• Journal of Korea Water Resources Association
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• v.55 no.12
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• pp.1065-1076
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• 2022

The purpose of this study was to investigate the effect of the expansion and withering of Salix subfragilis communities on the water quality in Namgang Dam reservoir. The distribution area of the Salix subfragilis communities was 0.12 km² in 2003 for the first time, but it was 3.58 km² in 2019, which has increased rapidly by about 30 times in 16 years. However, in 2013, the distribution area has decreased by 0.17 km² due to long-term immersion in high turbidity, and self-thinning in Salix subfragilis communities. The lake characteristics of reservoir showed a combination of lake type and river type in terms of average water depth, watershed area/lake surface area ratio, water residence time, flushing rate, and stratification. From the result of analyzing long-term changes in lake water quality, COD, TP, and chlorophyll-a in Salix subfragilis communities were significantly larger than those in the three points located in the central part of reservoir. In particular, the fact that the value of chlorophyll-a showed the maximum value in winter rather than summer, unlike the trend of the three points in the Namgang Dam water quality monitoring network, is thought to have occurred internally rather than externally. It can be estimated that one cause of this deterioration of the water quality in Namgang Dam reservoir is the huge amount of nutrients generated in the decomposition process of by-products such as fallen leaves, branches and withered trees in Salix subfragilis communities.

• Korean Journal of Soil Science and Fertilizer
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• v.1 no.1
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• pp.89-115
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• 1968

1. The experiment was carried out for investigating the interaction between potassium nutrition and thermoperiod (as an environment regulating factor) in relation to behaviors of several nutrients including phosphorus-32 and Potassium-42 in IPOMOEA BATAS. 2. To obtain same condition to trace the behaviors of phosphorus and potassum-42 they were simultaneously incorporated to roots. The determination of each CPM by counting twice with adequate interval and calculating true CPM of each isotope according to different half-life, was carried out with satisfactory. 3. Some specific symptoms i.e, chlorosis and withering of growing point under the condition of lower potassium level were found and was accelerated by the low night temperature. 4. A manganese shortage in growing point of the lower potassium level was found by activiation analysis and very low distribution ratio of phosphorus-32 and potassium-42 in the growing point of the lower potassium level was manifested, though the contents of nitrogen, phosphorus, potassium, sodium and magnesium were not in great difference. 5. In addition to the low water content with appearence of "hard", shorterning internode and lower ratio of roots to shoot as well as the symptoms of potassium deficiency such as brown spot in leaf blade and necrosis of leaf margin were appeared at later stage of experiment at the lower potassium level. 6. Very stimulating vegetative growth, e.g, large plant length, leaf expansion, increasing node number and fresh weight as well as high ratio of roots to shoot, high water content was resulted in the condition of higher potassium level. 7. A specific interaction between higher potassium level and thermoperiod was found, that is, the largest tuber production and the largest ratio of roots to shoot were resulted in the combined condition of higher potassium level and constant temperature while the largest plant length, fresh weight etc. i.e. the most stimulative vegetative growth was resulted in the combined condition of higher potassium level and low night temperature. 8. Comparatively low water content in the former condition of stimulative tuber production was resulted(especially at the tuber thickening stage), while high water content in the latter condition of stimulative vegetation was resulted though the higher potassium level made generally high water contents. 9. The nitrogen contents of soluble and insoluble did not make distinct difference between the lower and higher potassium level. 10. Though the phosphorus contents were not distinctly different by the potassium level, the lower potassium level made the percentage of phosphorus increased at tuber forming stage accumulating more phosphorus in roots, while the higher potassium level decreased percentage of phosphorus at that stage. 11. The higher potassium level made distinctly high potassium contents than the lower potassium level and increased contents at the tuber forming stage through both conditions. 12. The sodium contents were low in the condition of higher potassium level than the lower potassium level and decreased at tuber forming stage in both conditions, on the contary of potassium. 13. Except the noticeable deficeney of manganese in the growing point of the lower potassium level, mangense and magnesium contents in other organs did not make distinct difference according to the potassium level. 14. Generally more uptake and large absorption rate of phosphorus-32 and potassium-42 were resulted at the higher potassium level, and the most uptake, and the largest absorption rate of phosphorus and potassium-42 (especially potassium-42 at tuber forming stage) were resulted in the condition of higher potassium level and constant temperature which made the highest tuber production. 15. The higher potassium level stimulated the translocation of phoshorus-32 and potassium-42 from roots to shoots while the lower potassium level suppressed or blocked the translocation. 16. Therefore, very large distribution rate of $p^{32}$, $K^{42}$ in shoot, especially, in growing point, compared with roots was resulted in the higher potassium level. 17. The lower potassium level suppressed the translocation of phosporus-32 from roots to shoot more than that of potassium-42. 18. The uptake of potassium-42 and translocation in IPOMOEA BATATAS were more vivid than phosphorus-32. 19. A specific interaction between potassium nutrition and thermoperiod which resulted the largest tuber production etc. was discussed in relation to behaviors of minerals and potasium-42 etc. 20. Also, the specific effect of the lower and higher potassium level on the growth pattern of IPOMOEA BATATAS were discussed in relation to behaviors of minerals and isotopes. 21. An emphasize on the significance of the higher potassium level as well as the interaction with the regulating factor and problem of potassium level (gradient) for crops product ion were discussed from the point of dynamical and variable function of potassium.