Novel use of calcareous algae as a plant biostimulant

This work is based on the hypothesis that the depositions of the calcareous alga Lithothamnium sp. at the bottom of the ocean contain bioactive humic substances which may promote plant growth. To achieve this, micronized Lithothamnium sp. powder was investigated in terms of the degree of humification using a colorimetric approach; the bioactivity in comparison with that of auxin IAA (3-indole acetic acid) using a bioassay with Vigna radiata and the effect of foliar sprays on organically grown tomatoes. Humification and formation of humic acid were identified to a high degree in micronized Lithothamnium sp., which was highly bioactive showing auxin hormone-like activity. When applied as foliar sprays, rooting, growth, and yield were improved and concentrations of amino acids, sugars, and protein of tomato plants increased. Thus, the results presented a novel use for Lithothamnium sp., whereby the calcareous algae depositions provided a highly active humic acid for use as a plant biostimulant.