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Monitoring the Variability of Nitrogen and Cadmium Concentrations in Soils and Irrigation Water in the Almyros Area of Central Greece

The main purpose of this investigation was the monitoring of nitrogen (N) and cadmium (Cd) levels in soils and irrigation water samples in an intensively cultivated area in central Greece. From 2005 to 2007, soil as well as irrigation water samples were collected two periods a year (March and October) at the same sampling sites in the Almyros area. Nitrogen was measured in three forms (as nitrate, nitrite, and ammonium) using the anion chromatography method. Available and total Cd concentrations were measured using atomic absorption spectroscopy, after extraction with diethylenetriaminepentaacetic acid (DTPA) and aqua regia extraction solutions, respectively. The nitrate, nitrite, ammonium, and Cd concentrations were always less than the corresponding water standards. Cadmium concentration (total and DTPA extractable) in soil samples was high in the sites where phosphate fertilizers had been intensively used for the crops. Seasonal variation was found in all parameters measured between the autumn and spring of each year. No temporal variation was found, as there was no statistical difference in nitrate, nitrite, and ammonium or in Cd concentration among the years of the study. A spatial variation was observed in all the parameters and was illustrated by the respective thematic maps. Thematic maps of predictions of the measured variables, as well as for pH and electrical conductivity, were generated using geostatistics as a helpful tool in sustainable soil management of the study area. The spatial variability of available Cd was found to follow the variability of soil pH, as highly available Cd concentration was observed in highly acid soils. Significant correlations among nitrate, nitrite, ammonium, available and total Cd, and soil physicochemical parameters were obtained and discussed.