i""K ft'V Division of Agricu Sciences IVERSITY OF CALIFORNIA IRRIGATION N STEEP LAND ; f* >* ** », i»*\ CALIFORNIA AGRICULTURAL Experiment Station Extension Service CIRCULAR 509 * • Jr* > . *'*. iW IRRIGATION ON STEEP LAND BY LLOYD N. BROWN Extension Soils Specialist in the California Agricultural Extension Service FEBRUARY, 1962 UNIVERSITY OF CALIFORNIA • DIVISION OF AGRICULTURAL SCIENCES CALIFORNIA AGRICULTURAL EXPERIMENT STATION • EXTENSION SERVICE STEEP LAND irrigation of citrus, Riverside County. I RRIGATION ON STEEP land can be a problem on slopes of 2 per cent or more — that is, * where the land drops at least 2 feet within a distance of 100 feet (see below). In such cases proper irriga- tion methods will save water, conserve soil, and produce better h crops. Success will depend not only upon the method of irrigation, but also upon the rate at which water is applied, the cover on the soil, and texture of the soil. „ The main irrigation methods discussed in this circular are: furrows pages 6 to 17 STRIP CHECKS OR BORDERS page 18 RETURN WATER SYSTEMS page 19 ^ contour ditches pages 20 to 22 sprinklers page 23 1 BASIN IRRIGATION page 24 California farmers have been ingenious in developing many variations of these methods to meet the state's great variations in water supply, topography, soil, climate, and crops. This circular brings together these methods to help you adapt one or more to < your own situation. To make the proper choice it will be neces- sary to understand a few fundamentals of irrigation. . . . SOIL EROSION can be serious on land with a slope of 2 per cent or more. This is a 5 per cent slope: the land is 5 feet lower at point B — 100 feet from point A. B " 4 ' A FEW FUNDAMENTALS OF IRRIGATION Soil is a water reservoir for plants The purpose of irrigating is to fill the soil to field capacity to the depth oc- cupied by the plant roots. Roots usually require from one to several weeks to reduce this irrigated soil to the wilting point (see terms in the box on the right below) . Soils vary in water-retention Coarse or sandy soils will hold much less water at field capacity than fine or clay soils. Loam will hold about twice as much as sand, and clay will hold about twice as much as loam. Generally speaking, if the capacity of sand is One, loam would be Two, and clay Four. Expressed as actual per- centages of the weight of the dry soil: sand, about 7 per cent; loam, about 14 percent; and clay, about 28 per cent. Water must be available to roots Most plants can obtain all the water they need if the soil moisture is in the range from field capacity to approach- ing wilting point. For most soils, the wilting point is about one half of the field capacity. How often should you irrigate? It has been indicated that it is usually necessary to irrigate twice as often on sands as on loams, and twice as often on loams as on clay soils. This is in order to keep a water supply available to plants at all times. Assume, then, that you have three plants of equal size growing in large pots of sand, loam, and clay. These plants will all use water at the same rate, regardless of the tex- ture of the soil in which they are grow- ing. Therefore, the water in the sand will be used up sooner than in the loam; the water in the clay will last longer than that in the loam. When several days are required to ir- rigate an area, irrigation should be started in order that it be completed so that the last plants receive water be- fore they wilt. When to start irrigating Most crops have a definite pattern of water usage. During spring they start out using relatively small amounts. Summer brings peak need, with a les- sening during fall. For example, an orchard might require these amounts of water during these months: April 1 acre-inch May 3 acre-inches June 5 acre-inches July 6 acre-inches August 6 acre-inches September 3 acre-inches October 1 acre-inch When to start irrigating also depends on the amount of rainfall during the FIVE IRRIGATION TERMS FIELD CAPACITY: The amount of water held by the soil shortly after irrigation, pro- vided there is free downward movement through the soil. In other words, when irriga- tion water has completed its downward and horizontal movements, the soil is at field capacity. WILTING POINT: The point when the soil has not enough moisture available to prevent plants from wilting. ACRE-INCH: The amount of water necessary to cover one acre of ground with one inch of water. The equivalent of a one-inch rainfall. HEAD: The amount of irri- gation water delivered, and