Measuring "blood pressure" in trees: a new approach to efficient irrigation
By Ken Shackel
Plant Physiologist
University of California at Davis Agricultural Experiment Station

How do you know when a tree, or any plant for that matter, is thirsty?  If the tree gets a little thirsty before getting it's next drink of water, will it be more water use efficient?  The desire to answer these questions led UC Davis professor Ken Shackel to develop a small device that measures the tension on the water in the plant, a tension that is much like the pressure in our own blood vessels.  In plants, tension is the way water must be extracted from the soil, and all of the water that is lost by the leaves must be replaced by water extracted from the soil.  Quite a lot of water is lost from leaves, for example, a peach tree growing under the hot, dry summer conditions of California's central valley, can loose the equivalent of it's entire body weight every day.  Replacing this water would be like a 150 pound person having to drink 18 gallons of water daily, just to keep up with sweating!

Keeping pace with evaporation is quite a job for the plant when the soil is wet, but it gets even more difficult as the soil dries.  Plants must keep up this pace in order to remain active and productive, and this is the reason why farmers are reluctant to withhold water from crops.  When water is depleted in the soil, the plant starts to experience what is equivalent to high blood pressure in humans: the dryer the soil, the higher the tension required to pull the water.  When the tension within the plant gets to high, plant growth is reduced, leaves wilt, and the process normally used to harness the sun's energy (photosynthesis) grinds to a halt.
 

The device developed by professor Shackel is a hand-pump version of a pressure chamber (also known as a pressure "bomb") which has been used in plant-water research to measure the tension in plants since the 1960's.  The operation of the device is very simple: a leaf is removed from the tree and placed in the chamber with a bit of the stem of the leaf, the petiole, exposed to the outside, through a rubber seal.  Air pressure is then increased in the chamber until water just appears at the cut surface of the petiole.  The pressure required to begin extracting water from the leaf is equivalent to the tension on the water within the leaf.  If it takes a lot of pressure to extract water from the leaf, the plant is experiencing "high blood pressure"

Published results using this approach to diagnose plant water stress have been somewhat inconsistent when sunlit leaves have been used, but professor Shackel has found that the environment of the leaf may be a critical factor in fruit trees.  By covering the leaf with a reflective plastic envelope before measurement, which stops the process of water loss, professor Shackel has found remarkably uniform values that are closely related to common symptoms of water stress, such as lower plant and fruit growth rate.  These symptoms are usually difficult to detect until they become obvious, and then it is usually too late to reverse the damage that has been done.  The pressure required to extract water from a covered leaf is also much less than that required for a sunlit leaf, so it was possible to design a much more portable, hand-pump pressure chamber that could be easily used by growers.

In addition to the convenience of this device, professor Shackel has found that under some conditions a substantial amount of irrigation water can be saved by allowing trees to experience moderate water stress.  Savings of over 40% were achieved in a prune orchard over a 3 year study, without harming fruit yield, and with the added bonus that there was less water content in the fruit at the time of harvest.  In prunes, less water content means less energy is required to dry the fruit, so the grower pays less to have the fruit dried.  The pressure chamber has been tested in a number of other crops and works well in all of them.  In addition to saving water however, research in almonds, cherries, and other fruit trees has shown that there may be many opportunities where moderate water stress can be used to the growers advantage.  For instance, excessive tree growth can be reduced, hence reducing the need for pruning.  At the present time, a large scale demonstration project using this device to manage irrigation is underway in prune orchards across California.

See http://fruitsandnuts.ucdavis.edu/General_Management/The_Pressure_Chamber,_aka_The_Bomb.htm for a site on the internet with additional information about the pressure bomb.

On-site wastewater treatment systems r

Bruce Lesikar
Extension Agricultural Engineering Specialist
The Texas A&M University System

Fig 1: A subsurface drip system

A subsurface drip system distributes wastewater to the lawn through a system of tubing installed below the ground surface. It consists of four main components: a treatment device, a pump tank, a filtering device and a drip distribution system. Several treatment devices are available, including an aerobic unit, sand filter, trickling filter or constructed wet-land. The choice of treatment device depends on the type of drip tubing being used and the manufacturer's recommendations. The minimum treatment required is a septic tank to settle the solids. Most drip systems require additional treatment of the wastewater before it enters the filtering system. The pump tank stores the water until the drip field is ready for a dose of water. A high head pump delivers the water from the pump tank through the filtering device to the drip distribution system. The filtering device can be a sand, disk or screen filter. Its main purpose is to remove larger particles from the wastewater so they do not clog emitters. Depending on the wastewater quality, the filter may need to be an automatic cleaning system. The drip distribution system is made of a drip tubing approved by the manufacturer for use with waste-water. The collection manifold for the drip system needs to be connected back to the treatment device for flushing solids collecting inside the drip tubing back to the treatment device.

Fig 2: A subsurface drip system distributes water uniformly in the laws

The drip system has very small emitters that can become clogged with organic matter and solids if the system is improperly maintained. Drip distribution systems require an ongoing maintenance contract to operate and maintain the drip field. The treatment system needs to be pumped every 2 to 3 years to prevent solids from being dosed into the drip tubing and the filtering systems needs to be checked periodically.

