ALL THE DETAILS Want to know even more about fertilizer and its benefits? In All the Details you will discover in-depth information that will not only help you understand more about fertilizer but also show you how its use will help your garden. TABLE OF CONTENTS Nutrients Nitrogen Phosphorus Potassium Other Important Nutrients Micronutrients Soil Samples & ph How Do I Raise My Soil ph? How Do I Lower My Soil ph? How Can I Grow Acid-Loving Plants in Alkaline Soil? How Do I Apply Sulfur to Lower ph? What ph Should I Aim For? What Effect Does Acid-Forming Fertilizer Have? Forms of Fertilizer Fast-Release Fertilizers Slow-Release Fertilizers Controlled-Release Fertilizers New Fertilizer Technology Polyon Polyon and the Environment Shopping for Fertilizer Perform a Soil Test Buy Nutrients, Not "Fertilizer" Eamine the Cost Per Pound All Fertilizers Are NOT Created Equal How Fertilizer Works How Is Nitrogen Released in the Soil? Sources of Nitrogen
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 2 of 14 Nitrogen (N) Nitrogen (N) is a constituent of all living cells and is a necessary part of all proteins, enzymes, and metabolic processes involved in the synthesis and transfer of energy. Turf grass fertilizer nitrogen carriers are available in an array of forms such as granules, pellets, liquids, powders, and suspensions. Granules are the most popular and range in size from coarse (1 to 3 mm in diameter) to fine (< 1 mm in diameter) = greens grade fertilizers. Over 90% of all nitrogen fertilizers are produced synthetically by reacting atmospheric nitrogen and hydrogen gas to form ammonia. Large amounts of energy in the form of temperature and pressure are required for this process. Fast-release nitrogen sources are also sometimes referred to as quick release or water soluble sources. These forms of nitrogen are available as granules and liquids. Slowrelease nitrogen sources are also called water insoluble sources. These are either coated products (sulfur, polymer, plastic, resin) or controlled-release reacted products and are available as granules, powders, or suspensions. In warm, moist soils with a ph above 5.0, the majority of ammonium-source nitrogen (NH 4 + ) is converted to nitrate (NO 3 - ) by soil organisms rather quickly (within days). Therefore, most nitrogen taken up by plants is in the NO 3 - form, although NH 4 + is taken up when present in the soil solution. The nitrate ion carries a negative charge, which prevents its retention by the negativelycharged soil colloids. Since it is soluble and mobile, the nitrate ion is readily and easily available to plants. Nitrate moves in the soil solution and can be leached below the plant root zone when soil moisture is ecessive. Leaching losses of fertilizer nitrogen are minimal when rates of application conform to recommendations consistent with the yield potential for the crop and soil in question. Nitrate is also subject to denitrification, a process in which the nitrate ion is reduced through several intermediate steps to a gaseous nitrogen oides or to elemental nitrogen. What is Urea? Urea is a synthetic organic nitrogen fertilizer and one of the most widely used nitrogen sources due to its low cost and completely soluble nature. Urea is unavailable to turf grass plants until it is converted to ammonium. Once urea is applied, it is broken down into ammonium carbonate ((NH 4 ) 2 CO 3 ) by the enzyme urease (produced by soil bacteria). Direct applications of urea to the turf grass surface can result in the conversion of ammonium carbonate to ammonia and carbon dioide, resulting in ecess loss of ammonia as a gas. This loss can be avoided by irrigating immediately after application of urea fertilizers to incorporate the nitrogen.
