Materials and Methods of Construction
Building a good athletic field requires more than a clear set of specifications. The kind and quantity of materials to be used, how and when they are applied, and the manner in which the work is done are just as important. A number of things must be adjusted to the specific conditions of the individual job. The basic principles affecting the use of fertilizers, lime, and other materials, and the relationship of the kind and condition of the soil to methods of its preparation are vital factors in producing good turf at the lowest possible cost.
Soils and sands vary widely in the quantities of available plant nutrient materials which they contain. Nutrients most likely to be deficient are nitrogen, phosphate, and potash. Soil tests, available through the Agricultural Extension Service and private concerns, will provide adequate information on the need for phosphate and potash. When tests show medium to low levels of these materials, liberal applications should be made in preparing the seedbed for turf. Adequate quantities of phosphate and postash can be supplied by applications of 50 to 60 pounds per 1,000 square feet of 0-25-25 fertilizer or equivalent. The material should be applied prior to tillage operations and worked into the soil as deeply as possible.
Soil tests are not a reliable measure for determining the quantity of nitrogen that should be used. They show only the quantity of soluable nitrate nitrogen present. This type of nitrogen is utilized or lost very rapidly. The Pennsylvania State University soil testing laboratory does not test for nitrogen in samples submitted for turfgrass establishment.
Three basic facts control the use of nitrogen for turfgrass establishment. These are the needs of the grass itself, the kind of nitrogen applied, and the depth to which it is mixed into the soil. It seldom is necessary to apply more than 1 pound of quickly available nitrogen per 1,000 square feet to meet the normal requirements of the young seedling grass. If larger quantities are applied, total losses from leaching may be greater and there is danger of overstimulation that may make the young grass more susceptible to damping-off and other diseases. This immediately available nitrogen may be exhausted quickly, requiring reapplication within 3 to 4 weeks. The necessity for a second application in such a short time may be avoided by supplementing the intial application with an 3 to 4 pounds of nitrogen per 1,000 square feet derived from materials such as natural organics, ureaform compounds, IBDU (isobutylidene diurea), or sulfur-coated urea, which release nitrogen slowly. Thus there is less danger that the nitrogen will be lost through leaching and denitrification before it can be used by the grass roots.
It is best to apply fertilizers containing nitrogen just prior to seeding. These also should carry phosphate and potash, even though previous applications of these nutrients have been made. This will insure that liberal quantities of the nutrient materials will be available to developing seedlings. The starter fertilizer shoud be worked into the soil to a depth of not more than one inch. If a material containing nitrogen in soluable form is used, the nutrient ratio should be 1-1-1: one part nitrogen to one part of phosphate to one part of potash. A grade such as 10-10-10 would conform to this. The fertilizer should be applied at a rate that supplies 1 pound each nutrient per 1,000 square feet. If a fertilizer containing 35 percent or more of the total nitrogen as water insoluable nitrogen or controlled release nitrogen is used, the ration of nitrogen to the other nutrients can be increased to 2-1-1 or 3-1-1 and the material applied at a rate to supply 3 to 4 pounds of nitrogen per 1,000 square feet.
It sometimes is necessary to supply other essential nutrients, depending upon local soil conditions. Sandy soils are more likely to be deficient than silt or clay soils. Agricultural experiment stations in most states have made detailed studies of the need for trace elements. Ask your Agricultural Extension Service for its recommendations.
The soil reaction (degree of acidity or alkalinity) affects the activity of soil microorganisms, the availability of plant nutrients, the growth of grasses, and the activity of disease-causing fungi. Soil microbial activity is essential to the decomposition of clippings and other organic matter and to the breakdown of certain types of fertilizer materials and their subsequent conversion to nutrient forms that can be utilized by the plants. At pH values of 7.5 or under 5.5 certain plant nutrients become limiting through the formation of insoluable compounds. Most grasses make their growth in a pH range of 6.0 to 7.5. Fungi which cause 99 percent of our turf diseases are favored by high acidity. It is fortunate that grasses make their optimum growth, nutrients are most available, soil microorganism activity greatest, and fungi activity is reduced at a pH range of 6.0 to 7.5.
Lime is the most economical and most readily obtainable material for correcting soil acidity. Soil testing laboratories have equipment to make lime requirement tests. Properly take soil samples representative of the area should be submitted to them and lime applications based on the results of the test. Lime requirement test recommendations are based on standard ground limestone. Application rates should be enough to meet the full lime requirement. Lime should be applied prior to preliminary tillage operations and worked into the soil to a minimum of 5 to 6 inches.
