The effect of biostimulants and glyphosate on the vertical migration of elements in agricultural soils

Abstract The purpose of this study was to evaluate the vertical migration patterns of macro- and microelements in southern chernozem soils under the influence of binary mixtures of glyphosate-based herbicides and various classes of biostimulants. The intensification of contemporary agricultural systems has precipitated a fundamental shift in the biogeochemical cycling of nutrients and contaminants within the pedosphere. This study presented an exhaustive investigation into the vertical migration mechanics of macro- and microelements within a model soil continuum, specifically analysing the perturbations introduced by the co-application of glyphosate-based herbicides and diverse biostimulant classes (fulvic acids, potassium humates, and complex stubble biodestructors). High-resolution Energy Dispersive X-Ray Fluorescence (ED-XRF) spectrometry was utilised to quantify the redistribution of Fe, K, Ca, Mn, Zn, Cu, and Pb across three distinct soil horizons in controlled microcosms. The research delineated the diametrically opposed geochemical functions of humic fractions: fulvic acids (“BioFulvo”) acted as aggressive mobilising agents, stripping transition metals from the medial profile and exacerbating leaching risks (Fe depletion of -30.1% in the transit zone), whereas potassium humates functioned as stabilising geochemical barriers, effectively immobilising anthropogenic lead and retaining nutrients in the root zone. A critical discovery of this study was the identification of a “hyper-mobilisation” phenomenon arising from the synergistic interaction between glyphosate and fulvic acids, which induced a 39% surge in soluble iron concentrations, likely through the development of ternary phosphonate-fulvate-metal complexes. Conversely, microbial-humic biodestructors demonstrated a unique “biofortification” potential, maintaining high zinc and manganese bioavailability without compromising profile stability. These findings underscored the necessity of a differentiated approach to agrochemical management, suggesting that while fulvic acids enhance rapid nutrient transport, their combination with herbicides on sensitive soils poses significant environmental risks, which can be mitigated by the buffering capacity of high-molecular-weight humates