Studies on the range of production limits and control scheme for greenouse soils.

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Degradation of soils, including salt accumulation, is one of the seriou problems on agricultural production, particularly greenhouse culture for vegetables and flowers in Japan. This problem still remains as one of the major subjects in horticulture to be solved.In this report, we firstly analyzed some physical factor and chemical components of soils collected from three types of greenhouses with diferent periods of usage. From the analytical results with the ion chromatography, atomic absoption and spectrophotometry, there are significant relations in 5 % levels between the value of EC,accumulated rates of anion (SO_4^-, NO_3^-, Cl^-) and cation (Ca^<2+>, Mg^<2+>, K^+), and the ysage periods of greenhouse soils. Then, we tried to estimate the range of production limits for greenhouse soils using the yearly increasing rate of EC and some ionic contents calculated from the experimental results. Finally, as a countermeasure to the salinization caused in grenhouse soils, we have developed a new method to capture the salts accumulated on the surface of soil with using the sheet materials attached on the soil surface. Some basic characteristics for solute transport, and the amount of salts captured on the sheet, are experimentally observed with three different types of sheets.