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Chapter 10 Fertilization.

OBJECTIVES

After studying this chapter, the student should be able to

* Identify the nutrients required by turfgrass plants

* Discuss the different types of fertilizers

* List the factors that influence the selection of an appropriate fertility program

* Explain why nitrogen is the key nutrient in a turfgrass fertility program

* Distinguish between fast-release and slow-release nitrogen carriers

* Discuss the rate and frequency of fertilizer application for turfgrass

* Describe methods of fertilizer application

Introduction

As explained in Chapter 7, turfgrass plants require seventeen essential elements to grow and complete their life cycle. These nutrients are divided into three groups based on the amounts of each needed by plants (Figure 10-1). Carbon, hydrogen, and oxygen are obtained from air or water and are readily available to turfgrass. The other fourteen elements are removed from the soil by plant roots.

The three elements that receive the greatest attention from turfgrass managers are nitrogen, phosphorus, and potassium because they are usually added to the soil at regular intervals. They are referred to as primary nutrients because turfgrass requires larger quantities of nitrogen, phosphorus, and potassium than it does of the other eleven elements obtained from the soil. They are also called fertilizer nutrients because of their presence in most fertilizers. Of the three, nitrogen is most likely to be deficient in the soil.

Calcium, magnesium, and sulfur are called secondary elements. Calcium and magnesium are normally supplied to the soil by the application of liming materials. Sulfur is added to the soil by using fertilizers that contain the nutrient or acidifying materials for lowering soil pH such as elemental sulfur and aluminum sulfate. Some sulfur ends up in the soil because of air pollutants (sulfur dioxide) or the application of sulfur-containing pesticides.

Micronutrients or trace elements are materials required in very small amounts by plants. These minor nutrients are found in plants in quantities measured in parts per million (ppm). However, they are just as essential to turfgrass growth as the primary nutrients, no matter how minute the amount required by the plant (Figure 10-2). In many areas of the United States it is not necessary to apply micronutrients. With the exception of iron, micronutrient deficiencies are rare.

Fertilizer

Fertilization is the practice by which nutrients are supplied for plant growth. Most fertilizers are applied in a dry form with a spreader (Figure 10-3). Nutrients also are mixed with water and sprayed on turf. This latter practice is commonly performed by many lawn care services and is also common on putting greens. Most fertilizers contain nitrogen, phosphorus, and potassium and are called complete fertilizers. If, for some reason, it is not necessary to apply one of these primary nutrients, the turf manager may use a fertilizer that contains the other two. Individual carriers that supply nitrogen, phosphorus, or potassium alone are also available. In regions where secondary or micronutrients are deficient in the soil, fertilizers often contain these elements as well.

[FIGURE 10-3 OMITTED]

The fertilizer analysis states the percentage of nutrients in a fertilizer. Generally the analysis percentages are rounded down to whole numbers and called the grade. The fertilizer grade is the minimum guaranteed analysis of a fertilizer. The three numbers on a bag of fertilizer represent its grade. The first number in the sequence indicates the percentage of elemental nitrogen (N), the second is available phosphoric acid ([P.sub.2][O.sub.5]), and the third is soluble potash ([K.sub.2]O).

A 20-5-10 fertilizer contains by weight 20 percent nitrogen, 5 percent [P.sub.2][O.sub.5], and 10 percent [K.sub.2]O. A 50-pound bag of this fertilizer contains 10 pounds of nitrogen (0.20 x 50), 2.5 pounds of [P.sub.2][O.sub.5] (0.05 x 50), and 5 pounds of [K.sub.2]O (0.10 x 50). The actual amounts of elemental phosphorus and potassium are 44 percent and 83 percent of the grade numbers. For example, 4.4 percent of the weight of a bag of 30-10-10 fertilizer (0.44 x 0.10) is elemental phosphorus (Figure 10-4).

Fertilizer ratio is another important fertilizer term. A 30-10-10 fertilizer contains three parts of nitrogen for each one part of [P.sub.2][O.sub.5] and [K.sub.2]O. It is said to have a 3:1:1 ratio. The 20-5-10 fertilizer mentioned earlier has a 4:1:2 ratio. Rather than recommending a specific grade, turfgrass specialists often suggest using a fertilizer that has a certain ratio. If a 2:1:1 ratio is recommended, for example, the turf manager may choose a 20-10-10, 10-5-5, 14-7-7, or 18-9-9 fertilizer.

The correct fertilizer ratio depends on the quantity of available nutrients in the soil. The quantities of phosphorus and potassium that are available for plant use can be accurately determined by testing the soil. As discussed in Chapter 8, soil test results enable the turf manager to develop the most effective and efficient fertility program. The quantity of essential elements in the soil depends on the amount and type of fertilizer applied previously, the level of nutrients that occur naturally in the soil, and the extent of nutrient losses from the soil.

