Pipe Test

• A length of pipe is cut so height of substrate in container equals height of pipe with cap on bottom. A 3-inch diameter pipe is seen here; however, diameter is not important, just height. Cap on end has 4 small holes and base flattened so pipe stands upright.
• You will need to determine volume of the pipe section. Volume measurement can be accomplished by placing plastic bag in pipe, filling bag with water, and measuring volume. A 3-4 inch long pipe extension is placed on open end of pipe, facilitated by a coupling.
• Fill pipe and extension with substrate. Drop twice from 3 inches. Add substrate after each drop. Pipe and extension are placed in water so that water surface is near substrate surface. This will saturate the substrate. Remove after 3 hours and drain for 5 minutes. Remove top part of pipe as you level substrate surface.
• Secure a cloth with rubber band over top of pipe. Submerge for 10 minutes, lift from water and re-submerge. After 30 minutes, remove pipe from water with fingers covering holes in bottom of pipe. Drain excess water, and then remove fingers with pipe elevated over collection vessel. Drain for 10 minutes.
• Measure water collected. Water collected divided by pipe volume equals air space percentage. When water drained, air filled the void space so volume of air equals volume of water drained. Air space percentages often range from 10-30 percent by volume.
• Place wet substrate in large pre-weighed paper bag and weigh in grams. When substrate is air dry or dry to point where substrate would need water if plant were grown in substrate, weigh again. The difference in wet and air-dry substrate weight approximates the available water. This divided by pipe volume equals percent available water that is usually in the range of 25-35 percent.
• Dry substrate at 105C in forced air oven. The difference in wet and oven dry substrate weight is the total amount of water held in the substrate. This divided by the pipe volume equals total water holding capacity or container capacity that is usually in the range of 45-65 percent.
• The difference in total water holding capacity and available water is unavailable water. Total water holding capacity plus air space is equal to the total porosity of the substrate. Total porosity usually ranges from 50-85 percent of container volume. All computations are for a container equal in height to pipe.

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