Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2006
Publication Date: 9/20/2007
Citation: Zablotowicz, R.M., Locke, M.A., Gaston, L.A. 2007. Tillage and Cover Effects on Soil Microbial Properties and Fluometuron Degradation. Biology and Fertility of Soils 44:27-35. Interpretive Summary: Adoption of conservation management systems for cotton may improve soil quality and affect herbicide fate. Field and laboratory studies were conducted at Stoneville, MS, to evaluate the influence of tillage and a ryegrass cover crop in a cotton production system on soil microbial populations and enzyme activity, and herbicide degradation. Surface soils from ryegrass plots had the highest populations of various bacteria and fungi, while the highest soil enzymatic activity was observed in surface no-tillage ryegrass soils. Fluometuron degraded most rapidly in ryegrass residues and surface soil from both conventional and no-tillage ryegrass plots. These results indicate that a ryegrass cover crop system, under no tillage or incorporated under conventional tillage, stimulates biological components of soil quality and has the potential to promote rapid herbicide degradation in soils.
Technical Abstract: Field studies were conducted at Stoneville, MS, in 1994 and 1995 to determine the influence of tillage (no tillage [NT] or conventional tillage [CT]) and a ryegrass cover crop in a cotton production system on soil microbial populations and enzyme activity. Fluometuron degradation was evaluated under laboratory conditions using 14C-labeled herbicide. At planting, the surface 0-2 cm of NT soil had 59 to 74% greater soil organic carbon than CT soils in no cover crop plots, while organic carbon in surface soil from NT plots with a ryegrass cover crop were 106 and 112 % greater than CT ryegrass plots after the first and second year of ryegrass, respectively. Only minor and transient effects were observed on soil microbial populations due to tillage. However, surface 0-2 cm CT and NT soils under ryegrass had significantly greater populations of culturable total bacteria, gram-negative bacteria, fluorescent pseudomonads and total fungi. Ryegrass residues in NT soils maintained several hundred-fold greater microbial propagules densities than their underlying surface soils. The highest soil enzymatic activity (fluorescein diacetate hydrolysis, alkaline phosphatase and aryl acylamidase) was observed in surface (0-2 cm) NT soils under ryegrass, however, enzymatic activity in soils from surface CT ryegrass, and NT no ryegrass plots were generally greater than CT no-ryegrass plots. Fluometuron degradation in soil and ryegrass residues proceeded through sequential demethylation and incorporation of the trifluoromethylaniline ring into unextractable components. The most rapid degradation of 14C-fluometuron was observed in surface (0-2 cm) soil from CT and NT ryegrass plots. However, in the lower depth (2-10 cm) fluometuron degradation occurred more rapidly in CT compared to NT soils. A ryegrass cover crop system, under NT or incorporated under CT, stimulates biological parameters of soil quality (microbial populations and enzyme activity) and may promote accelerated herbicide degradation in surface soils.