Optimization of water, nitrogen and density in canola cultivation by central composite design

The optimum resource level in agro-ecosystems should be determined to decrease production costs، conserve resources and reduce environmental pollution which occurs as a result of excessive use of these resources. In order to determine the optimum use of water، nitrogen and canola density، an experiment was conducted using central composite design in the Research Field of Ferdowsi University in 2011. The treatments were designed based on low and high levels of irrigation (1500 and 4000 m3)، nitrogen (0 and 400 Kg urea ha-1) and canola density (50 and 150 plant m-2). Seed yield، nitrogen losses، nitrogen use efficiency (NUE) and water use efficiency (WUE) were measured as independent variables and changes of these variables were calculated by a regression model. Optimum levels of irrigation، nitrogen and canola density، respectively، were proposed to obtain the expected level of traits based on three scenarios: economic، environmental and economic-environmental. Increasing irrigation and fertilizer led to an increase in seed yield and nitrogen losses، whereas increasing canola density caused an increase in seed yield but a decrease in nitrogen losses. The optimum level of water، fertilizer and density were 3643 m3، 186 Kg N ha-1 and 149 plant m-2 in economic scenario. In the environmental scenario، the optimum levels of the treatments obtained were 1813، 12 and 150، respectively، and for the economic-environmental scenario were 2639، 105 and 144، respectively. In general، it seems that resource use based on the economic-environmental scenario is preferable to the other scenarios since it takes account not only of economic but also of environmental issues.