- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6450) Unit Title: IRRIGATION AND DRAINAGE ____________________________________________________________________________ (CLF6455) Topic: CONSERVING WATER IN Time Year(s) IRRIGATION 1 hour 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (H-3) - Identify three ways to determine when to irrigate (e.g., looking at plants, considering the possibilities for evapotranspiration, and using a tensiometer). (H-6) - Demonstrate how to test for soil moisture content by touch. Special Materials and Equipment: References: Hartmann, H. T., Flocker, W. J., & Kofranek, A. M. (1981). PLANT SCIENCE: GROWTH, DEVELOPMENT, AND UTILIZATION OF CULTIVATED PLANTS. Englewood Cliffs, NJ: Prentice-Hall. [1988 2nd edition now available] Editors of Sunset Books and Sunset Magazine. (1989). WATERWISE GARDENING. Menlo Park, CA: Lane Publishing Co. Editors of Sunset Books and Sunset Magazine. (1988). WESTERN GARDEN BOOK. Menlo Park, CA: Lane Publishing Co. Resources: Sunset Magazine, Lane Publishing Company, Menlo Park CA, 94025: Publications and reprints on water- conservation. East Bay Municipal Utilities District, P.O. Box 24055, Oakland, CA 94623 (415) 835-3000: Numerous Publications on water conserving landscaping. Urban Farmer Store, 2833 Vicente Street, San Francisco, CA 94116 (415) 661-2204 Drip irrigation supplies and information. Evaluation: Unit Exam TOPIC PRESENTATION: CONSERVING WATER IN IRRIGATION REVIEW: A. Water is more precious than ever. Not only in the arid West, but in all parts of our country, water is becoming more and more scarce in relation to the number of things we need it for. 1. Irrigation practices which conserve water are more important than ever. a. In most residential communities, landscape irrigation consumes more water than any other use. b. There are threats to the water supply in many locations. 1) Burgeoning populations need more water. 2) Erratic rainfall patterns affect some supplies, as do dwindling aquifers in other areas. 3) There is increased industrial and agricultural demand for water in many locations. 4) Water quality problems due to agricultural and industrial pollutants are becoming more apparent. c. Municipalities and water districts are becoming less tolerant of wasteful irrigation practices. d. Fortunately, irrigation systems can be designed to be more water-efficient than ever before. 2. The importance of saving water demands action beyond merely modifying irrigation techniques. An integrated approach to water conservation is necessary. Examples are: a. Weed control, pruning, and fertilizing b. Landscape design and plant selection c. Use of technological advances B. A number of steps can be taken in designing, installing and operating irrigation systems to reduce the use of water. Wasteful practices, which were at one time accepted or difficult to avoid, can no longer be tolerated. New methods make many of the following techniques easy to implement: 1. Water infrequently and deeply. a. Water is saved, and most plants respond better when irrigated deeply but less often. b. This encourages the development of deep root systems which the plant can rely on in times of drought. 2. Avoid runoff. a. Match water application rates to soil absorption ability. b. To prevent runoff, water in several short periods in sequence instead of in a single long irrigation. 3. Irrigate in the early morning hours. a. Lower temperatures mean less evaporative water loss. Water soaks into the ground instead of evaporating into the atmosphere. b. There is less wind before dawn than at any other time of day. This allows sprinklers to put water where it is needed instead of blowing onto unplanted areas. 4. Match precipitation rates. a. In designing an irrigation system, match precipitation rates and plan overlap of spray patterns so turf areas are watered evenly. b. If the whole lawn has to be watered early because one small area is going dry, much water is applied unnecessarily. 5. Don't water until needed. a. Before watering a lawn, wait until the first signs of wilt appear. b. A bluish-grey appearance to a lawn, or blades that don't spring back when stepped on, are signs that the lawn is ready for an irrigation. 6. Repair leaky pipes and fittings. a. Also, keep sprinkler heads free of debris which keeps them from functioning efficiently. b. Check the low heads in sprinkler circuits to make sure valves are not leaking water through to the system. 7. Use a syringe cycle. a. The syringe cycle is a brief, preliminary application of water before the regular cycle, lasting a minute or two. b. With the soil surface moistened, better infiltration to the root zone occurs with the regular cycle. 8. Use drip irrigation whenever possible. a. Drip irrigation can be used for all parts of the landscape except for lawns and some closely-planted ground covers. b. Correctly managed, drip irrigation will save at least a third compared to most sprinkler systems. 9. Automate the irrigation system. a. An irrigation controller, properly programmed, will save water. b. Water will get shut off on time. c. The timer can efficiently run short cycles, if necessary, to improve water infiltration. d. Plants get no more, and no less, water than they need. e. Controllers can be set to skip waterings if there is rain. C. While the following are not hard and fast rules to water by, these guidelines help in planning landscape irrigation 1. The warmer it is, the more often plants need water. 2. The more porous the soil, the more frequent the watering. 3. The larger the container the greater the water use. However, smaller containers usually dry out more quickly. 4. The larger the plant the more rapidly water is used. 5. Different plants have different water needs. 