ELIMINATING TILLAGE IN CITRUS SOIL MANAGEMENT <4* CALIFORNIA AGRICULTURAL EXTENSION SERVICE CIRCULAR 150 MARCH, 1949 THE COLLEGE OF AGRICULTURE • UNIVERSITY OF CALIFORNIA • BERKELEY The Pros and Cons of Noncultivation as a soil management practice have been the subject of much discus- sion among citrus growers in recent years. Growers are well agreed now that the less the soil is disturbed in the various cultural operations, the better will be production. The system of complete noncultivation, which involves no cover crop and no till- age, is quite new. It is the system about which growers are most in- terested in having information, instructions, and cost data. This Circular gives the best information available. The whole story is not known yet because only about 50,000 of California's 330,000 citrus acres are under the system of no cover crop and no tillage. Further, with few exceptions, the acreage has been under nontillage only a limited time. Some surveys have been made; some growers have kept fairly accurate records. All growers who have tried the system have formed opinions as to its value, and from them some conclusions can be drawn. A digest of these records and conclusions is given herein. Fig. 1. At right: View of the Hinckley grove at Bryn Mawr, under noncultivation since 1919. The Authors: J. C. Johnston is Extension Specialist in Citriculture. Wallace Sullivan is Extension Specialist in Farm Management and Associate on the Giannini Foundation. Cooperative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United States Department of Agriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. C. W. Rubel, Acting Director, California Agricultural Extension Service. Eliminating Tillage in Citrus Soil Management J. C. Johnston and Wallace Sullivan Cultivation has a limited usefulness in citrus soil management. Experiments in the past have shown that cultivation, of itself, does not conserve moisture by form- ing a mulch. Nor does tillage, of itself, increase yields by aerating the soil and thus increasing fertility. Cultivation in citrus orchards is useful when it is used to remove weed competition, to prepare irrigation works, or to turn cover crops and bulky organic matter into the soil. Cultivation may have injurious effects. Deep tillage destroys roots and interferes with tree feeding. Tillage often forms a hard, impervious layer known as plow- sole just below the depth of tillage. Such plowsoles may prevent adequate penetra- tion of water. Attempts to correct this condition by repeated cultivations tend to make the situation worse. On the other hand, soil structure may gradually im- prove and the rate of water penetration increase in the absence of repeated culti- vation. In view of these effects, more and more citrus growers are developing soil man- agement systems which reduce or elimi- nate tillage. These systems may be desig- nated as: 1. Winter cover cropping with summer tillage. 2. Permanent cover cropping with no tillage. 3. No cover cropping and no tillage. The first two of these systems are fairly well known to growers since they are older practices, and are in general use throughout the citrus districts. They will be discussed only briefly in this circular. The last-mentioned system, that of no cover cropping and no tillage, has been developed more recently and is not yet widespread in the citrus areas. This sys- tem—the methods employed, equipment needed, results noted, and costs involved— is the main subject of the discussion that follows. — E c «-" - ■ — w<«jr: /- Winter Cover Crop, Summer Wage This system is in general use, and is practical under a wide variety of soil and climatic conditions. This system consists of planting a cover crop in the fall, and irrigating to develop sufficient growth to provide a protective ground cover before the first rains occur. In many cases this can be accomplished at a substantial saving by merely omit- ting late summer tillage and permitting natural growth of winter weeds to de- velop. This method eliminates at least one disking and leaves the soil surface firm and in better condition to resist erosion. From the standpoint of competition with the trees, it is best to disk-in winter cover crops by February 15 or at least by March 1. However, this operation would expose some orchards to serious soil erosion. Excessive competition can be avoided by mowing the cover crop, or by disking one way across the slope with the disk blade set at a slight angle so as to cut the crop without turning the soil. All disking should be shallow to avoid root cutting. On many soils it is necessary to use some of the depth-control devices which are available. As soon as possible after the winter rains the orchard should be disked and prepared for irrigation. The disking should always be light, and if some litter is left on the surface, so much the better. It will improve water penetration during the irrigation season. Tillage through the summer should be just sufficient to keep weed growth under control. In most cases this will require cultivation only after every 2 or 3 irrigations. It is not neces- sary to cover the weed growth completely. This system is in general use in Cali- fornia and has proved to be practical and economical under a wide variety of soil and climatic conditions. It provides or- ganic matter to help maintain good soil structure and, on most soils, does not de- velop a serious plowsole. 