A computer simulation model of nitrogen transformations and transport in soil in a Corn Belt field was developed to predict nitrate concentrations in tile effluent as a function of farm management practices and climatic conditions. Water flow in the unsaturated and saturated zones, evapotranspiration, and nitrogen flow due to mass flow, dispersion, and diffusion are simulated along with nitrogen transformations of mineralization, immobilization, nitrification, and denitrification. Growth of corn (Zea mavs L.) and soybeans (GIycine max L.) is included. Predicted values of tile water flow, water table height, nitrate-nitrogen concentrations in the soil water profile and in the tile effluent compared favorably to measured values for a field for 1972; also, predictions of nitratenitrogen concentrations in tile effluent for 1970-71 agree well with actual data. Additional Index Words: nitrate, computer simulation, soybeans, evapotranspiration.
Depth profile measurements of 137Cs and 134Cs were carried out in 11 permanent pastures that had been exposed to fallout from the Chernobyl accident. In addition to gamma-ray spectrometric analysis, the selected pastures were characterized by several soil parameters, the influence of which on transfer was investigated. Sampling of soil and pasture grass was undertaken during a period extending from the Spring of 1987 to the Autumn of 1988. The results show that there has been limited downward migration of Chernobyl-derived caesium. In October 1988 more than 88% of the 137Cs attributable to Chernobyl was mainly confined to the top 10 cm of undisturbed soil, with 79% on average in the top 5 cm. The distribution of pre-Chernobyl caesium at the 11 sites was also evaluated. In an investigation of the influence of soil parameters on transfer to grass, a negative correlation with pH was observed in 1987. In April 1987 concentration ratios for 137Cs in grass ranged from 0.03 to 0.49. In general, comparison of the concentration ratio values showed a decreasing trend over the 18 months.
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