Watering is also one of the most basic practices in the maintenance of the home lawn but is the one most often done incorrectly. One only has to experience a summer drought to appreciate the need for periodic watering. Many landscape plants, including the turfgrasses, may not survive a dry summer without the judicious application of water.

Deep watering encourages the development of an extensive root system. A well-developed root system can use the nutrients and water in the soil more efficiently than shallow root systems.

Light, frequent sprinklings produce shallow, weak root systems, which encourage weed invasion. Shallow rooting does not allow efficient utilization of plant food or moisture in the soil.

Lawns should also be watered during excessively dry periods in winter to prevent desiccation. On sloping sites or on slowly permeable soils, water intermittently for short periods to reduce runoff.

Plants vary in their expression of drought stress. Leaves of some plants begin to droop, whereas other plants, such as the turfgrasses, dry up and the leaves roll and turn a dull purplish color. This process is termed dry wilt.

Just as the lack of water has a detrimental effect on plants, so does too much water. A plant’s root system must take in oxygen and give off carbon dioxide to live. When water is applied too frequently, soil becomes saturated, and the movement of oxygen into the soil and carbon dioxide out of the soil stops. This results in a condition known as wet wilt, and if not corrected, the plant may soon die.

There is variation in the relative need for water between the turfgrasses. Consideration of the differences when choosing a turf may significantly reduce irrigation needs during summer (Table 4.6).

Lightly water newly-seeded or sprigged areas at frequent intervals. Keep the seed or sprigs moist, not saturated, during this initial growth period. This may well mean that it is necessary to water as many as four or five times during hot, windy days. The first 10 days to 2 weeks are especially critical. If young plants are allowed to dry out, they may die. After about 2 weeks, root system development should be well under way. Watering frequency should be slowly reduced for about 1 month after seeding or sprigging. Then treat as an established turf.

Water newly sodded areas much like established turf except more frequently. After the sod is applied, soak it with enough water to ensure that the soil under the sod is wetted to a depth of 2 or 3 inches. Each time the sod begins to dry out, soak it again. Roots develop fairly rapidly, and within 2 weeks or so it should be treated like an established turf.

Early morning is the best time to water. Wind is usually calm and the temperature is low, so less water is lost to evaporation. The worst time to water is late evening because the grass stays wet all night, making it more susceptible to disease, and evaporation rates are at their lowest.

How much to water? When a turf needs to be watered, apply enough so that the soil is wetted to a depth of 4 to 6 inches. The type of soil has a great deal to do with how much water is needed to wet soil to the desired depth. In Figure 4.7, note the depth of wetting resulting from the application of 1 inch of water. According to this, it should take about 1/2 inch of water to achieve the desired wetting depth if the soil is high in sand and about 3/4 inch of water if the soil is a loam. For soils high in clay, an inch of water is usually necessary to wet the soil to the desired depth. It takes more than 600 gallons for each 1 inch of water over 1,000 square feet of lawn.

If water application rates are too light or too frequent, the turf may become weak and shallow-rooted, which, in turn, could make it more susceptible to stress injury (Figure 4.8).

Slope. Lawns with a high degree of slope present a particular problem. It is easy for water to run down the slope without penetrating the soil. Apply water at very slow rates from sprinklers near the top of the slope. Sprinklers on the slope or near the bottom of the slope may prove ineffective.

Fertilizer. The faster the turf grows, the more water it requires. Slow release fertilizers that contain materials like sulfur-coated urea or ureaformaldehyde as nitrogen sources do not produce high growth rates. Avoid heavy applications of fertilizers high in soluble nitrogen.

Management factors. Use of an aerifier or coring device helps to increase water movement into the soil. A surfactant or wetting agent may also help water movement into high clay soils.

Water quality. There are a variety of sources for irrigation water. Treated city water may have the highest quality, but it may be the most expensive. Rivers, ponds and wells usually supply less expensive water, but water quality problems with these sources are possible.

Many materials damage plants by polluting water supplies. Surface water supplies are especially susceptible to pollution. Not only can chemicals such as pesticides be a problem but also fine soil particles like silt and clay.

Dirty irrigation water can slowly seal the soil surface and cause serious drainage problems. Another cause of poor water quality may be the presence of high levels of soluble salts. Water testing by a competent lab is a very good practice, especially if there is any reason to suspect a problem.

No two irrigation systems are exactly alike because both equipment and designs vary. The ideal system has individually controlled zones so that the running time can be set in response to the soil type and topography of the area it covers. Many times, both lawns and ornamentals are in the same zone. This can result in over watering many ornamental plants.