2' Permanent Cover Crop, No Wfage This system requires unusual skill. It has succeeded on some deep, open soils, but is not recommended. Citrus growers have experimented with permanent cover crops over a long period of years but only a few have been suc- cessful. It is not a method of neglect, but requires more than usual skill in manage- ment. Most of the orchards in which the method has given good results are located on deep, open soils near the coast where competition for water is less important than in the hot interior. One of the most successful methods of growing permanent cover crops is to al- low native winter weeds and grasses to develop in the orchard until the early- maturing varieties have produced enough seed to ensure a good crop next year. The crop is then mowed to reduce competition with the trees and to discourage or elimi- nate the late-maturing varieties, which would compete with the trees for moisture and fertility late in the spring. The cut- tings are left in the orchard to provide a partial mulch. Growth must be kept under control until the weeds die down. This will require several mowings in most cases. The orchard remains practically free of cover crop growth till fall. Growers who have been most success- ful in maintaining this system have ap- plied irrigation water to only a limited area of soil, leaving most of the land too dry to support weed growth. This system is difficult to maintain, but where it is in use results are good. r 4. i ^ : - w n- V - - .* £**£ Fig. 2. Nontillage on a contour planting. Narrow furrows are best for this. The usual difficulty with all attempts to grow permanent cover crop is that Ber- muda grass comes in and displaces all other growth. Since Bermuda grass is dormant in winter and grows actively in summer, it has, with few exceptions, given the trees too much competition for satisfactory results. Problems created Permanent cover crops enable the grower to eliminate tillage, control ero- sion, and maintain the soil in excellent physical condition, but at the same time new and difficult problems are created. Gophers, field mice, and snails find an ideal environment, and their work is not easy to detect in a weedy grove. The dry organic matter which accumulates in the orchards is a serious fire hazard. Large amounts of undecomposed or- ganic matter may seriously reduce the availability of nitrogen. The decomposi- tion process itself uses nitrogen. When large amounts of organic matter are pres- ent and the nitrogen supply is limited, decay is slow. Under such conditions much of the nitrogen present is used up by the decay process and little is available to the plants. To correct this, nitrogen must be added in excess of that required by the decay organisms. Decomposition of or- ganic matter will then be rapid, and nitro- gen will be available to the plants. Irrigation is a problem. Sprinklers are best for the purpose but they cannot always be used, and if all of the soil is wet, excessive growth of summer weeds will result. Furrows are not very practi- cal, but various types of basins can be used. Some growers apply all of the water in small basins which are filled by means of a hose or portable pipe. The basins usually occupy only a limited area and are filled with cuttings from the cover crop to assist in preventing the growth of summer weeds. Cover crops which grow actively dur- ing summer cannot be recommended for citrus orchards, and in any case perma- nent cover crops cannot be recommended for general use. The fact is, that after many years of trial, only a very few grow- ers are using this method of soil manage- ment. [5] ~^N*f&£ wB?M **'■ *>■*&&£ Fig. 3. Above: This grove has not been cultivated since the trees were planted. The method of furrowing used here is not recommended since it forces vehicles to travel in furrows rather than on ridges. Furrows get packed, and water penetration is impaired. Below: Three broad furrows used here enable orchard traffic to stay on the ridges between. [6] 3 -Ho Cover Crop, No M/age Experience is limited, but this system is on an increase. Promises better soil condition and lower long-run expense. The system of soil management which employs no cover crop and no tillage be- gan to attract the attention of a large number of growers with the advent of oil and chemical sprays for killing weeds. Prior to that time the hoe was the main weed-killing instrument for nontilled or- chards. For orchards