Nutrient Losses

Losses are due to four causes. A large amount of nutrients is removed from the soil by the plants themselves. If grass clippings are allowed to remain on the turf, then most of these nutrients are returned to the soil and can be used by the turfgrass again. However, when the clippings are collected and removed from the site, the nutrients are no longer available to the plants. Some nutrients are converted to gaseous forms and diffuse into the atmosphere. Leaching by water from rain or irrigation results in nutrients being moved below the reach of turfgrass roots. A further, temporary loss occurs when nutrients become "fixed" in the soil. Because of various chemical reactions they are converted to insoluble, unavailable forms.

Effect of Maintenance on Nutrition Program

The level or degree of turfgrass maintenance has a major effect on the nutrition program. Low-maintenance, utility sites usually receive minimal fertilization because quality is relatively unimportant. One light fertilizer application per year may be sufficient. The turf manager desires a vigorous, dark green, dense turf on a higher maintenance site. Better quality turf can only be achieved by supplying greater amounts of fertilizer.
Figure 10-4
Useful fertilizer conversions.

To convert [P.sub.2][O.sub.5] to P multiply by 0.44

To convert P to [P.sub.2][O.sub.5] multiply by 2.29

To convert K2O to K multiply by 0.83

To convert K to K2O multiply by 1.2


Unsatisfactory turfgrass is often the direct result of insufficient fertilization. The quality of many turf areas could be improved dramatically by increasing the fertilization rate and number of fertilizer applications. Fertilizer is the best investment dollar for dollar in a successful turf management program.

Nitrogen

Nitrogen is the key nutrient in a turfgrass fertility program. With the exception of carbon, hydrogen, and oxygen, plants require more nitrogen than any other essential element. On a dry weight basis, a healthy turfgrass plant is composed of 3 to 5 percent nitrogen. This nutrient is more likely to be deficient than the other sixteen essential elements. There are several reasons for this. Abundant levels of nitrogen are not normally found in soils. When nitrogen-containing fertilizer is applied to the soil, significant quantities of this nutrient may be lost because of leaching and volatilization. As mentioned in Chapter 7, the nitrate ion (N[O.sub.3.sup.-) is the chemical form most commonly used by plants. It is very susceptible to leaching because it has a negative charge and is not stored in the soil on cation exchange sites. Volatilization is the loss of nitrogen to the atmosphere in a gaseous form. It is most common on alkaline soils when the nitrogen is not watered in after application.

Nitrogen losses are especially severe when the turfgrass is growing on a sandy soil and irrigation occurs frequently. Sandy soils are very prone to leaching, and heavy irrigation results in a larger amount of nitrogen being washed down beneath the root zone. Clipping removal also leads to nitrogen depletion.

Nitrogen has many important functions in a turfgrass plant. It is a component of chlorophyll, proteins, amino acids, enzymes, and numerous other plant substances. The effects of nitrogen fertilization are readily seen. Shortly after the fertilizer is applied the plants turn a darker green color and vertical shoot growth increases significantly.

Because nitrogen is the key nutrient in turfgrass nutrition, fertility programs are normally expressed in terms of how many pounds of nitrogen per 1,000 [ft.sup.2] (kilograms per 93 [m.sup.2]) are applied. Unfortunately, soil tests are not particularly helpful in determining nitrogen fertilization rates. (The reasons for this have been discussed in detail in Chapter 8.) Consequently, unless tissue testing is performed, turf managers must base their nitrogen fertility program on visual observations, general recommendations from turfgrass specialists, and other considerations (Figure 10-5).

The need to apply nitrogen can be determined by quality indicators such as color and density. The nutrient is an important component of the chlorophyll molecule, and nitrogen-deficient plants turn a yellowish green color. This condition is known as chlorosis. When grass becomes chlorotic and loses its desirable green color, the manager may want to apply fertilizer. However, before fertilizing, he or she should be certain that the turf has not turned color because of environmental stress or pest problems. It is also important to remember that turf does not have to be dark green to be healthy.
Figure 10-5
Some factors that effect the total amount of nitrogen that
should be applied during the growing season.

Quality indicators--color, density, and uniformity
Soil texture (sands may require more)
Amount of irrigation (irrigation results in more growth and use,
possibly more leaching)
Clippings (returned or removed)
Shade (less sun = less growth = less need for fertilizer)
Grass species and cultivars present
Need for recuperation (sports turf)
Type of fertilizer (fast-release versus slow-release nitrogen)
Disease problems (too much or too little nitrogen favors certain
diseases)
Length of growing season
Leaching concerns (likelihood of water pollution by nitrates)
Green speed (less nitrogen results in increased ball roll distance)
Budget


Density is the most important indicator. A thin, open turf populated with weeds is often caused by inadequate nitrogen fertility. A third indicator sometimes used to assess nitrogen levels is clipping yield. Low levels of available nitrogen result in a slower vertical growth rate and a reduced mowing frequency.

Nitrogen fertilization, based on these quality indicators, is greatly influenced by the degree of turf quality that is desired. A low-maintenance area may receive as little as 1 pound of nitrogen per 1,000 [ft.sup.2] a year, whereas the rate for a highquality bermudagrass turf may be as much as 12 to 16 pounds of nitrogen per 1,000 [ft.sup.2] a year. Other factors that affect how much nitrogen is applied include the soil texture, the amount of irrigation, whether clippings are removed, the type of nitrogen source used, the length of the growing season, the species and cultivars that compose the turf, the degree of shading, and the size of the maintenance budget. A sports turf usually requires extra nitrogen because the grass must be aggressive. Foliar analysis (tissue testing) can be used to help establish fertilizer needs. In most cases turf managers base their nitrogen rates on the appearance and performance of the turf.

