Practice No. 4. Balance Mineral Content of Soil
Unless you’ve had a soil test performed and know you have a particular mineral deficiency, avoid adding individual chemicals or minerals. Some soils are deficient in essential elements. Plants require sixteen essential elements for normal growth. Carbon, hydrogen, oxygen and nitrogen make up the top four elements. There are five more macro nutrients— phosphorus, sulphur, calcium, potassium, magnesium and eight micro nutrients or trace elements: boron, copper, iron, manganese, molybdenum, zinc, chlorine and nickel.
Instead, the addition of a variety of organic substances provides a balance of minerals and nutrients. A well-rounded diet is needed for optimum performance. It is important to have minerals balanced and available for use. Adding too much of one mineral often causes imbalances and therefore chemical deficiencies or even toxicities. Exclusive application of chemical fertilizers throws the chemical composition out of balance. A soil analysis can advise whether phosphorus, potassium or iron are needed if your practice is to use bag fertilizer (not recommended for creating organic landscapes).
Rock dust and powders are sometimes added to soils to improve the general mineral content of the soil. Adding rock dust is known as re-mineralization. It is nothing more than ground up rocks, similar to the action of glaciation. Rock dust, fine ground minerals and greensand are some of the more common amendments containing trace minerals without disturbing the balance in the soil. Even fine, ground up gravel will slowly add minerals to the soil.
Our alkaline soil causes certain minerals to be bound up, unable to be used. Iron, phosphorus, copper, zinc, boron, and manganese are the chief minerals that are unable to be taken up by plants in alkaline pH conditions. Adding organic matter to the soil buffers the alkalinity and helps release these bonds.
Many gardening articles that are published for national distribution recommend liming the soil. Adding lime to the soil increases the alkalinity. This should only be done if your soil tests with an acidic pH (below 7.0), probably below 6.0 pH. Most of our soils in the Texas Panhandle are alkaline, above 7.0 pH. Adding lime would increase the alkalinity and be detrimental to the growth and health of plants.
As mentioned earlier in the discussion about adding manures to our soils, please be aware if manure from dairy operations includes lime from barn use. Please avoid these manures which will tend to increase alkalinity as well.
Gypsum and Iron
Many people recommend applying gypsum to the soil to improve soil structure, particularly for clay soil. Gypsum is the common name for calcium sulfate, a water soluble form of calcium and is a good source for calcium and sulfur. Calcium's job in the soil is to help hold clay particles together into clumps, clods or peds. Most Texas soils are already high in calcium, therefore its addition will not significantly improve soil structure. Additionally, amending with sulfate sulfur will not significantly reduce the soil pH.
The most practical use of gypsum in Texas soils is to help in the displacement of sodium. A soil analysis will show your levels of calcium, sulfur and sodium. When sending for an analysis, ask for gypsum recommendations. Only then can you be assured that the addition of gypsum is beneficial, and not a waste of money or even a detriment (because of excess calcium). (Horticulture Update, March, 2003, Texas Cooperative Extension, “Gypsum: To Apply or Not to Apply?”).
Sulfur is sometimes added to decrease iron chlorosis in turfgrass by reducing soil alkalinity. Chlorosis is the inability of the plant to uptake iron present in the soil. One direct result of using elemental sulfur and sulfuric acid is an increase in soluble salts, especially in clay soil with poor drainage. The reduction of chlorosis is short lived, lasting only about 3-4 weeks. (“Iron Chlorosis in Turfgrass”, Dr. Richard Duble, Professor and Extension Turfgrass Specialist, Texas A & M University).
My turfgrass suffered from chlorosis prior to switching from chemical to organic gardening practices. Even after the initial year of adding when composted manure was only added once, my grass significantly greened, and continues to remain green, even during the heat of summer.