Atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) behavior was studied in four surface soils during incubations in laboratory conditions. Soils were chosen in relation to their cropping management (tillage and no tillage) and crop rotation system (continuous soybean [Glycine mar (L.) Merr.] and maize (Zea mays L.)-soybean rotation). A natural soil under brushwood was sampled as a reference. Atrazine use in field conditions was associated with maize cropping, thus only one soil received atrazine every other year. Atrazine behavior was characterized through the balance of 14C-U-ring atrazine radioactivity among the mineralized fraction, the extractable fraction, and the nonextractable bound residues. Soil organic matter capacity to form bound residues was characterized using soil size fractionation. Accelerated atrazine mineralization was only observed in the soil receiving atrazine in field conditions. Atrazine application every other year was enough to develop a microflora adapted to triazine ring mineralization. Bound residue formation was rapid and increased with soil organic matter content. The coarsest soil size fractions (2000-200 and 200-50 microm) containing the nonhumified organic matter presented the highest capacity to form bound residues. No effect of tillage system was observed, probably because of the uniform sampling depth at 20 cm, hiding the stratification pattern of soil organic matter in non-tilled soils.

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Summary Atrazine behaviour was investigated in the different pedological horizons from profiles of two non‐tilled soils, a Typic Argiustoll and an Entic Haplustoll from the Argentinean pampas. As atrazine use in field conditions was associated with maize cropping, only one type of soil received atrazine every other year. Atrazine behaviour was characterized through the balance of 14C‐U‐ring atrazine radioactivity among the mineralized fraction, the extractable fraction and the non‐extractable bound residues. The composition of the extractable fraction was characterized. Atrazine mineralization was the main dissipation mechanism in the superficial horizon of the Argiustoll because of microbial adaptation after repeated atrazine applications. In contrast, little atrazine mineralization was found in the Haplustoll profile, and it decreased with depth. The capacity of the soil organic matter to form bound residues was characterized using soil‐size fractionation. Atrazine‐bound residues depended on the soil organic matter content and the size of the fraction. Organic matter in the largest size fractions had a higher capacity to form atrazine‐bound residues. In the Argiustoll profile, the atrazine degradation capacity decreased in the subsurface horizons (Bt1 and Bt2), where a large part of bound residues were formed. The deepest horizon (BC) of this profile had a high capacity to degrade atrazine reaching this horizon after a lag period. In the Haplustoll profile, atrazine mineralization and bound residue formation followed the organic carbon mineralization pattern.

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.

One of the requirements for the forest restoration of soils disturbed by the oil-exploitation industry is that saplings be able to endure soil-adverse conditions. In this study, saplings of 20 species susceptible to be used in reforestation programs were evaluated for their ability to grow on substrates derived from soils disturbed by petroleum extractions in the Ecuadorian Amazon. Seeds of each species were planted in germination trays. Once seedlings reached 5 cm in height they were transplanted to plastic bags with three treatment substrates: two derived from petroleum-exploitation activity (soils from mud and drill cutting cells and from areas surrounding oil wells) and a control soil. Plant survival rate, stem height, and diameter were measured on a weekly basis until 14 weeks after transplantation, when we harvested the plants and also measured plant biomass and calculated the Dickson quality index for each species. Oil-exploitation by-product substrates impaired the performance of many saplings, with the substrate from mud and drill cutting cells being the one that most affected plant performance. Only saplings of five native species in the Amazon basin-Apeiba membranaceae, Cedrelinga cateniformis, Inga densiflora, Myroxylon balsamum, and Pouroma cecropiifolia-exhibited high or similar Dickson quality index values in all soil treatments and performed better than the rest. The use of these five species in remediation of soils disturbed by petroleum extraction in the Amazon basin could prove important because of their high potential to adapt to these disturbed sites.

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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.