6. Plants grow faster in spring and summer. D. One of the most important keys to saving water (and to keeping plants healthy!) is knowing when to water. There are several ways to determine when to irrigate. Experience with the landscape and local conditions is very important. A combination of several approaches is usually best. 1. Visual and tactile observation of plants and soil is one method of determining when to irrigate. a. Plants under moisture stress will usually show a duller, more ashen green-gray color. b. Shoot tips will become harder, darker, and leaves will curl. c. The soil will feel and appear crumbly and dry. Below is a feel chart for determining moisture in medium to fine textured soil: ============================================================================ DEGREE OF MOISTURE FEEL PERCENT OF FIELD CAPACITY ____________________________________________________________________________ Dry - Powder dry 0 Low (critical) - Crumbly, will not form a ball Less than 25 Fair (usual time - Forms a ball, but will crumble 25 - 50 to irrigate) upon being tossed several times Good - Forms a ball that will remain 50 - 75 intact after being tossed 5 times; will stick slightly with pressure. Excellent - Forms a durable ball and is 75 - 100 pliable; sticks readily; a sizable chunk will stick to the thumb after soil is squeezed firmly. Too wet - With firm pressure, some water In excess of can be squeezed from the ball. field capacity SOURCE: Strong, W. (1956). Irrigation frequencies and reservoir concept. In SPRINKLER IRRIGATION MANUAL: A TREATISE ON SPRINKER IRRIGATION INCLUDING REPORTS OF LECTURES AND DISCUSSIONS AT THE SPRINKLER IRRIGATION SYMPOSIUM, BOURNEMOUTH, 1956 (pp. 51-57). Ringwood, Hampshire, England: Wright Rain Ltd. [a manufacturer of sprinkler irrigation equipment]. [Material has no copyright notification.] ============================================================================ 2. Tensiometers and other water sensing devices are helpful, especially in perennial plantings like shrubs, trees, and lawns. a. These can be placed in several locations of the planting and can be placed at a variety of depths. b. The vacuum gauge on the top of the tensiometer will show an increase in reading as the soil moisture decreases. c. By charting the daily changes in the readings, the landscape manager can make judgements on when to irrigate. 3. Evapotranspiration (E.T.) is the total water loss by evaporation from the soil surface and transpiration from plants, from a given area, and during a specified amount of time. a. The E.T. rate serves as a guide to the gardener concerned with how much irrigation water must be applied to compensate for the water lost from the soil. b. The E.T. given over the news media is for grass, which has been selected as the standard or reference crop. E. While modifying irrigation practices can save a tremendous amount of water in the landscape, there are many other steps which can be taken to reduce the DEMAND for more water in the landscape. An integrated approach is important in conserving water in landscape horticulture. The following recommendations will help save water: 1. Plan a water conserving landscape. a. Eliminate or reduce the size of lawns. Lawns are highly water consumptive. If a lawn is not really necessary, or if it can be reduced in size, a lot of water can be saved. b. Choose plants which require less water. Drought tolerant plants and plants which use less water can make up the bulk of the landscape, with more water-consumptive species used sparingly. c. Make use of pavers and other non-water-using ground covers. Where it is practical, the careful use of paving can reduce water consumption. There are a number of new paving products on the market which look attractive, are easy to install, and help stretch available water. d. The term "xeriscape" is applied to landscapes which are designed to be water conserving. 2. Manage the soil to conserve water. a. Coarse-textured soils can be amended with organic material to hold water longer. b. Use of wetting agents and polymers improves water infiltration rates and soil water retention, respectively. c. Mulching is one of the easiest and most effective ways of conserving water, placing a 3-4 inch layer of mulch over the soil around and between plants cuts evaporation, keeps the plants' root zone cool, and keeps weeds out of the landscape. 3. Control the growth of plants. a. Weeds are very efficient at removing water from the soil. Preventing their establishment leaves more soil moisture for landscape plants. b. Prune out damaged, diseased, crowded, or misplaced branches on shrubs and trees; unnecessary foliage uses water needlessly. Also, in large-scale plantings such as freeway landscaping, plant growth regulators can be used to reduce the need for both water and labor in cutting back plants. c. High nitrogen fertilizers stimulate new growth which in turn demands more water use. Restrict the use of high-nitrogen fertilizers, especially during times of water shortage. 4. Lawns are the biggest water users in the landscape. Saving water in their maintenance accounts for a large proportion of landscape water conservation. a. Maintain a higher mowing height; taller grass blades shade the soil and reduce evaporative loss. b. Keep the mower blade sharp; a blade of grass cut by a sharp blade will heal more quickly, losing less water than one cut by a dull blade. c. Well-aerated soils permit better water infiltration. d. Dethatch: Thatch buildup on the turf reduces water penetration into the soil and traps moisture in the upper layer where it is lost to evaporation. Occasional verti-cutting will improve water use efficiency in lawns. F. Innovations in irrigation and landscape technology have made saving water easier. 1. Check valves keep irrigation lines from draining through the lowest head after each watering. 2. Rainguards measure rainfall and stop operation of irrigation controller if rainfall amounts are sufficient. 3. Automatic soil moisture sensors placed in the soil at strategic locations and will prevent irrigation from starting when the soil is sufficiently moist. 4. Wetting agents are surfactants that reduce surface tension of soil particles to improve water penetration and reduce runoff. 5. When placed in the soil, polymers absorb water, thus allowing roots to draw moisture as needed. Polymers are most effective for potted plants or sandy soil. G. During times of shortage, "graywater" (any household water that doesn't go down the toilet) can be an additional water source for the landscape. While only practical in residential situations, graywater can significantly add to the water "budget." Some restrictions accompany its use: 1. Graywater should not be allowed to puddle or run off. 2. Don't use graywater in sprinklers or sprayers. 3. Don't use graywater on vegetable gardens. 4. Consult local health officials before using graywater. 1/6/91 MH/clh #%&C