JAMES SUA, CGCS,CCPC,CTP, CGIA
Proper irrigation is one of the most challenging aspects of turfgrass management. It is important for supplementing rainfall, washing in certain fertilizers and pesticides, keeping the soil moist for seed germination, and cooling the turf on hot days. Proper irrigation practices have taken on even more significance in recent years with the increased important of water conservation.
Improper irrigation practices may be more harmful to turf than no irrigation at all. For example, light or occasional irrigation during extreme drought may cause the depletion of stored carbohydrates, reducing the vigour and drought tolerance of the turf. In such a situation, if irrigation cannot be maintained correctly, it may be advisable to allow the turf to go dormant. This is the natural defence mechanism of the plant. Following the drought, the turf will usually return to normal growth. The decision whether or not to irrigate depends on the use of the area, the turf quality desired, the severity of the drought, the availability of water, and budget. Under less server situations, improper-irrigation can increase both disease and weeds and can produce a meagre, shallow root system.
WHEN TO BEGIN IRRIGATION何時開始灌溉
As plant undergoes moisture stress, it suffers an overall reduction in growth rate and rigidity. The first visual symptom is often a loss of rigidity that is evident by “footprinting”, the appearance of footprints on the turf after walking over it. If the turf is under water stress, footprints will be highly visible because of the shoots’ inability to spring back. Turf that is wee-watered will barely show the footprinting effect, springing back almost immediately.
The next symptoms of water stress are a blue-green or grey leaf colour. Large, patchy areas of the turf will show this colour change first; if the turf is left unwatered, the size of the areas will increase and the symptoms will progress. Following the colour change, the grass will begin to show obvious signs of wilting. Depending on the species, these include drooping, folding, or rolling of the leaves.
Finally, if stress continues, the top begins to turn brown and die. The turf will enter a protective state of dormancy. Storage of water in the roots and crowns will keep the plant alive long after the shoots die.
FREQUENCY OF IRRIGATION灌溉的頻率
As mentioned above, to maintain maximum turf vigour and quality, it is ideal to initiate irrigation before visual symptoms are apparent. As irrigation frequency exceeds the optimum level needed to maintain the proper water balance in the plant, several negative effects will occur. For example, if turf becomes adapted to using excessive amounts of water, shoot and root growth will decline, resulting in reduced vigour and quality. The turf will become susceptible to disease, insects, and weed invasion and more vulnerable to traffic, environmental, and management stresses. The recuperative rate from all injury will be greatly reduced.
As a rule, daily irrigation is not recommended for mature stands of turfgrass. Such a practice keeps the soil surface constantly wet and encourage shallow rooting.
To help encourage the development of a deep, extensive root system, irrigate deeply but infrequently. Deep, infrequent irrigation will allow the surface to dry out, forcing roots to grow into lower depths of soil that contain water. Frequency of irrigation depends on soil type, species, management practices, and climatic conditions. Generally, about half the amount of the water needed each week should be applied every 3 to 4 days.
Frequency of Irrigation 灌溉頻率
Paspalumgrass雀稗草 Least frequent 頻率最低
Carpetgrass地毯草 Most frequent 頻率最高
QUANTITY OF WATER APPLIED澆水量
Since most of the root system of many turfgrasses grows in the upper 6 inches of soil, it is important to apply enough water to moisten the top 4 to 6 inches of soil. The degree of moisture can be determined with the use o a knife, spade, or soil probe.
In some situations, we can determine how much water to apply by using an evaporation pan placed in the turf area during watering. There is a close correlation between water lost or evaporated from the pan.
RATE OF WATER APPLICATION灌溉的速度
The slope of the turf area, soil type, degree of compaction, and presence of thatch will determine the rate of water application. Application should not excess the infiltration rate, runoff occurs, which significantly increases water wastage as well as increasing the potential for fertilizers and pesticides to move off the turf area and into the groundwater. Water must be applied slowly to fine-textured soil, sloping turf areas, and thatched or compacted soil. Coarse, sandy soils will usually take relatively large volumes of water in very short periods of time. Depending on the soil type, the rate may range from 0.1 to 1 inch per hour.
