The Arizona Cooperative Extension in Pima County advises that: "Soil tests are generally not necessary in this area. Our soils are typically highly alkaline and very low in organic matter." This is generally true, however soils can vary greatly in texture even between samples from different areas of the same yard. The soil in front of my house, for example, is sandy but the soil behind my house is almost pure clay. Fortunately, there is a simple and inexpensive method for determining soil texture using a sample of soil, a clean glass quart jar with a lid, and some water. A little bit of Calgon detergent can also be helpful.
Soil texture can be categorized in terms of the relative amounts of sand (large particles), silt (medium size particles), and clay (small particles).
Soil Texture Test
The test is simple:
- break up any large clumps in the sample of soil;
- fill the quart jar about 3/4 full with the sample soil;
- add enough water to almost fill the jar;
- optional: add a few drops of Calgon detergent;
- close the jar and shake well until the soil and water are thoroughly mixed;
- immediately set the jar in a place where it will not be disturbed for a day or so;
- when the water has cleared, the results can be observed. The larger sand particles will have settled onto the bottom, the medium size silt particles on top of that, the small clay particles on top of that, and organic matter on top of that and possibly floating on top of the water.
- Measure the depth of each layer to determine the relative portions of sand, silt, and clay.
A soil that's 10% to 100% clay and low in silt and/or sand is a clay soil. A soil that's 85% to 100% sand is a sandy soil. A soil with approximately equal amounts of sand and silt and a bit less clay is a loam soil.
Links
The Natural Resources Conservation Service Soils Website is an excellent resource for finding out general information about soil in your part of town.