My research aims to determine a sensitive and continuous plant-based measure for irrigation scheduling in citrus trees. My two research hypotheses are: 1. Navel orange trees can withstand a moderate irrigation reduction below their full crop evapo-transpiration requirement (ETc); and 2. Sap flow (SF) will be the most sensitive continuous indicator of the onset of plant water stress. Previous research has shown that regulated deficit irrigation (RDI) during the early fruit growth and the fruit ripening phases can save water without compromising yield. I am conducting this research in 2013 – 2015, using Navel orange trees at the Citrus Experiment Station at UC Riverside. The study consists of one control and three treatment groups (RDI1, RDI2, and RDI3). The control receives 100% ETc. during all phases. The RDI1 group receives 25% ETc in late spring and 100% ETc al other times. The RDI2 group receives 100% ETc during late spring and 75% ETc during fall. During the first year, I was unable to apply RDI in the fall. For the second year, 25% ETc in spring was achieved by installing 18 gate vale regulators; and 75% ETc in the fall is currently achieved by installing 18 inline vale regulators. I have been going out to the field twice a month to download data from sap flow sensors and dendrometers and once a month to measure stem water potential. The remaining research tasks are to complete the irrigation treatments this winter and measure orange yield for each treatment.

1. Maximum Yield – Minimum Cost:
Developing Plant-Based Measures to Determine Irrigation
Needs of Orange Trees
Emily Nguyen Wieber
Committee Members:
Dr. H. Jochen Schenk, Dr. Darren Sandquist, and Dr. Joel Abraham 1

2. Background
• CA’s citrus crops
→ Brings $ 1.3 billion yr-1(Cooley et al. 2009)
→ Uses 80% of water supplies(Cooley et al. 2009)
→ Citrus growers often over-irrigate(Cooley et al. 2009)
→ Water becomes scare
• How to irrigate effectively?
→ Regulated deficit irrigation (RDI or DI) during the early fruit growth(Golhamer and
Salinas 2000 ) and fruit ripening period(Aquado et al. 2012, Ballester et al. 2011, Garcia-Tejero et al.2011,Ginestar et al. 1996)
→ Uses plant-based measures(Aquado et al. 2012)
2

3. 3
Irrigation Based on Crop Evapotranspiration (ETc)
Allen et al. 1998

4. Three Plant-Based Measures: Overview
4
Plant-Based Measures Pros & Cons
Stem water
potential (Ψstem)
is measured with
Pressure Chamber
(Scholander et al. 1965)
+ Direct measure of
water need
- Destructive, labor
intensive, & discrete
Sap flow (SF)
is measured with
Sap Flow Sensor
(Smith and Allen 1996)
+ Continuous
- Indirect measure of
water need
Max. daily trunk
shrinkage (MDS)
is measured with
Point dendrometer
(Steppe et al. 2006 and
De Schepper and Steppe 2010)
+ Continuous
- Indirect measure of
water need

5. Measure stem with Pressure Chamber
5
Taiz and Zeiger 2010
Goldhammer and Salinas 2000

6. Measure SF Volume with SF Sensor
6
ICT International
Ortuno et al. 2006

7. Measure MDS with Point Dendrometer
7
Daily stem
diameter variation
Cochard et al. 2001 Ortuno et al. 2006

8. Study Species & Field Site
• Navel Orange Trees
→ Citrus sinensis (L.) Osbeck
→ Root stocks, Carrizo citrange
→ 4 years old
• Study Site & Irrigation treatments
→ UC Riverside’s Agricultural Experiment
Station
→ DI will applied during early fruit
growth and the fruit ripening periods (
~ June to July & Oct. to Dec. in 2013
and 2014 )
8

9. Field Site
9

10. Irrigation Regulations
10
Legend:
Green: 1.0 ETc (control)
Orange: DI1,
25% ETc 06/01 – 07/15
100% ETc rest of the yr
Purple: DI2,
25% ETc 06/01 – 07/5,
75% ETc 10/16 – 12/15
100% ETc rest of the year
: Tree will be instrumented
: Irrigation timer and/or
pressure regulator