Overfertilization can be just as detrimental as not applying enough nitrogen. Excessive rates cause physiologic changes in a plant such as thinner cell walls, more tender, succulent tissue, and reduced food reserves. These changes result in decreased heat, drought, cold, and wear tolerance. Disease resistance is also diminished. The application of too much nitrogen significantly increases the need for mowing because of the rapid shoot growth it stimulates.

The nitrogen found in most fertilizers is produced by nitrogen in the atmosphere reacting with natural gas (methane). The result of this reaction is the formation of ammonia, which is then combined with other chemicals such as nitric acid, sulfuric acid, phosphoric acid, and carbon dioxide. The end products of these reactions are four common nitrogen carriers--ammonium nitrate (33-0-0), ammonium sulfate (20-0-0), ammonium phosphate (11-48-0, 20-50-0), and urea (45-0-0). The form of nitrogen in these carriers is 100 percent water soluble and is immediately available for plant use. These carriers are said to be quickly available or fast-release sources of nitrogen. Urea is widely used on turfgrass.

Water-soluble nitrogen can be absorbed by turfgrass roots as long as there is sufficient moisture in the soil. Such high solubility has both advantages and disadvantages. Turfgrass responds rapidly after their application but the response is short term. This is because much of the nitrogen is immediately taken up by plants, leached below the root zone, or lost to the atmosphere as a gas. These forms of nitrogen are less expensive than more complex, insoluble carriers. Fast-release nitrogen is not greatly affected by soil temperature. However, it has a high burn potential and can injure turfgrass if applied incorrectly (Figure 10-6).

Some of the disadvantages associated with water-soluble carriers pose special problems for the turf manager. Turfgrass is one of the few crops that has fertilizer applied directly onto its foliage. This increases the likelihood of foliar burn. The short-term plant response characteristic of these carriers means that frequent fertilization may be required. Another problem is the inefficiency of the water-soluble forms. Nitrogen is wasted because the turfgrass plants are able to take up more nitrogen than they need, and leaching and gaseous losses may be significant. This can be a serious problem if the nitrates leach down into the groundwater.

Slowly available nitrogen carriers were developed to solve the problems associated with the quickly available forms. They are also referred to as slow-release or controlled-release. A certain percentage of the nitrogen in these carriers is not immediately soluble in water and therefore not initially available for plant use. The result is a lower burn potential, a long-term plant response, and greater efficiency (Figure 10-7). A steadier release pattern reduces the likelihood of plants absorbing more nitrogen than they need and decreases leaching losses.

Slowly available nitrogen carriers are more expensive than soluble forms because the manufacturing process is more costly.

[FIGURE 10-6 OMITTED]

Ureaformaldehyde (UF), sulfur-coated urea (SCU), polymer-coated urea (PCU), and isobutylidenediurea (IBDU) are examples of slowly available nitrogen carriers. All are produced by chemical processes that result in a certain percentage of the nitrogen in urea becoming temporarily unavailable for plant use.

Urea formaldehyde is synthesized by combining urea and formaldehyde. When a ureaformaldehyde (U:F) ratio of 1.3:1.0 is used, the resulting product has approximately 67 percent slowly soluble nitrogen. The other 33 percent is called cold water-soluble nitrogen (CWSN). It is composed of unreacted urea and low molecular weight, short-chain methylene ureas that immediately provide nitrogen to turfgrasses. The rest of the nitrogen does not become available until the larger molecules are broken down into smaller units by soil microorganisms, freeing the urea. The cold water-insoluble nitrogen (CWIN) that is soluble in hot water is intermediate or moderately slow release, and the fraction that is insoluable in hot-water (HWIN) is very slowly soluble.

The intermediate chain-length material is sometimes referred to as methylene urea. The longer the chain, the slower the release of the nitrogen.

One problem with UF is its dependence on higher temperatures for adequate nitrogen solubility. Microbial degradation of the slowly soluble forms is minimal at cool soil temperatures. Consequently, nitrogen availability is significantly reduced, and enough nitrogen may not be supplied by this carrier at certain times of the year. The nitrogen activity index (AI) is a measure of relative solubility. It is the percentage of CWIN that is soluble in hot (212[degrees]F, 100[degrees]C) water. The higher the AI, the more rapidly the slowly available nitrogen becomes soluble. A UF material should have an AI of at least 40 percent to ensure that sufficient quantities of nitrogen will be supplied to turfgrass during the year following application.

The solubility of a UF fertilizer is controlled by the UF ratio. A 1.9:1.0 ratio product results in shorter polymer chains, has 67 percent CWSN, and provides a much greater quantity of soluble nitrogen. This and similar ratios are popular where cooler soil temperatures cause reduced levels of microbial activity.