variously measured as cubic feet, gallons, or miner's inches. PER CENT SLOPE: The term given the fall (or rise) of lands in feet, compared to horizontal distance. (See page 4.) previous winter. In the case of perma- nent crops, such as orchards, a light winter's rainfall makes an earlier irri- gation necessary, to bring the soil which plant roots occupy to field ca- pacity. For annual crops, the soil which the roots will occupy should be at field capacity before planting. Soil is either wet or dry Rain on a dry field wets down a definite distance. The soil underneath remains dry. So it is with irrigation water — it wets to field capacity, but adjacent ground remains unchanged. Wet the entire root area An irrigation should wet all of the soil which the plant roots occupy. Rain is ideal because it falls evenly and wets the entire area. Irrigation can ap- proach this perfection if these warn- ings are heeded: Furrows, if spaced too far apart, will not wet all the soil be- tween them. Insufficient water in basins will not seep deeply enough. Sprinklers must be left at each setting long enough to allow proper penetration. Don't overirrigate As most of the soils discussed in this circular are of limited depth — under- lain by bedrock, hardpan, or clay- pan — overirrigation is likely to water- log the soil just above these impervious strata. This water may also seep to the base of the slope in such volume that it could drown out trees. Watch particu- FURROW IRRIGATION Below are two illustrations of furrows — one running from top to bottom, the other across the slope. FURROW DOWN THE SLOPE Two hazards go with this type of irrigation. If the slope is too steep, soil erosion can be a serious prob- lem. If the furrows are not placed at frequent intervals, the entire mass of soil may not be wetted. 4 i \ •.f/sLOPEl «: ->1 lit % \ :! I %- WETTED AREA WETTED AREA DR N ARE larly citrus crops and avocados: slight overirrigation can cause gummosis in citrus and root rot in avocados. Variations in soils Some soils will not give up the usual one half of the water they contain at field capacity. They must be irrigated more frequently. In the Sierra Nevada foothills there are red soils that pro- vide good examples of these exceptions. Variations in crops Some crops, when young, require a higher percentage of soil moisture. This is because the young plants have underdeveloped root systems. These should be given lighter, more frequent irrigations. A length of %-inch rod, sharpened at the end, will help you to find out to what depth water (either rain or irrigation) has penetrated. Press the rod into the wet ground. It will stop at the dry level. Be careful when you use the rod in rocky soil that you do not confuse rocks with dry soil. EASY-TO-MAKE SOIL TESTER FURROW ACROSS THE SLOPE This furrow should be flat enough so that soil does not wash — usually less than a 2 per cent slope. Nor- mally furrows should be about 6 feet apart, but experience can help to determine proper intervals. ^ *i*7 ..'.'■ V - mn SUCCESS COMES WITH CHANGE IN IRRIGATION TECHNIQUE /. -' T#- * Km* "V^'w. This olive orchard in Butte County was originally irrigated almost straight down the slope — left to right in the photo- graph — on a grade of 5 to 6 per cent. Growth and production were unsatisfac- tory. It was suggested that the furrows be run across the slope, as shown. Growth was vigorous, and crops increased con- siderably. The soil is about 18 inches deep. It is stony, and underlain by bedrock. With the old method of irrigation, a relatively small part of the soil was wetted. Now the water seeps down and wets the root areas. Caution: Do not overirrigate. It is particularly harmful for citrus and avo- cado crops. A SKILLFUL DOWN-THE-SLOPE IRRIGATION ON 4 PER CENT GRADE Here is a fine young grove of oranges in Riverside County that utilizes furrow irrigation on a slope that normally would be considered dangerously steep for this technique. However, there has been no evidence of erosion. The photograph was taken following the first irrigation after the furrows were made. Just prior to making the furrows, a heavy covercrop was worked into the soil. Remnants can be seen in the foreground. A very small amount of water was turned into each furrow to "set" the soil, to prevent washing with large heads during subsequent irriga- tions. This irrigation has sprouted the next cover- crop, and the soil will soon be full of small roots which will make it still more resistant to erosion. Note that the furrows pictured are at frequent enough intervals to assure wetting all the soil to field capacity. Once again, caution: The most critical point of irri- gation under these conditions is the first usage of the furrows. Water must flow very slowly and in small amounts. -.