Installation generally costs between $4,000 to $10,000, depending on the type of pretreatment, filtering device and monitoring system. The pretreatment system is a large component of the installation costs. A drip distribution system generally costs $2,000 to $3,000. Maintenance costs are about $300 to $600 per year, which includes periodic pump out, electricity and required maintenance visits.

Scheduling irrigations for lawns , and crops using air temperature data reported in the newspaper.

Ted Sammis Irrigation Engineer
New Mexico State University
Agricultural Experiment Station

Simple methods work the best when trying to determine the amount of irrigation water to apply to a landscape or crop. The simplest method is to get the current and predicted temperature data from the newspaper or an internet site and fill out a simple form on the internet that will calculate how much water to apply to your landscape or crops using a drip or sprinkler irrigation system. The form can be downloaded and run independently of the internet connection, and requires only the Netscape or Explore internet browser.

What you want to know when watering the lawn , or crops is how much water to apply and when to apply it . The when question is easy when using a sprinkler or drip system: irrigate every other day during the summer months and once a week during the rest of the growing season. How much to irrigate is also simple. Apply enough water to replace the water that has been removed by the crop since the previous irrigation. This is done using the Evapotranspiration Wizard which calculates daily water use for warm and cool season grasses. The wizard is set up for warm season and cool season grasses  and agriculture crops (Table 1).

You select the wizard program for the type of vegetation. If you are watering grass you also want to select the level of watering that produces the  desired visual quality of grass. Consequently, select the view button and a picture of the grass varieties under high, medium, and low water levels will be shown. The greener the grass, the more water it requires and the higher the water bill at the end of the month. For agriculture crop, economics dictates that you do not stress the crop for water.

You will also need the latitude of where the temperature data is measured. This can be acquired on the internet using Getty Thesaurus of Geographic Names . 

Table 1. Location of Evapotranspiration Wizard

Crop	Wizard Location on the internet
Warm season grass	http://weather.nmsu.edu/nmcrops/grasses/Warm-season/warmsgpetc.htm
Cool season grass	http://weather.nmsu.edu/nmcrops/grasses/Cool-season/coolsgpetc.htm
Agriculture Crops	http://weather.nmsu.edu/pet/JS_pet.htm

Output table from the Wizard gives the daily water use   (Evapotranspiration , ET) in inches/day. The time to run the irrigation system is the time necessary to apply that depth of water over the area of the yard or field divided by the efficiency of the system. The irrigation efficiency of a sprinkler and drip system can be estimated as 0.9 which means that 10% more water should be applied than the daily water use.

Table 2. Out put table from Evapotranspiration Wizard

Date	Max. Temp	Min Temp	Gdd	Pet (inches)	Crop Coef.	Et inches	Cum. Et inches
02/11/200	71	37	516	0.27	0.30	0.08	1.43
02/11/2000	68	34	530	0.26	0.31	0.08	1.51
02/13/2000	66	31	543	0.25	0.31	0.07	1.58
02/14/2000	74	43	556	0.22	0.32	0.07	1.65

For a sprinkler system , measure the depth of water application by putting a jar or can  in the yard and running the sprinkler system for 1 hr and then measure the depth of water in the jar. Generally, a sprinkler system will apply about  0.2-0.3 inches/hr. For a drip system used on turf or crops, the depth of water applied depends on the flow rate of the drip tubing usually given in gpm/100ft of tubing and the spacing between rows of tubing. The depth (in/hr)  = flow rate (gpm/100ft) /distance between rows (ft) * 0.95. Consequently, the application rate for drip tubing that has an application rate of 1 gpm/100ft ft that is spaced every 3.5 ft  is 0.3 inches/hr. The time to run the system is the calculated depth of application divided by the rate of application. Here is an example: it has been two days since irrigation and the Wizard has indicated a water use of 0.4 inch/day then the gross application should be 2days*0.4inches/day/0.9=0.88 inches and if the rate of application is 0.3 inches/hr then the irrigation system should be run for 0.88inches/0.3 inches/hr = 3hr.
 
 

About Western Regional Research Committee -W128
Microirrigation Technologies for Protection of Natural Resources and Optimum Production

The W128 regional research committee is composed of researchers, and extension personal from land grant universities and the Agriculture Research Service of the USDA that work together to promote knowledge about drip irrigation. The specific goals of the committee are:

To evaluate and refine microirrigation management strategies to promote natural resource protection and optimal crop production.
To improve, modify, and evaluate microirrigation system design and components for natural resource protection and optimal crop production.
To assess and develop decision criteria for adoption of microirrigation technologies.
To promote appropriate microirrigation technologies through formal and informal educational activities.

Additional information about the research and extension activities conducted by the committee can be acquired from their home page located at
http://www.cropinfo.net/W-128/w128.html. The contact person for additional information about drip irrigation is your local cooperative extension service person list in the phone book in the county government section, or contact one of the members of the W128 committee listed on the home page.
 
 

If you note any broken links or errors in this web site or have information to contribute or difficulty obtaining information about the W-128 working group, please contact
Dr. Clinton C. Shock
Malheur Agricultural Experiment Station, Oregon State University
595 Onion Avenue
Ontario, OR 97914
(541) 889-2174
FAX (541) 889-7831
Clinton.Shock@oregonstate.edu

Last updated  Monday July 14, 2008.