What does drip irrigation have to do with your soil type? The answer requires a little digging.
New drip irrigation installations can be expensive and require careful design and maintenance for maximum efficiency. To make sure you’re getting the most bang for your buck, it helps to get your hands a little dirty and learn your soil type.
That’s because your soil type can affect how well drip will work in your landscape. Ideally, the water from drip emitters would gradually spread out horizontally, and subsequently into adjacent plant roots.
But depending on your soil type, capillary action may be difficult and water from drip could potentially drain straight down into the ground.
Capillary action is the movement of water within the spaces of a porous soil due to the forces of adhesion, cohesion and surface tension. The adhesive aspect of capillary action allows water to stick to other substances and can allow for an upward force on the water. This would allow it to disperse evenly within the soil and reach nearby plant roots.
Ideal soil would allow for capillary action to occur easily. But with clay soil, water does not enter and exit the soil quickly since it’s composed of densely packed microscopic particles with very small pore spaces in between. And if your soil is sandy — composed of comparatively large, gritty particles — water can drain quickly through the larger pore spaces.
If you’ve lived in San Antonio for more than a few months, you’ve probably realized local soils can vary tremendously depending what area of town you’re in. Broadly, there are three types: clay, clay loam and sandy loam. Sandy soils feel gritty, silt and loam soils are usually smooth, and clay tends to be sticky.
To determine your soil type, use the U.S. Department of Agriculture’s “Guide to texture by feel” (pdf) or a ribbon test: squeeze a small, moistened ball of soil between your thumb and forefinger to create a ribbon. Sand or sandy soils won’t ribbon; loam, silt, silty clay loam, or clay loam soil ribbons less than 1 inch. Sandy clay loam, silty clay loam, or clay loam can ribbon 1 to 2 inches. Sandy clay, silty clay, or clay can ribbon more than 2 inches.
Even if your soil isn’t ideal, there are ways to amend your soil’s capillary action for drip irrigation. One of the most beneficial ways is by adding ½ inch of organic matter (like compost) to improve soil structure over time, allowing for improved water absorption and retention.
On the other hand, lightly hand watering before drip irrigation can help prime the soil and allow for a more even dispersal of water to reach the plant roots.
If you’re thinking of installing drip irrigation, point-source drip can be a better choice for maximum water-to-root contact, especially when compared to in-line drip tubing. That’s because with point-source drip you can maneuver the drip emitters directly over plant roots.
Remember, during Stage 3 watering rules drip irrigation is allowed either Monday or Friday, from 5-10 a.m. or 9 p.m. to midnight.
Caroline Hartmann is a Planner working in SAWS Conservation.