- **-*» -~^~-V "« -:-vbS: " l'_ " i <±£0&^ -,y / HOMEMADE" DEVICES REGULATE FLOW, AVOID UNDUE WASHING Native ingenuity comes to the rescue in devising methods and using materials at hand to get the job done. A case in point is the use of such items as rocks, burlap, paper, short boards, slats, weeds, and other materials to regulate the amount of water ad- mitted to a furrow. The upper photograph shows a pear orchard in El Dorado County, and the use of burlap dams. They can be seen in the ditch at the right. The lowest one is placed to divert the stream to the left and into a furrow. Note: If another burlap dam had been placed midway between the two nearest ones, there would have been less erosion. They usually are about ten inches square. Occasionally steep supply ditches are lined with burlap. The photograph left shows the supply ditch run- ning from upper left to lower right. Small rocks are used to regulate the height of water in the ditch, and the directing of water into the irrigation furrows. THE USE OF FLUMES TO CONTROL IRRIGATION WATER SUPPLY 12 The grade of about 20 per cent in pear orchard in El Dorado County (left) is much too steep to allow usage of a sup- ply ditch. Water from a pipe line is run down a portable V flume — and fed to the furrows, as desired, from 1-inch holes in the sides. Control is maintained by small slide gates covering the holes on the out- side of the flume. Rocks are placed in the flume below each opening, so that they allow a small pool to form, expediting the flow from the hole. Note, too, the small boards placed to prevent water splashing from the flume as it hits the rocks. The flumes are easy to construct and easy to move. The main irrigation system for the or- chard on page 12, below is a series of con- crete pipe lines. The furrows between them are quite long. When the ground has been newly cultivated, as shown, the en- tire length of the furrow cannot be irri- gated without causing some erosion. To avoid such difficulty, this owner has built a portable box flume. It is placed in the orchard about halfway between the pipe lines. Thus smaller heads can be run from both the pipe lines and the flume. (The flume is in 16-foot lengths, with the bot- ton board of each tapered so sections tele- scope) . Note the remnants of the recent covercrop which has been worked into the surface soil. GATED PIPE FOR WATER DISTRIBUTION Gated pipe (ordinarily slip- joint pipe with gates to release the water) is a convenient method of distributing water on sloping or uneven land. The photograph on the right below shows a 4-inch gated pipe used between hydrants on a concrete pipe line. This method, which can be used on cropland and in orchards, has advantages because you can easily control the amount of water admitted to each ditch. The photograph on the left shows a long line of 8-inch gated pipe. This method has the same advan- tages as those of the 4-inch pipe, and in addition makes unnecessary installation of a concrete pipeline. Caution: This type of metal pipe can be used only under low pressure. High pressure causes excessive leaking at the joints and may even rupture the pipe. ** 1 * Q * + (#> :W *r >■«■ A "ZIGZAG 77 PROTECTIVE FURROW SYSTEM This walnut orchard in Los Angeles County has been prepared for irrigation with a very effective, yet seemingly com- plicated, furrow system. The furrows "going away" from your vision were pre- pared first, across the slope, and prac- tically level. Those going from left to right in the photograph were made, using a blocking device, so that the water "zig- zags" through the orchard. This method can be used when the slope is as much as 3 or 4 per cent. The slope illustrated, however, is somewhat less. against winter storms, and again for sum- mer irrigation. After harvest, a cover- crop is sown, and the furrows are re- worked. The covercrop and the furrows adequately protect the orchard against erosion, which frequently results from heavy run-offs caused by storms. The covercrop is worked into the soil in the spring, and the system is prepared once more for summer irrigation. If weeds grow too vigorously, the orchard may have to be disked and furrowed during the summer. Because of cultural operations, it is nec- essary to prepare these furrows at least twice each year — once for protection This is one of many effective systems that can be used in stepping water down slopes without danger of washing. 