Effect of post emergent herbicides on soil microbial count (bacteria, actinomycetes and fungi) and soil dehydrogenase activity in arecanut plantation of coastal Karnataka

A field experiment was conducted to study the effect of post emergent herbicides and other weed management practices on soil bacteria, fungi and actinomycetes count and soil dehydrogenase activity of arecanut plantation in Coastal Karnataka during the rabi season of 2023-2024. In the investigation, observations recorded at initial soil sampling showed non-significant difference in treatment plots, microbial population viz., bacteria, fungi and actinomycetes. The populations of micro flora were differed due to different weed control treatments. The weedy check treatments resulted with high bacterial (29.00, 33.00 and 39.00 cfu×10-6g-1), fungi (22.33, 26.33 and 28.00 cfu×10-4g-1) and actinomycetes (6.00, 7.33 and 9.33 cfu×10-3g-1) population at 7, 15, and 30 days after treatment imposition, closely followed by farmer’s practice. Among different post emergent herbicides glyphosate 41% SL IPA salt @ 1230 g a.i. ha-1 at the 5-6 leaf stage registered highest bacterial (31.33 cfu×10-6g-1), fungi (23.33 cfu×10-4g-1) and actinomycetes (7.33 cfu×10-3 g-1) population recorded at 30 days after treatment imposition. In comparison, the application of saflufenacil 70% WG @ 52.5 g a.i. ha-1 as post-emergent at 5-6 leaf stage of weeds significantly resulted in the lowest bacterial (24.67 cfu×10-6g-1), fungi (18.33 cfu×10-4g-1) and actinomycetes (4.33 cfu×10-3 g-1) population recorded at 30 days after treatment imposition. Similarly, weedy check recorded the highest soil dehydrogenase activity (DHA) and among post emergent herbicides glyphosate 41% SL IPA salt recorded highest whereas saflufenacil 70% WG recorded lowest soil DHA 30 days after treatment imposition.