with heavy weed growth the cost of hoeing is prohibitive, particularly during the first two or three years. In some orchards where weeds were not a serious problem, the nontillage sys- tem was started 25 or 30 years ago and has been used continuously with grati- fying results. About 1940, oils and chemi- cals applied with various types of spray rigs were recognized as a cheap and effi- cient way of controlling weeds without disturbing the soil. USE OF NONTILLAGE In San Bernardino County in 1947, the office of the farm advisor made a survey by mail of citrus growers, asking them to report their acreage under this system. The results were as follows: Year starting Number of Total number the system growers of acres 1947 54 845.9 1946 83 1,389.3 1945 52 710.3 1944 27 443.9 1943 24 376.4 1942 20 416.4 1941 21 420.4 1940 29 567.3 1939 9 225.5 1938 6 187.0 1937 6 212.0 1936 4 58.5 Before 19, 36 6 . . 341 186.0 Total . . 6,038.9 It is estimated that there are now, in San Bernardino County, from 400 to 500 growers operating 10,000 acres under nontillage. A similar survey was made in 1947 in Ventura County, from which it is esti- mated that one third of the citrus acre- age is under some form of nontillage, using oils or chemicals as a means of con- trolling the weeds. This system is in wide use in Orange and Los Angeles counties, with smaller acreages in other citrus- growing areas in the state. It is likely that in all there are more than 50,000 acres under this system of soil management. NONTILLAGE METHODS The best time to place an orchard under this system of soil management is late spring or early summer, after the season most favorable for weed growth has passed and in time to permit the soil to become firm before the fall rains arrive. The orchard is worked up in the usual way and the land is carefully leveled and prepared for irrigation. No special irriga- tion method is required. Sprinklers, fur- rows or basins are satisfactory. If furrows are to be used, special care should be ex- ercised in leveling the land to obtain even distribution of water and to avoid the necessity of disturbing the soil after the system has been established. Broad, shallow furrows give best re- sults because they are easy to maintain and provide a minimum of interference with orchard traffic. Broad, shallow fur- rows also give better water distribution and reduce to a minimum clogging by leaves. One of the best arrangements is to have three wide furrows spaced so that orchard vehicles run on the ridges and straddle the middle furrow, rather than running in the furrows. In this way the adverse effect of orchard traffic on water penetration is minimized. [7] Narrow furrows will have to be used to give more even distribution of water where the grade is uneven or steep, or where there is a side slope which causes the water to run to one side of the furrow. In general, narrow furrows will be best if the grade is greater than one per cent. Don't delay spraying As soon as the weeds are about one inch high spraying should begin, and should be repeated as often as growth reaches that height. It is false economy to delay treatment. Delay means that more labor and more material will be needed, and more time required to elimi- nate the more resistant weeds. The spray is applied sparingly, the ob- ject being to wet the weeds without run- off. Pressure must be adapted to the material used, but 50 to 75 pounds per square inch will usually give good results. Excessive pressure causes fogging which frequently results in serious injury to the trees. Most weeds will be eliminated by repeated spraying, but some deep-rooted perennials, like morning glory and nut- grass, are very resistant and can be con- trolled best by a supplementary spray of 2,4-D. Citrus trees, especially lemon, are injured by 2,4-D and care must be used to avoid spray drift. The spray should be mixed according to the manufacturer's recommendation and applied when the air is calm. Pressure should be low enough to avoid fogging. Applications will vary The number of spray applications re- quired and the amount of oil used will vary widely according to kind of weed growth, the equipment used, and timing of the treatment. The number of applica- tions required the first year will usually be between 4 and 8, and by the third and fourth years this will usually be reduced to 1 or 2. The amount of spray material needed to cover an acre is variable but ranges between 40 and 100 gallons. The total amount used per acre per year ranges between 200 and 500 gallons the first year and will usually decrease to from 40 to 200 gallons per acre by the fourth year. This emphasizes the fact that the sys- tem, when once inaugurated, should be continued in order to get the full benefit of reduced long-run costs. SPRAY MATERIALS Any discussion of materials at this time is difficult because of frequent changes in availability, and the rapidity with which new materials are