IRON-ENRICHED AZOLLA AS A SLOW-RELEASE BIOFERTILIZER FOR CUCUMBER PLANTS GROWN IN A HYDROPONIC SYSTEM

The unique ability of dried plant residues Azolla to adsorb iron (Fe) was employed to formulate and test an organic Fe biofertilizer. A simp lified experimental system was established to examine the effectivenes s of Fe-enriched Azolla as a source of Fe for the remedy of Fe-deficie nt plants. The optimal Fe-enrichment level needed to achieve a complet e recovery of starved plant by the Fe-Azolla complex was tested using a bioassay system of hydroponically grown cucumbers. Dried Azolla plan ts were mixed a with a solution of ferrous sulfate (FeSO4) at pH 2.0, rinsed, and dried to form organic, compact material containing 4% (w/w ) Fe bound to Azolla. The Fe-Azolla complex was applied to the nutrien t solutions of Fe-deficient cucumber seedlings. Growth rates and devel opment measurements as well as chlorophyll and the Fe-containing catal ase activity tests have been performed. The effect of the slowly relea sed Fe in correcting Fe deficiency were followed for three weeks and c ompared with the efficiency of additions of several synthetic Fe chela tes. Iron-starved plants exhibited fast regreening of the chlorotic in terveinal tissues after the addition of Fe-Azolla complex to the nutri ent solutions. Iron starvation decreased the activity of catalase. Iro n-treated-starved plants exhibited recovery of catalase activity compa red to the low level activity measured untreated Fe-starved plants. Ir on-enriched Azolla treatment was found equivalent to Fe-EDTA and Fe-ED DHA. This study is the first step in our research program aimed to est ablish the application of Fe-enriched Azolla as a bioagent for the ben efit of Fe-deficient crops.