Substrate

Alternative Test Method

Physical property evaluation using container tests.

An alternative to using pipe cylinders is to conduct physical property tests in the container in which plants will be grown. (This may be very difficult for large heavy containers, in which case the pipe cylinder test is preferred.) A step-by-step procedure for determining physical properties using the container test is provided.

Container Test Procedure:

When a substrate is saturated and allowed to drain, air replaces the volume of water drained. Measuring the drainage water gives a quick measurement of drainable pore space or air space. If only a measurement of air space is desired, there is no need to determine the volume of water required to saturate the dry substrate in step 3.

1. Measure the container volume. Secure the drainage holes with tape and fill the container with water to within approximately 1/2 inch (13 mm) of the brim. Mark this line with a pencil. Carefully measure the volume of water by pouring it into a measuring cup. This volume of water is the container volume to be occupied by the substrate.

2. Dry the container inside. Do not remove the tape. Fill the container with dry substrate to the "fill line" marked in Step 1, using packing procedures as when potting a plant.

3. Using a measuring cup, slowly add water to the container and keep track of the volume of water used. Wet the substrate until it is saturated (a thin film of free water is present on the surface). Some dry substrate, such as peat moss or pine bark, is difficult to wet. It is very important that the substrate be thoroughly moist, because dry substrate repels water. If a wetting agent is used in production, then use a wetting agent at the recommended rate. Add small amounts of water as necessary to ensure complete wetting of the substrate, or saturation. The volume of water needed to saturate the substrate is the total pore space.

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