- - AGRICULTURE CORE CURRICULUM - - (CLF7000) Advanced Core Cluster: PLANT AND SOIL SCIENCE (CLF7550) Unit Title: MANAGEMENT PRACTICES NECESSARY FOR IRRIGATION AND DRAINAGE ____________________________________________________________________________ (CLF7552) Topic: IRRIGATING Time Taught in Year(s) 4 hours 3 AND 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome #: (J-7) - Design and demonstrate the set up of two types of irrigation systems. (J-6) - Identify three ways of determining when to irrigate. (J-5) - Describe how sprinkler irrigation can work as a frost protection method. Special Materials and Equipment: None References: University of California. FROST PROTECTION FOR NORTH COAST VINEYARDS. Leaflet 2743. Curriculum Development Project. LESSON PLANS FOR THE BASIC CORE CURRICULUM Russ, Norm. STANISLAUS ORCHARD HANDBOOK. Donahue, Roy L. SOILS. Ch 6. Pages 163 to 205. Evaluation: Quiz by instructor TOPIC PRESENTATION: IRRIGATING A. Irrigation requirements will vary with the crop, climate, season, soil conditions and method of application. 1. Each irrigation system has advantages and disadvantages. 2. Also, besides delivering water to our crops by these irrigation systems, we should also consider their use for fertilizing, climate control, and as a method of delivering pesticides. B. We have four basic irrigation systems, namely border or flood, furrow, sprinkler, and drip. C. Instructor, see Lesson Plans for the Basic Core Curriculum (CLF351) "Irrigation Systems" for a more detailed outline on the characteristics, advantages, and disadvantages of each system. D. The system of irrigation selected for a given parcel of land will be determined by the crop(s) grown, topography to the land, uses to be made of the water, cost of water, and the volume of water available. E. There are several ways to determine when to irrigate. Experience with crops and their location is very important. 1. Visual observation of plants 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. 2. Tensiometers are helpful, especially in perennial plantings like trees or vines. a. These can be placed in several locations of the planting and can be placed at a variety of depths. b. The vacuum gage on the top of the tensionmeter will show an increase in reading as the soil moisture decreases. c. By charting the daily changes in the readings a grower 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 is known in many farming communities. In fact, some radio farm weather reports include it in their broadcasts. b. This serves as a guide to the grower concerned with how much irrigation water must be applied to compensate for the water lost from the soil. c. The crop water use, E.T. given over the news media is for grass, which has been selected as the standard or reference crop. d. This E.T. for grass can easily be converted to other crops. e. Here is the method of converting E.T. for grass to grapevines: E.T. grapes (in/day) = E.T. grass X k X percent canopy. K factor is a crop coefficient which takes into account the transpiration characteristics of the plant. For grapevines and deciduous fruit trees, K is equal to approximately 0.8 percent. Percent canopy is the percent of the ground surface shaded by the leaf canopy. (A mature vineyard in July will have a 65 percent canopy.) The weather service has calculated the E.T. for grass to be .4 inches per day. So: E.T. grapes (in/day) = E.T. grass x k x percent canopy = .4 x .8 x .65 = 0.2 in/day This means that a vineyard in the San Joaquin Valley with a 65 percent canopy on a hot July day will lose 0.2 inches of water. F. Sprinklers can be used for frost protection of many crops. 1. The key to successful use is to start on time and use enough water. 2. Water must be continuously applied to all parts of the orchard or vineyard. 3. Alternating on and off to cover a larger area will lead to failure. 4. Once ice has started to form, the system must continue to supply water in large enough amounts so that all live surfaces are covered with water. 5. As long as water is being added, the ice enclosed plant will not be frozen. 6. Water should continuously be applied until the ice starts to melt rapidly, or too much evaporative cooling might take place as it melts. 7. Also keep in mind, as sprinklers are first started a temperature drop often occurs, but lasts only until they have made several revolutions and the plants are well wetted. This temperature drop is due to evaporation. 8. This system will work, however, one must have a thorough knowledge of the system and the effects of varying meteorological conditions. 9. See the reference given, U.C.D. Leaflet 2743 for more specific details. G. Irrigation water can also be used to reducing heat in orchards. Example: 1. High temperatures at the time of bud differentiation can cause cherries to "double". 2. This situation can be lessened by using over-tree sprinklers, combined with white wash on the trees and sod culture between tree rows. H. Over vine sprinkling of grapevines also reduces the incidence of powdery mildew. __________________________________________________________ ACTIVITY: 1. Have students design and demonstrate set-ups of sprinkler and flood irrigation systems. Remember to consider the crop, uses to be made of the water, cost of the water, and the volume of water available. __________________________________________________________ 7/25/90 sg #%&C