Develop a lawn fertilization program based on turfgrass requirements, soil tests, other maintenance practices and your desired results. A reasonable fertility program is another basic part of any lawn maintenance program. Lawns that are under fertilized have thin turf with poor color, while lawns that are over fertilized, especially with high levels of a soluble nitrogen fertilizer, may have thatch problems and be prone to more insect and disease damage. Any fertilization should be based on a soil test.

Your maintenance program also has a significant effect on your lawn’s fertilizer needs. If you remove grass clippings instead of returning them to the soil, the amount of fertilizer required may be doubled. Table 4.7 indicates the nutrients contained in clippings from a fertilized lawn. If rainfall or irrigation is heavy on a sandy soil, fertilization must be increased to replace nutrients lost through leaching.

All plants require some 15 or 16 different nutrients for best growth (Table 4.8). In most cases, the soil is a vast reservoir of these plant nutrients; however, it varies in the amount of nutrients it contains and in its ability to supply those nutrients to plants. When a plant requires more of a nutrient than the soil can supply or requires a nutrient not present in a given soil, then fertilizer must be used. Only a soil test determines the soil’s current plant nutrient status.

Of all the nutrients required by the turfgrass plant, nitrogen (N), phosphorus (P) and potassium (K) are usually not available in the soil in high enough quantities for good turf growth and must be periodically added as fertilizer. Other elements, such as iron, play important roles in the nutrition of plants. When nitrogen, phosphorus and potassium are balanced properly, other elements necessary for plant growth are usually present in sufficient amounts to produce good turf. If soils are highly acidic or alkaline, other nutrients such as iron or magnesium may be required in some instances.

The turfgrass plant requires more nitrogen than any of the other plant nutrients. It’s common for nitrogen levels in the plant to be as much as 4 or 5 percent. Nitrogen is a part of chlorophyll and has a great deal to do with nearly all growth and developmental processes in the plant.

As the amount of nitrogen supplied to the plant is increased, the rate of shoot or leaf growth increases. This increase is generally at the expense of root growth. Rapid leaf growth uses up all the food material being produced by the plant, and very little is left for the roots and other organs, including stolons or runners. Therefore, it is possible to produce a turf with high leaf growth and good green color but with a restricted root system. This is one reason why reasonable levels of nitrogen are usually desirable.

High nitrogen levels produce a plant with thin cell walls and a high water percentage in its tissue. The thickness of a cell wall is important when a fungus or an insect tries to invade the plant. A plant containing a high percentage of water requires more irrigation and is more susceptible to heat and drought stress.

The amount of nitrogen supplied to the turf plant has a great deal to do with the amount of food reserve the plant is able to store for periods of unfavorable weather, such as winter dormancy or summer dormancy. The plant manufactures food material (carbohydrates) in leaf tissue. Since leaves have priority over other plant parts for growth and since nitrogen stimulates leaf growth, the oversupply of nitrogen, especially just before normal dormancy, may promote leaf growth to the point of using up all the food material the plant can supply. If this happens, little food material is available for storage, and the plant may not live through the upcoming dormant period. The goal of a good fertility program should be to produce a reasonable amount of top growth but not at the expense of root growth.

For years, many textbooks have suggested that phosphorus is necessary for good root growth. This is true, but only in the sense that all plant nutrients are necessary for the optimum growth of all plant parts.

Phosphorus has a great deal to do with the process of energy transfer and storage within the plant. The roots are a primary organ for energy storage and are dependent on phosphorus levels in the plant. The formation and germination of the seed is a process that creates a high demand for phosphorus. A high level of energy must be stored in the seed for it to survive until it can germinate, and the rapid growth processes associated with germination require high energy.

Under most conditions, the turf plant is not maintained for its seed production, and its need for phosphorus is low. Most turf fertilizers are low in phosphorus except when a turf is to be established from seed, sod or sprigs. In this case, a fertilizer containing higher phosphorus levels is recommended.

Phosphorus is an element that moves slowly in the soil. It may take years for phosphorus to move just a few inches. Of course, the speed of movement depends on the amount of clay in the soil. The higher the clay content, the slower it moves. The slow movement of phosphorus in the soil and the relatively high demand for phosphorus in establishing turf makes it highly desirable to incorporate a fertilizer with an N-P-K ratio of 1-1-1 or 1-2-2 in the soil before seeding, sodding or sprigging.

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03/30/2002