The effects of drought stress on agricultural crop productivity have been studied for decades. Plant water status is a function of water availability in the soil, water transport, water use throughout the plant, and atmospheric evaporative demand. In the absence of a reliable plant-based tool to measure water stress, irrigation was historically scheduled using estimates of soil water availability and/or crop evapotranspiration. 

   In the early 1990’s UC Davis Professor Ken Shackel initiated a new research program focused on developing a plant based tool for measuring plant water stress and scheduling irrigation. Dr. Shackel was interested in using a pressure chamber to measure stem water potential, characterize plant water status, and time irrigation throughout the growing season.  Pressure chambers had been used for years prior to this research to characterize plant water status and water stress. However, there were no tree crop reference water potential values available that could be used to guide irrigation scheduling decisions. Beginning in the early 1990’s

Dr. Shackel’s research established stem water potential as an accurate and reliable measure of water stress in prune (McCutchan and Shackel 1992). Later, a team of UC researchers lead by Dr. Shackel, including UC Cooperative Extension Farm Advisors, Extension Specialists and graduate students, improved the methodology for measuring SWP (Fulton et al 2001), and developed diagnostic thresholds linking SWP to levels of stress in almonds, walnuts and prunes (Shackel et al 1997 and 2000).  

The Fruit and Nut Research and Information Center collaborated with Dr. Shackel and Charlie Turner (Academic Technology Services, UC Davis) to create a new “Irrigation Scheduling Using Stem Water Potential Measurements” website. Our new website calculates reference water potential for almond, walnut, prune, and grape crops using weather data obtained from nearby CIMIS weather stations and reference water potential models (Shackel et al 1997 and 2000). The home page includes an interactive google map enabling users to select the closest CIMIS station, or the station in the most similar microclimate. We also include pages with background information on tree water use physiology, and a chart outlining the physical symptoms associated with a range of stem water potential measurements in prune, almond, and walnut.

 

 

References

McCutchan, H. and K.A. Shackel. 1992. Stem water potential as a sensitive indicator of water stress in prune trees (Prunus domestica L. cv. French). J. Amer. Soc. Hort. Sci. 117:607–611

Shackel, K.A., H. Ahmadi,W. Biasi, R. Buchner, D. Goldhamer, S. Gurusinghe, J. Hasey, D. Kester, B. Krueger, B. Lampinen, G. McGourty, W. Micke, E. Mitcham, B. Olson, K. Pelletrau, H. Philips, D. Ramos, L. Schwankl, S. Sibbett, R. Snyder, S. Southwick, M. Stevenson, M. Thorpe, S. Weinbaum, and J. Yeager. 1997. Plant water status as an index of irrigation need in deciduous fruit trees. HortTechnology 7:23–29.

Shackel, K., B. Lampinen, S. Sibbett, and W. Olson. 2000. The relation of midday stem water potential to the growth and physiology of fruit trees under water limited conditions. Acta Hort. 537:425–430.

Fulton, A., R. Buchner, B. Olson, L. Schwankl, C. Giles, N. Bertagnia, J. Walton, and K. Shackel. 2001. Rapid equilibration of leaf and stem water potential under field conditions in almonds, walnuts and prunes. HortTechnology 11:609–615.

The Fruit and Nut Research and Information Center (FNRIC) is excited to announce the new pomegranate section of our website. Pomegranate cultivation has surged over the past decade in California. The industry has grown rapidly from 4,800 acres harvested in 2001 to 28,000 acres harvested in 2011 (NASS 2013).

University of California Farm Advisors and Extension Specialists have been working hard to meet the demand for information about successful cultivation of pomegranate in California’s unique climate and soils, including several growers meetings and a new Pomegranate Program website hosted by the Fresno County Cooperative Extension office. The extensive new pomegranate pages on our site were written by FNRIC staff and reviewed by experts in UC Cooperative Extension and the USDA Germplasm Repository.

Our new pomegranate section contains a wealth of information about:

   -  Propagation

   -  Scion selection

   -  Orchard establishment

   -  Pests

   -  Harvest and postharvest practices

   -  Images of a pomegranate cultivars

   -  Links to additional resources

Expert Reviewers:

Louise Ferguson, UCCE Specialist, Department of Plant Sciences at UC Davis

Maxwell Norton, UCCE Advisor in Merced and Mariposa Counties

Jeff Moersfelder, USDA ARS National Clonal Germplasm Repository

 

I am excited to announce a new peer–reviewed section of our website focused on sweet cherry production in California. Sweet cherry was originally introduced into the United States in 1629, and production has been well established in California since the 1800s. Today, California produces 68,000 tons of sweet cherries at a market value of almost 200 million dollars (USDA 2012).

This new website includes information on a wide range of topics including:

     -  Ideal climate and soil conditions

     -  Pollination

     -  Fruit development

     -  Common propagation techniques

     -  Scion and rootstock selection

     -  Orchard establishment

     -  Image gallery of common pests and diseases

 

Expert reviewers:

Joe Grant (UCCE Farm Advisor in San Joaquin County)

Kitren Glozer (Project Scientist in the Department of Plant Sciences at UC Davis)

 

The FNRIC is hosting our 2nd annual fruit and nut tree extension course in February 2014, taught by UC faculty and specialists. We were awarded funding for four scholarships and are currently accepting applications from California growers. If you meet one of the following criteria please apply.

1) new grower with less than three years of experience working with tree crops

2)  in the process of transitioning between crops (ex. from peach to almond)

3) farm less than 40 acres of tree crops

Link to online scholarship application.

Link to course webpages for more information.

Applications are due October 1^st. The FNRIC advisory board, composed of UC faculty, extension specialists, and farm advisors, will meet to select scholarship recipients soon after the deadline. If you have questions please contact Brooke Jacobs (bsjacobs@ucdavis.edu, 530-754-9708).