14 CUTBACK FURROW IRRIGATION - •VMOTWNHtw tf ^VM^«l\'Mm\)|'i}» ^/Wf<(n\)y.i)\)y))\^ An ingenious method to increase the wetted area in a furrow is the cutback furrow irriga- tion shown in the diagram. It is useful on slop- ing land where water does not wet a large enough percentage of the soil to promote ade- quate crop growth. The reason for this lack of soil wetting is that the water often flows in a small stream in the bottom of the furrow. If the furrow could flow nearly full, the wetted sur- face would be increased, with consequent greater infiltration. To use cutback furrow irrigation, you must have 3 (or 6, 9, etc.) parallel furrows between crop rows. In the diagram the water supply comes in the right furrow toward you, is de- flected by a dam to the center furrow and runs away from you; then it is deflected to the left furrow, where it runs toward you, etc. The fur- row dam and the connection between furrows must be made by hand. The spacing of the dams in the furrows is determined by the slope of the furrow. A change to this system of furrow irrigation can be very beneficial if trees are not getting adequate water for good growth and pro- duction. tffif(ortiV)\yv\)\\^\)f) A. FLOW OF WATER WETTED AREA 15 STEEP-SLOPE IRRIGATION ON ADOBE SOIL Here is a grove of orange trees, planted in adobe soil, with a slope of about 6 per cent. On drying, the soil cracks very badly which eliminates the use of any form of contour irrigation, because con- tour furrows just would not hold the water. If furrows are used at all, it is recommended that they run straight downhill. Small heads, run for a consid- erable time, give a satisfactory irrigation and avoid erosion. The upper photograph shows the metal supply pipe line at the left, with the noz- zles projecting toward the orchard. The lower photograph illustrates cracking of the adobe soil. 16 SUGGESTIONS FOR IMPROVING THIS ORCHARD'S IRRIGATION As can be seen, the Bartlett pear tree shown is stunted. The irrigation furrows have cut deeply into the soil, which is about two feet deep on bedrock. Even if they had not, they would still be inade- quate to wet the entire soil mass. This side-hill orchard could be irrigated suc- cessfully by any of these methods: 1. Contour furrows run across the slope on a grade of about 1% per cent. (At right angles to those shown in the pho- tograph.) Two furrows to the row would be sufficient, because the water would penetrate to the bedrock, seep down the slope, and wet all of the soil. 2. Contour ditches, as shown on page 20, could be employed in this orchard at intervals of about 60 feet. The orchard should then be planted to permanent cover. Irrigation water could be spilled over the bank of the ditch every few feet to guarantee complete wetting of the soil. 3. Sprinklers and a permanent covercrop would be very effective. (See page 23 for details.) 17 CLEVER ADAPTATION TO PREVENT WASTING WATER STRIP CHECKS OR BORDERS Most irrigated pastures are planted on soils with hardpan or dense clay subsoils. The Ladino clover pasture shown is an excellent example of a relatively new method of land preparation for the maximum usage of irrigation water. Formerly the land was graded so that the strip checks ran all the way to the drainage ditch. The length of time necessary to run the water in the strip checks in order to get good penetration often resulted in great waste. The new method of leveling is shown in the sketch below. The ridges extend only to the basin. The excess water from the checks irrigates the basin, shown in the foreground of the photograph. The small amount of excess water runs into the drainage ditch. BASIN DRAINAGE 4 DITCH WATER PENETRATION -\yi V) - 18 RETURN WATER SYSTEMS ANOTHER WATER SAVER: USE OF RETURN FLOW Irrigation water is becoming less abundant and more expensive. Therefore methods to use water more efficiently are in demand. One such practice, known as the "return- flow" system, is coming into widespread use. It consists of collecting runoff irrigation water and pumping it back into the irrigation system. In the photograph above, runoff water is being collected in a sump and pumped back into the irrigation lines to water the orchard in the background. Below, runoff water from the pasture shown is being pumped back into the irrigation system. i m CONTOUR DITCHES Steep land can be utilized for irrigated pastures if proper methods are used. Contour ditches are simple