Jan. 1 2004 12:00 AM

?When the pilgrims first arrived in America, they were taught by the indigenous people how to grow crops. One of the methods was to drop a small dead fish into the hole where the corn seed was placed,? said Don Johnson, general manager of J.R. Simplot, located in Boise, Idaho. The history of man-made fertilizer began thousands of years ago, when the Chinese applied lime-treated bones to the soil, and the farmers in Britain treated their soil with marl. But, before we get into all the details about fertilizer, let me first ask a question . . . have you ever opened a bag of fertilizer on one of your client?s property and asked yourself, what?s in this bag? What exactly is it that makes the grass so green? Well, here are just a few of the answers. Believe it or not, that bag contains the very same elements that make up the human body. When buying a bag of fertilizer, the first thing you will probably notice on the label are the three major macronutrients needed for plant survival. Those macronutrients, nitrogen (N), phosphorus (P) and potassium (K), are also known as N-P-K, and all are as essential to plants as they are to animals and human life. The amount of each nutrient is usually printed on a bag of fertilizer as a ratio; for example, 5-10-5 or 16-6-8. Each number represents the percentage by weight that each nutrient contributes to the whole product. For example, if a label on a 50-pound bag states that the analysis is 16-6-8, then nitrogen (N) is 16% of 50 pounds, which equals eight pounds of actual N. Phosphorus (P) is 6% of 50 pounds, which is three pounds of actual P, and potassium is 8% of 50 pounds, which is four pounds actual K. The nutrients (active ingredients) equal a grand total of 15 pounds out of the 50 pounds. The balance of weight in the bag of fertilizer is a carrier; the material on to which the fertilizer is sprayed, or impregnated, to permit it to be broadcast easier. The carrier can be designed to break down quickly to release the nutrients rapidly, or to break down slowly to retard the release of nutrients into the soil. ?The formula varies to meet different conditions at different times of the year,? explains Johnson. ?But, it really depends on the manager and what he wants. Some prefer a ?quick-release? fertilizer compared to a ?slow-release fertilizer?. ? Each manufacturer is required by the State Department of Agriculture to list the ?guaranteed? amount of N-P-K in a product. The amount of each nutrient can be more than what?s listed on the label, but should never be less than what the label shows. In addition to N-P-K, many fertilizers contain other nutrient elements as well. Some are deliberately added to give extra value to a product, but most are listed because they are beneficial nutrient contaminants that just happen to be in the parent source mix. A bag of fertilizer contains both macronutrients and micronutrients. Macronutrients include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). Micronutrients include iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), molybdenum (Mo), boron (B), and chloride (Cl). These trace elements help the plant in one way or another. For example, iron is essential for the process of photosynthesis, the process by which green plants and other organisms use the energy of light to convert carbon dioxide and water into simple sugar glucose. Photosynthesis provides the basic energy source for virtually all organisms. Plants thirst for a much greater amount of macronutrients than micronutrients, because nitrogen gives plants the ability to grow rapidly and produce large amounts of succulent, green foliage. ?But, before the plants can actually absorb the nitrogen, it must first be converted from a natural gas to ammonium, and further processed to urea,? said Johnson. ?The making of fertilizer involves a lot of chemistry; it?s important that we make the nitrogen in a form that is usable to the plant. If we apply nitrogen that the plant cannot absorb and use, it can have a reverse effect. It can lock up the soil and not allow the plant to feed.? Johnson, who has been in the business for 32 years, and is a former professor of Ventura Community College, Ventura, California, says phosphorus, one of the 16 elements necessary for plant growth, starts out as phosphate rock and then dissolves into a form plants can absorb. Some phosphorus is released as organic matter mineralizes, and some is dissolved from the soil minerals, but the rate of release is very limited. Considered the second most important element, phosphorus plays an important role in seedling development, cell building and root growth. Only about 10 to 20 percent of the applied phosphorus, which usually enters the plant as phosphate, is used by the plant within the year it is applied. Phosphorus sources tend to be one or another form of phosphoric acid, which is very stable in soil. Once it?s applied it stays in the soil, because it does not volatize nor leach through the soil, as do nitrogen and potassium. The most common visible signs of a lack of phosphorus in a plant appear first in the lower leaves because of the movement in the tissues. These are the