Installed: 12/96-------------------------------Updated: 8/22/09

The Irristat™ Page


A discussion of the contingencies leading to the invention of the Irristat™ (e.g., extensive experience from my work, with B.J. Davis, during our development of polyacrylamide gel electrophoresis, and problems with my bonsai hobby) quoted from my downloadable:

"Tenuous but contingent connections" (264K) (abstracted on, my Home Page) follows:

(if you don't already have it !)

"When I first moved to Westchester, I purchased a home on one third of an acre in a small development. Two thirds of the property had been clear-cut for construction, so I quickly planted the landscape densely with trees and bushes to hide the scar. I developed an interest in growing potted, dwarfed Bonsai trees. As time progressed, the landscape trees grew to tower over my property and steadily reduced the sunny area where I grew my Bonsais. In order to maintain a moderate-sized collection in the ever-contracting sunny space, I began to specialize in Mame Bonsai, potted trees usually less than 6 inches tall. In the fall of 1976, instead of mulching my collection into the hillside for their winter rest, I decided to build an étagère for my living room, illuminated with fluorescent lights, to be able to enjoy my trees throughout the year. When relative humidity of the air is low, as in a closed home during the cooler seasons, such trees need to be watered twice a day because of the large ratio of foliage to root mass and soil. For esthetic reasons, there were no dishes under the pots, so each of the 50 or so trees had to be dosed carefully so as not to wet the living room floor (or, alternatively, leave a tree dessicated), and it took about 30 min. each morning and evening. Everything was progressing swimmingly until November, when I had to attend the annual meeting of the American Society for Cell Biology. I prepared a shelf-map of the trees for my wife, with the number of squirts from a spray-bottle of water required for each pot, and went off to my meeting. When I returned, a few of my most prized Bonsai were dessicated and dead. It was too late in the season to move the trees out of the house---and I suddenly felt more trapped by these "pets" than I had ever felt about the care demanded by our numerous animal pets. There had to be a technological way out of this bind!

When first working out gel formulations for electrophoresis, BJ and I learned how readily slightly-cross-linked polyacrylamide gels would swell in water. An osmometer filled with a solution of non-ionic, long-chain, linear, hydrophilic polymer behind a water-permeable, polymer-impermeable membrane will, at equilibrium, develop a head-pressure equal to the chemical potential of the water in any medium in contact with the other side of membrane. As the concentration of such polymer inside the osmometer is increased, the osmotic potential rises faster than the increase in molarity [113] . In fact, a very-slightly-cross-linked gel will behave similarly, even though it can be considered to be a single molecule which, "ideally" should develop no osmotic pressure at all. Only when substantial levels of cross-linking are achieved, will a neutral gel behave "ideally" and not swell in distilled water.

Soil moisture availability can be measured by the chemical potential of water, which is equal to the osmotic potential. Therefore, I realized I could design a device, consisting of a small cylindrical chamber, a porous membrane or fine mesh across one end, a piece of slightly-cross-linked polyacrylamide gel (e. g., about 0.1 % cross-linking monomer) behind the membrane, a cylindrical piston behind the gel, and a flexible water conduit between the piston and a valve-seat closing the bottom ofthe cylinder. When this device is placed in soil in the root-zone of a plant, one end of the conduit attached to a pressurized water reservoir e. g., 0.5 to 15 Ibs./in.2) by narrow-bore (e. g., 0.03" I.D.) plastic capillary tubing, and the other, attached to a short length of tubing which leads to, or near to, the soil surface, this "Irristat" valve will open and close in negative feedback (Fig. 6). As the plant's demand for water varies (e. g., between night and day), much like a thermostat, the valve will hold the soil moisture at a pre-set level, determined by the composition and size of the gel and the size of the cylindrical chamber [114]. The 2 cm3 Irristat valve can support potted plants, agricultural crops and trees, and has been successfully and fairly extensively tested [115, 116]. It provides the most efficient possible irrigation. It is just now going into production for home and agricultural markets. Irristat valves now support all of my Bonsais, all of my houseplants and some of my foundation planting and landscape.

When musing on its possibilities for agriculture in arid lands, I tried to imagine the consequences of covering the Sahara Desert with a forest irrigated with the extensive fossil aquifers that lie beneath it. Unless the forest induced sufficient increase in natural rainfall by positive feedback [117], such a plan would eventually fail as the aquifers dried out. This has involved me with global weather modeling at the Goddard Institute for Space Studies in New York City [118]. Even this tangential excursion was contingent on connections to people and experiences leading to and from Disc Electrophores." This study is covered on CureForGlobalWarming.html

"In 1959, when my colleague, B. J. Davis, and I first worked out formulations of cross-linked, polyacrylamide gels to substitute for O. Smithies' starch gels (29) for zone electrophoresis (30,31,32), we had to determine the minimum level of cross-linking, with methylene-bis-acrylamide, to prevent significant osmotic swelling of the gels during, or after, the electrophoretic runs. At that time, I came to appreciate that, as the number of cross-links decreases (and therefore, the distance between them increases), the osmotic behavior of a gel begins to closely approach that of an equivalent solution of long-chain polymers. That is, a slightly-cross-linked gel behaves as if it consisted of a solution of an appreciable molal concentration of unhindered short-chain segments, yielding a finite, and quite respectable osmotic potential . As such a gel swells in contact with water, however, tension develops along the chain and the number of unhindered and unconstrained segments diminishes, reducing the osmotic potential much faster than can be accounted for by the "dilution" of the gel by swelling. A very useful measure of the actual degree of cross-linking within a gel is the number of times the volume of a dried gel increases when equilibrated by immersion in a large volume of distilled water. An uncross-linked "gel" (i.e., a true solution of individual polymer molecules) "swells" without limit in such a test." Quoted from The Irristat™.

