Author Topic: Introduction to Minerals  (Read 1986 times)


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Introduction to Minerals
« on: April 27, 2011, 02:01:24 PM »

Lime and Gypsum: pH, calcium and magnesium Lime is used to raise the soil pH (reduce acidity). It also supplies calcium (Ca). Gypsum (calcium sulfate dihydrate) is used to raise Ca levels.

There are two types of readily available limestone for raising soil
pH: calcitic (high-calcium) limestone and dolomitic limestone. 
Dolomitic limestone contains approximately 28 percent magnesium carbonate and approximately 35 percent calcium carbonate. Calcitic limestone contains no magnesium (Mg). Both of these products will elevate soil pH; however, they will affect the percent base saturation in the soil very differently. If dolomitic limestone is used continually, magnesium can accumulate to the point where it suppresses calcium levels in the soil.

Classic symptoms of calcium deficiency include necrosis around the base of the leaves and soft dead necrotic tissue at rapidly growing areas. Plants under chronic calcium deficiency have a much greater tendency to wilt than non-stressed plants.

If calcium or potassium is oversupplied and magnesium is deficient, turf can become chlorotic and appear yellowish green because it is unable to produce chlorophyll.

When using lime, it is important to know the calcium/magnesium ratio in the soil in order to choose the correct liming agent. This ratio can be calculated by dividing the exchangeable value (the amount that is free to move in the soil; the value returned by a soil test) of calcium by the exchangeable value of magnesium. For example, if the exchangeable value of calcium is 1,500 ppm and the exchangeable value of magnesium is 200 ppm, the calcium/magnesium ratio is 1,500/200 = 7.5. If the calcium/magnesium ratio is lower than 6, then calcitic lime (calcium carbonate) should be used. If the ratio is between 7 and 10 and magnesium is ranked lower than calcium on the soil test, dolomitic lime (calcium/magnesium carbonate) is preferred.

Many soil tests report the percent base saturation, which makes calculating the ratio of calcium to magnesium unnecessary. If percent base saturation is provided, the magnesium should be between 5 and 15 percent, and the calcium should be between 60 and 85 percent. If calcium is below this range, use calcitic lime, and if magnesium is needed, use dolomite. If they are both in the proper range, use either type and alternate with the other in succession. Ca and Mg do not need to be precisely within these ranges, but you should try to move toward the proper levels when using lime. If calcitic lime is not available, gypsum can be used to increase Ca levels. Gypsum does not affect soil pH and is more expensive than ground limestone.

Many people use pelletized lime on lawns. Pelletized lime consists of very finely ground limestone that is formed into pellets using a binder. Upon contact with moisture in the soil, the pellets disintegrate and the fine lime particles dissolve readily and provide for a rapid rise in pH. The pH increase is shorter lived than that produced by regular ground lime, which contains some larger particles that last longer. Pelletized lime is more expensive than ground limestone but is easier to apply and does not create a lot of dust.

Do not apply more than 50 pounds of ground limestone per 1000 square feet at one time, even if more than 50 pounds per 1000 square feet is called for. Apply pelletized lime at about half the rate of ground limestone, but apply it more often. Do not apply during hot or dry times of the season. Measure the pH a month or two after the first application to get an idea of its effect. Additional applications can be made in spring and fall until the desired pH is achieved. Keep in mind that lime does not move rapidly down into the soil, so the pH near the surface will be higher than it is a few inches below. Over time, the lime will move lower. If large applications are made, the difference between surface and sub-surface pH will be magnified. 
Therefore, small but frequent applications are suggested.

Nitrogen Nitrogen (N) is used in large amounts by plants and is especially important in keeping a lawn green. There are several forms of N in the soil. As organic materials decompose, N is released in the form of ammonium (NH3). Unless the soil is quite acid, bacteria convert ammonium to nitrite and then to nitrate (NO3). Nitrate-N is the form primarily used by most plants, including grass. However, it is also very soluble and subject to leaching (see ?Environmental Considerations? on the next page).

Soil tests taken in late fall, winter or early spring usually show a low N level. As the soil warms in late spring and summer, microbes break down organic matter and release N. For this reason, a standard soil test is not a reliable indicator of N availability in the soil, and many soil labs do not measure N in a standard test. Under most conditions, if a soil contains around 5 percent organic matter, there should be enough N. Many soil labs will perform a special nitrate-N test in the summer. This is a good way to determine if indeed there is enough N being released from organic matter.

Compost is an excellent source of slow release N. Blood meal (dried blood from animal processing) and some plant meals are also good sources. White clover can be seeded into the lawn or included when establishing a new one. The clover is a legume, a plant that uses bacteria in its root nodules to take N from the atmosphere and make it available to plants. Be sure to inoculate the seed with the proper bacteria. Some people like clover in a lawn; others do not.

Phosphorous Phosphorous (P) is essential for many plant functions and is noted for its importance in root growth and development. It is needed in fairly high amounts, although in smaller amounts than nitrogen and potassium. Most of the P in soils exists in chemical compounds that are rather insoluble. Only a small portion is soluble and readily available to plants. If the soil is acid, less P is available because even more of it is insoluble. Even if relatively soluble forms of P are added, most becomes insoluble. Because of its insolubility, P does not move readily down from the surface. Thus, it can take quite a while to increase P levels in the root zone of established turf. When establishing a new lawn, P should be added according to soil test and incorporated into the top few inches of the soil.

There are a few materials that can supply P. Rock phosphate is a ground up mineral that is mined. It has a fairly low amount of available P and what there is is made available slowly. It can be useful when constructing a new lawn and should be thought of as part of a long-term plan. Bone meal provides P fairly rapidly. In this respect it is similar to synthetic P fertilizers. The down side of bone meal is that it is relatively expensive. Compost is a good source of P. It releases P more slowly than bone meal, but considerably faster than rock phosphate. Leaving grass clippings on the lawn recycles phosphorus and can eliminate the need for specific phosphorus supplements.

Potassium Potassium (K) is required in large amounts by plants. It is important in regulating water movement within the plant. If K is in good supply, turf will have an improved ability to withstand drought. 
K is moderately resistant to leaching, unless the soil is sandy and contains little organic matter.

K can be supplied using potassium sulfate. This is an allowed product for organic lawn and turf care if it is mined and not synthesized. Potassium sulfate supplies K rapidly and is moderate in price. It also supplies sulfur. Sul-po-mag is a product that contains sulfur, potassium and magnesium and is useful if magnesium is also needed. 
Compost will also supply K, as will grass clippings. When K is applied to the soil surface, it will move down into the root zone at a reasonable pace, provided there is adequate water.

Micronutrients It is not usually necessary to apply micronutrients. 
Amendments such as compost should contain a reasonable supply. If soil pH is above 7.0, there is an increased chance of a micronutrient deficiency because most micronutrients are increasingly unavailable at high pH?s. Sandy soils with little organic matter may show certain micronutrient deficiencies. In such cases, it may be wise to keep the soil pH in the low sixes, at least until soil organic matter is in the desirable range. Excessive P can combine with iron or zinc, making them less available. This is another reason to avoid excess P.