Optimization of nitrogen fertilizer and plant spacing on the row parameters in ‎spinach cv. “Harrier” using response surface methodology

In this study, optimum level of nitrogen fertilizer and plant spacing on the row were investigated in spinach cv.”Harrier” based on the aims of four scenarios: economic, health of food, marketable and optimum production, using statistical response surface methodology. The independent variables including plant spacing on the row (7, 11 and 15 cm) and nitrogen fertilizer (0, 200 and 400 kg urea ha-1), were evaluated using central composite design at Research Field of University of Tehran. Leaf fresh weight, biomass, leaf area index, nitrogen use efficiency, nitrate concentration and total chlorophyll traits were considered as dependent variables. The fitting of data to second order polynomial equation and optimization of responses was performed using Mnitab16 software. Increasing of plant spacing on the row had alone a significant effect on total chlorophyll traits. High levels of nitrogen fertilizer had an increasing effect on dependent variables, except nitrogen use efficiency. The optimum combination of variables and desirability function for economic, environmental, marketable and optimal production limit scenarios were at plant spacing on the row of 7, 7.48, 7.24 and 7 cm, nitrogen fertilizer of 189.9, 60.6, 189.9 and 149.5 kg ha-1, and 0.97, 0.77, 0.9 and 0.82, respectively. Based on desirability function results, the model possesses a high power to simulate optimum level of independent variables at economic scenario than the others.