Effect of Calcium on the Accumulation of the Humic Substances in Cultivated Soils.

@In previous study, we investigated that the characteristics of humic substances in cultivated soils of Minami and Kita daito Islands in Japan. Soil organic matter (humin) accumulation in the sugarcane soils has been enhanced by the presence of exchangeable calcium. Liming materials, which are having high concentrations of calcium, can be effectively utilized to enhance the soil organic matter (humin). Generally, lower content of soil organic matter is due to high activity of microorganisms in tropical and subtropical islands. There were few researches about accumulation of soil organic matter in tropical and subtropical islands. This research was investigated that effect of calcium on the accumulation of humic substances used by incubation test.

@Incubation test was conducted to investigate the effect of calcium on the accumulation of humic substances in cultivated soils. 2 kinds soils were collected to examine. One soil is Red-yellow soil (Oxisols), another soils is Gray soil, both soils are located on Okinawa island, Japan. The pH and EC of Red-yellow soil were 4.5 and 3.1 mS/m, respectively. Content of exchangeable potassium, calcium and magnesium were 0.02, 0.037 and 0.016 mg/g, respectively. Content of exchangeable potassium, calcium and magnesium were0.84, 5.6 and 1.6 mg/g, respectively. The pH and EC of Gray soil were 8.5 and 219 mS/m, respectively. 3 kinds manures were selected which were pig manure, cattle manure and chicken manure. Carbon content of pig, cattle and chicken manure were 399, 145 and 287 mg/g, respectively. Ratio of manure and soil was 1g C : 75g soil. (pig manure=2.5g/75g soil, cattle=6.9g/75g soil, chicken=3.5g/75g soil ). Two soils with pig, cattle and chicken manure was incubated under 60% of maximum water holding capacity and 30Ž. Incubation test was conducted during 140 days (20weeks).