Oe. Plessner et al., IRON-ENRICHED AZOLLA AS A SLOW-RELEASE BIOFERTILIZER FOR CUCUMBER PLANTS GROWN IN A HYDROPONIC SYSTEM, Journal of plant nutrition, 21(11), 1998, pp. 2357-2367
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.