and successful. The photograph at left shows a ditch with a grade of about % per cent. The water is spilled over the lower edge by means of sod dams in the ditch (see arrows). Other methods of diversion are shown on page 22. Excess water collects in the next ditch which is usually about 75 feet be- low, supplementing irrigation water in the second ditch, and so with others down the grade. Use your judgment to assure complete irrigation; space ditches close enough to wet the entire area. The pasture shown in the photograph be- low is a good example of the use of con- tour ditches. Note how the dry pasture at the crest of the hill contrasts with that ir- rigated. The light patches in the right cen- ter of this picture indicate dry a:eas — the probable result of the ditches being too far apart to wet the entire area. SUCCESSFULLY IRRIGATED PASTURES ON HILLSIDES ORCHARDS, TOO— Deciduous orchards can also use this irrigation method in conjunc- tion with a permanent covercrop. Under these conditions, however, the ditches must be steeper, because the unpastured vegetation tends to clog them. Caution: When permanent covercrops are used in orchards, gophers become a problem, as it is not easy to detect their workings. Field mice sometimes build nests at the bases of trees, and girdle them. Consider the rodent problem before adopting a permanent cover- crop program. - 21 DIVERTING WATER FROM SUPPLY DITCHES Water can be diverted from the ditches to the field by many methods. Two are shown in the photos below. Here, the water is diverted from the field ditch by means of temporary partial dams. Rocks have been placed in the ditch to hold back the water so that part of it will overflow the lower sides. Some- times straw or weeds are used with the rocks to make a tighter dam. In some cases shovelfuls or blocks of sod are used instead of rocks. Water can be diverted at the same time from several of these dams. In this case a metal tapoon is used to divert all of the water in the supply ditch onto the field at one outlet. Note the unirrigated area at the left above the supply ditch. ; * SPRINKLER IRRIGATION SPRINKLER SYSTEM REPLACES FURROWS IN PEAR ORCHARD From clean cultivation and irrigation by furrows, this orchardist switched to per- - manent covercrop and sprinklers. The orchard is on a slope of about 5 per cent, with soil about 22 inches deep on bed- rock. Result of the old system was uneven application of irrigation water and soil - erosion. The new technique has proved very successful. v Irrigation water is delivered at a high point, so pumping is unnecessary to de- velop pressure. The water is distributed s through an underground 3-inch pipe, equipped with outlets for the portable ^ v sprinkler line. Each irrigation starts at the upper edge * t of the orchard, with the portable line moved progressively downhill — wetting every other middle. When the lower edge of the orchard has been irrigated, the sprinkler line is moved once again pro- gressively up the hill, and the alternate middles are irrigated. Thus complete wet- ting is accomplished. The covercrop is predominantly Ladino clover, ryegrass, and orchardgrass. It is mowed and left in place each year just before the props are put in the orchard. Once again, caution is advised with re- gard to careful control of rodents who may take up habitation in the covercrop. Note: Instead of the sprinkler heads shown in this picture, rotating sprinkler heads are now used extensively. 23 BASIN IRRIGATION During the first few years after planting, the root systems of trees do not develop to the point where they occupy the entire soil mass in an orchard. It is unnecessary, therefore, to irrigate the middles of the rows during this period. Tanking — shown in the top photo- graph — is simply the use of a circular basin around the tree, and watered as in- dicated. A second method using a long narrow basin is shown in the photograph below. A third technique employs the run- ning of a single furrow close to the tree rows, with a circular furrow around each tree. < As the root systems enlarge each year, in- crease the irrigated area for each tree. Generally, do not use such partial irriga- * tion more than two or three years. There are some exceptions to this. Widely spaced walnut trees, as shown in both photographs, can be wetted in this fash- ion for a longer period. Caution: Citrus and avocado trees should not be treated so that the irrigation water comes into direct contact with their trunks. Nor should the earth be mounded < against the trunks. A