Tuesday, November 6, 2007
212-9

Nitrogen, Phosphorus, and Potassium Losses from Flooded Rice Fields in Northern California.

Bruce Linquist1, Matthew D. Ruark2, James Hill3, Randall G. Mutters4, Chris A. Greer4, Johan Six5, and Chris Van Kessel6. (1) UC Davis, One Shields Ave, Davis, CA 95616, (2) Plant Sciences, University of California-Davis, One Shields Ave., Davis, CA 95616, (3) One Shields Avenue - 249 Hunt Hall, University of California-Davis, University of California-Davis, Department of Plant Science, Mail top 1, Davis, CA 95616, (4) University of California Cooperative Extension, 2279-B Del Oro Ave., Oroville, CA 95965, (5) University of California-Davis, Davis, CA 95616, (6) 1210A PES Building, University of California-Davis, University of California-Davis, Dept. of Plant Sciences, Davis, CA 95616-8515

Rice production accounts for approximately 200,000 ha of land in California’s Sacramento Valley.  Dissolved nutrient losses from these flooded fields can have agronomic, economic, and environmental impacts.  Increasing nitrogen (N) and phosphorus (P) concentrations in surface waters can cause increase eutrophication and alter natural in-stream processes.  Over the past 10 years, management of rice straw has changed from burning to incorporation.  While this has likely led to improvements in air quality, little is known regarding its effects on water quality.  The overall objective of this study was to determine the effects of straw management on seasonal and yearly N, P, and potassium (K) loading from rice production fields into the Sacramento Valley.  Specific objectives were to determine (1) water flux, (2) N loads and flow-weighted (FW) concentrations [as total dissolved nitrogen (TDN), nitrate, ammonium, and organic N), (3) P loads and FW-concentrations [as total dissolved reactive phosphorus (DRP) and total P], and (4) K loads and FW-concentrations [as dissolved potassium (DK)] from burned and straw-incorporated rice fields.  Between April 2006 and April 2007, paired fields (burned vs. incorporated) at four locations throughout the Sacramento Valley were studied.  The outlets of each field were outfitted with rectangle weirs and pressure sensors to record water flow.  Yearly losses of TDN, DRP, and DK ranged from 0.2 to 8.9, 0.1 to 5.7, and 0.5 to 7.8 kg ha-1, respectively.  Yearly FW-concentrations of TDN suggest that incorporated fields would lose greater amounts of TDN compared to burned fields.  However, TDN concentrations were noticeably higher during the winter months for incorporated fields, while burned fields had noticeably lower concentrations.  There were no apparent differences in DRP and DK between incorporated and burned fields.  The total water losses were significantly and positively correlated with TDN, DRP, and DK losses.

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