Assessing nutrient losses of reclaimed wastewater irrigation in paddy fields for sustainable agriculture

An experimental field study was performed during the growing season to assess water and nutrient balances in a paddy field over a 3-year period. The plots were separated according to irrigation water: groundwater (TR#1), wastewater (TR#2), and filtered wastewater with ultraviolet (UV) treatment (TR#3). The hydrology and water quality of rainfall, irrigation, surface water, and infiltration were monitored throughout the crop stages. More than half of the total water inflow of about 1840mm in each treatment was contributed by precipitation and the remainder by irrigation. The water balance analysis indicated that approximately 13% of the total outflow was lost by surface drainage, 30% was consumed by plant uptake, and 57% was lost by evapotranspiration and infiltration. The nitrogen (N) levels in the irrigation water in the mass inputs for TR#1 and TR#3 were 22% and 49%, respectively, while the output balances in the drainage water for TR#1 and TR#3 averaged 2% and 6%, respectively. The N in the crop harvest for TR#1 and TR#3 occupied 59.62 and 121.35kgha−1, respectively. The N in the fertilizer comprised a large proportion of the N in TR#1 while the N in the irrigation water and fertilizer were the major inputs in TR#3. The major P input was fertilizer in TR#3, and crop harvest was a main output in the P balance. In contrast, surface drainage and infiltration were relatively small components, due to the high drainage outlet height. The difference between inputs and crop harvest shows that it is possible to improve water quality by reducing the fertilization rates in paddy fields irrigated with reclaimed wastewater.