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Model 1505D Digital Pressure Chamber

The Model 1505D Pressure Chamber Instrument is a new release with changes that most users will appreciate. We have upgraded the Control Valve and internal piping to now allow direct connection to Nitrogen Cylinders with 207 Bar/3000 PSI pressure. The instrument is fitted with a 100 Bar Digital Gauge that offers features such as backlighting and multiple pressure scales: Bar, MPa and PSI.

The Instrument comes fitted with our most popular sealing gasket size – 1/4 inch Compression Gland Gasket and Insert. This gasket will seal a sample that is 1/4 inch in diameter down to a completely closed position. If you need other sealing options such as bladed grass or other semi-round sizes check our other options.

This is an excellent choice for research due to the large range of operating pressures. It is good for work on high stress level plants, pressure volume curves, and can also be used for routine water measurements for crop plants.

Maximum Operating Pressure 100 bar
Chamber Construction Solid Stock Stainless Steel
Read-out Digital Gauge: Bar, MPa and PSI
Size (L x W x H) 33 x 28 x 24 cm (13 x 11 x 10 inches)
Weight 8 kg (17 lbs)
Gauge 2.5″ Diameter Gauge
1/2 of 1% accuracy
100 bar (10 MPa) range

The instrument requires a nitrogen source. You can use it in a lab or green house with a large cylinder or buy a light weight Portable Tank to allow for field work.

How it Works

Simply put, the pressure chamber is just a device for applying pressure to a leaf or small shoot. Most of the leaf is inside the chamber, but the cut end of the stem (the petiole) is exposed outside the chamber (see illustration above). The amount of pressure it takes to cause water to appear at the cut surface of the petiole tells you how much tension the leaf is experiencing on its water supply. A high value of pressure means a high value of tension and a high degree of water stress. These stress levels vary within different species. The unit of pressure most commonly used is Bar (1 Bar = 14.5 PSI).

What is Plant Moisture Stress?

The water status of plants, and how to measure it, has received much attention in recent years and for good reason. Plant moisture stress (PMS), or plant water potential, indicates the demand for water within a plant. A PMS measurement indicates the water status of a plant from the “plant’s point of view.” PMS also tells how the environment affects the plant. High PMS levels cause many physiological processes, such as slowing or stopping photosynthesis. Conditions producing high PMS reduce plant growth and may eventually result in the death of the plant. PMS information can be used to evaluate the plants need for water or how well it is adapted to its environment.

Why Measure Plant Moisture Stress?

Measuring PMS gives an indication of a plants ability to grow and function and can be used as a guide for managing the plants moisture environment so as to improve growth and crop yield. Air temperature, wind speed, humidity, and soil moisture are all integrated by the plant into one single value — PMS. A measure of PMS thus gives an evaluation of the moisture status of a plant from the plants point of view. It is an excellent tool for aiding in irrigation scheduling for crop plants such as almond, walnut, prunes, cotton, and wine grapes or for any application where plant growth is managed such as in nurseries, greenhouses, seedlings or reforestation.

Principle of Operation

The pressure chamber can be thought of as measuring the “blood pressure” of the plant — except that for plants it is water rather than blood. And the water is not pumped by a heart using pressure, but rather pulled with a suction force as water evaporates from the leaves. Water within the plant mainly moves through very small inter-connected cells, collectively called xylem, which are essentially a network of pipes carrying water from the roots to the leaves. The water in the xylem is under tension. As the soil dries or humidity, wind or heat load increases, it becomes increasingly difficult for the roots to keep pace with evaporation from the leaves. This causes the tension to increase. Under these conditions you could say that the plant begins to experience “high blood pressure.”

Since tension is measured, negative values are typically reported. An easy way to remember this is to think of water stress as a “deficit.” The more the stress the more the plant is experiencing a deficit of water. The scientific name given to this deficit is the “water potential” of the plant. The actual physics of how the water moves from the leaf is more complex than just “squeezing” water out of a leaf, or just bringing water back to where it was when the leaf was cut. However, in practice, the only important factor is for the operator to recognise when water just begins to appear at the cut end of the petiole. The Plant Moisture Stress (PMS) reading at any given time reflects the plant’s interaction with the water supply and the demand for water placed upon the plant by its environment (see diagram on back cover). Since these factors are almost always changing, PMS is nearly always changing. The time of measurement therefore requires careful consideration — PMS is most at midday and least just before sunrise. Pre-sunrise PMS values will usually reflect average soil moisture tension, if the soil is uniformly irrigated. Midday PMS values reflect the tension experienced by the plant as it pulls water from the soil to satisfy the water demand of the atmosphere.