Changes in some growth and yield indices of Spinach (Spinacia oleracea L.) under nitrogen fertilization and plant density

The Identification of the factors affecting the yield and edible quality of spinach (Spinach oleracea L.) and their interaction with the environmental conditions are the most important issues in crop production management. In this experiment, the effect of three levels of plant density (71, 45 and 33 plant m-2), six levels of nitrogen fertilizer (100, 200, 250, 300, 350 and 400 kg urea ha-1) and control on yield, growth indices and quality of spinach was evaluated in the field condition. These experiments were carried in 2014-15 and 2015-16, in a randomized complete block design with three replicates. The results showed that interaction effects of nitrogen fertilizer and plant density and year only had Significant effcet on nitrate content (p < 0.001). Nitrogen fertilizer increased biomass, yield, growth parameters like leaf area index, crop growth rate, and qualitative parameters like nitrate content, potassium percentage, chlorophyll a,b and total traits while had not significant effect on net assimilation rate and relative growth rate. Interaction effects of plant density and year had a significant effect on all traits except potassium percentage (p < 0.001). The increase in plant density led to increase in the biomass, leaf area index and nitrate content but chlorophyll content was significantly decreased. It is suggested that in autumn cropping in Karaj region, and under high light and temperature conditions, 71 plants m-2 and 250kg urea ha-1 could be better to estimate the aims of economic profitability for highest yield and maintaining a healthy level of nitrate in the plant tissue.