JWSS - Journal of Water and Soil Science

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In order to evaluate the effects of nitrogen fertilizer levels on grain yield and nitrogen use efficiency in corn cultivars, a split plot experiment based on randomized complete block design with three replications was conducted at the Research Farm of Islamic Azad University of Ardabil during 2006-2007 cropping seasons. Factors consisted of nitrogen fertilizer at four levels (0, 80, 160 and 240 kg/ha) and corn cultivars at three levels (SC-310, SC-404 and DC-370). The results showed that grain yield was significantly affected by nitrogen levels, corn cultivar and nitrogen level × corn cultivars. The highest grain yield was related to application of 240 kg/ha nitrogen with SC-404 cultivar. Nitrogen levels of 160 and 240 kg/ha had similar yields, but more yield than 80 kg/ha. With increasing of nitrogen levels, plant height, the number of grains per ear rows significantly increased. Comparisons of means showed that increasing the application of nitrogen fertilizer decreased nitrogen use efficiency. Nitrogen use efficiency decreased from 17.13 kg/kg with application of 80 kg/ha nitrogen fertilizer to 12.4 kg/kg in application of 240 kg/ha nitrogen fertilizer. Nitrogen use efficiency was affected by corn cultivar. Nitrogen use efficiency in SC-404 was higher than SC-301. In conclusion, in order to increase grain yield and nitrogen use efficiency, SC-404 hybrid should be applied with 160 kg N/ha in climatic conditions of Ardabil Plain.

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In this research, a comprehensive simulation model for water cycle and the nitrogen dynamics modeling including all the important processes involved in nitrogen transformations such as fertilizer dissolution, nitrification, denitrification, ammonium volatilization, mineralization, immobilization as well as all the important nitrogen transportation processes including nitrogen uptake by the plant, soil particles adsorption, upward flux, surface runoff losses and drain losses, was used for fertilizer management modeling in a sugarcane farmland in Imam Khomeini Agro-Industrial Company using a system dynamics approach. For evaluating the model the data collected from Imam Agro-Industrial Company equipped with a tile drainage system with shallow ground water and located in Khuzestan province, Iran, were used. The statistical analysis of the observed and simulated data showed that the RMSE for determining the accuracy of simulation of the nitrate and ammonium concentration in drainage water is 1.73 mg/L and 0.48 mg/L, respectively. The results indicated that there is good agreement between the observed and the simulated data. Nine scenarios of fertilization at different levels of urea fertilizer were modeled including one scenario of 400 kg/ha, two spilit scenarios of 350 kg/ha, two spilit scenarios of 325 kg/ha, two spilit scenarios of 300 kg/ha, one scenario of 280 kg/ha and one scenario of 210 kg/ha. Results of the modeling showed that the scenario of 210 kg/ha has the highest nitrogen use efficiency (52.3%) and the lowest nitrogen losses consisted of denitrification, ammonium volatilization and drainage losses (17.82, 7.16 and 92.59 kg/ha, respectively). The results revealed that increasing the consumption of urea fertilizer greater than 210 kg/ha increased the overall nitrogen losses and reduced the nitrogen use efficiency. Meanwhile, this model can be used for managing the fertilizer and controlling the nitrate and ammonium concentrations in the drainage water to prevent the environmental pollution. Also, the system dynamics approach was found as an effective technique for simulating the complex water-soil-plant-drainage system.