vision of Agricultural Science UNIVERSITY OF CALIFORN CALIFORNIA AGRICULTURAL EXPERIMENT STATION BULLETIN 849 This bulletin summarizes the results of studies with petroleum mulches. It reports the findings of field, laboratory and greenhouse trials on the influence of petroleum mulch on soil temperatures, soil moisture, crop responses, and weed control. Effective rates, methods and timing of applications, as well as width of mulch bands, are sug- gested. Additional studies covering the important considerations of soil preparation and degradation of asphalt residues are summarized. This bulletin will aid vegetable growers and other agricultural personnel to assess the potential value of petroleum mulches in their cultural operations. MARCH, 1971 THE AUTHORS: Frank H. Takatori is Specialist in the Agricultural Experiment Station, Plant Sciences, Riverside. L. F. Lippert is Associate Professor of Vegetable Crops and Associate Olericulturist, Plant Sciences, Riverside. James M. Lyons is Professor of Vegetable Crops and Plant Physiologist in the Ex- 4 periment Station, Davis. CONTENTS Page Physical Nature of Petroleum Mulch 3 Delineation of Petroleum Mulch Studies 4 Land Preparation and Field Cultural Practices 4 Spray Equipment 4 Spray Concentration 4 Calibration of Spray Equipment 5 Temperature and Moisture Measurements 6 Responses from Petroleum Mulch 6 Soil Temperatures 6 Soil Moisture 11 Crop Responses 14 The Influence of Asphalt Residues on Vegetables 16 The Influence of Petroleum Mulch Overlays on Herbicide Performance 19 General Considerations for a Successful Mulching Operation 22 Literature Cited 23 An "Abstract" of the findings reported in this bulletin appears on page 24. [2] PETROLEUM MULCH STUDIES FOR ROW CROPS IN CALIFORNIA PHYSICAL NATURE OF Petroleum mulch is a liquid emulsion of asphaltic resins of suitable consistency and viscosity for spray application. The liquid phase of the emulsion is generally water, and the asphalt content ranges between 50 and 60 per cent by weight. These mulch materials are applied with- out heating. Table 1 PHYSICAL PROPERTIES, DOCAL 1055 AGRI-MULCH (TM)* Viscosity, SSF at 77°F 70 Asphalt content, per cent by weight 58.5 Penetration of residue, dmm/100g/5 sec/77°F 180 pH 3.0 Sieve, maximum 0.10 * (TM) Registered trademark of Douglas Oil Co., Paramount, California. The physical specification of a typical commercial product is given in table 1. 1 Submitted for publication May 14, 1970. PETROLEUM MULCH Petroleum mulch is applied as a spray directly over the seed row. Upon drying, the material forms a black con- tinuous coating, between 10 and 20 mm thick, over the soil surface. The film is in intimate contact with the surface soil particles but does not penetrate deeply into the soil (figure 1). The thin film is little damaged by wind, rain, or irrigation, but is readily destroyed by cultural operations such as cultivation. The pliable texture of the material does not impede the emergence of most seedlings. Under normal condi- tions, the film remains intact throughout the germination period and is eventually destroyed by normal cultural practices. Test materials have been stored for one season without noticeable change in characteristics; however, the recom- mendations of the manufacturer concern- ing storage conditions should be followed. Fig. 1. Field plot established for comparative evaluations of petroleum mulch (background) and black and clear polyethylene films. DELINEATION OF PETROLEUM MULCH STUDIES Land preparation and field cultural practices The majority of the field tests were con- ducted at the Citrus Research Center, University of California, Riverside, on Ramona fine sandy loam soils. Field preparations included pre-irrigation, deep plowing, and rototilling of the soil before the beds were formed. After bed shaping, the soil was compressed with a 200-lb lawn roller to insure a firm, smooth mulching surface. In tests which were planted to vegetables the planters were attached to the bed shaper and the area seeded prior to the firming opera- tion. The test area was irrigated im- mediately after the mulching operation until the beds were completely saturated. Subsequent irrigations were dictated by the nature of the trials or by the water requirements of the crops. Spray equipment The asphalt emulsion was applied with a portable sprayer utilizing a pressurized system capable of maintaining 35 psi nozzle pressure. The spray system (figure 2), including the compressor and storage tanks, was mounted on either an Allis Chalmers Model G tractor or Farmall "Cub" tractor. PETROLEUM MULCH SPRAY SYSTEM PORTABLE COMPRESSOR WITH SURGE TANK %?