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 3 of 14 Urea has a quick initial release rate of nitrogen with short duration, and a high foliar burn potential (salt inde). Urea-based fertilizer programs should involve low application rates (< 1/2 pound N per 1000 square feet) made frequently (every two to four weeks) to reduce the loss potential. Phosphorus (P) Like nitrogen, phosphorus (P) is an essential part of the process of photosynthesis and is the second most essential element or nutrient for plant growth. Phosphorus does not move or leach readily due to its low water solubility; therefore, phosphorus applications are not needed as regularly as nitrogen applications. A soil test is the best indicator of the phosphorus level in the soil. The phosphorus content may range in turf grass tissues between 0.1 to 1.0% by weight with sufficient values ranging from 0.2 to 0.4%. Iron deficiencies normally result from high phosphorus or alkaline soils. The highest concentration of phosphorus is in new leaves but is readily mobile throughout the plant. Phosphorus Deficiency Symptoms Since phosphorus is fairly mobile in plants, deficiency symptoms normally occur in older tissues. Phosphorus deficiency symptoms in turf grass plants include slow growth and stunted plants possessing dark green, lower, older leaves. These older leaves eventually show a dull blue-green color with a reddish to purple pigmentation along the leaf margins due to sugar accumulation. Eventually, leaf tips turn red and may develop red streaks down the leaf blades. Phosphorus deficiencies usually occur when root growth is restricted and when soil temperatures and oygen levels decrease. Early spring and fall are two seasons when root growth is slowed; hence phosphorus in the soil is not readily encountered during those times. Common Sources of Phosphorus The immediate source of phosphorus for plants is dissolved in the soil solution itself. Plants absorb phosphorus primarily as the H 2 PO 4 - and HPO 4 2- ions predominant in most soils. The H 2 PO 4 - ion is more readily absorbed than the HPO 4 2- by most plants. A soil solution containing only a few parts per million of phosphate ions is usually considered adequate for plant growth. Concentrations of phosphate ions in the soil solution may be as low as 0.001 parts per million. Phosphate ions are absorbed from the soil solution and used by plants. The soil solution is replenished from soil minerals, soil organic matter decomposition, or applied fertilizers.
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 4 of 14 In young plants, phosphorus is most abundant in tissue at the growing point. It is readily translocated (moved about) from older tissue to younger tissue, and as plants mature, most of the element moves into the seeds and/or fruits. Phosphorus is responsible for characteristics of plant growth such as utilization of starch and sugar, cell nucleus formation, cell division and multiplication, fat and albumin formation, cell organization, and transfer of heredity. Potassium (K) Potassium is absorbed by plants in larger amounts than any other mineral element ecept nitrogen and, in some cases, calcium. Potassium is supplied to plants by soil minerals, organic materials, and inorganic fertilizer. Potassium, unlike nitrogen and phosphorus, is not found in organic combination with plant tissues. Potassium plays an essential role in the metabolic processes of plants and is required in adequate amounts in several enzymatic reactions, particularly those involving the adenosine phosphates (ATP and ADP), which are the energy carriers in the metabolic processes of both plants and animals. Potassium also is essential in carbohydrate metabolism, a process by which energy is obtained from sugar. There is evidence that potassium also plays a role in photosynthesis and protein synthesis. Potassium is directly involved in maintaining the water status of turf grass plants, the turgor pressure of its cells, and the opening and closing of stomata. As the potassium concentration increases, cell walls thicken and the water content of tissues decreases and plants become more turgid (swollen, distended). Cold tolerance is also influenced by the plants P to K relationship. A 1:2 P to K ratio in the leaf tissue increases the cold tolerance of turf grasses. The critical level of potassium in plants is about four times that of phosphorus. Leaf tissue analysis by weight for potassium consists of 1 to 5%. Sufficient levels range from 1.5 to 3%. Potassium deficiency occurs when tissue levels drop below 1%. Potassium Deficiency Symptoms Potassium deficiency symptoms include interveinal yellowing of older leaves and the rolling and burning of the leaf tips. Leaf veins finally appear yellow and leaf margins appear scorched. Potassium is a mobile element and can be translocated to younger tissues if a shortage in potassium occurs.
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 5 of 14 Potassium Sources Muriate of potash (KCl) is the potassium-containing fertilizer source most often used. Other sources of potassium include sulfate of potash (K 2 SO 4 ), potassium magnesium sulfate (K 2 Mg(SO 4 ) 2 ), and potassium nitrate (KNO 3 ). Other Important Nutrients Three other nutrients that are needed by the plant are calcium, magnesium, and sulfur. Calcium (Ca) Calcium improves general plant vigor and promotes growth of young roots and shoots. Calcium, an essential part of plant cell wall structure, also provides for normal transport and retention of other elements as well as strength in the plant. It is also thought to counteract the effect of alkali salts and organic acids within a plant. Calcium is absorbed as the cation Ca 2+ and eists in a delicate balance with magnesium and potassium in the plant. Too much of any one of these elements may cause insufficiencies of the other two. Magnesium (Mg) Magnesium helps regulate uptake of other plant foods and aids in seed formation. It is also important in the dark green color of plants and to the ability of a plant to manufacture food from sunlight. Magnesium is part of the chlorophyll in all green plants and essential for photosynthesis. It also helps activate many plant enzymes needed for growth. Magnesium, a relatively mobile element in the plant, is absorbed as the cation Mg 2+ and can be readily translocated from older to younger plant parts in the event of a deficiency. Sulfur (S) Sulfur helps maintain a dark green color while encouraging more vigorous plant growth. In most soils, sulfur is present primarily in the organic fraction which becomes available upon decomposition of organic matter and crop residues. Sulfur may be supplied to the soil from the atmosphere through rainwater. Sulfur is taken up by plants primarily in the form of sulfate (S0 4 2- ) ions and reduced and assembled into organic compounds. It is a constituent of the amino acids cystine, cysteine, and methionine and proteins that contain these amino acids. It is found in vitamins, enzymes and coenzymes.