being developed and offered for sale. For this reason it will be best to discuss the problem with the local farm advisor. Further informa- tion is contained in California Agricul- tural Extension Service Circular 137, entitled "General-Contact Weed Killer," by A. S. Crafts. A formula for a fortified oil emulsion concentrate given by Dr. Crafts is: Aromatic distillate (per cent aro- matics 40 or more, viscosity 50 sec. or less) 30 lbs. Pentachlorophenol 2 lbs. Oronite wetting agent 2 lbs. For very young weeds this concentrate is sufficient for 100 gallons of spray, 96 gallons of water being used to make up the final emulsion. For more resistant weeds, use less water. Heater oil commonly used The material most commonly used in citrus orchards is ordinary orchard heater oil. It may be used straight or diluted with water. When it is diluted with water it is often fortified with special weed oils or by sulfur, dinitro compounds or chlor- inated phenols. The preparation and use of these materials are discussed in Exten- sion Circular 137. It is well to keep in mind that weeds are much more easily killed when they first come up than after they are 2 or 3 inches high. Less spray is required and greater dilution is prac- tical if they are treated early. [8 Fig. 4. Horse-drawn rig on the Hardison Del Tio Ranch near Saticoy, where E. Domingo Hardison is manager. This equipment is suitable for controlling the average weed stand after several years of nontillage. For spot work two men cover 2 to 4 acres in a 9-hour day. Advantages: horse power cheap and convenient, weed coverage accurate, no spray material on skirts of trees, low gallonage per acre, will operate in any orchard or terrain. Disadvantages: two men required to operate, low acreage covered per day, hoses wear out rapidly. EQUIPMENT NEEDS A variety of special equipment is now available on the market but some growers find it more economical to construct their own equipment or to use conventional spray rigs which they already own. In most cases it is best to use a boom which will spray a whole middle at one time. Such a rig can be operated by one man and it will cover as much as three acres in one hour. Booms should be provided with adequate shields to reduce fogging and to lift low-hanging branches as the weeds under the trees are being sprayed. Spaces between trees are usually sprayed with hand nozzles. For small acreages and after weeds have been largely eliminated, hand- operated nozzles are more economical. It is desirable to have good agitation in the tank so all types of sprays can be used. Because of the high cost of oil, the cur- rent tendency is toward the use of a mix- ture of oil and water and this requires agitation. Smaller capacity needed When purchasing equipment it is well to keep in mind that weed growth de- creases to a minimum in three to four years, and it is not wise to buy equipment which has greater capacity than is nec- essary. On small acreages and around home grounds oil can be applied by means of a knapsack sprayer. When 4-gallon tanks are used and filled with 3% gallons of spray, a man will usually apply 16 to 18 tanks in an 8-hour day, or 2 tanks of spray per hour. In a young orchard where most of the area must be sprayed, it will require about 75 gallons of spray per acre and will require about 11 hours of labor. [9] W J ^ j ■< .... . , , , . Fig. 5. Tractor-mounted weed-spraying rig designed and built at Camulos Ranch, Piru, where Harry Forbes is manager. Above: sliding boom on front moves back and forth to spray between trees. Below: adjustable booms on rear make rig adaptable to any orchard. One man can give solid coverage to 15 acres in a 9-hour day, or he can spot-work weeds in a light stand on 50 to 75 acres a day. Advantages of this rig: one man can operate, large acreage covered per day, adjustable booms. Disadvantages: low spray-material capacity, spray material gets on skirts of trees, large gallonage per acre is required. Total cost of this outfit is given as $500, including $230 for tractor, $143 for power take-off and special transmission, $65 for sprayer equipment, and $40 for labor of construction. [10] 'VI * •«.' ' Fig. 6. A trailer type of boom spray used on the Whittemore ranch. One man driving and operating can cover 10 acres in three hours. Note covers over the ends of the boom which prevent fogging of oil. Fig. 7. E. M. Whittemore is shown with the spray rig he and his son designed for use on their groves in Highland. Below: the rig, with one wheel removed for picture. The 12-gallon tank is mounted be- tween two bicycle wheels equipped with balloon tires. The small en- gine operates a gear pump with pressure release valve, pressure gauge, return flow pipe, and sedi- ment trap. Light conduit tubing is used for handle. Power unit and equipment balance on center when tank is empty or full. ^^^, [11] RESULTS NOTED Experience with nontillage is still lim- ited and many of the