11. Measurable Variables
• Plant-Based Measures
→ Ψstem, SF, & MDS
→ The most sensitive measure will be use for 2nd year irrigation
scheduling
• Yield
→ Total fruit yield per tree (kg tree-1)
→ Ratio of total fruit yield to total amount of irrigated water
→ Fruit size, juice content, pH
11

12. Predicted results
12
ψstem: DI2 most negative; more
negative in summer than in winter
SF: DI2 lowest; increase in summer
MDS: DI2 highest; increase in early
summer

13. Predicted Results (Cont.)
13
0.00
0.50
1.00
1.50
2.00
15-Jun 15-Jul 14-Aug 13-Sep 13-Oct 12-Nov 12-DecSignalIntensity
Ψstem SF MDS
Signal intensity: SF > Ψstem and MDS

14. 14
Predicted Results (Cont.)
Fruit yield & quality: DI2 = control > DI1

15. Conclusions based on Predicted Results
• Plant-Based Measures
→ SF is expected to have highest signal intensity, and most sensitive
indirect measure of water need
→ Ψstem and MDS are expected to have equally lower signal intensities
• Fruit yield
→ DI2 is expected to save more water but yield the same as the
control
→ DI2 is expected to save more water & yield more than DI1
15

16. Significance
• Recommendation to growers for improving irrigation
scheduling
• This could lead to ~ 19% water savings yr-1
• Increased sustainability for CA’s citrus industry
16