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 6 of 14 What Are the Micronutrients? Seven of the siteen elements necessary for plant growth are needed in such small quantities that they are referred to as micronutrients. These elements include Manganese, Iron, Copper, Zinc, Boron, Molybdenum, and Chlorine. Manganese (Mn) Manganese is mainly absorbed by plants in the ionic form Mn 2+. Manganese may substitute for magnesium by activating certain phosphate-transferring enzymes, which in turn affect many metabolic processes. High manganese concentration may induce iron deficiency in plants. Manganese availability is closely related to the degree of soil acidity. Deficient plants are usually found on slightly acid or alkaline soils. Liming Florida soils to ph above 6.5 frequently causes manganese deficiency. Iron (Fe) Iron is a constituent of many organic compounds in plants. It is essential for the synthesis of chlorophyll. Iron deficiency is often induced by alkaline soil ph and can be induced by high levels of manganese. High iron can also cause manganese deficiency. Copper (Cu) Copper is essential for growth and activates many enzymes. A deficiency interferes with protein synthesis and causes a buildup of soluble nitrogen compounds. Ecess quantities of copper may also induce iron deficiency. Zinc (Zn) Zinc is essential for plant growth because it controls the synthesis of indoleacetic acid, which dramatically regulates plant growth. Zinc is also active in many enzymatic reactions. Boron (B) Boron primarily regulates the metabolism of carbohydrates in plants. The need varies greatly with different crops. Rates required for responsive crops may cause serious damage to boron-sensitive crops. Boron deficiency may occur on both alkaline and acid soils but is more prevalent on the calcareous, alkaline soils. Molybdenum (Mo)
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 7 of 14 Molybdenum functions largely in the enzyme systems of nitrogen fiation and nitrate reduction. Plants that can neither fi nitrogen nor incorporate nitrate into their metabolic system because of inadequate molybdenum become nitrogen deficient. Molybdenum is required in minute amounts. Chlorine (Cl) Chlorine is needed in relatively large quantities in plant nutrition. However, the abundance of chlorine from many sources in the environment means that chlorine deficiencies in plants are rare. Ecess and toicity of chlorine are more frequently occurring problems than are deficiencies. Soil Samples & ph How Do I Raise My Soil ph? Applying limestone to the soil raises the ph. Before putting limestone on your soil, test your soil s current ph level. The soil s ph level shows the amount of limestone needed to raise your soil s ph to your desired level. You should always test before applying limestone to make sure that your soil isn t already alkaline. How Do I Lower My Soil ph? In some soils, lowering soil ph permanently is almost impossible because of naturallyoccurring lime in the soil, such as sea shells, marl, or limestone. Soil at construction sites may contain large amounts of mortar and concrete, which are both alkaline. In situations like the ones mentioned, too much lime eists that can be neutralized. Choose plants that tolerate a high soil ph. Can't I Do Anything to Help My Acid-Loving Plants Grow in High-pH Soil? Yes, but there is a lot of work involved in maintaining the necessary ph level. Applying sulfur will temporarily lower your soil s ph, but will last only as long as it takes for the microorganisms in the soil to break down the elemental sulfur. With some forms of sulfur, this process may only take a few weeks and then the soil ph rises to its original level. Applying a large amount of sulfur may also burn and damage plants. How Do I Apply Sulfur to Lower My Soil's ph? Follow the instructions given on the product you purchase; however, the maimum amount of sulfur applied should be between 5 to 10 pounds per 1000 square feet. Repeated annual treatments may acidify the soil enough to protect against micronutrient
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 8 of 14 deficiencies caused by high soil ph. Carefully watch your plant s responses to the sulfur before beginning a sulfur treatment program for your plants. When you purchase sulfur, be aware that most sulfate sulfur does not affect soil ph. While ammonium sulfate, iron sulfate, and aluminum sulfate will acidify the soil, gypsum (calcium sulfate), Epsom Salt (magnesium sulfate, and potassium sulfate will not lower your soil s ph level. Organic matter, such as manure, peat, and composted leaves, may help reverse the alkalinity of your soil when they are applied in heavy amounts such as 200 pounds per 100 square feet. Semiannual or annual applications will be sufficient since these materials take time to be broken down. What ph Should I Aim for in My Landscape? Do not set a predetermined ph level that you must reach at all costs. Also, make sure you test your soil s ph level before trying to adjust the level. Applying lime or sulfur when it is not necessary will damage plants just as much as not applying these compounds when they are needed. What Effect Does Acid-Forming Fertilizer Have on Soil ph? In soil that is already acidic, this fertilizer will lower the soil s ph. However, this fertilizer will not lower the ph of soil with naturally-occurring limestone or shells. How Fertilizer Works How are the different forms of Nitrogen Released in the Soil? Even though all nutrients are taken up by plants through their roots, the availability of nitrogen to the plant varies. 