Soil Properties and Fallow Season Vegetation Response to Prescribed Fire in Crop Residue.

Residue management programs vary based on residue, with prescribed fire serving as a critical practice in Mid-South agriculture. 128 soil samples (0-2.5cm) were collected across tilled, no-till, and burned treatments of wheat (Triticum spp.) stubble located on the Macon Ridge Research Station, Winnsboro, La. Samples were collected pre-burn and at 1, 24, 168, and 720-hrs post-burn and analyzed for chemical (SOM and macronutrients) and biological (microbial community structure and enzyme activities) properties. No difference was measured in SOM up to 168-hrs post-burn; however, SOM decreased (2.62 to 2.33 g kg^-1) at 720-hrs post-burn. Tillage decreased SOM by 8%. Nitrate-N increased 1-hr and 168-hrs post-burn, decreasing to pre-burn levels at 24 and 720-hrs post-burn. A similar increase at 1-hr post-burn was observed in no-till samples. Despite no treatment differences in NH₄⁺-N concentrations, highest concentrations were observed 24-hrs post-burn (25 mg kg^-1) before decreasing to pre-burn concentrations 720-hrs post burn. This decrease in NH₄⁺-N coupled with observed increase in NO₃^--N in burned soils may suggest increased nitrification rates. β-glucosidase activity was lowest 1-hr post-burn but increased to its maximum 168-hrs post-burn. A decrease in β-glucosidase activity was also observed in no-till samples; however, recovery rate was slower than observed in burned samples. β-glucosidase activity was lowest in tilled samples. Total bacteria were greatest under prescribed fire. Saprophytic fungi were greatest in tilled samples. Fungi and fungi:bacteria (mol%) were greatest up to 1-hr post-burn at which point the community began shifting from saprophytic fungi to AMF at 168-hrs post-burn. From 168- to 720-hrs post-burn, Gram positive bacteria dominated the microbial community. While prescribed fire influenced soil chemical and biological properties, observed differences in no-till samples suggests additional factors need to be identified. Prescribed fire effects on these soil properties cause shifts in soil microbial communities that may have far reaching implications.