In plant cultivation, nutrient retention is associated with variable and permanent charges in the soil. In this study, we cultivated mini tomato plants in 2 types of soil and investigated the absorption of nutrients in these plants. Andosols have a variable charge, whereas Fluvisols have a permanent charge. Our results showed that in plants grown in Andosols, the nitrogen content of plants varied with soil (pH=5.3, 5.8, 6.3, and 6.8) and was 3.48%, 2.83%, 2.44%, and 2.90%, respectively. The potassium content of plants grown at soil pH=5.3, 5.8, 6.3, and 6.8 was 4.34%, 5.08%, 3.86%, and 4.89%, respectively. For plants grown in Fluvisols, the nitrogen content in all plants was approximately 2.00%. The potassium content in all plants was approximately 3.00%. Therefore, we suggest that soil with a variable charge affects nutrition absorption in mini tomatoes in a manner depending on the soil pH.

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This study was an investigation of suitable condition of recirculation rate in a closed recirculating system for larviculture of red sea bream, Pagrus major. The rearing experiments were conducted at different recirculation rates in a closed recirculating system: 3 and 6 cycles/day in experiment 1, 0.5, 1, 2, 3 cycles /day in experiment 2, and 0 cycle /day (stagnant rearing condition) as the control. No difference was found in the concentration of ammonia and nitrite nitrogen in the rearing water between the treatments of 3 and 6 cycles/day in experiment 1, while in experiment 2 with recirculation rate of 1 to 3 cycles/day, the lower the recirculation rate, the higher the concentrations of ammonia and nitrite nitrogen in the rearing water were shown. Similar changes of the density of live bacteria in the rearing water were shown in all experiment lots. Larvae in recirculation conditions grew well and did not exhibit significant differences among the treatments, while the larval growth was significantly worse in the stagnant rearing condition. In the treatment of 3 cycles /day, the higher the recirculation rate, the higher the survival rate of the larvae with total length of 30mm. The survival rates between the treatments of 3 cycles /day and 6 cycles /day were not different. These results suggested that the suitable recirculation rate for larviculture in a closed recirculating system were 3-6 cycles /day with the suitable water quality, ammonia concentration < 1mg/l, the high survival rate of 45.8-48.9%, and the high rearing density over 5,000 fish/kl. And the laviculture at the extremely small daily water exchanging rates of 0.6-0.9% /day in this study gained a foothold in zero-emission of seed production.

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