An experiment was conducted at the Main Agricultural Research Station, University of Agricultural Sciences, Dharwad, Karnataka, India during 2014 to study the effect of horizontal constructed wetland treatment of domestic sewage effluent on its quality and effect of its irrigation on soil nitrogen dynamics both temporally and spatially. The analytical results revealed that there was improvement in the quality of sewage effluent after passing through the constructed wetland treatment system which was reflected by reduction in pH, EC, BOD, COD and TSS. A notable reduction in BOD (54 per cent) was observed in treated sewage effluent as compared with that of untreated sewage effluent. The mean BOD of 256 mg L-1 in untreated sewage effluent was reduced to 118 mg L-1 after the treatment. The groundwater registered the lowest COD of 14 mg L-1 among different sources of irrigation water. The mean COD of treated sewage effluent was 251mg L-1 as compared with that of 410 mg L-1 in untreated sewage effluent. A reduction in total suspended soils to the extent of 42 per cent was observed from 480 to 278 mg L-1 after passing through constructed wetland. The constructed wetland system acted as a mechanical and biological filter and removed suspended particles from the water. Sources of irrigation water, fertilizer levels and their interaction had a significant effect on ammoniacal nitrogen (NH4 + -N), nitrate nitrogen (NO3 - -N), organic nitrogen and total nitrogen content in soil. Treated sewage effluent had higher concentration of ammoniacal and nitrate nitrogen than untreated sewage effluent. The soil ammoniacal nitrogen was the dominant inorganic nitrogen form present in the soil. Organic and total nitrogen content in the sewage irrigated plots were significantly superior over groundwater irrigated plots. Among different N fractions, the predominance was in the order of ON > NH4 + -N > NO3 - - N. | Studies on the effect of treated sewage effluent irrigation on N dynamics in soil
