By Utah State Extension Corner in Morgan, Utah
In light of Earth Day, here are some interesting facts about earth, and by earth I mean soil. Soil could be considered “the foundation for all life” supporting billions of microorganisms, macroorganisms, and of course the plants we love and rely on every day. Most gardeners understand that healthy soil supports healthy plants, but what does it mean to have healthy soil?
First, we should know how soil is made. Soil is simply weathered rock that has been broken down over time by wind, rain, snow, freezing and thawing, and by organisms. Soil close to the surface is topsoil, below that is subsoil. If you have ever tried landscaping around a newly built house and have had some challenges growing plants, it is probably because the yard was left with compacted subsoil as all the good topsoil has been scraped away during construction.
The best way to create and maintain healthy soil is by adding organic matter. Organic matter (OM) is any material that was once living. For gardens this includes grass clippings, plant debris, plant roots, fallen leaves, compost and manure. Worms, ants, beetles and fungi break down OM adding nutrients to the soil and improving soil structure. Soil structure is different from soil texture. Soil texture is your percentage of the particles sand, silt and clay. Soil structure refers to the interaction between soil particles creating aggregates, which allow more pore space for air and water. It takes 4-5 years for good soil structure development.
Sand is the largest soil particle, then silt and then clay (clay being the smallest). Sand does not hold water and nutrients as well as clay. It is difficult to alter the texture of your soil. For example, heavy clay soil in a small vegetable garden would require up to 200 pounds of sand to alter the soil texture. It would take up to 10,000 pounds of sand for a one acre clayey field. Furthermore, adding fine sand to clay can result in sand-coated clay clods, or concrete! The best solution is organic matter.
There are several soil amendments and additives out there. On the east coast, where soil is very acidic, gardeners will occasionally use lime to try to increase soil pH (or lower the acidity). Here in Utah our soil (and our water) is alkaline, or low in acid, with an average pH between 7.5 and 8.2. Very alkaline or very acidic soil can reduce nutrient availability to plants. A common example in Utah is iron chlorosis from limited available iron due to our alkaline soil. Soil acidifiers such as sulphur can alter soil pH temporarily but because of the high calcium in Utah soils (which acts as a buffer), acidifiers are only a temporary fix. Acid-loving plants such as blueberries perform best in containers where soil can be controlled and acidifiers are added regularly.
Another common soil amendment in gypsum. Gypsum is calcium sulfate. It has no direct effect on soil pH, and because most soils contain adequate calcium I generally do not recommend adding gypsum. Gypsum can be useful when soil is high in salt. If your soil is very high in salt, particularly sodium, adding gypsum will help leach the sodium. You will still need to apply a lot of water to leach out the salt.
Most of us struggle with our Utah soils, but hey- it could be worse. Bottom line: build your topsoil by regularly adding organic matter!
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