questions which are raised in regard to the method cannot be answered until we have used the method for a greater period of time and until re- sults from careful research are available. Soil condition . . . The most important effect which has been observed is the improvement in physical condition of the soil. Water pen- etration is improved. This has generally resulted in more efficient irrigation, and in some cases it has become necessary to install new pipe lines and shorten the runs. It is possible, however, for the sur- face of the soil to silt over and then, in spite of the fact that the soil becomes more permeable, water penetration is not improved. This effect can be minimized by scattering a little manure or other or- ganic material in the furrows. The effect of nontillage on the organic matter content of the soil has not been determined. In the Hinckley orchard at Bryn Mawr, where nontillage has been practiced since 1919, the soil remains in good condition. (See figure 1.) Fertilizer practice . . . Fertilizer practice has not been materi- ally changed in most cases, except of course that no cover crop is raised and no fertilizer is worked into the soil. Most growers are using only chemical nitrogen but many are using manure. There is no evidence that those who are using manure have any advantage over those using only nitrogen, except in the few cases where manure has been used to improve water infiltration. There is a tendency for grow- ers to use less nitrogen under this system. T. A. Lombard of Rancho Sespe has re- ported that it takes less fertilizer to main- tain an adequate nitrogen level in the soil under nontillage. 1 Reported in California Citrograph 29(8): 112, June, 1944. Erosion . . . Erosion has been reduced under non- tillage. At first glance this does not look reasonable, but even on steep slopes grow- ers have found it to be true. There are two principal reasons. First, the soil absorbs water more rapidly and the runoff is therefore reduced; and second, the sur- face is firm and is not readily washed away as is the case with loose plowed soil. Some serious erosion has occurred where water from other land has been allowed to enter nontilled orchards, and in cases where a sharp fall occurs at the end of the furrows, some cutting takes place. The application of strawy manure in such areas will usually give adequate control. Yield . . . Yield has no doubt been increased in some cases where the soil is shallow and where water penetration is poor, but there is little evidence of a general im- provement in yield under nontillage. An indirect increase in yield may come as a result of less disturbance to skirts of trees, which allows an increase in their bearing area. Because root cutting, such as occurs in conventional tillage, is elimi- nated, improvement has been observed in general appearance and condition of old trees. The effect on maturity of fruit is not well known. With both lemons and oranges, growers frequently report earlier maturity. Mr. E. C. Moore of Tulare County has reported earlier maturity of navels under nontillage in years when the spring was cooler than normal. 2 Oil on soil . . . The effect of oil spray on soil appears to be negligible. Even where as much as 600 gallons per acre have been used in one application, no adverse effect has been observed. Chemical tests have shown that 2 As reported in California Citrograph 30: 380-381, July, 1945, and in Citrus Leaves 25: 30-31, June, 1945. [12 i «fy T:,t-^ •*m$ "■ so*'*'! Tk ■»- r Mz*:**- Fig. 8. In nontillage, trees grow skirts to the ground and hang more fruit. This low fruit is easy and cheap to harvest. Fig. 9. Another advantage of nontillage: heaters need never be moved, thus saving labor. 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Handling fruit . . . The work involved in picking, loading, and hauling fruit, pest control, pruning, and other operations is made much easier in weed-free orchards with firm surface soil than in orchards under different man- agement. Picking crews and trucks can operate in noncultivated orchards one or two days after a heavy rain, which will leave tilled orchards too muddy to be worked in for a week or more. The problem of rodent control is greatly diminished. Field mice and go- phers avoid bare open ground and if they do come into the orchard their work is easily detected. Snails are also discour- aged. Several growers have reported that snails have disappeared completely when their groves were placed under nontillage. Frost hazard • . • The frost hazard may be somewhat re- duced in nontilled orchards. Bare, firm soil absorbs more heat during the day than loose soil or soil which is covered by a blanket of mulch or a cover crop. At night bare, firm soil not only contains more heat but it releases heat more readily than loose soil or soil which is insulated by a mulch or cover crop. This effect of reduced cultivation on temperature has not