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The Economic Impact of Water Quality on Citrus Production
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 Material Information
Title: The Economic Impact of Water Quality on Citrus Production
Physical Description: Fact Sheet
Creator: Wade, Mark A.
Publisher: University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
Place of Publication: Gainesville, Fla.
Publication Date: 2000
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Acquisition: Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Melanie Mercer.
Publication Status: Published
General Note: "Published November 2000."
General Note: "FE 217"
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Source Institution: University of Florida Institutional Repository
Holding Location: University of Florida
Rights Management: All rights reserved by the submitter.
System ID: IR00001865:00001

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The Economic Impact of Water Quality on Citrus Production1 Mark A. Wade2 1. This is EDIS document FE 217, a publication of the Department of Food and Resource Economics, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL. Published November 2000. Please visit the EDIS website at http://edis.ifas.ufl.edu. 2. Mark A. Wade, assistant professor, Department of Food and Resource Economics, University of Florida, Indian River Research and Education Center, Fort Pierce, FL. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Christine Taylor Waddill, Dean. Introduction Water is a vital component in the commercial production of citrus in Florida. Research since the 1960s has consistently shown that proper water management, primarily through irrigation, can increase tree size, yield, fruit size, and juice content. Water quality also has an impact on crop physiology and yield. Previous researchers have demonstrated that a general relationship between crop yield and water quality (primarily salinity level) exists, and that, beyond some given threshold level, lowering water quality (increasing salinity level) will gradually reduce fruit yield to zero. While this extremely low level of water quality is not the norm, it does illustrate that low quality irrigation water (LQIW) does impact fruit yields. The question then becomesby how much? Effects of Low Quality Irrigation Water In an attempt to analyze the impact of water quality, as measured by total dissolved solids or TDS, on citrus yield, researchers from the University of Florida's Department of Food and Resource Economics began working with citrus growers from Brevard and Indian River Counties. During the 1996-97 crop year, data was collected on TDS levels, tree age, tree density, variety, rootstock, rainfall, and yield. The effects of LQIW on oranges, organic oranges, and grapefruit were evaluated at different TDS levels by performing incremental regressions and comparing average yields for different TDS classes. The resulting coefficients provide an indication of the proportional impact of water quality (TDS) on citrus yield, when all other factors are held constant. Results Sample size, mean TDS level, standard deviation, and minimum and maximum TDS values for the study are listed by commodity in Table 1. The estimated coefficient on the TDS variable in the orange regression model was .2545. The estimated coefficient for TDS suggests that orange yield will be reduced by 2.5 percent for every 10 percent increase in TDS above the mean TDS level. This response is independent of any variations in tree age, tree density, variety or rootstock. The estimated coefficient in the TDS variable in the organic orange regression model was .3831.

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The Economic Impact of Water Quality on Citrus Production 2 This implies that TDS levels 10 percent above the mean will reduce organic orange yield by 3.8 percent. Many grapefruit growers during the 1996-97 crop year delayed fruit harvest in response to low grapefruit prices, picked only the highest quality fruit, or left most or all of the trees unpicked. Therefore, grapefruit modeling was hampered by a lack of quality harvest data and failed to yield any significant correlation between TDS level and yield. While the coefficient provides a measure of the overall strength of the relationship between TDS level and yield, it does not tell us when TDS levels first start to decrease yield. To answer this question, the orange data observations were placed in order of ascending TDS level and incremental regressions were run. The results show that even at the lowest TDS level (616 ppm) yields were slightly affected. As the TDS levels rose, yield losses increased. These results suggest that TDS levels above 715 ppm have a significantly negative impact on orange yield. Given that coefficient values between 1,230 and 2,533 levels are similar, it would suggest that blending higher quality surface water with LQIW to lower TDS levels would not be effective unless the blending brings the TDS level below 1,200. Citrus Yields by TDS Category Mean yield and economic values can be compared based on TDS levels for citrus production. Separating the TDS levels into three categories (low, medium, and high) allows for a more meaningful interpretation of the impact of water quality on citrus yield. Orange and organic orange yields were as expected, with increasingly higher TDS levels reducing yield. The grapefruit data does not follow this trend for reasons discussed above (Table 2). The economic impact of reduced citrus yield is also depicted in Table 2. Average on-tree Florida orange and grapefruit prices for the 1996-97 season (November 1996 June 1997) were used. Oranges were priced at $3.63 per box and grapefruit was priced at $1.37 per box. A separate price for organic oranges was not used, but it is possible that premium pricing may offset some of the economic impact of reduced yields. The economic value of citrus produced per acre was highest when irrigation water was of the best quality, or had the lowest level of TDS. Again, the grapefruit model did not demonstrate this relationship. Conclusion Citrus growers in Brevard and Indian River Counties have concerns about the use of lower quality irrigation water and its impact on yield and fruit quality. Previous research has determined that fruit yield and quality can be negatively affected when lower quality irrigation water is used, but has failed to quantify the degree to which yield is affected. This study found that yield was decreased by 2.5 percent for oranges and 3.8 percent for organic oranges for each 10 percent increase in TDS level above the sample mean. Orange yield decreased significantly at TDS levels above 715 ppm. It must be pointed out that the analysis used data from only the 1996-97 season, which had unusually high rainfall, record crop yields, and low prices. These factors must be considered when interpreting the results. Additional research on the impact of water quality on citrus yield is currently ongoing. Acknowledgments Appreciation is extended to the St. John's River Water Management District (SJRWMD) for funding the original research project and the development of this document. Additional information on water quality and other related topics can be found on the SJRWMD website at http://sjr.state.fl.us, and the University of Florida EDIS website at http://edis.ifas.ufl.edu. References Boman, B. "Managing Salinity in Citrus Irrigation Water." Indian River REC Report 99-6. Institute of Food and Agricultural Sciences, University of Florida, Indian River Research and Education Center, Fort Pierce, FL, 1999. Boman, B. and N. Morris. "Grove Design and Development." Indian River REC Report 99-8. Institute of Food and Agricultural Sciences, University of Florida, Indian River Research and Education Center, Fort Pierce, FL, 1999.

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The Economic Impact of Water Quality on Citrus Production 3 Byrne, P.J. and T.J. Stevens. Economic Impact of Lower Quality Irrigation Water on Citrus Production in Brevard and Indian River Counties: Phase II. Department of Food and Resource Economics, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, 1998. Haman, D.Z., J.C. Capece, and A.G. Smajstrla. "Irrigating with High Salinity Water." Bulletin 322. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, 1997.

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The Economic Impact of Water Quality on Citrus Production 4 Table 1. Descriptive statistics for TDS levels. Type Sample Size Mean (Average) TDS Level Standard Deviation Minimum TDS Value Maximum TDS Value Oranges 70 1,209.80456.91616 2,533 Organic Oranges 34 849.59 214.92616 1,337 Grapefruit 57 1,215.40 437.37 532 2,423 Table 2. Citrus yields and economic value by TDS category. TDS Category Yield (boxes per acre) Economic Value of Yield (dollars per acre) Oranges Organic Oranges Grapefruit Oranges Organic Oranges Grapefruit Low (500-1,000 TDS) 384.4229.54350.19 1,395.37833.23497.76 Medium (1,000-1,500 TDS) 301.63219.14453.47 1,094.92795.48621.25 High (>1,500 TDS) 260.13152.73392.47 944.27554.51541.79 ALL 316.14 224.97 404.49 1,147.59 816.64 554.15