The effects of Fe-chelate type and PH on substrate grown roses

Substrate grown roses appear to be susceptible to chlorosis, which indicates problems with Fe or Mn uptake and hence yield reduction. In common practice this problem is often treated by the addition of extra Fe-chelate, or the use of Fe-EDDHA instead of Fe-DTPA. In previous tests, it was shown that the pH in the root environment is a major factor in the prevention of chlorosis. Moreover, the application of Fe-EDDHA does not always show satisfying improvements in practice. The interaction between Fe-chelate types (EDDHA and DTPA) and pH was studied with roses cv. ‘Kiss’ and ‘Escimo’ on glasswool substrate, reusing drainage water. pH levels compared were about 7, 5.8 and 4.5. The treatments resulted in significant chlorosis and consequently yield reduction at high pH with both cultivars and both chelate types. Highest yields were obtained at low pH, especially with ‘Escimo’. The Fe uptake was clearly affected by the pH with both chelate types. At high pH the Fe-uptake was significantly higher with Fe-EDDHA; however the Mn contents in the plant were significantly lower with these treatments. The uptake of Zn and Cu was also affected by specific combinations of pH and the type of chelate. It was concluded that an optimal pH control was the best method of preventing chlorosis. The choice of the chelate type was less effective and could enhance Mn deficiency.