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Complete guidelines to developing and maintaining the most effective, environment-friendly irrigation systems for golf courses
Golf Course Irrigation offers valuable insight on the design, installation, management, and maintenance of irrigation systems-the most important management tool used on today's golf courses. Without manufacturers' bias, this useful resource provides hands-on guidance to the highest quality irrigation systems, including specifications and applications of the best pump stations, controllers, sprinkler heads, nozzles, valves, sensors, and other components that make the difference in top-quality irrigation systems.
Typically regarded as significant users of water, golf courses are under increasing scrutiny by governmental and environmental groups, making it essential that the up-to-date information found here-on such topics as water supply, plant irrigation requirements, application uniformity, and construction management-be at the fingertips of every golf course professional. While fostering the best playing conditions, these systems conserve water and energy with such technology as low-pressure heads and controls that use "if/then" logic to automatically adjust to changing conditions, which can improve playability while saving money.
Golf Course Irrigation is a practical tool to help golf course architects, builders, superintendents, irrigation consultants, designers, and installers to improve aesthetics and playing conditions in the face of diminishing natural resources. It is also an informative reference for golf course owners, developers, local officials, students, and fans of the game.
JAMES BARRETT, ASIC, CID, CLIA, is the founder of James Barrett Associates, Inc., in Roseland, New Jersey. He has designed more than 260 golf course irrigation systems.
BRIAN VINCHESI, ASIC, CID, CIC, CLIA, CGIA, CLIM, is President of Irrigation Consulting, Inc., in Pepperell, Massachusetts.
ROBERT DOBSON, CID, CIC, is President of Middletown Sprinkler Company in Port Monmouth, New Jersey.
PAUL ROCHE, CID, CIC, CLIA, is Irrigation Division Manager at S.V. Moffett Co., Inc., in Rochester, New York.
DAVID ZOLDOSKE, EdD, CID, is Director of the Center for Irrigation Technology at the California State University in Fresno.
Environmental Design and Management PracticesBy James Barrett Brian Vinchesi Robert Dobson Paul Roche David Zoldoske
John Wiley & Sons
Plant Irrigation Requirements
This chapter introduces the relationships between the turfgrass plant, the host soil, and the irrigation water, which are key to proper irrigation design and management. It provides information on water movement through different soils and water uptake by plant roots. It discusses the concept of evapotranspiration (consumptive use) and its role in the calculation of water requirements. The chapter also includes information on various turfgrass types, their water requirements, and their relative drought tolerances.
Irrigation concerns the relationship between how a soil holds and stores water and how a plant uses water. Although you do not need to know a great deal about soil physics or plant physiology for proper irrigation, you do need to have a general knowledge of soils and to be familiar with how a plant, in this case turfgrass, uses water and uptakes it from the soil. There are a number of terms and concepts you should be familiar with in order to understand the soil-plant-water relationship.
A soil is made up of various amounts of sand, silt, clay, and organic material, as well as pore space. The pore space is filled with either air or water. The idealmixture is 50 percent soil, 25 percent water, and 25 percent air. Under these conditions the turf expends a minimal amount of energy to uptake water and nutrients.
Texture is defined as the relative proportions of sand, silt, and clay in a soil. Texture cannot be changed or destroyed. Using an estimate of the percentage of each type, a soil can be classified in one of the 11 categories shown in the textural triangle in Figure 1.1. For example, as indicated in the textural triangle, a soil consisting of 50 percent sand, 30 percent clay, and 20 percent silt would be classified as a sandy clay loam.
The structure of a soil is defined by the arrangement of the various components that make up the soil texture. There are many types of soil structures, each with a specific name for its formation. In irrigation, a structure that allows for a high water-holding capacity is preferred. This structure is one that has medium-size pore spaces that allows for some drainage but does not hold the water too tightly to the soil particles, such as clays. The structure of a soil can be easily changed with the use of various types of mechanical equipment such as rototillers, aerifiers, or bulldozers.
If you were to dig a deep hole in the ground with a backhoe and then jump into the hole, you could see how a soil consists of different layers. Each time the soil changes color, structure, texture, or other characteristics, there will be a distinct layer. These layers are called soil horizons. The makeup of all of the horizons in a soil create the soil profile. In a soil profile, the top layer, the soil growing the turf, is the first, or A, horizon. A small difference in the soil characteristics may make it the A1, A2, or A3 horizon. A significant change in the soil will change it to the B horizon. The C horizon is usually the parent material from which the upper horizons descended. In an undisturbed soil these horizons can be very old and quite consistent over large areas. On a golf course, significant grading has probably taken place as well as substantial amount of cutting and filling. As a result, the soil profile has been manipulated and the sequencing of the horizons disturbed. It is not uncommon to have the C horizon on top, with the original A horizon buried and the new A horizon probably brought in from another area of the site or imported onto the site. In dealing with a manipulated soil, it is important to figure out how the soil characteristics change with depth. On golf courses it is not uncommon to have a highly compacted impermeable layer of soil beneath the topsoil, or the A horizon, causing some irrigation and drainage problems.
