Below Ground Practices
For gardeners, nothing is more important for a beautifully thriving garden than soil health. Soil is more than just dirt, more than just the surface of our planet we walk, drive and build on. Its the growing medium of plants, an active community beneath our feet. There are three major components of any soil, the physical, biological and chemical. For truly healthy soil, all three components need to be in balance. A rudimentary understanding of soil and below ground gardening practices is vitally important to creating organic landscapes.
Tilth is the physical quality or condition of the soil. Fertile soil needs good texture, drainage and soil structure.
- Texture is the proportion of sand, silt and clay particles, organic content is not taken into consideration.
- Drainage is the rate and extent of water and air movement in the soil, either across the surface or downward.
- Structure is the way the soil particles are grouped together. Their size and how well they hold together are critical.
The biological component of the soil includes the organic content, both plant and animal matter. The addition of organic matter improves soil structure and drainage (it has no bearing on texture). Good soil structure is a product of biological activity. Humus plays a central role in forming rounded aggregates. Earthworms secrete the sticky gums that help hold the soil particles together. The organic content is both the residue of decomposed plant and animal matter – humus-- and the living organic matter. Macro and microbial animal life, the bacteria, fungi, nematodes, protozoa, amoebas, actinomysetes, earthworms, arthropods and living roots are some of the living organic matter. Soil biological life aids plants in healthy growth, in fact, plants attract specific microbial life that benefit them.
In agriculture, the importance of having the optimum soil life is becoming more and more important as the emphasis is shifting from chemical additives to maximizing the biological part of the soil. For a more in depth discussion of bacterial or fungal dominated soils for crops, or your home landscape, Soil Foodweb, Inc.is one of the pioneering labs in the country. Click on the link for a detailed explanation.
The chemical component of soil includes the pH (acid or alkaline), macro nutrients, micro nutrients and the whether the soil is saline and/or sodic, or whether other contaminants (lead, arsenic, etc.) are present.
Soil pH is expressed from a range of 0 – 14, with 7.0 being neutral. Acidic soils range from a pH of 0 – 6.9. Alkaline soils range from 7.1 – 14. Our Texas Panhandle soils range from 7.2 to 9, (usually 7.5 – 8.5). The solubility, the availability of nutrients to plants, is best at a pH of 6.3 -6.8, or slightly acidic soil. The further from neutral pH your soil tests out to be, some nutrients become less soluble, less available to the plants. Extreme acidity and alkalinity also interfere with the soil organisms and the breakdown of organic matter, resulting in decreased nutrient release. At pH of 7.0 and above, the nutrients iron, phosphorus, copper, zinc, boron and manganese become less available.
Macro nutrients must be in balance for fertility. Over applying one mineral nutrient can interfere with the absorption of another mineral nutrient. Macro nutrients are carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, calcium, potassium and manganese.
The micro nutrients must also be in balance for fertility. Likewise over applying one mineral micro nutrient can interfere with the absorption of another mineral nutrient. The micro nutrients are boron, copper, iron, chlorine, manganese, molybdenum, nickel and zinc.
Excessive levels of sodium (saline and sodic soils) are not present in healthy soils. Also absent are contaminants (lead or arsenic, etc). High pH soil coupled with high levels of soluble sodium is referred to as sodic soils. There are areas of naturally occurring sodic soils throughout the southwest. However, the problem of salinity or salt buildup results from irrigation and fertilizers with a high salt content. This is an increasing problem throughout the southwest.
Practice No. 2. Analyze Your Soil
If your soil is healthy, filled with an active soil food web, you'll have healthy plants. It's important before beginning soil amending to analyze your soil, to have a base record. Elementary soil test kits that test the pH can be purchased from many sources, and are a start, however, a analysis from a reputable lab is best. It is also important to know your soil's texture, chemical analysis, deficiencies and organic content. If you suspect other problems, be sure to send your queries along with the soil sample.
The soil texture and structure varies greatly throughout the Texas Panhandle; indeed, throughout Amarillo as well. Soils range from heavy compacted clay, caliche to sandy soil. A few areas of the Texas Panhandle may be blessed with a loam soil. Nearly all soils are alkaline, and nearly all are highly deficient in organic matter. Your location may have just a few inches of top soil of heavy clay with a caliche or even rock base underneath. Dig down as far as practical to find out what kind of soil you have.
There are a few ways to test your soil itself for texture. Texture refers to the size of particles that make up the soil and their proportion in the soil. Sand, silt and clay refer to relative sizes of the soil particles with sand being the largest particle, and clay the finest. It is easy to make a rough estimate of the texture by feeling the soil. A soil with only 20% clay particles will behave as sticky, gummy clayey soil.
The feel test – rub some moist soil between your fingers.
- Sand will feel gritty.
- Silt will feel smooth.
- Clay soil feels sticky.
Ball Squeeze test – Squeeze a moistened ball of soil in your hand.
- Coarse textures (sand or sandy loam) soils break with slight pressure.
- Sandy loams and silt loams stay together but change shape easily.
- Fine textured (clayey or clayey loam) soils resist breaking.
Ribbon test – squeeze a moistened ball of soil out between your thumb and fingers.
- Sandy soils won't ribbon.
- Loam, silt, silty clay loam or clay loam soil ribbons less than 1 inch.
- Sandy clay, silty clay, or clay may behave as a heavy clayey soil. A soil needs 45 percent to over 60 percent sand to behave as a sandy soil.
The above tests will just give you a rough estimate of the texture, For a more exact test, send your soil sample into an established lab. Use a lab that will analyze the organic content, as well as the chemical content of the soil. Specify which tests you want, complete with a description of the way the soil will be used (turf, vegetable garden, orchard, flower bed,etc.) and how the soil has been used in the past.
- Texas Plant and Soil Lab in Edinburg, TX , (www.txplant-soillab.com, 956-383-0739) is an alternative to the Texas AgriLife Extension soil tests. Texas Plant and Soil Lab standard test will also give you organic content percentage in your soil and make helpful recommendations.
- Servi-Tech Labs, www.servitechlabs.com. 6921 S. Bell Street, Amarillo, TX 79109 806-677-0093, or 1-800-557-7509. Finally, a local soil testing lab. They can also test for soil organic content when selected.
- Soil FoodWeb, Inc. http://oregonfoodweb.com/testing.html for state of the art biological testing.
Be sure to let the lab know how the soil has been used and what your future purpose will be. Allow 1 – 3 weeks to receive the results. Results are obtained quicker if sent in during the off season, usually before March. After you have the results, read their recommendations. It might be necessary to call for explanation or additional advice (extra fee may apply). If your soil shows deficiencies, only then should additional minerals be applied.
Re-test your soil every three to five years to document your progress in building the soil. Amending correctly for your soil conditions and plants saves time and money in the long run.