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<br /> Salinity levels increased in bottom
<br /> basins particularly during the early sea- S.C. Scardaci is former Farm Advisor, UC
<br /> son when water holding periods of Cooperative Extension, Colusa County. UC
<br /> more than 30 days were in effect. In Davis:M.C. Shannon is Research Geneti-
<br /> some fields where salinity was exces- cist, USDA-ARS George E. Brown,Jr. Sa-
<br /> sive,grain yield was significantly re- linity Laboratory,Riverside;S.R. Grattan
<br /> duced. In contrast,water can be held is Plant-water Relations Specialist. Depart-
<br /> for the same period in fields low in sa- ment of Land,Air and Water Resources,
<br /> linity without affecting yields. UC Davis:and A.U. Eke and S.R. Roberts
<br /> The type of irrigation system and are former Staff Research Associates, S.
<br /> 'r pattern of water flow greatly influ- Goldman-Smith is former Post Graduate
<br /> enced salinity patterns in fields.In con- Researcher,and J.E.Hill is Agronomist,
<br /> 6 ventional and static systems,salinity Department of Agronomy and Range Sci-
<br /> levels increased as the distance from ence, UC Davis. We would like to acknowl-
<br /> the water inlet increased.Salinity was edge the late Max Spyres,former Colusa
<br /> highest in these areas during the early- County rice grower,for his pioneering
<br /> season water holding period.Water work in identifying salinity as a problem in
<br /> depths in rice fields are typically raised local rice fields and for his preliminary
<br /> to about 8 inches at 60 to 70 days after studies on the problem. Max's encourage-
<br /> planting to protect the developing meat was instrumental in conducting this
<br /> pollen from cold nighttime tempera- work. We also thank the numerous rice
<br /> tures. Raising water at this time dilutes growers whose cooperation made this work
<br /> Above,Rice grown in water at 6.8 dS/m, salts in the field water,countering possible. This project was partially funded
<br /> two to three times the threshold for salinity the increased salinity resulting from through the USDA Presidential Water
<br /> damage,shows severe leaf necrosis.In evapoconcentration.This is important Quality Initiative:The Sacramento River
<br /> basins where salinity is a problem,growers as it helps to moderate and control Rice Water Quality Demonstration Project,
<br /> can adopt mitigations such as adding fresh earl season salinity problems and dumber 94-EWQD 9520.
<br /> water or recirculating water among basins. Y y P
<br /> minimize late-season problems dur-
<br /> apparently is not a new phenomenon: ing pollination. References
<br /> in the early 1970s,when water holding Previous salt-tolerance guidelines in- Ayers RS,Westcot DW. 1985.Water qual-
<br /> was only required for several days,sa- dicated that rice yields are not ad- ity for agriculture. FAO Irrigation and Drain-
<br /> linity in outflow water was also higher versely affected until EC (root-zone age paper No 20(rev.1).FAO United Na-
<br /> than in inflow water.However,the cur- salinity) exceeds 3.0 dS/m or when EC. tions, Rome, Italy. 174 p.
<br /> [GCID]Glenn-Colusa Irrigation District.1997.
<br /> rent longer holding times appear to in- (inlet water salinity) exceeds 2.0 dS/m Water Measurement Report.Willows,CA.
<br /> crease the problem in salinity-prone (Ayers and Westcot 1985).However, an Henderson DW,Tanji KK,Biggar JW,et
<br /> areas.Salinity problems appear to be ex- independent field study (see p. 189) in- al. 1974.Water Quality in Rice Fields.Water
<br /> acerbated in areas irrigated with non- dicates that rice growth and/orgrain Science and Engineering Papers Dept.
<br /> of Water Science and Engineeringg((nnow
<br /> district water from drain or well water yield are reduced when the mean sea- Land,Air and Water Resources), UC Davis.
<br /> sources with higher salinity levels. sonal EC,.,,(field water salinity) exceeds Hill JE,Scardaci SC,Roberts SR,et al.1995.
<br /> When our studies were conducted, 1.9 dS/nl.Since ECr1„increases from top Rice irrigation systems for tailwater manage-
<br /> most district irrigation water on the to bottom basins in conventional s Y•s- mens.UC DANR Pub 21490(revised). 14 p.
<br /> Khatun S, Flowers TJ. 1995. Effects of
<br /> west side of the Sacramento Valley was terns and within basins in static sys- salinity on seed set in rice. Plant Cell
<br /> low in salinity (< 0.70 dS/m), while tents, ECS,should be substantially Environ 18:61-7.
<br /> some nondistrict water had salinity lev- lower than this threshold to maintain aLee MJ, Ross LJ,Wang RG. 1993. Integrat-
<br /> ing environmental toxicology and monitor-
<br /> els between 0.70 and 1.5 dS/m.The mean mean seasonal ECr,below 1.9 dS/m. ing in the development and maintenance of
<br /> summertime salinity level in the Colusa Rice growers should monitor salinity a water quality program:California's rice
<br /> Basin Drain at the Davis Weir was high- periodically in fields and basins where herbicide scenario(Ch. 18). In:Jolley FL,
<br /> est in 1994 1.2 dS/m when tail-water salinity may be problematic.When sa- Wang erneRGM (t:Int Effective and Safe Waste
<br /> ( � Y Y P Management:Interfacing Sciences and Engi-
<br /> outflow restrictions were in effect in linity is a problem,modifications may neering with Monitoring and Risk Analysis
<br /> portions of the Colusa Basin.They were be needed,such as adding fresh water Ann Arbor,MI:Lewis.
<br /> also high during the 19761977 to salt-affected basins or perhaps recir- Maas EV. 1990.Crop salt tolerance. In:
<br /> g g - Tanji KK(ed.).Agricultural Salinity Assess-
<br /> drought,when water availability was culating water among basins to reduce merit and Management Manual.ASCE
<br /> limited (GCID 1997).These findings in- the salinity in the lower basin. UC Co- Manuals&Reports on Engineering Practices
<br /> dicate that the quality of nondistrict operative Extension can offer valuable No 71. New York.p 262-304.
<br /> Shannon MC,Rhoades JD, Draper JH,et
<br /> water sources may be adversely af- assistance to growers in diagnosing sa- al. 1998.Assessment of salt tolerance in rice
<br /> fected under conditions of low water linity problems and better managing cultivars in response to salinity problems in
<br /> availability or restricted flow. rice farms. California.Crop Sci 38:394-8.
<br /> 188 CALIFORNIA AGRICUL1URE.VOLUME 56.NUMBER 6
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