yet been studied ade- quately, and the subject of heat exchanges in the soils is a complicated one. Growers report temperatures about 2° higher in nontilled orchards than in covercropped orchards. This increase in temperature may be the cause of the earlier maturity which has been observed in some orchards. COST STUDIES Many incidental advantages of this system over others have already been pointed out. The main question is, how- ever : What does it cost compared to other systems of management? Costs should be considered in a broad sense to include the time element, effect on cost of other operations, health and vigor of trees, and yield and quality of fruit. Some growers have reported that the increase in yields resulting from nontill- age, particularly in shallow soils, has more than covered their total cost of weed control. Others on deep, fertile soils have not noted any appreciable increase. Gen- erally, growers have said that the hours of labor for irrigation have been reduced, and the efficiency in the use of water has been improved. Certainly the cost of fur- rowing out year after year has been prac- tically eliminated. Picking, hauling, pest control, pruning and other orchard work are facilitated by having a firm surface free from weeds, clods, dust or mud on which to work. San Bernardino County costs A summary of 26 records of the cost of operations on noncultivated citrus or- chards, using spray materials for weed control, is given in table 1. The first column shows the number of records in- cluded in the averages for each year, followed by the total number of acres and the year in which the system was started. Wages for labor averaged about $1.00 an hour and included owner or family labor. Field power and equipment costs ranged from 25 cents to $1.50 an hour. The cost of oil or spray material varied from 6 to 16 cents a gallon. The first two years under this system are the high-cost years, after which, if the system has been well managed, costs per acre decline rapidly. This is shown in the last column of total costs. Costs per acre vary widely on different ranches. In the five records reporting first year's opera- tion, costs varied from $11.48 to $49.03. Spray material used per acre varied from 29 gallons to 213 gallons. Many factors will cause this wide variation. Weed pop- ulation is probably the most important. Orchards heavily infested with Bermuda grass, morning glory, and nutgrass will require frequent applications of oil the [15] Table 3: AVERAGE COSTS PER ACRE FOR CULTIVATION (INCLUDING FURROWING) IN CITRUS ORCHARDS, 1946 County Kind of citrus Number of records Total acres Average costs per acre Orange Lemon Valencia 18 61 226.6 787.4 $24.68 26.08 Ventura. Lemon Valencia 11 20 701.0 668.5 27.33 17.81 San Bernardino Lemon Valencia Navel 18 23 29 216.6 154.0 307.8 22.43 20.18 23.40 Los Angeles Lemon Valencia Navel 23 50 38 321.0 373.0 259.0 20.47 24.52 21.78 Santa Barbara Lemon 32 659.0 29.70 San Diego Lemon Valencia 19 10 193.0 126.5 21.24 33.27 Source of Data: Enterprise Efficiency Studies, 1946, Agricultural Extension Service, University of Cali- fornia. Issued by Counties. first two years. Many growers apply ex- cessive amounts of oil per application or fail to spray at the stage of weed growth to get the most efficient kill. Types of spray rigs, nozzles, and pres- sure are very important items in keeping costs down. Nontillage is a system that requires the strictest of attention to all details. Orange County costs Table 2 gives the summary of a similar survey made in Orange County with 23 records, covering 421 acres with the same general pattern of costs. The first three years average about $10 an acre more than the San Bernardino records. This is accounted for by more rainfall and gen- erally heavier soils, inducing a heavier growth and a greater variety of weeds. Observations in other counties indicate higher costs on heavy soils and areas near the ocean. Here again the first two years under noncultivation are shown to be the expensive ones. Tillage costs compared Average cost per acre for cultivation (conventional tillage) is given in table 3 for comparison. These figures for the year 1946 include furrowing out for irriga- tion. This study includes 352 records covering 4,993 acres in five counties. Average costs varied from $17.80 to $33.27 per acre. It would appear from these studies that the nontillage system would cost about one third more the first two years, the same the third year, and 50 per cent less after the third year than conventional tillage. The proportions would be greater in orchards with heavy soils and dense weed growth, and less on light gravelly soils with few weeds and light rainfall. In view of the high cost the first two or three years, the grower— before adopting the nontillage system— should be reason- ably sure that he will have facilities and materials necessary to continue it over a period of years. 25w-4,'49(B3007)