Experiments to assess the capability of different combinations of Fe-compounds and adjuvants to provide iron (Fe) via foliar application to Fe-deficient plants have been carried out. A total of 80 formulations containing i) one of five Fe-compounds (FeSO4.7H2O, Fe(III)-citrate, Fe(III)-EDTA, Fe(III)-DTPA, Fe(III)-IDHA), ii) a surfactant (Mistol, alkyl-polyglucoside1 or alkyl-polyglucoside2) and iii) an adjuvant (glycerol, methanol or glycine-betaine) were studied with respect to leaf wetting ability and surface tension. From the initial formulations only 26 resulted in adequate leaf wetting, 20 with alkyl-polyglucoside2 and 3 each with Mistol and alkyl-polyglucoside1, and some of them (4 with alkyl-polyglucoside2, 1 with Mistol and 3 with alkyl-polyglucoside1) were found to have inadequate surface tension values for use as foliar fertilizers. In a second experiment, 20 formulations containing alkyl-polyglucoside2 and one each of the five Fe-compounds and adjuvants listed above, were used for a foliar experiment with Fe-deficient peach trees (Prunus persica (L.) Batsch) grown under field conditions. Iron-deficient shoots were sprayed only once and leaf re-greening was assessed over 6 weeks for leaf chlorophyll content (via SPAD measurements) and percentage of green leaf area (via image analysis). Foliar Fe application always resulted in leaf chlorophyll increases, although different degrees of re-greening were observed for the various Fe-compounds tested. Best results were obtained after treatment with formulations containing (in a decreasing order): Fe(II)-sulfate, Fe(III)-citrate, Fe(III)-EDTA, Fe(III)-IDHA and Fe(III)-DTPA. A positive effect of adding glycerol, methanol or glycine-betaine was often observed, although the effect depended on each Fe-containing compound, indicating the existence of significant interactions between spray components. Results are of importance while trying to critically evaluate the potential of Fe sprays as a viable strategy to remedy plant Fe deficiency under field conditions.

This study was supported by the Spanish Ministry of Science and Education (Projects AGL2003-1999 and AGL2004-0194, co-financed with FEDER) and the Commission of European Communities (project Isafruit). V. Fernández was supported by a “I3P” post-doctoral contract financed by the CSIC, co-financed by the European Social Fund.

The original publication is available at: http://springerlink.com/content/x25444326264v705/

Peer reviewed