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Plant Science Today (PST)

Research communications

Vol. 13 No. sp2 (2026): Recent Advances in Agriculture

. Response of Bradyrhizobium and soil microbial communities to premix herbicides in blackgram: Soil microbial dynamics as influenced by premix herbicides

DOI
https://doi.org/10.14719/pst.12071
Submitted
1 October 2025
Published
12-05-2026

Abstract

Premix herbicides, which combine active ingredients with different modes of action, offer broad-spectrum weed control at lower doses. However, their potential non-target effects on beneficial soil microorganisms warrant careful evaluation. We examined the response of blackgram specific Bradyrhizobium strain BMBS 47 and rhizospheric microbial communities to two premix herbicides viz., pendimethalin (30%) + imazethapyr (2%) (Penza 32%EC) and propaquizafop (2.5%) + imazethapyr (3.75%) (Shaked 6.25% ME). Laboratory sensitivity assays, conducted using the disc diffusion method across a wide range of concentrations, revealed no inhibition zones, indicating complete tolerance of Bradyrhizobium to both the formulations. Field experiments further demonstrated that soil microbial populations responded variably to weed management treatments. Rhizobium counts were significantly higher in plots treated with pendimethalin + imazethapyr, reflecting favourable rhizosphere conditions due to early weed suppression, while comparatively lower counts occurred under sequential herbicide applications or hand weeding. Soil that received pendimethalin + imazethapyr application recorded a higher fungal population (6.20 log₁₀ CFU g-1) which was comparable to weedy check (5.56 log₁₀ CFU g-1) at 30 DAS. Phosphorus-solubilizing bacteria remained unaffected across treatments, suggesting that their stability was maintained under adequate soil phosphorus conditions. Free-living nitrogen fixers and actinomycetes showed time and treatment-specific variations, whereas fungal population were either stable or enhanced under pendimethalin + imazethapyr, confirming the absence of detrimental effects. Interestingly, the weedy check supported relatively higher microbial abundance at 30 days after sowing, attributed to diverse weed root exudates and reduced soil disturbance. Overall, the findings indicated that premix herbicides, particularly pendimethalin + imazethapyr, can be integrated into blackgram weed management programmes without compromising the short-term survival of beneficial soil microbes, thereby sustaining both biological nitrogen fixation and soil fertility.

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