1. Hydrolysis involves dissolving fertilizer with water. Fast-release fertilizers are readily available to the plant when they are applied. No chemical decomposition is required for the release of these sources of nitrogen. 2. Microbial activity, which involves soil microorganisms breaking down nutrients in the soil into forms that are usable by the plant. Microbial activity is dependent on the environment due to the need for soil microorganisms to function. Etreme environmental conditions (too hot, cold, or dry) may reduce or delay nitrogen release from microbial degradation.
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 9 of 14 Nitrogen Sources (Fertilizers) and their Means of Release Nitrogen Sources Hydrolysis Microbial * IBDU Organic Milogranite Urea Formaldehyde Poly-coated Urea Methylene Urea Sulfur-coated Urea Ammonium Nitrate Ammonium Sulfate Urea Calcium Nitrate Mono- or Diammonium Phosphate * Microbial nitrogen release generally increases with increasing soil temperatures, moisture, oygen levels, and neutral soil ph. Different Forms of Fertilizer Fast-Release Fertilizers Fast-release or water-soluble nitrogen sources result in a fast growth response from turf grass plants in terms of shoot growth and greening. This occurs approimately two days after application with peak release in seven to ten days and then tapering off to original levels in three to si weeks. Of course, this depends on the application rate and amount of subsequent water applied. Eamples of fast-release nitrogen sources include urea and synthetic organics such as ammonium nitrate, ammonium sulfate, potassium nitrate, and calcium nitrate.
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 10 of 14 Fast-release or soluble nitrogen sources have "salt" like characteristics. They dissolve readily in water to form cations and anions (dissociate). The greater availability of these ions corresponds to a greater burn potential (higher salt inde). These fertilizers behave like salts in that they attract water, and thus will pull moisture from plants they contact. If these fertilizers are applied at ecessive rates or when days are hot and dry, turf grass plants can suffer salt burn. Burn potential of a fertilizer can be lowered by making applications only to dry turf grass plants with air temperatures below 80 F. Irrigating or watering in the soluble nitrogen immediately after its application further reduces the chance of burning turf grass plant tissue. The nitrogen in fast release sources is either in ammonium or nitrate form. Other disadvantages of using fast-release or water-soluble nitrogen sources can be minimized by frequently applying small amounts. Using rates at or below 1/2 pound of nitrogen per 1000 square feet will minimize these problems but will increase the application frequency and treatment costs. Slow-Release Fertilizers Slow-release fertilizers are either organic materials that must be broken down by microbial activity before nutrients are available to plants, or are slowly soluble or coated fertilizers, which depend on soil moisture to release them. Slow-release fertilizer is used to define organic fertilizer materials like hoof and horn and urea formaldehyde, as well as chemical fertilizers of low solubility like dicalcium phosphate and magnesium-ammonium phosphate. Urea Formaldehyde-UF A fertilizer may be chemically altered to render a portion of it water insoluble. For instance, urea is chemically modified to make Ureaform (urea formaldehyde) -- a fertilizer that is 38% nitrogen, 70% of which is water-insoluble. This percentage is often listed on fertilizer labels as the "Percent W.I.N.," or the percent of water-insoluble nitrogen. This form of nitrogen is released gradually by microbial activity in the soil. Because microbial activity is greatly affected by soil temperature, ph, aeration, and teture, these variables can affect the release of nitrogen from Ureaform. For eample, there will be less fertilizer breakdown in acid soils with poor aeration -- an environment unfavorable to soil microorganisms. Ureaform is used for turf grass, landscaping, ornamental, horticulture, and greenhouse crops.
