Evaluation of Nitrogen Use Efficiency in Wheat (Triticum aestivum L.) eat Cropping Systems of Iran

Nitrogen fertilizers, plays an essential role in crop production and additionally its application has environmental drawbacks. So, nitrogen dynamics between cropping systems and environment is one of the most important agronomic management practices. Improving nitrogen use efficiency (NUE) is an important target in wheat cropping systems, it increases profitability through greater yields and reduction of the greenhouse gas emissions associated with the production and it could be reduce environmental hazards. There are many definitions related to NUE in the context of crop production and as well as in the literature review. One of the fundamental definition related to Moll et al (1982). According to Moll et al. (1982) definitions’ NUE as grain dry matter yield per unit of nitrogen available from the soil and fertilizer and divided it into two components 1-Nitrogen-uptake efficiency that is crop nitrogen uptake to nitrogen available and 2- Nitrogen-utilization efficiency which is grain dry matter yield to crop nitrogen uptake. Wheat is one of the most extend cultivated crops in the world. It is estimated in Iran, about 2.3 million ha of wheat cropping systems are under irrigated cultivation. The specific objectives of the present study were to 1- investigation and analysis nitrogen use efficiency variations and its components in wheat cropping systems by using simulation model.2-Determine how nitrogen use efficiency and its components (component analysis) is affected by nitrogen fertilizer levels. We used CENTURY model to evaluate nitrogen use efficiency in wheat cropping systems. For this purpose 14 wheat cropping system from different locations were selected. Soil data was collected from Soil and Water Research Institute and weather data from 2000 to 2014 were obtained from Iran Meteorological Organization for 14 selected stations.The CENTURY model simulates the long-term dynamics of Carbon (C), Nitrogen (N), for different Plant-Soil Systems. The model can simulate the dynamics of agricultural crop systems. The crop systems have different plant production submodels which are linked to a common soil organic matter submodel. The soil organic matter submodel simulates the flow of C, N through plant litter and the different inorganic and organic pools in the soil. CENTURY model runs in monthly time step with calculating monthly precipitation (cm), monthly mean of minimum and maximum temperature (c°), site latitude and longitude, sand, silt and clay (%), soil bulk density (g/cm3), rooting depth (cm), C and N content of the top 20 cm of soil and management information such as planting date, first and last month of wheat growth, number and amounts of fertilization, amount of irrigation water and its schedules are required. For model validation we used three statistical measures including Normalized Root Mean Squared Error (nRMSE), Willmott (1982) index or (d index) and linear regression coefficients between actual values and predicted values. Results, revealed that average nitrogen use efficiency in wheat cropping systems of Iran was 28.3 kg grain per kg of nitrogen applied. The highest and lowest mean nitrogen use efficiency were 36.02 and 21.26 kg grain per kg N that observed respectively in (Tabriz, Shiraz, Gorgan) and (Kerman, Zabol, Birjand). Regression of nitrogen use efficiency vs. yield showed that with increasing nitrogen use efficiency, yield is raised (b=0.14 kg kg-1). Separation of nitrogen use efficiency to its components indicated that on range of value (80-120 kgha-1) use of nitrogen, relative contribution of nitrogen uptake and utilization efficiency separately were 64 and 36 percent. When use of nitrogen fertilizer was increased up to value (121-160 kg ha-1) relative contribution of nitrogen uptake and nitrogen utilization was changed to 33 and 67 percent, respectively. It seems that, when in cropping system nitrogen uptake will be dominant, agronomic management practice and in versus, if nitrogen utilization efficiency will be more important choice of superior cultivars are emphasizes the improvement of nitrogen use efficiency.