Evaluation of the influnce of water management and different methods of nitrogen application on rice yield and water use efficiency

Simultaneous improvement of water and nitrogen use efficiency in paddy fields is necessary to reduce the environmental- related issues. Rice, as one of the most important crop, provides the main food of more than half of the world's population. According to the latest available statistics, in the crop year 1396-97, the rice cultivated area the country was 622991 ha, which mainly belongd to the five provinces of Gilan (35.3%), Mazandaran (34.3%), Khuzestan (10.9%), Golestan (9.9%) and Fars (3.4%). Among different provinces, Mazandaran province is the main producer of rice in the country with the production of 1113715 tons of rice. Additionally, rice is the predominant crop in Mazandaran province.

The required field data of Daylamani rice cultivar were obtained during two rice growing seasons (2011-2012) from one ha consolidated paddy field in Sari, Mazandaran province. Data from 2011 were used for calibration and data from 2012 were used for validation of the CERES-Rice model of DSSAT V4.7.5 software package. By using the validated model, the effect of different scenarios of water and nitrogen fertilizer management on water use efficiency (WUE), economic water use efficiency (EWP), physiological efficiency of nitrogen consumption for grain production (NUEg), harvest index and nitrogen harvest index (NHI) were evaluated. The calibrated model was then applied to evaluate the combined effect of three types of irrigation management including continuous flooding (I1), intermittent irrigation with 5 (I2) and 8 (I3) days irrigation frequency and six N fertilizer management treatments including N1 (50% at planting (P), 25% at tillering (T) and 25% at clustering (C)), N2 (25% at P, 50% at T and 25% C), N3 (25% at P, 25% C and 50% at T), N4 (fertilization at C), N5 (fertilization at T) and N6 (fertilization at P).

The minimum (832 kg/ha) and maximum (3640 kg/ha) grain yield were obtained in I1N6 and I3N5, respectively. The simulations showed that the effect of fertilization time and type of irrigation were not independent of each other. I3N5 resulted in maximum HI (0.39), minimum soil evaporation (173.4 mm), maximum WUE (one kg/m3), maximum EWP (12×104 Rials/m3), minimum nitrate losses (52.47 kg/ha), the highest nitrogen fertilizer uptake (99 kg/ha), maximum NUEg (one) and minimum nitrogen stress (0.05). Also, the maximum NHI (0.37) belonged to the I2N5 treatment.

Based on the results, among the applied managements, according to the components of crop yield, harvest index, water productivity, EWP, NUEg, nitrogen uptake, nitrate leaching and NHI, 8 days irrigation frequency was the best option in terms of irrigation management. Also, the use of I3N5 treatment as a superior combined- treatment under both fertilizer and irrigation management in the present study is recommended in terms of water and N use efficiency in the paddy fields of the province.