A soil's intake (infiltration) rate is a measure of how fast the soil will take in water, measured in inches per hour. In a dry, bare soil, the soil intake rate will initially be very high, but it slowly decreases to a point where it becomes consistent over time. Although the rate will be high at the beginning, in irrigation it is the leveled-off or basic intake rate that is of interest. Ideally, an irrigation system would never apply water at a rate greater than the intake rate of the particular soil being irrigated. On a United States Golf Association (USGA) regulation green, this ideal is easily obtainable, as the intake rate is significantly higher than the precipitation rate of the sprinklers. On a push-up green (constructed simply by shaping the existing soil-no drainage, gravel layer, or soil amendments are installed), however, the precipitation rate may exceed the intake rate of the soil. To properly schedule irrigation and prevent runoff and puddles, the intake rate of the soil must be considered (Figure 1.2). If the precipitation rate of the irrigation system exceeds the soil intake rate, cycle and soak scheduling may be necessary to apply the required water efficiently.
Turf cover, compaction, and thatch all decrease the soil's intake rate. Compaction during construction, or even by the sprinklers operating at a pressure that is too low, will influence the intake rate over time. Thatch buildup will decrease the intake rate, as may the long-term use of effluent water, depending on its quality. If you have identified your soil type from the textural triangle, then a water intake rate can be estimated from information provided in a textbook on soils.
Soil Water Storage and Movement
The storage and movement of water in a soil is of great importance in scheduling irrigation efficiently and effectively. As the soil goes from wet to dry, the relationship of the water to the soil changes, as well as the type of movement and amount of storage (Figure 1.3). If you were to start with a dry soil and then irrigate it until it puddles or runoff occurs, the soil would have all its pore space filled with water and the soil would be saturated. If you stopped irrigating, the soil pore spaces would start to drain over the next 24 to 48 hours, and all of the water movement would be gravitational. At some point in time, the gravitational movement and drainage would slow to a very low rate. At this point the soil pore space would be approximately 25 percent water and 25 percent air. The soil particles would be holding the water to them with adhesive forces (soil to water), thus keeping the pore spaces from draining any further. At this point the soil is said to be at field capacity. Field capacity in regard to soil moisture can be defined as the point where water is most available to the plant. Because the turf consumes water between irrigation or rainfall events, the amount of water available to the plant continues to decrease. The movement of water at this stage is caused by capillary action. The cohesive (water-to-water) forces move the water from the soil pore spaces to the roots for uptake by the turf. This will occur for some time, with the turf having to exert more and more force to pull the remaining water away from the soil particles as the soil dries out. This process will continue until the soil reaches the permanent wilting point. At this point, the soil moisture will be severely depleted and the turf can no longer exert enough energy to pull the water away from the soil. At the permanent wilting point there is still water in the soil, but it is held so tightly by the soil that the plant cannot use it. The remaining moisture is hygroscopic water, which can be removed only by applying heat to force drying (i.e., "oven dried" soils).
Between field capacity and permanent wilting point is the available water-holding capacity of the soil. Again, if you have generalized the type of soil from the textural triangle, a soils text or Internet site can provide information on the particulars of a soil's water-holding capacity in either inches of water per foot of soil or inches of water per inch of soil. For example, a sandy clay loam may hold 1.6 in. of water per ft of soil. Although this is the total amount of water held between field capacity and permanent wilting point, all this water may not be available to the plant. It is difficult for plants to obtain water below the root zone, so root zone depth is an important consideration in irrigation scheduling, as it severely limits water availability and thus dictates the irrigation interval.
By relating the root zone depth to the available water-holding capacity of the soil, the amount of water available to the turf can be determined. For example, if the turf has a 6 in. root zone and the sandy clay loam (mentioned earlier) has a capacity of 1.6 in. per ft, the available water-holding capacity would be 0.8 in. (1.6 in./ft x 0.5 ft). A 3 in. root zone would have half the available water-holding capacity of a 6 in. root zone, or 0.4 in. (1.6 in./ft x .25 ft).
