Date of Award

6-2012

Degree Name

MS in Agriculture - Soil Science

Department

Earth and Soil Sciences

Advisor

Brent Hallock

Abstract

BASELINE GROUNDWATER COMPOSITION AND QUALITY BELOW IRRIGATED ALMOND AND WALNUT ORCHARDS IN DURHAM, CA, USA.

Candace A. Gallion

This study investigated groundwater quality in the Durham, California, USA area. The goal of the study was to determine baseline groundwater quality for the study area, whether crop type or time of year influenced groundwater quality, whether groundwater quality was significantly different among sample sites, and if groundwater quality test factors were correlated, and if any limiting factors for irrigation were present. Groundwater samples were collected and analyzed from eleven wells in almond (A2, A4, A5, A6, A7 and A8) and walnut (W1, W2, W3, W4 and W5) orchards and samples were sent to a laboratory to be analyzed for calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), sulfate (SO4), bicarbonate (HCO3), iron (Fe), chloride (Cl), and nitrate (NO3) concentrations, total dissolved solids (TDS), hardness, pH, electrical conductivity (EC), and sodium adsorption ratio (S.A.R.). Groundwater samples were collected in September 2008, March 2009, May 2009 and September 2009. Results were analyzed using One-Way ANOVA testing and a correlation analysis, both at alpha levels equal to 0.05. Not many differences were discovered among sampling times or between tree types. Potassium was the only factor significantly different between the almond (0.98 ppm) and walnut (0.73 ppm) sites, a trend possibly resulting from greater usage of potassium fertilizer in almond orchards as compared to walnut orchards. Sodium adsorption ratio was greater in March 2009 (0.35) and May 2009 (0.34) than either September sample (both 0.26) due to leaching of sodium into groundwater following rain events. Mean potassium concentration was greater in March 2009 (1.49 ppm) than in May 2009 (0.69 ppm), September 2008 (0.75 ppm) or September 2009 (0.63 ppm), also due to leaching of potassium into groundwater during the rainy winter months. Many differences were found among the sampling sites. In general, W1, W3, W5, A2, A4, A6 and A8 had lower concentrations of the test factors, and therefore purer groundwater, than W2, W4, A5 and A7. The majority of the test factors had significant, positive correlations with other test factors, with the exception of pH; pH had primarily significant negative correlations with the other test factors. Test factors were not present in groundwater at levels to cause any severe irrigation restrictions. Slight-to-moderate limitation levels were found for HCO3 (all sample sites), TDS and EC (W2, W4, A5, and A7), and NO3 (W1, W2, W3, W4, A4, A5, and A7). Overall, groundwater at the sampled sites was suitable for use as irrigation water, not many tree type or temporal differences in groundwater quality were discovered, many differences were found among sample sites, and many correlations were present among test factors. The information gathered and interpreted in this study will be useful for making management decisions regarding use of the tested groundwater for irrigation.

Keywords: groundwater quality, irrigation suitability

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