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 11 of 14 Isobutylidene diurea (IBDU) IBDU (isobutylidene diurea) is similar to Ureaform, but contains 32% nitrogen, 90% of which is insoluble. However, IBDU is less dependent on microbial activity than Ureaform. Nitrogen is released when soil moisture is adequate. Breakdown is increased in acid soils. IBDU is used most widely as a lawn fertilizer. In the presence of water (irrigation of rainfall), IBDU hydrolyzes back to urea and butyric acid. IBDU s nitrogen release rate is predominately affected by moisture and particle size. IBDU nitrogen release does not depend on temperature, thus releases quicker in cool weather compared to other slow release nitrogen sources. Higher soil moisture and smaller particle size of IBDU fertilizers result in a faster release rate. Controlled-Release Synthetic Nitrogen Source Fertilizers Controlled-Release Fertilizers consist of urea or other soluble nitrogen sources being coated with a semi-permeable barrier (coating). The nitrogen release rate is slow due to the coating preventing water from reacting with the soluble nitrogen source. Sulfur Coated Urea (SCU) SCU is formulated by moving granulated or prilled urea through a stream of molten sulfur. The sulfur coating is then sealed with a wa layer to protect the surface from being quickly broken down by soil microorganisms as well as to strengthen the outer shell and decrease the initial rate of urea release. Urea is gradually released by the diffusion of water through the sulfurcoated barriers. Initial release occurs through cracks, pin holes, and imperfections that are in the sulfur coating due to either shipping and handling or may occur as the product cools after formulation. Because of the non-uniformity in the thickness and the integrity of the sulfur coating, the urea granules will crack at different times, thus ehibiting variable nitrogen release rates. Therefore, the slow release pattern of SCU is the result of averaging the release of individual granules with some releasing immediately and others delayed. Plastic or Resin Coated Urea (PCU)
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 12 of 14 This is a relatively new technology that is very similar to SCU with the difference being that a plastic polymer resin is used as a coating on PCU as opposed to the sulfur and wa used on SCU. Resin coated fertilizers rely on osmosis (water influ) rather than coating imperfections to allow for the release of the water-soluble nitrogen. Once water is inside the PCU granules, water dissolves some of the solid fertilizer. This creates a highly concentrated solution, which then diffuses back through the resin coating (barrier) and out into the soil. This continues until all of the fertilizer has dissolved and diffused out. Nutrient release of PCU fertilizers is controlled by diffusion and is fairly constant over time and essentially all of the fertilizer is released over time. PCU fertilizers have a more predictable controlled release pattern or characteristic than the SCU fertilizers. Release rates for PCU fertilizers vary from 70 to 270 days depending on the thickness of the resin coating. Higher temperatures also increase the release rate and decrease the length of feeding or release. Multiply-Coated Urea Multiple coating of urea is a recent development. Urea is first coated with molten sulfur to form one layer or coating and then coated with a polymer that further protects the urea, and in combination with the sulfur layer, determines the rate of release. An advantage in addition to the controlled release rate is better resistance to abrasion than SCU s. New Fertilizer Technology Polyon Polyon is a polyurethane coated fertilizer manufactured by Pursell Industries, Inc. Gardeners who use plant foods containing Polyon -coated nutrients enjoy season-long feeding with one application. Polyon is distinguished by a unique green coating that bonds to fertilizer granules. Depending on the thickness of the coating, the green Polyon -coated granules are timed to release for 2, 3, 6, or 9 months (measured at 72 F soil temperature). The length of timed-release varies depending on each product s formula. That means that you can choose a fertilizer that lasts as long as you need it. This steady, predictable release feeds plants slowly, as they can use it.
