Indian Journal of Microbiology

Effect of micronutrients on cyanobacterial growth, nitrogen fixation and paddy-yield was examined. Critical and toxic levels of Zn, Bo, Cu and Mn for ARA and growth varied with the micronutrient and cyanobacterium. Mn was observed to be least toxic while Cu was most toxic. Westiellopsis prolifica was highly resistant and Anabaena sphaerica was most sensitive to micronutrients. Nitrogen fixation was observed to be less sensitive than growth. In calcareous soil, the recom-mended level of zinc as ZnSO₄ (5 kg ha⁻¹) for paddy was favourable for ARA of autochthonous cyanobacteria. However, the recommended level (1.5 kg ha⁻¹) of boron as borax was found to be inhibitory. Foliar spray of 0.04% boron as boric acid was effective in augmenting cyanobacterial-ARA.