Effect of NO3-N in the additional nutrient solution on the growth, yield, and NO3 content in spinach plant grown in hydroponics

The effect of NO3-N in the additional nutrient solution 6 to 18 days before harvest on the growth, yield, and NO3 content in spinach (Spinacia olevacea L. cv. 'Sunlight') plants was studied. There was no significant difference in top fresh weight and yield between the plants exposed to 6 and 8 me.liter(-1) NO3-N for 14 days before iarvest. The NO3 content in plants grown in 6 me.liter(-1) NO3-N solution in this period decreased to the critical amount of European standard of 3000ppm NO3 in the autumn crop, whereas residual concentration of NO3-N in the nutrient solution decreased to 24.8ppm and 33.4ppm at 6 and 8 me.liter(-1), respectively. Economically satisfactory growth and yield were obtained in the plants grown with 3/4 strength of Enshi-shoho nutrient solution until the appropriate plant size was attained and then they were transferred to a NO3-N-free solution 6 days prior to harvesting. The NO3 content in those plants decreased to 700ppm in FW basis, whereas residual concentration of NO3-N in the solution decreased significantly by lengthening the NO3-N starvation period.