The Sources and Methods for Abating Nitrate and Cadmium Pollutants in the Northern Rice Paddies

A series of tests was carried out during 1998 and 1999 in Mazandaran and Gilan provinces to evaluate the detrimental effects of imbalanced fertilizer use and other related mismanagement practices on the environment as well as determining the sources of cadmium and nitrate pollution. In a lysimeter study at Amol Rice Research Station, nitrates in the leachate waters from nine different treatments of sources and rates of urea and sulfur _ coated urea and in surface run offs (from Talar river waters in the spring and fall seasons) were determined. Also ammonium and nitrate in ground waters from 13 hand _ dug and domestic wells were measured in connection with this research. Soil samples were collected froth 64 selected rice Daddy fields in Mazandaran and Gilan provinces and the variations in the concentration of phosphorus and cadmium in these samples were determined for a period of two years. In the meantime, the cadmium contents of triple super phosphate fertilizer used in the area were measured. Finally, the cadmium levels in soils, samples of rice straw and polished grain were measured for 32 rice paddy farms in the same region and the measurements compared with the standard figures obtained worldwide. The results indicated that the principle cause of high nitrate levels in ground waters could be the incorrect and the unscientific methods of using urea. Urea as compared with the sulfur _ coated urea resulted in more nitrate in the leachate water. Likewise, a 100% probability was found for nitrate increases in the leachate waters in relation to the one time application of urea at the start of planting season. However, when urea was applied in split applications the nitrate concentration in the leachates decreased. In fact, nitrate concentration in the leachates form one time urea application was five times that of leachates from split applications of urea during the growing season which resulted in negligible levels of nitrate being leached. Nitrate concentrations in the river water increased downstream as more runoffs and leachates from farms and domestic sewages were being added to the river. This effect was more pronounced in the fall than in the spring. Measurements of nitrates in groundwater for the two _ year period showed and increase of 4.4 mg/I in the second year. The average concentrations of phosphorus and cadmium in the soils of rice paddies had reached a level of 34 and 2.19 mg/kg, respectively. The results showed an increase of 6.5% (2 mg/kg) for phosphorus and 15.5% (0.32 mg/kg) for cadmium in the tested soils. Furthermore, there was a positive correlation coefficient between soil phosphorus and cadmium contents. The average cadmium concentrations in soils, rice straw and polished grain were 2.16, 0.55 and 0.34 mg/kg, respectively, indicating a 2