Pressure Chamber technology continues to receive a lot of interest as water resources are stretched. Although the technology has been around for years, the recent publication of crop levels for Walnut has increased interest from growers as the Pressure Bomb becomes a standard method for plant based irrigation decisions in the orchard. The Pressure Bomb has been shown especially helpful in the Walnut orchard for helping discern when to begin irrigation for the season. Plant based measurements are also extremely helpful in keeping the orchard well irrigated for optimal growth but not over-irrigated during pre-harvest which can lead to disease and problems at harvest.
The Pressure Bomb allows you to monitor the stress level in the tree. There are many “shades of grey” between “well-irrigated” and “water-stressed” trees. The Pressure Bomb allows you to monitor these shades of grey and keep the tree well irrigated during times of growth yet the ability to stress slightly during and right prior to harvest.
Using a plant based monitoring system like the Pressure Bomb you monitor exactly what the tree is experiencing not just one of the environmental stresses. Plant water stress is a sum of four environmental influences; soil moisture, humidity, wind and direct sunlight or heat load. (See graphic below) While most monitoring systems only monitor one of these influences, the plant based measurement takes all four into consideration.
Taking the measurement is simple. A foil-laminate bag is placed on a lower canopy, shaded leaf for at least 10 minutes. The leaf is then cut off with the bag still in place and sealed into the chamber. The chamber is pressurized with nitrogen gas until water is forced up to the cut surface. (See graphic below)
The next question is which instrument works best with Walnut trees. There are three instruments that will work well for Walnut. Each has different qualities that appeal to different growers.
The Model 615 is our newest instrument and is the product of our customers input. The instrument comes fitted in a dust-proof case that has 5 tie-down rings for easy mounting on an ATV (4-Wheeler). The 22 cubic foot tank is removable for quick replacement or can be trans-filled. The instrument comes with a shoulder strap and bail-spring handle for easy transport by hand. The instrument is fitted with our Compression Gland Sealing System which works excellent with Walnut. For most walnut a 1/8 inch insert and gasket is good. If you are working with other crops that are larger petiole, you can also use the 1/4 inch sealing system.
The Model 600 is also a popular instrument. It does not come with a tank and thus needs the Portable Tank. This durable field unit is normally placed in a plastic box lined with foam or a blanket and strapped to a 4-wheeler when used in orchard applications. It can also be hand-carried. It is also fitted with the Compression Gland Sealing System which works excellent with Walnut. For most walnut a 1/8 inch insert and gasket is good. If you are working with other crops that are larger petiole, you can also use the 1/4 inch sealing system.
The Pump-Up Chamber is a good low-cost alternative for a grower with small acerage. No source of pressure is needed since it works like a bicycle pump and the pressure is created by pumping the instrument up and down. It is a highly portable and light weight instrument. The pump is capable of producing about 7 psi or 1/2 Bar per stroke. When ordering for use with Walnut you can normally use the Small or Large Lid.
If you have any questions concerning the use of any of these
instruments with Walnut or any other crop, please contact us directly.
Using the Pressure Chamber for Irrigation Management in Walnut. UCCE contributors: Allan Fulton, Richard Buchner, Joe Grant and Joe Connell. ANR Publication 8503. May 2014.
Pressure Chambers help with crucial tree nut watering decisions – Kenneth A. Shackel, July 11, 2018. Western Farm Press