donut-shaped cir- cular basin, with the inner margin a few inches from the tree, is recommended. METHODS USED FOR IRRIGATING YOUNG FRUIT TREES 24 A NEW IDEA: DRAG-LINE HOSE SPRINKLERS Shown in these two photographs is a new system of sprinkler irrigation developed during the past sev- eral years. It consists of an underground pipeline with occasional outlets. The above-ground part consists of a hose about 150 feet long connected to the outlet and with 2 to 5 sprinklers about 20 feet apart at the opposite end. To irrigate, turn on the water as with a garden sprinkler and from time to time drag the sprinklers to new locations. Various sized nozzles can be used on the sprinklers to regulate the rate of application to the infiltration rate of the soil. This system has proved to be very effective on steep lands to minimize runoff and soil erosion. It is also finding some use for applying water evenly on flat lands. "fWi IN BRIEF. . . Irrigation of steep slopes is a difficult un- dertaking. You do not necessarily have a "best" method for a certain situation, but rather several alternatives. IN ORCHARDS, land on less than about 6 to 8 per cent slope can be ( square planted and irrigated effectively by the fur- row system. Land less than about 20 per cent slope can be planted on the contour and irrigated by either furrows or sprinklers. On steeper lands sprinklers must be used because furrows will break a over the lower side. * ON PASTURES, strip checks can be used on land up to 6 to 8 per cent slope. On steeper land contour ditches or sprinklers can be used. 26 HOW THE UNIVERSITY OF CALIFORNIA * WORKS WITH AGRICULTURE As one of the nation's Land-Grant institutions, the University of California plays a multiple role in service to agriculture. This involves teaching, research, and conveying the facts developed by research to those who may put them to good use in the best v* interest of all the people. These activities are combined in the University's Division of Agricultural Sciences. This statewide framework includes: The College of Agriculture providing instruction in agriculture and related sciences on campuses at Berkeley, Davis, Los Angeles, and Riverside. The Schools of Forestry and Veterinary Medicine function as separate professional schools within the Division but are closely related to the College of Agriculture. ^ The Agricultural Experiment Station conducting research on the four campuses . mentioned above as well as on numerous field stations, experimental areas, and farms throughout the state. Closely allied with the Experiment Station are the Giannini pf Foundation of Agricultural Economics and the Kearney Foundation of Soil Science. The Agricultural Extension Service with 53 offices serving 56 counties carrying out the responsibility of "extending" research results to the people. The Service cooperates with the Experiment Station in local research on thousands of farms. It also conducts > youth educational activities through the 4-H Club program. In order that the information in our publications may be more intelligible it is sometimes necessary to use trade names of products or equipment rather than complicated descriptive or chemical iden- tifications. In so doing it is unavoidable in some cases that similar products which are on the market under other trade names may not be cited. No endorsement of named products is intended nor is criticism implied of similar products which are not mentioned. <► Co-operative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United States Department of Agriculture co-operaling. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. George B. Alcorn, Director, California Agricultural Extension Service. 15m-2,'62(C5973)J.F. it works here . . . Many experiments conducted in the laboratories by staff members of the Division of Agricultural Sciences show promise of benefiting crops or animals. it may work here . . . Laboratory findings are often given further tests under controlled conditions in greenhouses (new plant varieties, for instance). but will it work here? Possibly not. Some (these new plant varieties, for instance) fail miserably when the Experiment Station and Extension Service staff members collaborate in field testing the experiments. if it does ... if field tests indicate higher yields, greater resistance to pests or disease, drought or moisture — if the development benefits mankind, the facts will be made available. Thus is science applied to agriculture by the University of California • Division of Agricultural Sciences