[FIGURE 10-7 OMITTED]

Sulfur-coated urea is simply urea granules that have been covered with sulfur. The urea is water soluble, but the sulfur coat produces an insoluble barrier. The granule is also coated with a thin layer of wax to seal any cracks or defects in the sulfur coat. Eventually the coating is burst open because of the diffusion of water into the granule through micropores, cracks, and imperfections, and the nitrogen is released. The wax is degraded by microorganisms.

The coating thickness varies among particles. Those that have a thin or imperfect coat will release first. Approximately 30 percent of the nitrogen in most SCU products is quickly available. By blending particles with thin, medium, and thick coats, manufacturers can make products that release nitrogen steadily for ten to fifteen weeks.

Sulfur-coated urea is popular because it is the least expensive of the slowly available nitrogen sources. However, problems can result if the fertilizer is damaged during handling. If the sulfur coats are cracked, the particles are no longer slow release.

A method of producing a more precise form of slowly available nitrogen is to surround urea with a polymer, plastic, or resin coating. These ultrathin coats are tough and durable. Moisture is absorbed by the coating and dissolves the urea; then the solution diffuses out into the soil. Most of these products are relatively new and are often called polymer-coated ureas (PCUs). They have a very uniform release rate, the length of which depends primarily on the thickness of the coating (Figure 10-8).

A PCU is more expensive than an SCU because coating urea with a polymer is more expensive than coating it with sulfur. Another technique is to apply a thinner than usual coating of sulfur to urea, then covering it with a polymer coat thinner than that used on a normal PCU. The resulting product is cheaper than a PCU but has a more precise release pattern than an SCU.

IBDU is similar to UF but is less affected by soil temperature. The nitrogen dissolves in water slowly, but does not depend on microbial decomposition. Particle size has the major effect on solubility. Smaller particles dissolve more readily and release soluble nitrogen faster than larger particles. A blend of different-sized particles results in a fertilizer that releases nitrogen relatively uniformly for three or four months. However, low or high soil pH can impede nitrogen release. IBDU is popular for late-season feeding because it can release nitrogen at colder soil temperatures like the soluble sources but without leaching problems, and will not cause a spurt of topgrowth if a few warm days occur.

[FIGURE 10-8 OMITTED]

Organic matter releases nitrogen gradually because the nutrient is tied up in complex molecules. The nitrogen becomes available after microorganisms break down the complex molecules into simpler forms.

Milorganite is a natural organic fertilizer produced from sewage sludge by the Milwaukee Sewage Commission. Other products are derived from dried blood, bone and seed meal, fish scraps, poultry feathers and manure, and compost. Ringer, Sustane, and Nature Safe are examples of natural fertilizers (Figure 10-9). Besides being slowly available nitrogen sources, natural organic fertilizers also provide the other essential nutrients and have been shown to suppress turf diseases. They have a very low burn potential but are more expensive nitrogen sources than other types of fertilizers (Figure 10-10). This is because the natural organic materials contain small amounts of nitrogen and often have to be shipped long distances. Sometimes urea is added to them to increase the percentage of nitrogen.

Natural organic fertilizers are viewed positively by the public because they are recycled waste and are considered to be "environmentally sound" products.

Fast-release and slow-release nitrogen carriers have advantages and disadvantages. Many companies that manufacture turfgrass fertilizers mix soluble and insoluble carriers to ensure both a rapid and a long-term response (Figure 10-11).

[FIGURE 10-9 OMITTED]

Potassium

Potassium has numerous functions in a plant. It counteracts many of the negative effects of nitrogen such as decreased plant tolerance to cold, heat, drought, and diseases. If turfgrass is supplied with adequate amounts of potassium, the ability of the plants to tolerate stress is increased.

Muriate of potash (potassium chloride) is the carrier commonly added to a fertilizer. It has a high burn potential (Figure 10-12). Potassium sulfate has a lower burn potential and releases potassium more gradually than muriate of potash. Though more expensive, potassium sulfate is a better choice for quality turf areas. Slow-release, polymer-coated potassium fertilizers are also available.

Potassium is susceptible to leaching. The problem, however, is more severe with nitrogen. Plants will absorb significantly greater amounts of potassium than they require. This is known as "luxury consumption." Large quantities of potassium may be removed if clippings are collected. This is more of a problem with muriate of potash than it is with potassium sulfate or polymer-coated sources. Soil tests can be used to estimate potassium needs. Turf fertilizers with a 2:1 N:[K.sub.2]O ratio are often recommended unless soil test results indicate that less or more potassium is needed. Some turf managers use 1:1 ratios in an attempt to increase the winter hardiness or drought tolerance of their grass. Potassium is very important in regulating water absorption and retention in a plant.

Phosphorus

Phosphorus has many important roles in a plant. A prominent characteristic is its ability to promote rooting. Adequate levels of phosphorus are crucial at the time of establishment. The nutrient should be incorporated into the soil before planting, and then, after planting, the new seedlings or sod should be top-dressed with phosphorus fertilizer. All application should be based on soil test results.