Physical conditioning material
Soil compaction is one of the most common causes of poor turf on athletic fields constructed from natural or modified soil mixes. It is caused by squeezing together of the soil particles during trampling and by the use of heavy construction or maintenance equipment. Heavy soils with high proportions of fine silt and clay compact more than lighter sandy types containing large quantities of coarse particles.
Compaction reduces the rate of movement of air and water through the soil. This results in stagnant conditions that prevent grass roots from functioning normally. They first become shallow and eventually die. As a result the turf weakens, loses its vigor and density, and is more subject to injury.
The effects of compaction can be minimized by adding conditioning materials when the field is built. Materials most commonly used for this purpose are sand and some form of organic matter. The quantity and quality of sand used will depend upon the character of the soil to be treated. Heavy clays and silts may require as much as 50 to 60 percent sand by volume, mixed to a five inch depth, to improve their resistance to compaction while retaining the firmness necessary for good playing conditions. Soils with higher contents of natural sand do not require as much addtional sand for conditioning.
Sand for soil modification
The effectiveness of sand for soil modification is dependent on particle size, particle size range, and the amount of sand used. Graded sands with the fines removed are best adapted for use as physical conditioners. The specifications should designate the type (i.e., washed ground silica rock) and the percent of each particle size in the range previously designated. Research at The Pennsylvania State University indicates that a uniform coarse sand (80 percent between 1.0 and 0.50 mm and 95 percent between 2.0 and 0.5 mm) to be more effective than finer and less uniform mortar and concrete sands. It is suggested that at least 80 percent of the sand be between 2.0 and 0.5 or between 1.0 and 0.25 mm. Narrower size ranges would be desirable, but locating a nearby source and the high cost of such material are limitations to specifying narrow ranges of sand size. Some of the finer and non-uniform sands that are available may be acceptable as amendments, but considerably larger quantities are required to obtain desirable results. Non-uniform sized sand contains many different sizes of particles, and the beneficial effect of particle bridging may be lost as smaller particles fill the voids created by larger particles.
Sands for soilless construction
Sands used for soilless construction should be finer textured than sands used for soil modification. Sands having approximately 60 percent in the medium size range (0.5 mm to 0.25 mm) and 95 percent in the very coarse to fine sand range (2.0 mm to 0.125 mm) currently are recommended. The reasoning is that if the coarse fractions equal or predominate the medium fraction, the sand tends to be droughty and unstable. A sand high in very fine and fine fractions has slower drainage characteristics and may restrict water infiltration. If the sand has equal distribution of coarse, medium, and fine particles the result is a harder surface with reduced drainage potential. Thus, the key fraction must be medium sized sand to insure reasonable water holding capacity and firmness. The sand size recommended by Purdue University for PAT fields is approximately 0.125 mm to 0.5 mm (fine to medium sand).
Various types of organic materials also are effective in reducing soil compaction. Raw or cultivated reed sedge peats are well adapted for this purpose. They have a high moisture-absorptive capacity, and improve aeration of the soil. Where peats are used, it is seldom necessary to apply them at rates of over 10 percent by volume. Depending upon the depth to which they are mixed, this would require 1 to 3 cubic yards of peat per 1,000 square feet of area. Organic matter may be mixed into the top 2 to 3 inches of sand fields to improve the moisture holding capacity, especially during the establishment period.
Other types of organic materials may be used to make soils more resistant to compaction. These include such things as sewage sludge, tannery wastes, seed hulls, and well-rotted sawdust. Most of these materials, because of their faster rates of decomposition, are effective for a much shorter time than peats. The quantity applied must be estimated on the basis of moisture content, physical character, and relative persistance in the soil. Sewage sludge may contain 30 percent or more water, so that relatively high rates of application will be necessary to obtain the required quantity of dry matter. Seed hulls usually are light and fluffy and are difficult to mix uniformly into soil when applied at heavy rates. Rotted sawdust decomposes relatively slowly and can be used at volumes approximating the rate of application for peats.
The maximum value of any soil-conditioning material is obtained only when it is uniformly mixed into the soil to the specified depth. Various tools, such as rotary hoes, rotovators, or disks, can be used. The operation should be checked repeatedly to assure that a thorough job is done. When both peat and sand are to be used, the peat should be spread first with the sand following. The heavy sand will help to work the lighter peat throughout the mixture.
