Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2002
Publication Date: 8/1/2002
Citation: DING, G.S., HERBERT, S., NOVAK, J.M., XING, B. LONG-TERM TILLAGE EFFECTS ON SOIL METOLACHLOR SORPTION AND DESORPTION BEHAVIOR. CHEMOSPHERE. 2002. V. 48. P. 897-904.
Interpretive Summary: The amount of soil organic matter (SOM) has a strong influence on the quantity of pesticides retained by soils. While we understand the effects of tillage management on controlling the amount of SOM, very little information is known about how tillage management influences the quality of SOM and its ability to bind pesticides. In order to minimize potential water contamination by pesticides, it is important that we know how tillag management influences the quality of SOM and its reaction with pesticides. We examined the effects of two different types of tillage operations (conservation vs. conventional) on the qualitative chemistry of SOM and its ability to bind metolachlor (a herbicide). We found that conservation tillage favors the formation of sugar-like compounds in SOM that can bind more metolachlor than SOM under conventional tillage. Since more metolachlor is bound by SOM under conservative tillage, less metolachlor is savailable to leach to water bodies.
Technical Abstract: Sorption and desorption are important processes that influence the amount of pesticides retained by soils. Pesticide sorption is well known to be influenced by the quantity of organic matter, however, the effects of organic matter quality on pesticide binding are unknown. This study examined the sorption and desorption characteristics of metolachlor (herbicide) in whole soil samples and their humic fractions extracted from soils under long-term conservation tillage (CnT) and conventional tillage (CT) management. Soil humic fractions like humic acid (HA) were extracted using alkali solution techniques and humin (unextracted carbon material) was purified using acid washing techniques. Metolachlor sorption and desorption experiments were conducted with whole soils, HA, and humin fractions using batch-equilibrium methods. Sorption nonlinearity and hysteresis index values for HA and humin from soils under CnT were higher than humic fractions under CT. Metolachlor sorbed to humic fractions from soils under CT had a much lower hysteresis index indicating a stronger resistence to desorption. Metolachlor sorption/desorption differences between the humic fractions were explained by the humic fractions in soils under CnT having a lower distribution of carbon in aromatic-type structures compared to humic fractions in soil under CT. Long-term tillage management, therefore, has a strong influence on the qualitative properties of the humic fractions in the soil organic matter pool that will also significantly influence herbicide binding and potential leaching in a sandy Coastal Plain soil.