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Corn was mainly cultivated in slope land during summer season when heavy rain falls so that soil loss occurs severely. Especially, soil disturbance and exposure of topsoil by conventional tillage intensifies soil loss by heavy rain. The aim of this study was to develop surface covering and tillage methods for reducing soil loss in corn cultivation. The experiment was conducted in 17% sloped lysimeter with 8 treatments including strip tillage after surface covering with rye residue, strip tillage after residue covering of several crops and sod culture, black polyethylene film covering after conventional tillage and control. Amount of runoff water and eroded soil, and corn growth were investigated. Amounts of runoff water in all plots except black polyethylene plot ranged from 152 to 375 m 3 ha -1 , accounting for 13~32% of 1,158 m 3 ha -1 in control. Amount of eroded soil decreased by 94 to 99% (3 to 89 kg ha -1 ) in plots of strip tillage after covering with crop residues compared to control with 1,739 kg ha -1 . Corn yields in plots of strip tillage after covering with crop residues ranged from 6.0 to 6.9 Mg ha -1 , while that of control was 6.5 Mg ha -1. The results suggest that strip tillage methods after surface covering with crop residues are very effective on soil conservation of slope land in corn cultivation.

BACKGROUND:The reclaimed lands for agricultural use managed by the Korean government is consisted of 17,145 hectares of lands under construction and 13,384 hectares of completed lands. In order to utilize these reclaimed lands as competitive agricultural complexes, the government is preparing to develop comprehensive development plans for multiple purposes. For rational land-use planning and soil management, information of the soil chemical properties is necessary. METHODS AND RESULTS: From 2013 to 2016, soil samples were collected from 85 representative sampling sites of the reclaimed lands and analyzed for soil chemical properties including electric conductivity (EC), pH, soil organic matter (SOM), and nutrients. The annual mean soil EC ranged from 5.1 to 8.3 dS m -1 and have continued to decrease over the years (estimation equation with EC as dependent and year as independent variable was y = 0.0736x 2 -1.4985x + 9.8305, R 2 = 0.9753). The pH ranged from 7.3 to 7.6, which was higher than the optimum range (5.5~7.0) for agricultural soils. Soil organic matter (8 to 11 g kg -1 ) was lower level than the optimum range (20~30 kg -1 ). Available silicate (Av.SiO 2 ) ranged from 169 to 229 mg kg -1 , which was close to the minimum content (≥157 mg kg -1 ) for rice paddy field. Available phosphate (Av.P 2 O 5 ) content (24~39 mg kg -1 ) was lower than the optimum range (80~120 mg kg -1 ) for rice paddy field. CONCLUSION: For efficient agricultural use of reclaimed lands under government management, our results suggest that the application of organic matter and supplying deficient nutrients as well as desalinization is required.

Several our studies have focused recently on the mass production of the freshwater Cladoceran Moina macrocopa which can substitute Artemia nauplii for the culture of larval marin fish. A 6 weeks experiment was conducted to investigate the effects of enrichment on the fatty acid composition of Moina macrocopa through feeding Schizochytrium sp. containing highly unsaturated fatty acids and to study the impacts of n-3-HUFA enriched Moina on improving survival rate and fatty acid compostion of larval rockfish Sebastes schlegeli. After feeding for 6 weeks, the Moina-fed fry resulted in a higher survival rate of 99.2% compared to the Artemia-fed fry 12.8%. In addition, the Moina-fed fry had the fast growth rate 45.6mm compare to the Artemia-fed fry 25.7 mm at the end of the experiment. The Moina-fed fry showed significantly higher level of 16.47% DHA than their Artemia-fed fry counterparts of the level of 3.97% with respect to DHA. PL, the cell membrane components in living food organisms, constituted 63.8% of the Moina, which was significantly higher than in the 40.1% of the Artemia. The present study indicate that Moina macrocopa can be used as Artemia substitute and improving the survival rate rockfish larvae through enchriment Schizochytrium sp.

This research was conducted to investigate the possibility of reeds (Phragmites australis) application to increase the low organic matter content in the reclaimed soil. Reed is not only a perennial vegetation native growing in the reclaimed land and a plant promising for soil organic resources as it is regenerated every year and also has a lot of biomass. In order to establish the system to increase the soil organic matter content, the reed residue was put into the soil using a tractor in different periods. After the growth, the reed straw was put into the soil at mid-September, mid-November and mid-February of the following year during 1 st , 2 nd and 3 rd year. Soil chemistry showed no difference in pH and EC was slightly higher at constant three years of return plot. Carbon content increased at all treatments with increasing the number of application regardless of the treatment season. The amount of soil organic content increased with increasing the number of application comparing to 4.65 g kg -1 in soil with the preserved reed. This also increased to 8.01 g kg -1 , 6.85 g kg -1 and 7.02 g kg -1 when the treatment was continued at mid-September, mid-November and mid-February for three years, respectively. This clearly showed that the application of reed straw to the soil was effective to improve soil fertility. Therefore, in order to increase the organic content of the reclaimed soil, it would be effective that the body part of reed is returned to the soil at mid-September of each year after the growth of reed is completed.