The major problem with phosphorus is its "fixation" in the soil. At a soil pH below 6.0 and above 7.0 phosphorus becomes tied up in unavailable, insoluble forms. Maintaining the correct soil pH increases phosphorus availability. Super-phosphate was for many years the primary phosphorus carrier. Today, ammonium phosphates are used in most fertilizers (Table 10-1).

Phosphorus has been identified as a potential water pollutant. If large enough quantities accumulate in lakes and ponds, algal blooms and other water-quality problems can occur (Figure 10-13). Turfgrass fertilizers are occasionally the source of some of the phosphorus that is found in bodies of water. The fertilizer runs off into the lake or pond because it is applied too close to the water or on a slope near the water. Some may be accidentally spread on an adjacent driveway or road where it can wash into a storm drain that empties into a body of water. If some of the phosphorus lands on bare soil, it will move with the soil if erosion occurs.

It is important that phosphorus be applied only when soil test results show a need. Many turf areas have adequate phosphorus levels because it is not readily lost once it is in the soil. When phosphorus is used, it should be watered in after the application. However, too much irrigation will result in runoff. Fertilizer should not be applied if a heavy rain is predicted.

Some states are considering regulating the use of phosphorus-containing fertilizers. Some municipalities already have regulations in place.

[FIGURE 10-13 OMITTED]

Fertilizer Programs

Fertilizer application rates and the number of applications are determined by many factors, such as the desired level of quality, weather conditions, the length of the growing season, soil texture, the amount of irrigation provided, and whether clippings are removed. Environmental conditions affect the fertilizer program. Shaded turf, because it grows more slowly, is usually fertilized less than grass growing in the full sun. Turf use influences fertility requirements. An athletic field often needs more fertilizer than a lawn because sports turf has to recover from wear injury.

The species and cultivars that compose the turf have a major effect on fertilizer programs. Creeping bentgrass and improved bermudagrass are considered heavy feeders because they grow vigorously and need abundant amounts of nutrients to support this growth. Grasses that have a slow growth rate such as the fine fescues, centipedegrass, and carpetgrass need significantly less fertilization. Soil test results help the turf manager to develop the program.

Application dates also depend on many of the same variables listed earlier. Weather conditions have the greatest influence on timing. Fertilization should occur at the beginning of or during periods when temperature and moisture conditions favor active turfgrass growth. The grass needs the nutrients when it is growing vigorously. Fertilization should be avoided at times when environmental and disease stress occurs. For example, a midsummer fertilizer application can be detrimental to cool season turf because it results in decreased heat, drought, and disease tolerance.

The most important time to fertilize cool season grasses is in late summer or early fall. A late fall fertilization in November is also beneficial. The fertilizer is usually applied when the rate of shoot growth has slowed significantly but the grass is still green. It promotes root growth and earlier spring greenup. A third application in the spring is recommended as well for better quality turf. Often a lower nitrogen rate is used at this time.

The most important time to fertilize warm season grasses is in late spring. A second application in the summer is recommended. Early spring and late summer fertilization may also be necessary (Table 10-2).

The most common fertilizer application rate is 1/2 to 1 pound of nitrogen per 1,000 [ft.sup.2] (1.1-2.2 kilograms per 93 [m.sup.2]). Golf course putting greens are an exception. They usually receive frequent, light rates. Turf requires fewer applications when slow-release nitrogen sources are used rather than fast-release products. Because of less nutrient storage capacity and greater leaching potential, sandy soils are fertilized at lower rates and more frequently than loam and clay soils.

The turf manager should use soil test results and Cooperative Extension Service recommendations as the basis for a fertility program. Nitrogen, phosphorus, and potassium receive the most attention, but other essential elements should not be overlooked. Iron deficiencies occur, especially on soils that are alkaline, sandy, or high in organic matter. Sometimes the application of iron causes grass to become a darker green color. Nitrogen also improves color. However, iron will not stimulate the rapid shoot growth that nitrogen will. Consequently, iron can be used to give turf a better color without increasing its maintenance requirements or causing the grass to be less tolerant of environmental stress. Liquid foliar applications often work best, but results are not long-lasting due to the removal of iron on the leaf tissue when the grass is cut.

Magnesium and calcium may be deficient on very sandy soils. Sand golf greens often require the addition of other nutrients besides nitrogen, phosphorus, and potassium. Relatively specific fertilizer programs for golf courses, lawns, athletic fields, and other turf areas are discussed in Chapters 20, 21, and 22.

Application Methods

Granular Fertilizers

The majority of the fertilizer used on turfgrass is in a dry or granular form. It is distributed with a drop, rotary, or pendulum-type spreader. The drop, or gravity-type, spreader has a series of openings at the bottom of the hopper through which granular fertilizer drops a few inches to the ground directly beneath (Figure 10-14). The rate of application can be changed by adjusting the size of the openings. Drop spreaders provide a very precise, uniform distribution pattern.

The width of homeowner-type drop spreaders is usually 2 feet (0.6 meter), but wider models are available. Drop spreaders are normally preferred for the application of fine or very light particles such as ground limestone, or granular pesticides that must stick to the foliage. Too much overlapping or misses between application swaths can result in streaking because of uneven nitrogen distribution.