Seed preparation is a critical operation in constructing an athletic area. Improper seedbed preparation or preparation under adverse weather or soil moisture conditions may result in complete seeding failure. Working soils containing excessive moisture, especially with heavy equipment, will destroy the physical condition of the soil. Destruction of the soil physical condition increases soil compaction with a resultant reduction in aeration and drainage of the soil. Compaction impedes the movement of fertilizer nutrients, water, and air into the soil. The basic premise in modifying soils with sand and/or organic matter is to reduce the compactability of the soil.
In addition, the physical condition of the soil can be destroyed by overtillage. This is especially true if a rapidly revolving tine type rotary tiller is used. This machine tends to beat the soil to the degree that soil structure is destroyed. Rotovators, on the other hand, are quite satisfactory for seedbed preparation. Rotovators, in contrast to rotary tillers, are equipped with shovel-like cultivators which revolve relatively slowly. Plowing provides an acceptable method of tillage provided care is taken to work out, by disking and floating, the uneveness caused by the furrows. Depending on the soil involved, tillage by disking alone may be satisfactory.
The final seedbed should be a homogeneous mixture of the original soil, physical amendments (sand and organic matter), lime, and fertilizer. When mixing sand and organic matter into the soil, the organic matter should be laid down first with the sand on top. Tillage tends to float the light organic materials upwards while the heavy sand moves downward. Layers of any given material must be avoided. Disruption of the soil continuity may cause serious drainage problems. Tillage depth should be a minimum of 6 inches. If no drainage blanket is used under the topsoil, tillage should be sufficiently deep to mix a minimum of 3 inches of the subsoil with the topsoil. This will provide a transition zone between the subsoil and the topsoil without a sharp line of demarcation between the two.
Prior to application of the starter fertilizer, the seedbed should be firmed to indicate the presence of pockets or soft spots in the seedbed. Such areas must be eliminated by regrading. The starter fertilizer may be worked into the top 1 inch of soil with a York rake or similar tool.
Grasses and seed mixtures
The species and variety of grass and the quality of the seed are important items in constructing an athletic field. Turf should be composed of those species tha are most wear resistant and at the same time capable of quickly healing injuries caused by play. Good seed of high purity and germination is necessary to produce a dense, vigorous turf that can be used in the shortest possible time.
In the northern section of Pennsylvania and at elevations above 1,000 to 1,200 feet in southern sections of the Commonwealth, recommended seedings are Kentucky bluegrass blends with or without improved turf type ryegrasses; tall fescues alone; and mixtures of Kentucky bluegrass and fine fescue with or without improved turf type ryegrasses. In the southern sections of Pennsylvania (with less than 1,000-foot elevation), best results are obtained from Kentucky bluegrass blends with or without improved turf type ryegrasses and from tall fescue alone. The use of fine fescue for athletic fields should be avoided in southern Pennsylvania. The use of tall fescue is questionable throughout Pennsylvania unless you do not use the athletic field for two growing seasons, to allow the grass to develop a well-established root system. Tall fescue should not be used for baseball infields or field hockey fields; the coarseness and potential clumping of this bunch type grass may deflect the roll of the ball.
Kentucky bluegrass varieties vary greatly in their genetic base and consequently show considerable variation in resistance and/or susceptibility to various turfgrass diseases, growth habit, vigor, density, color, mowing height tolerance, and nutrient requirements. For these reasons blends of Kentucky bluegrass varieties are preferred over the use of a single variety. When seed specifications call for Kentucky bluegrass blends, a minimum of three and maximum of five varieties should be used with no single variety being less than 20 percent of the blend.
Seedings of Kentucky bluegrass blends or Kentucky bluegrass and fine fescue mixtures may be supplemented with 10 to 15 percent improved turf type ryegrass is desired. In certain unusual situations as much as 50 percent turf type ryegrass may be suggested. When seedings are made at other than optimum times such as early to mid-summer and late fall, it is desirable to include 15 to 20 percent improved ryegrass in the mixture. These ryegrasses are quite compatible with Kentucky bluegrass and have better mowability and persistance than the older common types.
For the latest varietal recommendations for Kentucky bluegrass, fine fescue, and turf type ryegrass, obtain Special Circular 168 Turfgrass Seed Mixtures from your county Extension office.
