.5. The highest nitrogen content (50.3 g kg -1 ) was found in flowers part, followed by its leaves, roots and stems. The green manure yields of crotalaria increased when the harvest time was later. The green manure yield of crotalaria was biggest in 50kg ha -1 which was low in seeding rate. It tended to decrease when the seeding rate was higher, and the nitrogen yield had the same tendency. Therefore, the appropriate seeding rate was 50kg ha -1 and the time for application to soil was considered to be the flowering stage.