Amount of water soils absorb in an hour without runoff
Soil Type土壤種類 Under Healthy Sod 健康的生草土
Coarse sandy loam粗糙的砂質壤土 1.3 inch per hour 每小時1.3英吋
Sandy loam砂質壤土 1.0 inch per hour每小時1.0英吋
Silt loam泥質壤土 0.6 inch per hour每小時0.6英吋
Silty clay loam泥質黏壤土 0.5 inch per hour每小時0.5英吋
Compacted clay緊實的黏土 0.2 inch per hour每小時0.2英吋
TIME OF DAY TO IRRIGATE灌溉的時間
Water according to the Weather 根據天候澆水
Water Less澆水量較少 Water More澆水量較多
Cooler temperature涼爽的氣溫 High temperature高溫
Cloudy or overcast有雲遮蓋 Bright sunlight大太陽
Low wind微風 High wind大風
High humidity濕度高 Low humidity濕度低
Rain or showers下雨或陣雨 No rain沒有下雨
Technically, turfgrasses can be irrigated any time of day or night. However, depending on the situation, certain times of the day may be more advantageous than others.
The amount of water lost as a result of evaporation is lower at night because of reduced wind movement, cooler temperatures, and higher humidity. Reduced wind also allows for a better water distribution pattern. Night may be a more convenient time in some situations, particularly if an automatic irrigation system is used. Evening or night irrigation has less chance of interfering with the use of the turf area and disrupting scheduled management practices. Irrigating at night also allows adequate time for internal soil drainage. Since wet soil is more prone to compaction than dryer soil, this additional drainage time can be particularly important on highly trafficked turf.
One serious drawback of night irrigation is that disease activity may increase on turf watered at night. Fungal spore germination and fungal penetration into plant tissue requires several hours of free water on the leaves of the turf, so reducing evaporation can make turf more susceptible to disease.
Midday or mid-afternoon irrigation has its own advantages and disadvantages. First, as much as 50 percent of the applied water may evaporate before it even hits the ground. Disease activity resulting from freestanding water is greatly reduced, but if the water application rate exceeds the infiltration rate or if a drainage problem exists, the turf may be subject to scald. Scald is the scorched appearance of turf that has been submerged or partially submerged on bright, sunny days, when water temperature increases to a point that injures plant tissue. In addition, because of more wind, sprinkler water distribution patterns may be disrupted. Midday watering may also interfere with the intended use of the site.
Early morning irrigation combines several of the advantages of night and midday watering. For example, winds are reduced, humidity is high, and solar radiation is low. Theses factors help to reduce evaporation. Early or mid-morning irrigation also avoids prolonged free water on the turfgrass leaves, discouraging disease development. Reduced wind movement allows proper water distribution from sprinkler.
There is also less chance of interfering with the use of the area. Finally, the application of water in the morning removes guttation water from the surface of the plant tissue. Fluid excluded from the plant leaf tissue that is rich in organic and inorganic substances is called guttation water, and it provides a medium for pathogens that cause turf disease.
TURFGRASS WATER USE AND MANAGING DROUGHT
Water Use Rate水的使用速度
Water use rate reflects the total amount of water required for turfgrass growth plus the quantity of water transpired from the grass and evaporated from the soil. The water use rate of most turfgrasses ranges from 2.5 ml to 7.5 ml per day, with maximum values as high as 12 ml per day. Species or cultivars vary in the amount of water they use.
Cultural practices can have a significant effect on the amount of water used by turfgrass. For example, turfgrasses mowed excessively high will use more water because they have more leaf area available for transpiration. However, the higher cut promotes deeper rooting, which offsets the increased water usage. A higher cut will also insulate the soil from high temperature and excessive evaporation. Therefore, from a water-use standpoint, turfgrasses should be mowed from the mid-to-high range of the recommended height for that particular species. A sharp, well-adjusted mower should always be used. The tearing and shredding of leaves caused by a dull mower blade will increase water use. Any cultural practice that results in increased leaf surface area will also increase water use.
Nitrogen fertilization should be carefully managed; generally, increasing it beyond a minimum-to-adequate level will increase water use significantly. Turfgrasses irrigated infrequently but deeply tend to use less water. Finally, the total amount of water used on compacted turf sites tends to increase as a result of reduced infiltration rates and increased runoff.
