Effect of withdrawal of NO3-N or all nutrient from the NFT system prior to harvest on the growth, NO3 content in the spinach [Spinacia oleracea] plant and the final mineral concentration in the nutrient solution

The spinach plant (Spinacia oleracea L. cv. Joker and cv. Orion) was grown in the capillary NFT system in which NO3-N (Experiment 1 ; summer crop) or all nutrients (Experiment 2 ; autumn crop) was withdrawn for 2 to 6 days prior to harvest. In Exp. 1, the top fresh weight slightly decreased by the withdrawal of NO3-N supply for 6 days prior to harvest, while, the leaf nitrate content decreased from 3, 395 ppm to 2, 199 ppm and residual NO3-N in the solution decreased from 7.8 me·liter-1 to 1.0 me·liter-1. These values are below the critical level of leaf nitrate content by European standard and of residual nitrate level in the nutrient solution by Japanese standard. In Exp. 2, the withdrawal of all nutrients for 2 to 4 days prior to harvest had no effect on top fresh weight. But the leaf nitrate content decreased from 3, 232 ppm to 2, 870 ppm or 2, 342 ppm ; the residual NO3-N in the solution decreased from 1.4 me·liter-1 to 0.7 me·liter-1 or 0.2 me·liter-1 in the 2- or 4-day treatment, respectively. These values are below the critical concentration of European and Japanese standards. In addition, all the major elemental concentration in the waste water was decreased by the withdrawal of all nutrients.