older leaves, and they show symptoms as a lack of chlorophyll, a deepening of the green color, or a reddish color in the leaves. The third ingredient, potassium, assists plants in forming starches and protein. It is sourced from either rock or water, using the process of evaporation or electrolysis to draw minerals to the region. It comes in a form of potassium sulfate or potassium chloride (muriate of potash). Both are equally effective sources. ?Potassium helps the overall cell structure of a plant by making it more resistant to disease and physical damage to turf with heavy foot traffic,? Johnson explains. When crops are continually grown in the same soil, the phosphorus is depleted and must be replenished by phosphate fertilizers. Just as humans obtain these chemicals from the plants we eat, plants must obtain their phosphorus from the soil. Phosphorus is the second most abundant mineral in the human body, and is part of every chemical reaction in the body. This element can be found in the energy molecule that powers our body called adenosine triphosphate (ATP). In addition, it is responsible for bone and tooth development. When thinking about applying fertilizer to a landscape, there are several things to consider. The ratio of nutrients would differ, depending on the needs of the turf or plants involved. The best way to determine this is with a soil test. That way, you can be sure that you?re applying precisely what the plant needs. Another important item to consider is whether organic or chemical fertilizers would best suit your needs ? are you looking for a shorter-term rapid growth spurt, or longer-term sustenance? ?The health of the soil is much more important than just feeding the plant,? said Marilyn Chambers, president of Tri-C Enterprises, Chino, California. ?Organic fertilizers contain natural ingredients with 50 different kinds of minerals, N-P-K and organic acid, which provides nutrients for the plant. Organic fertilizers are considered insoluble, ?slow- release? fertilizers because they depend on microbial and chemical action in the soil to make nutrients available to the plant. They are responsible for producing green lawns without excessive leaf and shoot growth, or the risk of leaf burning. These fertilizers are de-signed to provide a steady supply of nitrogen to the grass over a longer time period. And they are less likely to wash off lawns or down into groundwater, because they are water-insoluble. Although it takes longer for those nutrients to reach the plant, it sustains plants for a longer period of time.? Chemical fertilizers are either mixed or manufactured, and have the advantage of lower cost. Consequently, most fertilizers used today are from chemical sources. ?Quick-release,? water-soluble (inorganic) fertilizers become available to plants almost as soon as they are applied to the lawn. For example, a water-soluble (inorganic) nitrogen fertilizer will produce rapid leaf and shoot growth. Understanding how plants absorb nutrients can help you determine what fertilizer to buy. There are four stages plants must go through to absorb the nutrients. The first stage is called diffusion. The instructions on a bag of granular fertilizer almost always recommend watering after application to dissolve the product. In order for the nutrients to be moved into the soil in a form the plant can use, the granules must first be dissolved in water. This creates a very high concentration of nutrients in a small amount of soil. As this high concentration of nutrients moves toward the root mass, it grabs lesser concentrations of other nutrients, usually micronutrients, and carries them with the main stream toward the roothairs. The second stage, called mass flow, occurs a few days after application. Subsequent irrigation continues to dissolve the fertilizer granules at a steadier rate, creating a consistent flow of nutrients into the rootzone. Most plant benefit is derived from mass flow feeding, provided the nutrients are the ones that are deficient. Root interception is the third stage. It is defined as the process whereby the root comes into contact with nutrients as it grows. For example, the potassium ion (K ), diffuses in the soil after irrigation and pushes through the soil, penetrating the root of the plant. Once the ion (K ) is inside the cell, it moves rapidly by mass flow in the transpiration stream (xylem tissue). Therefore, the root is responsible for moving the nutrients to other regions where nutrients are more concentrated. This mechanism further enhances the role of the first stage called diffusion. In the fourth stage, foliar absorption of nutrients, is a popular method of fertilization. To be done properly, it does require some expertise along with agronomically appropriate fertilizer materials. The results from foliar feeding can be quite dramatic if the deficient nutrient is accurately identified and then applied. Most plants are capable of responding to foliar feeding if the leaf cuticle is not too thick. Understanding how plants absorb nutrients, how fertilizers work, and what?s in the bag can take the mystery out of how to make plants look better and healthier.

January 2004