The envitonraental fate of glyphosate [Ai-(phosphonomethyl)glycinc] was studied in six crop residue (CR) types, three from maize [Zea mays L) (Ml, M2, and M3) and thtee from soybean [Glycine max (L.) Mem] (SI, S2, and S3). Glyphosate adsorption was characterized through isotherms. The glyphosate distribution in CRs was characterized through the balance of '''C-glyphosate radioactivity among the mineralized fraction, the e.xcractabk fractions (water and NH^OH), and the nonextractable fraction. Crop residues wete characterized by elemental composition, organic C, total N, and biochemical parameters (soluble fraction, cellulose, hemicellulose, and lignin). Total microbial activity (TMA) was also assessed. Limited and reversible glyphosate adsorption on soybean and maize CRs was determined. The sorption coefficient A^f index range for maize CR was 1.5 to 8.3 L kg"' and 2.6 to 7.4 L kg"' for soybean CR. Organic C and hemicellulose partially explained adsorption variability. The addition of mineralized and nonextractable fractions of the initial '''C-glyphosate applied on the CRs averaged 56%; however, differences were detected between soybean and maize CRs. Mineralization and nonextractable residues were 30.7 + 11 and 32.5 + 6% (soybean CR) and 44.3 ± 12 and 17 + 7% (maize CR), respectively.We hypothesized that glyphosate molecules could be used initially by microorganisms as a labile C source. High variability in ' ''C-glyphosate mineralization was observed in all crop residues, suggesting that the magnitude of the glyphosate mineralization process would be regulated by accessibility and the lability of^other carbonate sources.

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The recognition of glyphosate [(-phosphonomethyl) glycine] behavioral patterns can be readily examined using a pedoclimatic gradient. In the present study, glyphosate adsorption-desorption and degradation were examined under different scenarios in relationship to soil properties and soil use applications. Three sites with varied pedoclimatic conditions and two crop sequences were selected. Adsorption-desorption and glyphosate distribution in mineralized, extractable, and nonextractable fractions were assessed under laboratory conditions. Glyphosate sorption was characterized by isotherms and glyphosate degradation using the distribution of C-glyphosate radioactivity among mineralized fractions, two extractable fractions (in water, ER1; in NHOH, ER2), and nonextractable fractions. Results showed sorption indices (distribution coefficient and Freundlich sorption coefficient : 13.4 ± 0.3-64.1 ± 0.9 L kg and 16.2-60.6, respectively), and hysteresis increased among soil sites associated with decreasing soil particle size <2 μm, soil organic matter, and other soil properties associated with soil granulometry. A multiple stepwise regression analysis was applied to estimate the relationship between values and soil properties. Cation exchange capacity, water field capacity, and Bray-1 P were the soil properties retained in the equation. Soils under continuous soybean [ (L.) Merr.] (monoculture) treatment exhibited reduced glyphosate adsorption and decreased hysteresis desorption relative to soils under rotation. To our knowledge, these results are the first to demonstrate that soils with identical properties exhibited different glyphosate retention capacities based on crop sequence. We propose possible explanations for this observation. Our results suggested that characterization of the variability in soil property gradients can serve to determine glyphosate behavioral patterns, which can establish a criterion for use in reducing potential environmental risks.

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This article presents original geospatial data on soil adsorption coefficient (Kd) for two widely used herbicides in agriculture, glyphosate and atrazine. Besides Kds, the dataset includes site-specific soil data: pH, total nitrogen, total organic carbon, Na, K, Ca, Mg, Zn, Mn, Cu, cation exchange capacity, percentage of sand, silt and clay, water holding capacity, aluminum and iron oxides, as well as climatic and topographic variables. The quantification of herbicides soil retention was made on a sample of soils selected by Conditionated Latin Hypercube method to capture the underlying edaphoclimatic variability in Cordoba, Argentina. The glyphosate data presented here has been used to evaluate statistical methods for model-based digital mapping (F. Giannini Kurina, S. Hang, R. Macchiavelli, M. Balzarini, 2019) [1]. The dataset is made publicly available to enable future analyzes on processes that leads the dynamics of both herbicides in soil.