Young Dae Choi has his expertise in soil chemistry. He has been working on plant nutrient and soil fertility management at the National Institute of Crop science in Korea for years. His research interests are the change of soil properties and soil management technology for sustainable upland crop cultivation in converted paddy field. Recent research subjects are assessment of long-term variability of soil environment by change of the usage pattern on paddy field and developing additional nitrogen fertilization method for yield increase in intensive cultivation of soybean at paddy field.
Recently, need of increasing upland crop cultivation in paddy field elevated due to growing importance of activating upland farming and overproduction of rice in South Korea. A yield of soybean decreased according to increase cultivation period in paddy field. The cause was widely known as soil organic matter content and soil nitrogen supply decrease. But paradoxical results existed. And the cause of yield decrease was also assumed that pH decrease according to cation leaching and phosphate availability decrease according to iron oxidation were related to. In order to prevent decreasing yield, it is necessary to identified the root cause. The objective of this study was to research for soil phosphate availability through investigating change of soil phosphorus distribution according to cultivation period of sorghum in paddy field. When converts paddy to upland, oxidation condition lasts and change of soil iron material occurs. Because high phosphorus adsorption coefficient lasted due to change of oxidation state in soil iron but soil organic phosphorus decreased exponentially, it was assumed that soil phosphate availability and crop productivity was limiting factor. This suggests that the limiting factor of soil fertility can be changed from C, N to P and change of soil management practices is required depending on the soil characteristics before cultivating upland crop such as amorphous iron content and phosphorus adsorption coefficient in converted paddy field.
Yang Gyu Ku, he is working in the department of Horticulture Industry, Wonkwang University, Republic of Korea, and it is a Good Agriculture Management Center, Wonkwang University.
Under abnormal climate conditions, due to the climate change, vegetable crops grown in the open field may encounter unfavorable growth conditions, resulting in physiological disruption, which may lead to economic damage. Chinese cabbage grown in the autumn season is confronted with drought conditions in a certain period, especially at an early growth stage after planting. The effects of drought stress on plant growth characteristics as well as carotenoid, free amino acid and proline contents were investigated in Chinese cabbage. The plant material used in this study was “Bool-am No. 3” Chinese cabbage. Chinese cabbage seeds were germinated, and all seedlings were transplanted into plastic containers (22 cm diameter×23 cm high) containing a commercial growth medium, followed by control and drought treatments. The soil water content was measured and maintained at 10% for the drought-stressed plants and at 30% for the control plants, for 3 weeks. The results showed that plant growth parameters were lower in the drought-stressed plants than in the control plants. The carotenoid and proline contents were unaffected in Chinese cabbage by drought treatment. The total free amino acid content tended to decrease in both drought-stressed and control plants over time; however, the decrease was greater in the drought-treated plants than in the control plants over the three week period. Consequently, the total free amino acid content was found to be lower in the drought-stressed plants than in the control plants.