Management of Nitrogen, Irrigation and Planting Density in Persian shallot (Allium hirtifolium) by Using Central Composite Optimizing Method

Determination of resource optimum level in agro-ecosystems caused to decrease in production costs، conservation of resource and reducing of environmental pollutions which was happen by excessive use of these resources. In order to determinate optimum use of nitrogen، water and density، an experimental was conducted by central composite design in research field of Ferdowsi University in 2012. The treatments was designed based on low and high levels of nitrogen (100 and 300 kg Urea/ha)، irrigation (1500 and 3500 m3 water) and density (10 and 18 plant/m2) by Minitab software. Bulb yield، nitrogen losses، nitrogen use efficiency and water use efficiency was measured as independent variables and changes of these variables were calculated by regression model. Optimum level of nitrogen، irrigation and density was suggested to obtain expected amount of traits based on three scenarios: economic، environmental and integrated (economic-environmental). Increasing of fertilizer and irrigation led to increase in bulb yield and nitrogen losses، whereas increasing of density caused to increase in bulb yield but decrease in nitrogen losses. The optimum level of nitrogen fertilizer، irrigation and density were 260 kg N/ha، 2227 m3 water/ha and 16. 7 plant/m2 in economic scenario. In environmental scenario، the optimum level of the treatments was obtained 100، 1500 and 16. 54 respectively، and for economic-environmental scenario were 169، 2025 and 17. 7، respectively. In general، it seems that resource use based on integrated scenario is preferred to other scenarios due to consider not only economic but also environmental issues.