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 13 of 14 Pound per pound, fertilizers containing Polyon -coated nitrogen are a better value than fertilizers that release all of their nitrogen quickly, only to be washed away. Polyon s timed-release approach to feeding reduces waste, fertilizer runoff or pollution, and saves both time and money. Most plant foods containing Polyon -coated nutrients feed plants both now and later, so some of the granules in the bag are not coated at all. This is by design. The thoughtful mi of both fast and timed-release plant food provides some instant feeding and planned, long-lasting nutrition. Polyon and the Environment Fertilizer s potential harm to the environment has received considerable attention over the past few years. When fertilizer is used ecessively, nutrients wash off into nearly lakes, streams, and ponds. Since fertilizer encourages growth, the algae in the water multiply quickly, causing ecessive algae blooms. Fish and other organisms will no longer be able to survive in the polluted waters. Groundwater may also become contaminated and made unsuitable for drinking. Fertilizers like Polyon decrease the amount of runoff that ends up going into the groundwater due to its controlled-release formula. By releasing the eact amount of fertilizer the plant can use, the nutrients end up in the plant as opposed to running off the soil and into the water supply. How Do I Shop for Fertilizer? Follow these steps when shopping for fertilizer: 1. Perform a Soil Test. This is the only way to be sure of the level of nutrients currently in your soil. Only after you conduct your soil test will you truly know the nutrients lacking in your soil that you need to boost through applying fertilizer. 2. Buy nutrients, not "fertilizer. Know the nutrients your soil needs before you go to buy fertilizer. If you buy a fertilizer that contains a wide variety of nutrients that you do not need, you may be spending more money and getting less of the nutrients you want. Remember, nitrogen is necessary for new, green growth and most soils do not provide enough to plants. Phosphorus and potassium, however, may eist in levels that are sufficient for the plants you are growing.
Gardening123.com: ALL THE DETAILS of Fertilizer Education Page 14 of 14 3. Eamine the Cost per Pound. Since bags of fertilizer are not the same weight, and their concentration of nutrients differs as well, it can be difficult to compare the costs. Comparing the cost per pound of the three major nutrients is one way to generally compare the different products. Add the nitrogen, phosphorus, and potassium percentages given on the bag. Multiply that number by the number of pounds in the fertilizer bag to get the number of pounds of nutrients in the fertilizer. Divide the cost of the bag by this number to determine the average cost of nutrients per pound. For eample, suppose you choose a 50-lb bag of 10-10-10 fertilizer. This bag would contain 15 pounds of nutrients (30% N-P-K total in 50 pounds). If the bag costs $5.00, the cost of nutrients would be a little over $0.33 per pound. 4. All Fertilizers are NOT created equal. One of the major deterrents against purchasing the new controlled-release fertilizers like Polyon is the increased cost per pound of these fertilizers. However, you must look past the price and eamine the actual nutrients the plant receives. For eample, many water-soluble fertilizers release their nutrients into the soil all at once. At this time, a tremendous amount on nitrogen is available to the plant. However, there is only so much nitrogen the plant can absorb during the initial application. Once the water-soluble fertilizer sinks down below the drip line, the plant s roots are unable to absorb the rest of the nutrients. Those wasted nutrients then seep into the groundwater. Also, heavy concentrations of water-soluble fertilizers may pull water out of the plant, causing burning. With controlled-release fertilizers like Polyon, water-soluble nitrogen pellets are coated with different amounts of polyurethane. When this fertilizer is applied to the soil, only a portion of the fertilizer is readily available to the plant. The plant is able to absorb these nutrients while the other coated portion of the fertilizer still remains near the plant s roots. As time passes and soil temperatures rise, water is allowed into some of the coated fertilizer and some of the fertilizer is diffused back into the soil where it is absorbed by the plant. This process results in steady nutrition available when the plant can use the nutrients. Controlled-release fertilizers release amounts of nutrients the plant absorbs when the plant can do so. When buying fertilizer, do not simply purchase the fertilizer with the most nutrients. Purchase the fertilizer with the necessary nutrients that will be fully absorbed and utilized by your plants. Polyon is a Registered Trademark of Pursell Industries, Inc. Used with permission.