Monday, November 13, 2006

Winter Flooding of Harvested Rice Fields Alters Soil and Rice Straw Enzymatic Activity and Soil Microbial Community Structure.

Robert M. Zablotowicz, USDA-ARS-SWSRU, PO Box 350, Stoneville, MS 38776, Clifford H. Koger, USDA-ARS-CG&PRU, 141 Experiment Station Road, Stoneville, MS 38776, and Timothy Walker, Mississippi State University, Delta Research & Ext. Center, PO Box 197, Stoneville, MS 38776.

Winter flooding of rice fields can be used to manage rice straw residue and weeds, and provide a habitat for migratory waterfowl habitat. This study was conducted on a Tunica clay in Stoneville Mississippi to assess the interactions of flooding and tillage on soil - straw enzymatic activity and soil microbial community structure as measured by total fatty acid methyl ester (FAME) of a harvested rice field.   A split plot design was used consisting of 14 weeks of flooding (November to February) or non-flooded as the mainplots, and rice straw remaining on the soil surface or incorporated by tillage as subplots.   Straw sampled from flooded plots had higher fluorescein diacetate (FDA) hydrolysis and ß-glucosidase activity during flooding compared to straw from non-flooded plots.  Activity of two soil enzymes, FDA hydrolysis and dehydrogenase, was greater in flooded plots compared to non-flooded plots with little or no effect of tillage.  However, the effect of flooding on ß-glucosidase activity in soil was not consistent.  Principal component analysis of total FAMEs indicated that the soil microbial community was altered in response to flooding but not tillage. In flooded plots 26% of the original rice straw remained, while in non-flooded plots 51% of the rice straw remained. The stimulation of microbial activity and alteration of soil microbial communities can contribute to enhanced rice straw degradation under flooded conditions.