Potassium, Calcium,Magnesium- How They Relate to Plant Growth by CARL SCHWARTZKOPF, Mid-Continent Agronomist, USGA Green Section Potassium, calcium and magnesium play an walls to thicken and help the plant to remain important role in soil-plant relationships. These upright. elements are not only essential to the complex Potassium plays a vital role in the winter biochemistry of plant growth, but their pres- survival of turfgrass, disease resistance, and in ence in the soil in adequate amounts and in increasing the overa II hardi ness of the grass suitable proportions to one another and to the plant. Deficiency symptoms of potassium on other exchangeable cations, such as aluminum, turfgrass are yellow-streaked leaves, followed hydrogen and NH4 +, is necessary if the soil by browning and dying at tips and margins. is to be a suitable medium for plant-root development. Should one element be in excess, SOURCES OF POTASSIUM ft may "tie-up" or make it unavailable to the Hardwood ashes s,uppl ied much of the plant. potassium in the United States through the first part of the 19th Century. A decline in the POTASSIUM potash industry resulted after the hardwood Potassium is absorbed by plants in larger forests along the Atlantic Coast were depleted. amounts than any other mi neral element except The first factory that processed KCL (murate nitrogen and possibly calcium. This element of potash) was in Germany, and the Germans plays an important part in many of the vital monopolized the potassium market until World physiological processes in the plant; the exact War I. The embargo placed on potassium mechanism by which potassium functions is not exports forced development of the resources of known. It is needed for the plant cell's the United States and of other countries as metabolic processes and apparently has a role in well. Most potassium today comes from New influencing the uptake of certain other mineral Mexico, California, and Utah. elements, in regulating the rate of respiration, affecting the rate of transpiration and in CALCIUM influencing the action of enzymes, as well as in Calcium, as potassium, is absorbed by the aiding the synthesis and translocation of carbo- turfgrass plant in the ionic form. The calcium in hydrates. Potassium also has a counterbalancing the soil other than what was added as lime or in effect on the results of a nitrogen excess. It fertilizer material originated in the rocks and enhances the synthesis and translocation of mi nerals from which the soi I was formed. carbohydrates, thereby encouraging. the cell Calcium is a part of many minerals, such as Injury to turf from the misapplication of plant nutrients. NOVEMBE R 1972 dolomite, calcite and calcium feldspars. Upon different forms. Crystalline calcium carbonates their disintegration and decomposition, calcium are referred to as calcite or calcitic limestone. is released. Crystalline calcium-magnesium is known com- Calcium is an extremely important mineral monly as dolomite. in plant nutrition. Many soils, particularly in humid regions, contain this element in amounts MAGNESIUM so small that plant growth is limited. Turf- Magnesium is also absorbed by plants in grasses as a group are able to tolerate low levels the ionic forms. This absorption takes place of calcium; however, abnormal growth has been from the soil solution or possibly by contact observed with extremely low levels. One of the exchange. primary roles assigned to calcium in the plant is Magnesium plays a vital role in photosyn- the key role it plays in the cell walls. Calcium is thesis, as it is. the central atom in the also important in root development, since short chlorophyll molecule. It is involved in many roots are observed on calcium deficient plants. enzyme reactions. It reacts with phosphorus in The first sign of calcium deficiency in older uptake and transport. Magnesium is also quite plants is the appearance of a reddish-brown mobile in the plant, and yellow deficiency discoloration in the tissue between the veins symptoms fi rst appear on the older leaves, as it along the margin of the blade. The most moves to the younger plants. obvious method of correcting this deficiency is by the appl ication of calcitic or dolomitic lime. SOURCE OF MAGNESIUM Should calcium be required without changing Magnesium in the soil originates in the the pH that would result from the use of lime, decomposition of rocks containing minerals gypsum may be used. such as brotite, dolomite and olivine. Upon Liming is the addition to the soil of any decomposition, these minerals set magnesium calcium-containing compound that is capable of into the surrounding soil solution. Once in the reducing acidity. The correct use of lime refers soil sol ution, magnesium may be 1) leached, 2) only to calcium oxide (CaO), but the term absorbed by living organisms, and 3) adsorbed almost universally includes such materials as by surrounding particles. calcium hydroxide, calcium carbonate, cal- cium-magnesium carbonate and calcium silicate MAGNESIUM IN THE SOIL slags. The coarse-textured soils of the humid A description of various liming materials region are those in which a magnesium defi- describing their availability and manufacture ciency is generally manifested. These soil types follows: usually contain small amounts of exchangeable magnesium. This condition is aggravated by the addition of large quantities of fertilizer salts Calcium Oxide - Calcium oxide (CaO), which contain little or no magnesium. The also known as unslaked lime, burned lime, or magnesium in the soil is released by ion quicklime, is a white powder that is quite exchange when these fertilizers are added; the disagreeable to handle. It is manufactured by larger quantities of chlorides and sulphates heating calcite limestone in an oven or furnace. speeds its removal by leaching. Magnesium can The carbon dioxide is driven off, with calcium be supplied in dolomitic limestone, or as oxide remaining. This product is most fre- magnesium sulphate, if soil pH is to remain the quently handled in paper bags because of its same. A deficiency of magnesium is less of a powdery and caustic nature. This material problem on finer-textured soi Is and on soils reacts quickly when added to the soil. When found in the arid regions. I n some semi-arid unusually rapid results are desired, either locations, magnesium compounds may actually calcium oxide or calcium hydroxide should be be precipitated in the soil profile. used. When the appearance of a plant and Calcium Hydroxide - Calcium hydroxide environmental factors indicate a nutritional (Ca(OHh) is commonly referred to as slaked disorder, steps should be taken to verify the lime, hydrated lime or builder's lime. It is problem before attempting to correct it hap- simi lar to calcium oxide in that it is a white hazardly with nutrients that are not needed. powdery substance, difficult and unpleasant to Since nutrient deficiencies on turfgrasses are handle. Slaked lime is prepared by the hydra- difficult to visually diagnose, a suspected tion of calcium oxide. A large amount of heat is deficiency should be verified with soil or tissue generated; upon completion of the reaction, the tests before trying to correct the problem. A material is dried and packaged. most important criterion for a soil test is that it Calcium and Mixed Calcium-Magnesium should measure the nutrient in the soil that is Carbonates - The carbonates of calcium and available to the plant. Many times nutrients in magnesium occur widely in nature and in many the soil are held tightly and are unavailable. 2 USGA GREEN SECTION RECORD.