Simulation of soil nitrogen balance in wheat (Triticum aestivum L.) production in Gorgan, Iran

Environmental and economic challenges resulting from the application of nitrogen fertilizers have increased concerns about its productivity in the agricultural systems. This study was conducted to evaluate SSM-Wheat model to simulate nitrogen budgeting with various nitrogen application scenarios (Dry land-without nitrogen, Dry land-low nitrogen, Irrigated-without nitrogen, Irrigated-conventional, Irrigated-high nitrogen and Irrigated-very high nitrogen) in rainfed and irrigated conditions in the wheat-based cropping systems of Gorgan region in Iran in a 21-years period (1990-2010). Results indicated that the average total losses of nitrogen were significantly different among different scenarios. In all scenarios, the proportion of nitrogen loss (81%), as gaseous was more than that of leaching (19%). Nitrogen loss by nitrification ranged between 5.9 and 59.2 kg.ha-1 with average 23.2 kg.ha-1 while nitrogen volatilization ranged between 0 and 14.9 kg.ha-1 with an average 5.8 kg.ha-1. Also, the maximum nitrogen leached was associated with irrigated wheat-high nitrogen scenario that had significant difference with other scenarios. However, the lowest amount observed in the rainfed wheat-without nitrogen scenario that had no significant difference with irrigated wheat-without nitrogen scenario. The highest productivity was observed in irrigated wheat-conventional scenarios (26 kg.kg-1) and irrigated wheat high nitrogen (25.9 kg.kg-1) which was significantly different than the other scenarios. Therefore, irrigated wheat- conventional scenario was identified as suitable scenario in wheat production in Gorgan, Iran, due to cost saving, low leaching, less environmental pollution, adequate irrigation and less fertilizer use.