Recommended grasses and seeding rates
The quality of seed depends upon its purity and viability. Purity refers to that percentage of a pound which is seed of the species, variety, or mixture named. Thus, a pound of Kentucky bluegrass seed that shows 90 percent purity would contain nine-tenths of a pound of seed of that species. The remaining one-tenth pound would consist of inert matter, such as stems and chaff, and seeds of other grasses or weeds.
The viability of seed refers to that percentage of pure seed in a pound that will germinate when subjected to a standard laboratory germination test. If a pound of commercial seed is 90 percent pure shows 80 percent germination, only 72 percent (80 percent of 90 percent), or less than three-quarters of the pound is viable seed. Since purity and germination percentages may vary widely for different grasses and with individual lots of seed, rates of seeding must be adjusted to the actual figures for any lot. The rates specified in the prior table are based on the following purity and germination percentages for the various grasses.
Methods of seeding
The most important items in seeding turfgrass areas are uniform distribution, proper cover, and firm soil around the seed. Various types of mechanical seeders will distribute seed uniformly when they are correctly calibrated and operated. These can be divided into two general classes: (1) the hopper and cyclone types which drop the seed on the surface of the seedbed, and (2) the cultipacker type which distributes and covers the seed, and firms the soil in one operation. If the hopper or cyclone type is used, seed must be covered by light raking, harrowing, or dragging, and these operations must be followed by light rolling to firm the soil. In either case, the seeder should be calibrated to determine the proper setting for the kind of seed and desired seeding rate.
Calibrating can be done in various ways. A simple method is to hang a shallow pan under the seed hopper and operate the equipment at a standard speed for a given distance at a trial setting. The distance traveled multiplied by the width of the hopper will give the area covered. Seed discharged into the pan can be weighed to show the quantity used on the area covered. Settings then can be adjusted to deliver more or less as desired. Cyclone seeders normally are calibrated by a trial and error method. If a known amount of seed is placed in the hopper and completely run out, the amount of seed applied to a specific area can be calculated. By adjusting the hopper opening and repeating this process, reasonably accurate calibration can be optained.
To secure maximum uniformity in distribution, it is desirable to set the machine to deliver half of the total rate desired. This will permit making two passes over the area. Best results are obtained when the second pass is made at a right angle to the first.
Hydroseeding is also an acceptable method of seeding athletic fields. Lime, fertilizer, and mulch should not be mixed with the seed in the hydroseeder. Frequently, with this combination, the seed does not have firm contact with the soil. Lime and fertilizer should be worked into the seedbed in the conventional manner prior to hydroseeding. Hydromulch should be applied in a separate operation following hydroseeding.
Dormant seeding may be used to advantage when construction schedules prevent seeding at optimum times. The object is to gain several weeks’ growing conditions in early spring. The principle of dormant seeding is to sow seed during winter when weather conditions normally prevent germination and seedling establishment of all species. It should be emphasized that dormant seedings seldom are as successful as conventional seedings. Unusually warm spells during the winter may initiate germination, with seed and/or seedling loss during subsequent freezing weather.
Mulches are used primarily to protect against washing prior to germination and establishment of the new turf, and to prevent rapid drying out of the seedbed which might delay or injure germination. They are effective, also, in protecting late fall seedings from winter injury.
Hydromulching, using various wood fiber products, is an excellent and rapid method of mulching. The wood fiber and water slurry tend to bind the mulch to the soil and eliminate the need for “tie-down” materials often necessary with other mulching materials. Mulching rates with these products vary from 1,000 to 1,500 pounds per acre.
Other materials commonly used are straw of cereal grains such as wheat or oats, or some form of hay or coarse grass clippings. Mulching rates with these materials vary from 1½ to 2 tons per acre, depending upon how uniformly they are spread. Machines have been developed that spread mulch mechanically. These do an excellent job and should be used if available. However, hand spreading is not difficult and can be done rapidly.
Various methods can be used to hold the mulch in place. It can be weighed down by placing boards or brush at intervals over the area. These can be removed as soon as the mulch has been thoroughly wetted down and flattened into place, and before the seed has germinated. A system of stakes and tie-down strings also is effective. For best results, the stakes should be placed on 40-foot centers and the strings stretched between them in a systematic design.
