Bakersfield.com

The pressure chamber, also known as the pressure bomb, is a device equipped with a small gas cylinder, high pressure gauge, and a thick-walled metal chamber with a top in which a plant leaf petiole can be sealed.  The amount of pressure that is required to force water from the cut base of a pressurized leaf or petiole provides an estimate of the water status of the plant.

Over the past two decades much of the irrigation research conducted on perennial fruit and nut crops in California, and much of the world, has used pressure chamber measurements of plant water status as the key indicator of the degree of water stress experienced by a tree.  Some of this research has focused on improving or maintaining crop yields and/or quality by reducing irrigation during certain crop developmental periods.  Saving water and improving fruit and nut quality by reducing irrigation in this manner is referred to as ‘regulated deficit irrigation.’  Researchers use specific plant water potential measurements, usually measured in ‘bars’ of pressure in the U.S.A., as triggers for beginning or ending periods of deficit irrigation.

Many growers continue to estimate crop irrigation needs by measuring water depletion in the soil adjacent to the plant, or by measuring weather variables that estimate crop evapotranspiration requirements.  While these methods can provide excellent results, they do not measure the water status of the plant as directly and immediately as the pressure chamber does.  Soils vary considerably in ability to provide water to the tree, and similar levels of soil water depletion do not usually result in the same degree of stress to the tree.

For growers to fully realize the benefits in water saving and fruit and nut quality that irrigation research tied to crop water status appear to promise, purchasing a pressure bomb and developing experience with it is required.  Growers, understandably, have been reluctant to use pressure chambers. The pressure chamber is relatively expensive compared to the cost of tensiometers, for example (however, not so in comparison to possible water savings and improvement in crop yield possible with regulated deficit irrigation).  The pressure chamber requires training for proper operation and some experience in its use for those that will interpret the results from the field.  The pressure chamber, also, is not a stand alone instrument.  The grower will still have to measure soil water depletion in order to schedule the amount of water necessary to refill and/or leach the plant root zone.

The time has come for more growers to begin applying and fine tuning the impressive store of new information that agricultural researchers have been developing related to plant water stress and regulated deficit irrigation in many fruit and nut crops.  A pressure chamber will be required to do that effectively.