Week 18: Evaluating soil health with our five simple senses

A few brave students tasted a small amount of soil, another held a handful of soil to her ear, “I can hear the ocean!’ she exclaimed. She was joking. In reality, in a sensory evaluation of soil health, we tend to rely most heavily on our visual and tactile observations. Before we get into what’s good and what’s bad, let’s establish what is.

Soil, dirt’s preferred noun, is that composite beneath our feet. It’s a combination of organic matter (humus), oxygen, water, and minerals. Humus, the organic component of the soil, is a composite itself, made up of decayed plant and animal matter. Oxygen and water facilitate life, allowing for the movement of nutrients. Minerals like sand, silt, and clay define the character of the soil.

How’s about this soil? Rich chocolate brownie with just the right amount of moist, fluffy, organic goodness. For growing veggies, the overall ratio that we are looking for is 5% humus, 25% oxygen, 25% water, and 45% mineral. The dark color of this soil speaks of its organic matter, the fluffiness of its water and oxygen.

As for texture, soils that are overly sandy will feel gritty, silty soils will feel like dry flour, and a too clay-y soil will feel smooth and slippery, especially once exposed to water.

Here’s Carolina offering an explanation of the soil texture triangle (expanded below). The triangle places Loam in the center. Loam is a made-up name for the just-right ratio of sand, silt, and clay.
If you are looking for a finer understanding of your soil’s mineral composition, the jar test is for you. Simply place a large handful of soil into a quart size jar and fill the jar with water (up until the neck begins to curve in). Then, wait for contents to settle. Sand will fall to the bottom of the jar within an hour. Silt will sit just above sand, settling out over night. Clay will sit above silt, taking a few days to separate itself from water that remains. Now, you have an easy illustration of the relative presence of our three main minerals.

Now, if you’ve smelt, felt, heard, seen, touched, jar tested your soil and you are still curious, UVM’s Soil Lab Test is a good next step. Tests are relatively inexpensive and can be tailored to your garden’s focus. Come back soon for more on soil amendments.


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