Where equipment is available, the mulch cover can be sprayed with a solution of cut-back asphalt at a rate of one-tenth gallon per square yard. The asphalt serves as a binding material that holds the mulch in place. This method requires special spraying equipment. It is expensive and there is little evidence that it is effective enough to justify the additional cost and trouble involved. Also, several latex based sprayable mulches do an acceptable job.
If the mulch has not been spread uniformly and is so heavy on certain areas that the young seedlings have difficulty growing through it, part of it should be removed. Where the grass shows green above the mulch it can be left on without danger of injury to the turf.
Sodding is the quickest but most expensive method of initially establishing turf. Its use on an athletic field is best suited to those situations requiring a mature, wear resistant turf cover in a short time. A properly laid sod on a well-prepared sodbed will knit and be ready for use within 4 to 6 weeks. In contrast, one full growing season is needed to produce comparable turf by seeding.
Sodding generally is not recommended for sand field construction unless sod grown on a comparable sand can be found. Sod produced on heavy soil may impede water infiltration into the sand. Sod produced with commercial sod netting should be avoided on all fields. Player cleats penetrating the sod may become entangled in the netting, causing the player to fall or to rip out large pieces of sod.
A successful sodding operation depends on the quality of sod, its condition, and the care used in preparing the bed and laying the sod. Unless quality sod is used, results will not justify the high cost involved in establishing turf by this method. It should be dense and well knit so that sod can be cut as thin as possible, and in long strips that can be rolled to facilitate handling. Thinly cut sod weighs less, lies better, and roots quickly. Quality sod of the grasses adapted for use on athletic fields should have a maximum root and soil thickness of one-half to three-quarters of an inch. It should be cut in strips 12 to 18 inches wide and 4 to 6 feet long. This makes a convenient size roll for handling. If cut sod is to be held for several days before laying, it should be spread out flat, grass side up, in a cool place and kept moist. Rolled or stacked sod will weaken and yellow rapidly and will not be in good conditiion to start growth promptly when laid.
Preparation of the sodbed, including liming, fertilizing, and soil conditioning, should be the same as for seedbeds. The surface should be firmed by rolling, and, if dry, it should be wet down with a fine spray just prior to laying sod.
The first course of sod should be laid to a line that has been squared to the longitudinal axis of the field. Sods of the next course are matched against the first so that the joints between pieces inn the adjacent courses do not coincide. The sod is tamped lightly as it is set to insure good contact with the soil surface at all points. Any openings that occur in the seams between pieces should be filled with prepared topdressing to prevent excessive drying out at these spots. In periods of dry weather, a regular watering program should be followed until the sod has rooted.
Freshly laid sod should not be rolled. Rolling at this time often causes the sod to creep ahead of the roller and usually does more harm than good. After rooting has occurred, a light roller can be used to smooth out minor irregularities.
Establishment of turf by vegetative planting is limited to those grasses that spread by creeping stems or runners. The process consists fo shredding sod grown in nurseries for this purpose and planting the material on a prepared seedbed. The shredded sod can be broadcast over the entire area or planted in spaced rows. If broadcast, it must be covered to a depth of a quarter of an inch to half an inch with prepared topdressing soil. If planted in rows (sprigging), the runners are set in open furrows 2 to 3 inches deep and covered by backfilling soil over them. In either case, seedbed preparation should be the same as for seeding, and the entire area firmed by light rolling after planting.
From 5 to 10 bushels of shredded planting stock will be required per 1,000 square feet of area to be planted if the broadcast method is used. When planted in rows, one bushel of planting stock will plant about 600 linear feet of row. Rows can be spaced from 12 inches (or less) to 2 feet, depending on the kind of grass and how quickly complete cover is required. Zoysia rows require closer spacing than Bermudagrass because of zoysia’s slower growth rate.
Plugging involves the planting of blocks or plugs of sod at measured intervals throughout the area. Size and spacing of plugs must be determined by the amount of planting material available and the desired rate of spread. Plugs should fit tightly into the prepared hole and then be firmly tamped into place.
The only grasses adapted to Pennsylvania conditions, and which are practical to plant vegetatively, are Bermudagrass, zoysia, and creeping bentgrass. Since Bermudagrass and zoysia are climatically adapted only to the extreme southeastern part of Pennsylvania and creeping bentgrass does not make a satisfactory athletic field turf, vegetative planting has only a very limited application.