17. References
Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300, 6541.
Aquado, A., Frias, J., Garcia-Tejero, I., Romero, F., Muriel, J., and Capote, N. (2012). Towards the improvements of fruit-quality parameters in citrus under deficit irrigation strategies.
International Scholarly Research Network, 2012. 1-9.
Ballester, C., Castel, J., Intrigliolo, D. S., & Castel, J. R. (2011). Response of Clementina de Nules citrus trees to summer deficit irrigation. Yield components and fruit composition. Agricultural
Water Management, 98(6), 1027-1932.
Blake, C. (2008). California citrus industry braces for impact of Asian citrus psyllid. Western Farm Press. Retried on November 15, 2012 from http://westernfarmpress.com/orchard-
crops/california-citrus-industry-braces-impact-asian-citrus-psyllid
California Economy. Retrieved on November 15, 2012 from http://www.netstate.com/economy/ca_economy.htm
Cochard, H., S. Forestier, and T. Ameglio. 2001. A new validation of the Scholander pressure chamber technique based on stem diameter variations. Journal of Experimental Botany 52, 1361-
1365.
Cooley, H., Christian-Smith, J., & Gleick, P. (2009). Sustaining California agriculture in an uncertain future. Pacific Institute, July Report, 1-81.
De Schepper, V. and K. Steppe. 2010. Development and verification of a water and sugar transport model using measured stem diameter variations. Journal of Experimental Botany 61, 2083-
2099.
Dinar, A. (2012, October). The water situation in California and the citrus industry. Power point presentation presented at the citrus conference, Porterville, Ca.
Garcia-Tejero, I., Hugo Duran-Zuazo, V., Luis Muriel-Fernandez, J., Martinez-Garcia, G., & Antonio Jimenez-Bocanegra, J. (2011). Benefits of low-frequency irrigation in citrus orchards. Agronomy
for Sustainable Development, 31(4), 779-791.
Garcia-Tejero, I. F., Duran-Zuazo, V. H., Arriaga, J., & Muriel-Fernandez, J. L. (2012). Relationships between trunk- and fruit-diameter growths under deficit-irrigation programmes in orange trees.
Scientia Horticulturae, 133, 64-71.
Garcia-Tejero, I. F., Duran-Zuazo, V. H., Muriel-Fernandez, J. L., & Jimenez-Bocanegra, J. A. (2011). Linking canopy temperature and trunk diameter fluctuations with other physiological water
status tools for water stress management in citrus orchards. Functional Plant Biology, 38(2), 106-117.
Ginestar, C. and Castel, J.R., 1996. Responses of young clementine citrus trees to water stress during different phenological periods. Journal of Horticultural Science, 71(4): 551-559.
Goldhamer D.A. & Salinas M. 2000. Evaluation of regulated deficit irrigation on mature orange trees grown under high evaporative demand. In: Proceedings of the International Society of
Citriculture IX Congress, Orlando, FL, pp. 227-231.
Grismer, M.E., Snyder, R.L., & Faber, B.A. (2000). Avocado and citrus orchards along the coast may use less water. California Agriculture, 25-29.
O’Brien, J. M. (2012, October 21). The vine nerds. Wired Science. Retrieved November 15, 2012, from http://www.wired.com/wiredscience/2012/10/mf-fruition-sciences-winemakers/all/
Ortuno, M. F., Alarcon, J. J., Nicolas, E., & Torrecillas, A. (2004). Interpreting trunk diameter changes in young lemon trees under deficit irrigation. Plant Science, 167(2), 275-280.
Ortuno, M. F., Garcia-Orellana, Y., Conejero, W., Ruiz-Sanchez, M. C., Alarcon, J. J., & Torrecillas, A. (2006). Stem and leaf water potentials, gas exchange, sap flow, and trunk diameter
fluctuations for detecting water stress in lemon trees. Trees-Structure and Function, 20(1), 1-8.
Scholander, P. F., H. T. Hammel, E. D. Bradstreet, and E. A. Hemmingsen. 1965. Sap pressure in vascular plants. Science 148, 339-346.
Smith, D. M. and S. J. Allen. 1996. Measurement of sap flow in plant stems. Journal of Experimental Botany 47, 1833-1844.
Spiegel-Roy, P, & Goldschimdt, E. E. (1996). The biology of citrus. Cambridge: Cambridge University Press.
Taiz, L., Zeiger, E. (2010). Plant Physiology (5th ed.). Sunderland, Massachusetts: Sinauer Associates Inc.
Steppe, K., D. J. W. De Pauw, R. Lemeur, and P. A. Vanrolleghem. 2006. A mathematical model linking tree sap flow dynamics to daily stem diameter fluctuations and radial stem growth. Tree
Physiology 26, 257-273.
Steppe, K., De Pauw, D. J. W., & Lemeur, R. (2008). A step towards new irrigation scheduling strategies using plant-based measurements and mathematical modelling. Irrigation Science, 26(6),
505-517.
Takele, E., Menge, J. A., Pehrson, J. E., Meyer, J. L., Coggins, C. W., Arpaia, M. L., et al. (1993). ECONOMIC-ANALYSIS OF INTEGRATED CROP MANAGEMENT-PRACTICES OF NAVEL ORANGES.
Journal of the American Society for Horticultural Science, 118(6), 910-915.
Takele, E., Meyer, J. L., Arpaia, M. L., Stottlemyer, D. E., & Witney, G. W. (1996). Economic analysis of irrigation and fertilization management of avocados. Hortscience, 31(1), 156-159.
USDA 2008. Farm and ranch irrigation survey. United States Department of Agriculture, Washington, D.C. Retrieved on November 15, 2012, from
http://www.agcensus.usda.gov/Publications/2007/Online_Highlights/Farm_and_Ranch_Irrigation_Survey/index.asp 17

18. Acknowledgements
18
• UCR’s Agricultural Experiment Station
→ Dr. Peggy Lemaux
→ Susie Lee
→ UCR Staff (Robert)
• Cal State Fullerton
→ Ed Read
→ Miguel Macias
• Family
→ Bob Wieber

19. Questions and Commences
19