Simulation of nitrate transport in Mazandaran paddy field during canola cultivation season for water resources management

In this research، the appropriateness of DRAINMOD-N model was evaluated for the simulation of nitrate transport with subsurface drainage in paddy fields. During a canola growing season from November 2011 to April 2012، the nitrate concentration of drainage water and soil saturation extracts of two depths of 30 and 60 cm was measured in consolidated paddy fields of Sari Agricultural Sciences and Natural Resources University. Drainage treatments included: three conventional subsurface drainage systems with mineral envelope including drainage system with drain depth of 0. 9 m and drain spacing of 30 m (D0. 9L30S)، drain depth of 0. 65 m and drain spacing of 30 m (D0. 65L30S)، and drain depth of 0. 65 m and drain spacing of 15 m (D0. 65L15S) and a conventional subsurface drainage system with artificial envelope with drain depth of 0. 65 m and drain spacing of 15 m (D0. 65L15F). The model was calibrated by adjusting nitrification and denitrification coefficients. In order to test the model results، five statistical indices including model efficiency (EF)، percent error (PE)، coefficient of determination (R2)، root mean square error (RMSE)، and average deviation (AD) were used. The values of EF، PE، R2، RMSE، and AD were، respectively، 0. 71، 2. 66، 0. 72، 0. 94، and 0. 56 for the calibration phase. Based on the results، the DRAINMOD-N model performed well for nitrate loss simulation in the calibration phase، but at validation phase the values of EF، PE، R2، RMSE، and AD were، 0. 12، -19. 89، 0. 851/01 and 0. 56 respectively، which was from the weak simulation accuracy.