Rotary spreaders are also called centrifugal, broadcast, or cyclone spreaders. Most have a plate, called an impeller, which is attached beneath the hopper and spins as the spreader wheels turn. When fertilizer drops through the adjustable openings at the bottom of the hopper, it falls onto the rotating impeller and is thrown away from the spreader in a semicircular pattern (Figure 10-15).

[FIGURE 10-14 OMITTED]

Application is faster with a rotary spreader because it broadcasts granular materials over a wider area than the drop type. The spreading width normally ranges from 6 feet (1.8 meters) for small spreaders to 60 feet (18.3 meters) for very large ones. Streaking is less likely with rotaries because the swaths are overlapped and the edge of the distribution pattern is not as sharp as that produced by a drop spreader.

A rotary spreader does not provide as accurate and uniform an application as a drop spreader, but the distribution can be quite satisfactory if the proper overlap is used. Spreading mixed materials of different sizes is a problem because larger, heavier granules are thrown farther than smaller, lighter particles. Foliar-applied granular pesticides are not usually spread with a rotary spreader because of unsatisfactory distribution. Ground limestone will often drift when applied with a rotary spreader. The speed at which the spreader is pushed or driven has a major impact on application rate.

Pendulum-type spreaders have a spout that moves from side to side. They are pulled by a tractor or turf vehicle, have a large hopper capacity, and can throw dry materials a great distance when the spout moves rapidly.

Spreaders should be thoroughly cleaned after use. They must be accurately calibrated (openings set at the proper size) to ensure that the correct amount of material is applied. Spreader care and calibration are discussed in Appendix C.

Liquid Fertilizers

The application of fertilizer in a liquid form has become popular with many lawn care companies and golf course superintendents. The fertilizer is sprayed on the turf and is often mixed with pesticides. On golf courses, at certain times, such low rates of nutrients are applied to greens that it would be impossible to apply them uniformly with a spreader. Liquid application is usually less expensive than granular applications, though the initial cost of the sprayer equipment is quite high compared to the cost of a spreader. Generally 3 to 5 gallons (11.4 to 19.0 liters) of the fertilizer-water mixture is applied per 1,000 [ft.sup.2] to ensure that the fertilizer is washed into the root zone. Urea is the most widely used fertilizer material because it is soluble in water. Unfortunately, urea has a high burn potential and releases most of its nitrogen in a few weeks, so ideally it should be sprayed frequently at light rates. Products are now available that have a lower burn potential and somewhat longer-lasting effects.

[FIGURE 10-15 OMITTED]

The application of small amounts of nutrients in low spray volumes (0.5 gallon per 1,000 [ft.sup.2]) directly to the foliage is called foliar feeding. Some of the fertilizer is absorbed by the turfgrass leaves. Foliar feeding is used to supply micronutrients such as iron and nitrogen.

Fertigation is the application of nutrients through the irrigation system (Figure 10-16). Minute amounts of fertilizer are regularly metered into the irrigation lines and distributed along with the irrigation water through the sprinkler heads. The irrigation system must be capable of distributing water very uniformly. The advantages of fertigation include a more efficient plant use of nutrients, a steadier growth rate, and a savings on labor costs. Fertigation occurs on some golf courses, but is not yet widely used.

Its use will increase because on many new golf courses the irrigation systems are designed to accommodate fertilizer injection systems. Fertigation is very popular during the grow-in period on recently constructed golf courses because there is no need to drive tractors pulling fertilizer spreaders over the easily-injured young grass.

[FIGURE 10-16A OMITTED]

[FIGURE 10-16B OMITTED]

Fertilizer Burn

Fertilizer or foliar burn can be a serious problem if fertilizers are applied improperly. Soluble, fast-release nutrient sources in both liquid and granular forms should be watered in following application. Irrigation moves the fertilizer off the foliage into the soil and prevents burning of the leaves. It does not occur after foliar feeding because very low fertilizer rates are applied. The foliage should be dry when granular fertilizers are applied (Figure 10-17). Fast-release nitrogen generally should not be applied at rates higher than 0.5 pound of nitrogen per 1,000 [ft.sup.2].

If an overapplication of fertilizer occurs, heavy irrigation is recommended. If a spill of granular fertilizer occurs, as much fertilizer as possible should be picked up before irrigating.

[FIGURE 10-17 OMITTED]

SELF-EVALUATION

1. The two nutrients generally supplied by liming materials are -- and --.

2. Nitrogen losses on a sandy soil can be severe because of --.

3. The ratio of a 30-15-15 fertilizer is --.

4. The second number in a fertilizer grade represents the percentage of -- in the bag.

5. A 30-pound bag of 25-12-12 fertilizer contains -- pound(s) of nitrogen.

6. Water-soluble nitrogen is said to be quickly --.

7. SCU is the abbreviation for --.

8. -- is more temperature dependent than SCU and IBDU.

9. An example of a fast-release nitrogen carrier is --.

10. -- increases the ability of a plant to tolerate stress.

11. The major problem with -- is its conversion to unavailable forms in the soil.

12. If cool season turfgrasses were to be fertilized only once a year, the best time would be in --. 13. Sandy soils are fertilized at -- rates and more -- than loam or clay soils.

