Differential herbicide persistence and shifts in soil bacterial communities in Alfisol and Inceptisol

Amarachi Grace Nwokocha (Department of Agriculture and Industrial Technology, Babcock University)
Sani Idris (Department of Soil Science, Faculty of Agriculture/Institute of Agricultural , Research Ahmadu Bello University, 1044 Samaru, Zaria)
Adeniyi Ogunjobi (Department of Microbiology, University of Ibadan)
Olajire Fagbola (Department of Soil Resources Management, University of Ibadan)
Sonny T.M. Lee (Division of Biology, Kansas State University, Manhattan, Kansas)

SAINS TANAH - Journal of Soil Science and Agroclimatology
Vol 22, No 1 (2025): June

Weeds significantly reduce crop yields and promote herbicide use, accounting for 80% of agricultural pesticides. However, herbicide persistence and toxicity adversely affect soil microbial communities, impacting soil health and productivity. This study compared the effects of organic (Vinegar-weed-care: acetic acid) and chemical herbicides (PrimextraGold: Atrazine + S-metolachlor; Imazapyr: Isopropyl amine) on soil bacteria in Alfisol and Inceptisol from Ibadan, Nigeria. Soils were analysed for physical properties and microbial DNA, and herbicide degradation was tracked using GC-MS at 0, 4, 8, and 12 weeks. Alfisol exhibited higher fertility with pH 6.2, organic carbon 3.9 g kg-1, nitrogen 0.7 g kg-1, and phosphorus 25.9 mg kg-1, compared to Inceptisol (pH 5.5, organic carbon 1.9 g kg-1, nitrogen 0.6 g kg-1, phosphorus 20.8 mg kg-1). Herbicide persistence was greater in Alfisol: metolachlor (84.94%) and Imazapyr (61.00%) vs. Inceptisol (52.55% and 50.15%, respectively). Organic herbicide metabolites also persisted more in Alfisol (35.13%) than in Inceptisol (28.00%). In non-sterile Alfisol, biodegradation of PrimextraGold and Imazapyr was lower (43.46% and 10.30%) than in sterile soils (53.97% and 16.17%), while the organic herbicide biodegraded more in non-sterile (23.49%) than in sterile (17.08%). In non-sterile Inceptisol, Imazapyr degraded less (8.94%–31.72%) than in sterile (29.49%–34.75%), but atrazine degraded more in non-sterile (61.96%–68.17%). Organic acetamide degraded better in non-sterile Inceptisol (23.42%–90.5%) than in sterile (12.47%–30.7%). Chemical herbicides reduced Candidatus Udaeobacter, Pedosphaera, and Chthoniobacter in Alfisol, while organic herbicides enhanced them in both soils. These findings highlight the ecological benefits of soil-friendly organic herbicides.