Most of paddy fields have covered by Azolla filiculoides in Guilan province. Effects of this plant, can consider from different aspects including: environmental pollution, plant nitrogen nutrition and difficulty land ready for rice seedling. Influence on nitrogen mineralization is another effect of Azolla. This effect is more important than others, because Azolla filiculoides has coexistence with Anabaena azollae, which can fixate nitrogen of atmosphere. Determining amount of nitrogen mineralization, in these conditions, can be important because it influence on pollution of waters, nitrate cycles and rice inorganic nutrition. Azolla can transform readily to compost, because it is rich of nitrogen. In these conditions, circumstance of nitrate and ammonium production is notable. In this study, nitrogen mineralization was compared between soil of paddy field and soil paddy field mixed with Azolla and Azolla compost. Rate of nitrogen mineralization was determined by spilt plot with four repetitions. Main factors were included soil of paddy field and soil of paddy field mixed with azolla and azolla compost. Sub factor was time of mineralization in six weeks. Samples were put in plastic bags in spring (MAY) and these bags were put in field. Sampling was carried out every week, and concentration of total nitrogen, nitrate and ammonium were measured each interval. The result was revealed that, rate of mineralization of total nitrogen and nitrate in 3 treatments was significantly different (p< 0.01). Treatments of time mineralization also were significantly different (p< 0.05). Amount of ammonium was statistically different, but sum of nitrate and ammonium was significantly different.