14. -- spreaders distribute fertilizer more uniformly than -- spreaders.

15. The micronutrient that is most likely to be deficient is --.

16. Algal blooms are associated with -- runoff.

17. Warm season grasses generally need heaviest fertilization in the --.

18. -- and nitrogen can be applied to make grass greener.

19. Establish a fertilizer program for a quality lawn in your area.

20. Discuss the advantages and disadvantages of water-soluble (immediately available) nitrogen sources such as urea.

21. Why are natural organic fertilizers becoming popular?
Table 10-1 Characteristics of Nutrient Sources

                                              APPROXIMATE
                                               NUTRIENT
                                              PERCENTAGE

                                              [P.sub.2]
SOURCE                               N        [O.sub.5]    [K.sub.2]O

Ammonium nitrate                     33           0            0
Ammonium sulfate                     21           0            0
Urea                                 45           0            0
IBDU (isobutylidene-diurea)          31           0            0
Ureaformaldehyde                     38           0            0
Methylene urea                       38           0            0
Sulfur-coated urea                   32           0            0
Polymer-coated urea               39-44           0            0
Milorganite                           6           2            0
Monammonium phosphate                11          48            0
Diammonium phosphate                 20          50            0
Superphosphate                        0          20            0
Triple (treble)                       0          45            0
  superphosphate
Potassium chloride                    0           0           60
  (muriate of potash)
Potassium sulfate                     0           0           50
Potassium nitrate                    13           0           44
Ferrous sulfate                       0           0            0
Ferrous ammonium sulfate              7           0            0
Chelated iron                         0           0            0

SOURCE                           COMMENTS

Ammonium nitrate                 Fast-release nitrogen source
Ammonium sulfate                 Fast release, strong acidifying
                                   effect, contains 24% sulfur
Urea                             Fast release
IBDU (isobutylidene-diurea)      Slow release
Ureaformaldehyde                 Slow release
Methylene urea                   Similar to UF but has more
                                   water-soluble nitrogen
Sulfur-coated urea               Slow release
Polymer-coated urea              Slow release
Milorganite                      Activated sewage sludge, slow release
Monammonium phosphate            Phosphorus source in many fertilizers
Diammonium phosphate             Higher N than monoammonium phosphate
Superphosphate                   Contains calcium and sulfur
Triple (treble)                  Contains calcium and sulfur
  superphosphate
Potassium chloride               Most common potassium source, high
  (muriate of potash)              burn potential
Potassium sulfate                Acidifying effect
Potassium nitrate
Ferrous sulfate                  Contains 20% iron and 18% sulfur,
                                   usually foliarly applied
Ferrous ammonium sulfate         Contains 14% iron and 15% sulfur,
                                   usually foliarly applied
Chelated iron                    Contains 6-7% iron,longer residual
                                  response than the other sources

Table 10-2 Examples of Fertilizer Application Schedules
Recommended in Four Regions of the United States

                                 JAN.    FEB.    MAR.    APR.

Central Texas Lawns
  Common bermudagrass                                      X
  Hybrid bermudagrass                                      X
  Buffalograss
  Tall fescue                                      X
Southern California (minimum
fertilization schedule that
will produce an acceptable
lawn)
  Warm season grass                                        X
  Cool season grass                                X
Southern Florida
Bermudagrass Lawn
  High maintenance                                 X       X
  Low maintenance                                  X
Northern Florida
Centipedegrass Lawn
  Higher maintenance                                       X
  Low maintenance                                          X
New York State
  Good-quality lawn
  Low-maintenance lawn

                                  MAY    JUNE    JULY    AUG.

Central Texas Lawns
  Common bermudagrass                      X               X
  Hybrid bermudagrass              X       X       X       X
  Buffalograss                     X
  Tall fescue
Southern California (minimum
fertilization schedule that
will produce an acceptable
lawn)
  Warm season grass                X
  Cool season grass                X
Southern Florida
Bermudagrass Lawn
  High maintenance                 X               X
  Low maintenance                  X               X
Northern Florida
Centipedegrass Lawn
  Higher maintenance                       X
  Low maintenance
New York State
  Good-quality lawn                X
  Low-maintenance lawn

                                 SEPT.   OCT.    NOV.    DEC.

Central Texas Lawns
  Common bermudagrass              X
  Hybrid bermudagrass              X
  Buffalograss                     X
  Tall fescue                      X
Southern California (minimum
fertilization schedule that
will produce an acceptable
lawn)
  Warm season grass                X       X
  Cool season grass                        X       X
Southern Florida
Bermudagrass Lawn
  High maintenance                 X               X
  Low maintenance                  X
Northern Florida
Centipedegrass Lawn
  Higher maintenance
  Low maintenance
New York State
  Good-quality lawn                X               X
  Low-maintenance lawn             X

Figure 10-1
Essential elements required by turfgrasses.

