Limiting nutrient emission from a cut rose closed system by high-flux irrigation and low nutrient concentrations?

A two-year project was aimed at decreasing nutrient emission from closed nutrient systems by using high irrigation rates in order to allow lower EC levels in the presence of accumulated Na and Cl. Experimental variables were growing media, irrigation frequencies, EC and NaCl concentrations for cut rose 'Frisco'. Growing media used in the 3 L containers were coir dust and three perlite fractions. Irrigation frequencies were very high compared to normal horticultural practice, i.e. approximately 1, 1.9 and 3.8 L plant(-1) day(-1) throughout the experimental period. No effects of the irrigation frequency or interaction of irrigation frequency with growing media or EC were found on production. Coir dust and fine perlite showed the highest production in the treatments, followed by the middle fraction perlite. Root FW, aboveground FW production and number of stems was lowest in the perlite 1-7 mm (coarse) treatment. It is suggested that the decreased growth in coarse perlite is the result of a higher resistance to root penetration. From the root growth/production data, gas analysis in the rhizosphere, AFP and root ADH activity measurements it was concluded that oxygen deficiency did not occur in the growing media at the relatively high irrigation rates. EC (0.9 and 1.9 mS cm(-1)) and NaCl addition (0 and 10 mM) were used in order to simulate Na accumulating conditions in closed systems. A significant (negative) effect of NaCl on production was only apparent in the low EC treatment. Without NaCl in the nutrient solution, stem weight was highest at low EC. The apparent negative effect of NaCl at low nutrient-EC was particularly related to higher Cl concentrations in the leaves. The project confirmed that NaCl concentrations of 10 mM can be tolerated by cut rose provided nutritional elements are not below certain limiting concentrations.