Water quality of irrigated rice crop and yield as a function of drainage season

The State of Rio Grande do Sul (RS) has intense water use for irrigated rice production, generating concerns regarding the quality of this water, which will be returned to the water sources at the end of the harvest. Therefore, this study aimed to evaluate the quality of water from rice fields and yield as a function of drainage time.  The treatments were: T1: drainage from full flowering (R4) according to Counce et al. (2000); T2: 7 days after R4; T3: 14 days after R4; T4: 21 days after R4; T5: 28 days after R4; T6 (control): 35 days after R4. At the moment of drainage the leaf height was quantified and the water samples were then collected, where the pH, electrical conductivity, nitrogen (ammonium and nitrate), phosphorus, potassium and sodium solution in solution were quantified of grain yield. All parameters related to water quality studied are in accordance with CONAMA Resolution 357/2005. The productivity results indicate that it is possible to drain irrigated rice from 14 days after full flowering.