                 OBTAINED FROM AIR AND WATER

                 Carbon
                 Hydrogen
                 Oxygen

                 OBTAINED FROM THE SOIL

                 Element       Chemical   Available Form
                                Symbol

Primary          Nitrogen         N       N[O.sub.3.sup.-,
                                          N[H.sub.4.sup.+]
(fertilizer)     Phosphorus       P       [H.sub.2]P[O.sub.4.sup.-],
                                          HP[O.sub.4.sup.--]
nutrients        Potassium        K       [K.sup.+]
                 Calcium          Ca      [Ca.sup.++]
Secondary        Magnesium        Mg      [Mg.sup.++]
nutrients        Sulfur           S       S[O.sub.4.sup.--]
                 Iron             Fe      [Fe.sup.++], [Fe.sup.+++]
Minor or         Manganese        Mn      [Mn.sup.++]
micronutrients   Copper           Cu      [Cu.sup.++]
                 Boron            B       [H.sub.2]B[O.sub.3.sup.-]
                                          and others
                 Zinc             Zn      [Zn.sup.++]
                 Chlorine         Cl      [Cl.sup.-]
                 Molybdenum       Mo      Mo[O.sub.4.sup.--]
                 Nickel           Ni      [Ni.sup.++]

Figure 10-2
Relative concentrations of the essential elements in
turfgrass plants and nutrient deficiency symptoms.

                 CONCENTRATION
ELEMENT          IN DRY TISSUE        DEFICIENCY SYMPTOMS

Nitrogen         2.5-6.0%             Older leaves yellow-green,
                                      reduced shoot growth

Potassium        1.0-4.0%             Interveinal yellowing
                                      especially on older leaves,
                                      leaf tips and margins
                                      scorched

Phosphorus       0.2-0.6%             Older leaves dark green first,
                                      then appear purple or reddish

Calcium          0.2-1.0%             Deficiency rare, new leaves
                                      reddish-brown and stunted

Magnesium        0.1-0.5%             Interveinal chlorosis, a
                                      striped appearance, cherry-
                                      red margins

Sulfur           0.2-0.6%             Yellowing of older leaves

Iron             50-500 ppm           Interveinal yellowing of
                                      new leaves

Manganese        Very small amounts   Rare, similar to iron
                                      deficiency

Copper           Very small amounts   Never a problem

Zinc             Very small amounts   Rare, growth stunted, thin
                                      and shriveled leaves, appears
                                      desiccated

Boron            Very small amounts   Rare, cholorotic, stunted
                                      growth

Molybdenum       Very small amounts   Rare, older leaves pale green

Chlorine         Very small amounts   Never a problem

Nickel           Very small amounts   Never a problem

Figure 10-10
Information from the label on a bag of Milorganite. The salt index
is a measure of burn potential. The higher the number, the greater
the potential. The guaranteed analysis shows that almost 90 percent
of the nitrogen is in a slowrelease form (5.25 / 6).

SALT INDEX

MATERIAL                INDEX

Potassium Chloride       116
Ammonium Nitrate         109
Sodium Nitrate           100
Urea                      75
Potassium Nitrate         74
Ammonium Sulfate          69
Calcium Nitrate           53
Sulfate of Potash         46
Methylene Urea            24
Urea Form                 10
IBDU                       5
Milorganite                2

GUARANTEED ANALYSIS

Total Nitrogen (N)                                           6.
        0.75% Water-Soluble Nitrogen
  5.25% Water-Insoluble Nitrogen (Slowly Available)
Available Phosphate ([P.sub.2][O.sub.5])                     2.
Calcium (Ca)                                                 1.
Total Iron (Fe)                                              4.
      Nutrients Derived from Biosolids
      Net Weight: 50 lbs. (22.7 kilos)
    Also available in half-ton and one-ton sacks.

Figure 10-11
This label shows a combination of quickly available and slowly
available nitrogen. Onethird of the nitrogen is slow release.
(30% of the total weight of the fertilizer bag is nitrogen,10%
of the total weight of the bag is slow-release nitrogen: 10/30=33.3%.)

Turfgrass Fertilizer
30-6-12

GUARANTEED ANALYSIS

Total Nitrogen                                     30.0%
  1.1% ammoniacal nitrogen
  5.2% nitrate nitrogen
  23.7% urea nitrogen *
Available Phosphate ([P.sub.2][O.sub.5])            6.0%
Soluble Potash ([K.sub.2]O)                          12%

Derived from: ammoniacal phosphate, ammoniacal sulfate,
polymer-coated urea, muriate of potash

* 10.0% slowly available nitrogen from polymer-coated urea

Figure 10-12
Salt index values for various chemicals applied to turfgrass. The
higher the salt index value, the higher the burn potential.

                                SALT INDEX
CHEMICAL                           VALUE

Muriate of potash                  114
Ammonium nitrate                   105
Sodium nitrate                     100
Urea                                75
Ammonium sulfate                    69
Potassium sulfate                   46
Magnesium sulfate                   44
Ureaformaldehyde                    10
Gypsum                               8
Superphosphate                       8
IBDU                                 5
Milorganite                          2
Dolomitic limestone                  1
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Author:Emmons, Robert D.
Publication:Turfgrass Science and Management, 4th ed.
Date:Jan 1, 2008
Words:6779
Previous Article:Chapter 9 Establishment.
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