SPATIAL VARIABILITY OF CYANAZINE DISSIPATION IN SOIL FROM A CONSERVATION MANAGED FIELD

Authors: STADDON, W - EASTERN KENTUCKY UNIV; Locke, Martin; Zablotowicz, Robert

Submitted to: American Chemical Society Symposium Series
Publication Type: Book / Chapter
Publication Acceptance Date: 5/1/2002
Publication Date: 3/1/2004
Citation: Staddon, W.J., Locke, M.A., Zablotowicz, R.M. 2004. Spatial variability of cyanazine dissipation in soil from a conservation managed field. American Chemical Society Symposium Series. In: Nett, Mary T., Locke, Martin A., and Pennington, Dean A., editors. Water Quality Assessments in the Mississippi Delta. Oxford University Press, pp. 179-193.

Interpretive Summary: Assessing spatial characteristics of soils may provide the basis for using precision application technology to reduce herbicide input. Spatial variability of cyanazine dissipation in relation to soil characteristics was evaluated in soil from a conservation tillage cotton field as part of the Mississippi Delta Management Systems Evaluation Areas (MSEA) Project. Cyanazine dissipation was most influenced by soil pH and texture, with the longest residual herbicide remaining in areas of the field where soil was more acidic and had a higher clay content. These observations demonstrate the importance of knowing where trends in soil characteristics occur within a field so that varying rates of chemicals can be applied as needed.

Technical Abstract: Assessment of soil spatial characteristics may provide the basis for using precision application of herbicides to reduce chemical inputs. Spatial variability of cyanazine degradation and sorption in relation to soil characteristics was examined in soil from a reduced tillage cotton field (2 ha, no-tillage, wheat cover crop) in the Mississippi Management Systems Evaluation Areas (MSEA) Deep Hollow watershed. Soil was sampled in a grid (n=100), and samples were collected in spring, 1999. Soil characteristics evaluated included pH, organic matter (OM), texture, cyanazine sorption, and microbial metabolic activity. Cyanazine degradation during laboratory incubation (28 d) was assessed using 14**C labeled cyanazine. Subsamples were extracted with methanol, processed, and analyzed by TLC. Cyanazine sorption was measured using batch methods. Half lives of cyanazine ranged from 5 to 26 days with greatest persistence correlated with the highest clay content (r=0.73) and negatively correlated with pH (r=.80). Major metabolites observed were cyanazine amide and polar hydroxy derivatives. Spatial trends were modeled using a surface quadratic equation and/or geostatistics, and data were detrended where appropriate. Many parameters, such as cyanazine sorption, showed highly significant trends across the field. Cyanazine half-life and metabolite accumulation had spatial structure that could be modeled with a semivariogram, while no spatial structure was observed for soil organic matter.