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Technical Report

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Arkansas, Soybeans, Rice, water, salt


A computer model was developed which described salt and water balances for a silt loam soil common to the Grand Praire physiographic region of Arkansas. A ten year period of weather data (1966-75) was used as input data for two divergent cases in regard to salt accumulation. Case one was a rice-soybean rotation with soybean irrigated, while case two was a rice-soybean-soybean rotation with soybean not irrigated. Salts considered were calcium, magnesium, sodium, sulfate and chloride as well as the precipitate, calcium carbonate. Where soybeans were not irrigated less evapotranspiration, more infiltration and less runoff were observed during the fallow season than in the case where soybeans were irrigated. Other differences in the water balances were small. Annual salt additions were substantially larger in the case where soybeans were irrigated and rice occurred more frequently in the rotation. A majority of salt additions were found during the rice season for either case studied. As irrigation water concentration increased for a given salt, the accumulation of that salt in the soil also increased in a linear manner. The rate of this increase was largest for sulfate and chloride, and smallest for magnesium.

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