Effect of monocrotophos and butachlor on N-fixing cyanobacteria and associated biochemical activities

Both the pesticides caused stimulation of growth and nitrogen fixation at lower concentrations and partial/complete inhibition at higher concentrations. Anabaena sp. was found to be the most susceptible and Westiellopsis prolifica as the most tolerant strain to the pesticides. The glutamine synthetase activity and release of free amino acids in the culture medium of cyanobacteria were also reduced in presence of pesticides. It is suggested that the NH₄⁺ that remained underutilized due to reduced activity of glutamine synthetase might be released in the growth medium, which might also be available to the paddy crop under the conditions of the treatment.