Evaluating the Response of Soil Organic Matter Mineralization and Microbial Biomass to Glyphosate under Slightly Alkaline Conditions

Farmyard manure (M) is an essential source of soil organic matter (SOM). Glyphosate (G) is a widely used active ingredient in agricultural production for weed control. Factors influencing SOM can also play a role in global greenhouse gas emissions. Even if it is not applied directly to the soil, glyphosate can reach the soil. It can either boost microbial activity by contributing C, N, and P or suppress it by inhibiting 5-enolpyruvylshikimate-3-phosphate synthase; both mechanisms may affect SOM mineralization. To evaluate this effect, an incubation study was conducted using a clay-textured, slightly alkaline soil with varying doses of M (0, 2.5, 5%) and G (0, 100, 200 mg kg⁻¹), and the soils were incubated at 30 °C. To evaluate the influence of glyphosate on soil organic matter dynamics, SOM concentration was assessed together with two key microbial activity indicators: microbial biomass carbon (MBC) and basal soil respiration (BSR). SOM (measured only on day 56), MBC and BSR were assessed on days 28 and 56 of the incubation. The results showed that increasing M doses led to significant (P