ARS | Publication request: Effect of Differing Irrigation Water Sources on Nitrogen Fixation in Rice Fields

Submitted to: Mississippi Academy of Sciences Proceedings
Publication Type: Abstract
Publication Acceptance Date: October 30, 2002
Publication Date: February 1, 2003
Citation: Towery, S., Zimba, P.V., Zablotowicz, R.M., Mischke, C.C. 2003. Effect of differing irrigation water sources on nitrogen fixation in rice fields. Mississippi Academy of Sciences Proceedings 48:34.

Technical Abstract: Little research has been published on how different water sources affect potential nitrogen fixation in Mississippi rice fields. Water samples were collected from two fields irrigated with different water sources (well water and surface water sources) and nutrient (N, P, Si) concentrations were determined. Replicate sediment samples were analyzed for algal pigments (HPLC) and for nitrogen fixation (acetylene reduction method, GC). Nutrient levels in the surface water were higher than those in the well water. The nitrogen fixation potential was spatially and temporally heterogeneous, with the rice field receiving surface water having higher nitrogen fixation rates than the field irrigated with well water. Surface waters appeared to support elevated cyanobacterial-mediated nitrogen fixation rates (63% increase in light dependant nitrogen fixation rates relative to well water irrigation). Bacterial nitrogen fixation rates were 250% higher in the field receiving well water relative to surface water irrigation. Nitrogen fixation normalized to algal biomass (chl a) was higher in the surface water irrigated field. HPLC analyses revealed the presence of clorophytes, cyanobacteria, and bacillariophytes (diatoms). The seed population from surface waters may be an important source of nitrogen fixing organisms and irrigation management should consider the source of water used in irrigation of rice fields.