Effects of two commonly used herbicides on soil microbial activity under conservation tillage

•The effect of herbicide on soil health and microbial community determines global food sustainability and security.•Two herbicides (glyphosate and paraquat) were used on two different grass species.•Soil phytochemical, soil microbial parameters and functional activity of microorganisms were determined.•Glyphosate stimulated an increase in soil available nitrogen, improved soil microbial activities compared to paraquat.•Glyphosate is a better choice for weed control in soil conservation tillage practice. Global food sustainability and security are largely dependent on soil health and the microbial community. However, research has shown that soil health and microbial community have been incidentally affected by herbicide application during weed management, especially in conservation agriculture. Hence, we present a study on the effects of a one-time application of two commonly used herbicides (glyphosate and paraquat) on nitrogen mineralization, microbial respiration, biomass, and functional activity of microorganisms in soil. Field application of both herbicides was carried out on two different grass species (Panicum maximum and Axonopus compresus) at the Federal University of Technology Teaching and Research Farm Akure, southwest Nigeria. Results showed that incubated soils treated with glyphosate were generally improved and significantly different (p≤0.05) for all parameters accessed. Glyphosate application on Panicum maximum gave the highest CO2-C mg g−1 day−1 compared with other treatments. Also, treatments involving glyphosate application on both Panicum maximum and Axonopus compresus gave a higher and significant (p≤0.05) microbial biomass value, and improved physicochemical properties except cation exchange capacity (CEC), calcium (Ca2+), and magnesium (Mg2+). A higher mean value for both NH4+ and NO3− was similarly recorded for glyphosate-applied treatments, with values significantly different (p≤0.05) from all other treatment means across the experimental weeks. However, based on functional analysis, the application of glyphosate caused an increase in (carbon metabolism, 2-oxocarboxylic acid metabolism, biosynthesis of amino acids) and decrease in (nucleotide metabolism, carbohydrate metabolism). Results obtained in this study will be helpful in ecological remediation, agricultural planning, and increasing soil fertility. [Display omitted]