Amount of water needed to soak soil 6 to 8 inches deep and time required for the soil to absorb water
Amount of water Absorption time
Sandy loam砂質壤士 0.5英吋inch 30分鐘minutes
Loam soil壤土 1.0英吋inch 2小時hours
Compacted clay soil緊實黏土 1 to到 1.3英吋inches 5小時hours
Sooner or later, every gardener will be faced with varying degrees of drought. Several cultural practices can alleviate drought stress and help ensure a full and speedy recovery of the turf when favourable conditions return. Mowing, fertilization, irrigation, cultivation, and thatch and weed control can all influence the turf’s response to drought stress conditions.
Proper irrigation practices are critical during a drought. Turfgrass should be irrigated deeply but infrequently. To avoid runoff, it may be necessary to apply the required amount of water in several short intervals, a few hours at a time. In addition, thatch should be removed or reduced and compacted soil aerified to ensure maximum water movement into the soil. To minimize evaporation, irrigation should be done from night to early morning. As a general rule, turfgrasses grown under limited soil moisture have better drought tolerance than those grown under adequate soil moisture conditions, as a result of a hardening of the plant. Therefore, light, frequent irrigations should be avoided; such a practice encourages multiple growth spurts of the shoots that may exhaust stored carbohydrates, reduce root growth, increase succulence, and prevent the hardening of tissue. Turfgrasses in this condition are more prone to serious drought injury and are slower to recover when the drought has ended.
Finally, if a minimal water supply is not available or the cultural practices described above cannot be carried out, it may be advisable to allow the turf to enter dormancy. Dormancy will allow a more rapid recovery from drought than a physiological state that vacillates between semi-active growth and dormancy. Turfgrasses that go into dormancy lose all green colour. The resulting brown cover can be sprayed green with a variety of dyes formulated for such purposes.
TYPES OF IRRIGATION SYSTEMS灌溉系統的類型
Aboveground irrigation system. It is important to have the right sprinkler to water the turf correctly and to avoid wasting water. Types of sprinklers include oscillating, traveling, pulsating and turrent. The traveling sprinkler works best in odd-shaped areas. For a more restricted area, use the oscillating, pulsating or turrent sprinkler
Underground irrigation system. The underground irrigation system with an automatic timer is popular because of the convenience of not having to move hoses, sprinklers, and turn water on and off. Because automatic timers do not account for the changing water requirements of the turf unless a moisture sensor is attached.
A moisture sensor measures the amount of moisture in the soil and regulates the sprinkler system accordingly. It will automatically turn the water on and off when needed. A moisture sensor saves money by reducing unnecessary water applications. Additionally, leaching of fertilizers past the root zone is likely to occur. Rainout devices also can be installed to avoid irrigating when it’s raining.
Oscillating sprinkler振盪式龍頭 Traveling sprinkler可移動式龍頭
Pulsating sprinkler脈衝式龍頭 Turrent spinkler連續流水式龍頭
Water Conversion Table省水比照表
1 inch of water per 1,000 square feet = 623.37 gallons or 83.33 cubic feet
1 inch of water per acre = 27,154 gallons or 3,630 cubic feet
1 cubic foot of water = 7.48 gallons or 62.37 pounds
1 gallon of water = 0.1337 cubic foot or 8.34 pounds
Wetting agents reduce the surface tension of water, allowing it to wet a resistant surface. Said to “make water wetter”, these agents are very effective in the rewetting of water-repelling soils. They have also been said to increase water infiltration and drainage and reduce evaporation, soil compaction, wilting, disease, dew formation, and thatch accumulation. They can aid the movement of pesticides through thatch and into the soil.
潮溼劑能夠降低水份的表面張力，充份溼潤表土。除了 “讓水更溼” 之外，潮溼劑對於親水性較差的土壤有很好的溼潤力。同時也可以加強水份的滲透及排水能力，減少水份蒸發及土壤的緊實，降低枯萎，疾病及露水的形成，還有枯草層的累積。另外也可幫助殺蟲劑透過枯草層進入土壤。
WATER CONSERVATION TIPS省水的小偏方
1. Mow as infrequently as possible, but follow the one-third rule.
2. Mow with sharp blade.
3. Water deeply and infrequently.
4. Water at night or early morning.
5. Hand-water areas prone to runoff.
6. Core or aerify compacted soil.
7. Remove or reduce thatch.
8. Avoid excessive nitrogen fertilization.
9. Use pesticides judiciously to avoid injury to turf.
10. Use a soil probe to determine soil moisture content.