Elias Soltani, Afshin Soltani, Zeinali Ebrahim:
Estimation of Nitrogen Losses under Wheat Production in Gorgan, Northeast of Iran, using CropSyst Model

ELIAS SOLTANI, AFSHIN SOLTANI, ZEINALI EBRAHIM
Gorgan University of Agricultural Sciences and Natural Resources, Agronomy, Iran

Nitrogen is the most important nutrient in crop production, but it can be harmful for environment through leaching of NO₃ to groundwater and gaseous loss of N₂O. Crop models are useful tools to simulate the plant growth, production, as well as to estimate the fate of nitrogen (N) in different production systems. This study was conducted in Gorgan, Northwast of Iran (1) to evaluate the CropSyst model to predict the fate and residual N of wheat production system and (2) to estimate N losses in different wheat management scenarios.

The updated CropSyst-wheat model was used to simulate the growth and production of wheat. Evaluation of CropSyst to predict N uptake and residual N in soil profile were performed using 16 local fields. Simulation of N losses in wheat production systems were conducted during 1967-2009 (40 years). Simulation scenarios were (1) irrigated cultivation (average input; AI), (2) irrigated cultivation (High input; HI) and rainfed cultivation (low input; LI).

Results indicated that CropSyst model could satisfactorily predict yield, N uptake, residual N of wheat production system. Wheat yield of scenarios were 4400, 4500 and 4000 (kg ha^-1) for AI, HI and LI respectively. The LI yield was significantly lower than AI and HI. Total N losses in AI, HI and LI were 13.5, 18.1 and 9.8 (kg N ha^-1) respectively. The highest losses of N occurred through gaseous loss (45 to 63% of total N losses) in which volatilisation (NH₃(g)) contributed about 45 to 61% of total N losses and scenarios showed significant differences. Nitrate leaching of scenarios were not significantly different and were about 3kg N ha^-1. It can be concluded that the application of urea as topdressing led to increased N losses (NH₃ volatilisation) and changing of type of fertiliser and fertiliser management could reduce these N losses.

Keywords: Denitrification, N leaching, N losses, NH₃ volatilisation, wheat

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Contact Address: Elias Soltani, Gorgan University of Agricultural Sciences and Natural Resources, AgronomyBasij Squre, 49138-15739 Gorgan, Iran, e-mail: elias.soltaniyahoo.com