University of Guilan Caspian Journal of Environmental Sciences 1735-3033 17 1 2019 03 01 Nitrate pollution reduction using biological fertilizers in paddy fields, the South Caspian Sea basin, Guilan Province, Iran 63 71 3345 10.22124/cjes.2019.3345 EN Majid Ashouri Department of Agriculture, Islamic Azad University of Lahijan branch, Lahijan, Iran Journal Article 2018 07 12 Application of chemical fertilizers, especially urea, causes groundwater pollution. Therefore, to decrease environmental pollution, biological fertilizers may be employed. In order to investigate the effect of irrigation levels, Azospirillum and nitrogen levels on rice yield and its components, an experiment was conducted in the north of Iran during the crop season in 2013. The experiment was arranged in a split-split plot based on a completely randomized block design with 3 replications in which irrigation level was the main factor. The levels of factors used were: I₁= continuous submergence and I₂= 11 days’ irrigation interval; A₁= application and A₂= no application of Azospirillum as the sub factor; and nitrogen fertilizer levels as a sub-sub factor includingN₁= 0, N₂= 30, N₃= 60 and N₄= 90 kg ha^-1. Continuous submergence and 11 days’ irrigation interval produced 4247 and 2720 kg ha^-1, while the application of Azospirillum and the treatment without it produced 4064 and 2903 kg ha^-1, respectively. Moreover, N₄, N₃, N₂ and N₁ produced 3950, 3800, 3225 and 2700 kg ha^-1, while I₁A₁N₄ and I₁A₁N₃had maximum and I₂A₂N₁ had minimum mean values with 5381, 5330 and 1882 kg ha^-1, respectively. Therefore, it is concluded that the application of a balanced nitrogen fertilizer with Azospirillum could prevent the indiscriminate use of chemical fertilizers and reduce nitrate pollution, leading towards more sustainable agriculture in the north of Iran. https://cjes.guilan.ac.ir/article_3345_cd1815a61c9488eb022854dd7802b3de.pdf