The detailed technical background describing the Irristat™, U.S. Patent 4,182,357, can be found in my unpublished downloadable:

The Irristat™ : "A Key to a New Irrigation Technology" (77K), which is abstracted below:

(if you don't already have it !)


"With existing irrigation technology, it would be too expensive and wasteful of water even to try to support highly productive agriculture on the vast tracts of hilly, erosion-prone, semi-arid lands which have soils that vary in depth and permeability almost from one plant location to the next. Inexpensive, self-regulating, moisture-sensitive irrigation-valves used one-to-a-plant in drip-irrigation systems, might compensate perfectly for such variability with little waste of water and at a reasonable cost for the device and its installation. Relevant plant physiology, soil physics and physical chemistry are reviewed to define the sensitivity required for such a device. Analysis reveals that previously described designs lack the required sensitivity. The characteristics of osmotic tensiometers are examined for their suitability as moisture sensors for such valves, and the non-ideal osmotic behavior of polymers and hydrogels (e.g., very slightly cross-linked polyacrylamide) is shown to provide the requisite sensitivity for a workable design. The 2-cubic centimeter Irristat™, and its operating characteristics, are then described. Its performance at a number of test-installations is briefly reviewed and its advantages in agricultural applications are outlined."

Figure 1

You can also download,

"The Irristat™: A Moisture-Sensitive Self-Regulating Water Valve for Drip Irrigation Systems" (132K), Drip/Trickle Irrigation in Action Vol. 2 ASAE Pub. 10-85, St. Joseph, Mich., pp.623-629; (Proc. of the Third Intern. Drip/Trickle Irrigation Congress, Nov. 18-21, 1985, Fresno, CA),

which contains a description of the Irristat™, a general discussion of its applications in agriculture, including a description of a system I installed for R. G. Evans and E. Proebsting for 60 mature sweet cherry trees at the Irrigated Agriculture Research and Extension Center of Washington State University, Prosser, WA. An excerpt of the introductory portion follows:



The Irristat™ (Figs. l & 2) uses a uniquely formulated, synthetic polyacrylamide gel as its moisture-sensing element. It is buried in the soil near a plant's roots (e.g., Fig. 3).

------ --Fig. 2 Irristat™-----------------------------Fig. 3 Potted Plant with Irristat™

Water is conducted by capillary tubing from a water supply, through a thin-walled rubber tube within the Irristat™ (See Fig. 1), and then through an attached length of capillary tubing to, or near to the soil surface. The water percolates down through the soil, passes through the Irristat's™ porous polyester fiber membrane, and reaches the moisture-sensing element,the gel.

As the gel becomes more moist, it swells, pushing the Irristat's™ piston against the rubber tube. When the moisture in the soil surrounding the Irristat™ reaches a predetermined set-point, the swollen gel causes the piston to pinch the rubber tube closed, cutting off the supply of water.

As the plant draws moisture from the soil, the gel shrinks, reversing the cycle. When the moisture level falls below the Irristat's™ set-point, the piston moves back, relieving the pressure on the rubber tube, and water begins to flow (Fig. 4).

Fig. 4 Open-Close Cycle

Buried in the soil, Irristats™ will function reliably for many years. The body parts and piston are molded of polypropylene; the water conduit is made of silicone rubber; the semi-permeable membrane, of Dacron-like polyester fibers; and the moisture-sensitive gel, of slightly-cross-linked polyacrylamide. All are chemically, biologically and physically durable.


You can also download:

Evans, R.G., Proebsting, E.L., and Kroeger, M.W. " Water-Sensitive Valves for Monitoring Crop Water Use Patterns" (528K) Presented at the Metting of ASAE, Chicago IL, December 16-19, 1986,

which describes the performance of the Irristat™ on the 60 cherry trees referred to above, and is abstracted below:

(if you don't already have it !)


"Water application and pan evaporation data were collected for two and one-half years on mature sweet cherry trees. They show that it is possible to inexpensively monitor daily and seasonal crop water use patterns for perennial, woody plants. Such data have been previously unavailable. Linear regression analyses showed high correlation between pan evaporation and the water applied by a soil water-sensitive, self-regulating valve/sensor located in the root zone. Water applications were affected by the location of the valve/sensor with respect to the application point. Daily analyses of the data provide an indication of the crop coefficients throughout the season. The Irristat valve/sensor can be used in crop water use investigations for many crops, but it is particularly advantageous with perennial, woody horticultural crops."

You can also download:

"The Irristat™ Instruction Manual: Irristat™ for Potted Plants" (176K) ;


"Irrigation of New Plantings in Competition with Established Major Plantings" (44K) by S. Bogyo, Pres. Irristat International, Inc.; a discussion of the use of Irristats in Landscaping Applications.

(if you don't already have it !)


For access to information on Drip, Trickle and Microirigation technology in general, go to TRICKLE_L and the WWW Virtual Irrigation Library, and for specific access to a listing of of Irrigation Industries clich here.

For access to Soil Water Content Sensor technology, go to SOWACS.

For information on the use of Polyacylamide in Agriculture to control erosion, go to USDA at Kimberley.

For more information about IRRISTAT INTERNATIONAL INC., and the Irristat™ contact