In scheduling irrigation frequency, it is best to replenish the available water supply before reaching the permanent wilting point. Target levels have been identified for different crop types, including turfgrass. A target level is referred to as management allowable depletion (MAD). It is a management decision as to how much of the available water should be depleted before the next irrigation occurs. For turfgrass, the MAD has been determined to be about 50 percent by most agronomists. For example, applying a MAD of 50 percent to 0.8 in. of available water at field capacity results in a target of 0.4 in. of water being extracted by the turfgrass (0.8 in. x 0.50) before the next irrigation event. The next irrigation will be a net water application of 0.4 in. to fully refill the root zone. The time (days) it takes the turfgrass to consume the target MAD of 0.4 in. of water is referred to as the irrigation interval.
Water evaporates from soil and transpires from plant leaves. Together, these two phenomena are referred to as evapotranspiration (ET). There are several methods used to estimate the ET rate or value. For research purposes, a weighing lysimeter has been used to measure the loss of water from turfgrass plots. Typically, soil is placed in a box that is supported beneath by a weighing scale. Turfgrass is planted on the soil surface, well irrigated, and properly maintained. The surface area of the planted turfgrass and the change in weight due to evapotranspiration (water use) are measured. These two measurements form the water use requirements. These measurements are usually expressed in fractions of an inch of water consumed per day, or daily ET rate.
Lysimeters are too complex and expensive for normal water management, so weather conditions, such as wind speed, temperature, sunlight intensity, humidity, and other parameters are often measured to calculate the amount of ET or plant water use. Researchers, such as Penman (1948), developed formulas from their investigations to estimate potential crop water use based on changing weather conditions. A modified Penman equation is currently used by most publicly accessible weather stations in California to estimate crop water demand.
There are several variations of the ET definition or measurement that may be available. They all have slightly different meanings. [ET.sub.c] or ET crop is the water use rate of the crop (turf) that is being scheduled or managed. [ET.sub.c] is the amount of water that evaporates from the soil surface and transpires from the leaf surface to the atmosphere.
Calculating the ET of turf for an irrigation schedule usually begins with the acquisition of a reference ET value. Reference [ET.sub.o], as defined by Doorenbos and Pruitt (1975), denotes the "the rate of evaporation from an extensive surface of green grass cover, of uniform height, actively growing, completely shading the ground, and not short of water." This is the most common example of the use of the Penman equation to calculate evapotranspiration for a specific reference plant cover. Other examples often available are [ET.sub.p] and sometimes [ET.sub.r]. These are modifications of the Penman equation that calculate ET's for reference crops other than turf. The Irrigation Association website includes an extensive list of ET sources for the United States.
Such calculations are widely used in the western United States by the U.S. Bureau of Reclamation to estimate agricultural crop water use requirements. This measurement is based on work developed by Jensen et al. (1970), in which [ET.sub.r] "represents the upper limit or maximum evapotranspiration that occurs under given climatic conditions with a field having a well-watered agricultural crop with an aerodynamically rough surface, such as alfalfa with 12 in. to 18 in. of top growth." The ET of the plant cover being managed ([ET.sub.c]) is related to the various ET's ([ET.sub.o], [ET.sub.p], [ET.sub.r]) by a value known as the crop coefficient ([K.sub.c]). The mathematical relationship is defined as:
[K.sub.c] = [ET.sub.c]/ [ET.sub.o] or [ET.sub.r]
[K.sub.c] = crop coefficient
[ET.sub.c] = evapotranspiration of the crop or turf being managed
[ET.sub.o] = evapotranspiration-grass-based
[ET.sub.p] or [ET.sub.r] = evapotranspiration-alfalfa-based
However, because [ET.sub.o] uses grass as a basis, versus [ET.sub.r], which uses alfalfa, the resultant crop coefficients can vary considerably. That is why it is critical to match the proper reference ET with the correct [K.sub.c] adjustments. Using [ET.sub.o]-based [K.sub.c]'s with [ET.sub.r] reference values, or vice versa, can result in significant errors in water use estimates.
Crop coefficients are seasonally adjusted values that take into account the crop type, stage of growth, and crop cover. For example, the difference in [K.sub.c] between a Bermudagrass and a tall fescue grass could be substantial. The [K.sub.c] developed during April for Bermudagrass is 0.72 or 72 percent of [ET.sub.o]. For tall fescue during April, the [K.sub.c] is 1.04 or 104 percent of [ET.sub.o]. This is a potential difference of 30 percent for applied water. Other months vary to a lesser degree. Also note that the [K.sub.c] values used in the preceding example apply to southern California geographic conditions.
Excerpted from Golf Course Irrigation by James Barrett Brian Vinchesi Robert Dobson Paul Roche David Zoldoske Excerpted by permission.
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