< QUICK COUPLER ' 1/4" HIGH PRESSURE HOSE 3/4" PIPE AND GAS COCK 3«"H0SE QUICK COUPLER TEE JET SPRAY NOZZLES FLAT SPRAY TIP * 8 008 FUNNEL (BELL REDUCER) l" GAS COCK l\3/4" 45 "JOINT EXHAUST VALVE RESERVOIR TANK 3/4" PIPE 8 GAS COCK QUICK COUPLER Fig. 2. Schematic diagram of tractor-mounted, pressurized spray system for petroleum mulches. The sprayer was adapted with "Tee Jet" nozzles No. 8004-8010, generally 8008, under 35 psi delivery pressure. r Two spray nozzles in line spaced 8-12 inches apart were directed to spray for- ward and rearward over each seed row to insure good coverage of the soil surface and to provide a continuous deposit (film) of asphalt. Gear pumps have been used to spray asphalt mulches, but they must be modi- fied for greater spacing between the gear teeth. Even with this alteration the working parts tend to clog. The high speeds and shearing action of the pump tends to break the emulsion, that is, separate the water from the solids, thereby resulting in the precipitation of asphalt solids which clog the gears and the spray system (Scudder and Darby, 1964). Clogging may be a major problem with any system but can be - minimized by screening the petroleum mulch through window screen during filling of the tank. Also, additional screening units may be installed in the flow system. Spray concentration The effective concentration of petroleum mulch per acre has been established within rather wide ranges. Concentra- tions from 125 to 1,000 gallons "per full r acre coverage" have been used. It was found that rates from 250 to 500 gallons generally gave adequate results. The benefits obtained from rates in excess of 500 gallons per acre are not sufficient to warrant the additonal expense of the mulch. The term "full acre coverage" is used as a means of convenience. If two i factors are known, i.e., row spacing and band width of mulch, the actual gallon- age of mulch applied per acre can be determined. For example, with a rate of 500 gallons per full acre coverage and a 6-inch band sprayed on single rows spaced 30 inches apart, the material [4 151 40 133 35 1 < CO rr u 113 ^30 uj _i U) cr Ld III 94 *- 25 h- CO * .-H co -^ OO OS OS O OS C3 M ^h lO o iO °. CM -S oc 00 01 co OS PM «i 03 H 3 *o in co rt< cm 00 co CO O CO O CM' ^ 00 OS OS O 03 M 1 0O CO 115 11 -fi 1— 1 CO CM -° 00 OO 05 CO OS 10 Ttl -* CO T-H CM i-H O0 O I— os cci 00 00 OS os 00 a; b£ o o o 03 03 O 85.4 91.2 94.0 100 1 00 OS CM Pm CJ <3 03 H 3 «o N H CO CD CM lO -H ->*l .— 1 CO -^ 00 OS OS O OS 03 TH M N CO CD CM OS # r-' co (M ,Q 00 os os OS 0> "08 Q »o 10 uo u; CO CO CO cc "-». -\ -\ ~- a> m n a •c ' « >c- IC soil surface with a minimum of clods to obtain maximum performance from pe- troleum mulches under field application. Equipment for seedbed preparation for petroleum mulching has been developed and described by Frost (1966). Influence of the thickness of the film on soil temperature. The thick- ness of the asphalt film in difficult to measure because the soil particles on the surface of the soil are fused with the film and presents a nonuniform surface with larger quantities of mulch in the air spaces between the soil particles than on the particles themselves. Thus, film thickness was evaluated on the basis of the volume of material applied per acre. It was assumed that when the band width was held constant, a rate of 500 gal/full acre coverage would produce a film be- tween 10 and 20 mm thick. Reducing the application rate by half (250 gal/full acre coverage) would create a film ap- proximately half as thick, and doubling the rate to 1,000 gal/full acre coverage would produce a film twice as thick. Three different materials were tested in the field at rates of 125, 250, 375 and 500 gal/full acreage coverage applied as a 6-inch band. Prior to mulch applica- tion the soil was rototilled twice and pressed with a 200-lb lawn roller to form as smooth a surface as possible. The soil temperatures obtained for the three ma- terials at the four mulch concentrations are given in table 2. The 125 gal rate for all three materials failed to increase soil temperature. The soil particles were visible in many areas of the band, indicating that the film was not continuous at this low concentration. Petroleum mulch concentrations of 250, 375 and 500 gal/full acre coverage in- creased soil temperatures significantly over both the 125-gal rate and the non- mulched control. The differences in temperatures among the three higher rates, in most instances, was only 1° or 2°F. 10] } r *^^BF* ■ ' x ^%^% *"! ^^^ *&L - * \ '"" . j \:% . I d 4 * i?\ ,« ^r '2"-.'X'*« >4„- Jl- * » «5*£>flK a?i2S^w Fig. 8. Evidence of moisture conservation in the soil area protected by the asphalt deposit from a petroleum mulch band. These data further suggest that the effectiveness of petroleum mulch is de- pendent on the development of a con- tinuous black film. Beyond the volume of material required to produce a con- tinuous film, additional material does not strongly influence soil temperatures. On a carefully prepared seed bed, lower rates (approximately 250-300 gal/full acre coverage) will provide this con- tinuous film, whereas, in the presence of clods, holes, or debris, even very large quantities (in excess of 500 gal/full acre) may fail to effectively cover the soil surface. Soil moisture The bulk of the soil moisture lost from an open surface is by evaporation. Al- though somewhat porous, the mulching film restricts the evaporation rate which reduces the loss of soil moisture (figure 8). Effect of width of mulch band on moisture retention. The same 6-inch- wide band which provided the most eco- nomical temperature response also was adequate for a significant conservation of moisture during the early seedling stage (Lippert, et al., 1964). Moisture content of the soil was determined from a noncropped test area in which pe- troleum mulch bands of 0, 3, 6, 12 and 24-inch widths were replicated four times on 40-inch raised beds. Mulch ap- plication was at the rate of 500 gallons per full acre coverage and band widths were controlled by use of wooden tem- plates over the bed area. The total plot was furrow irrigated to saturation after mulch application and recorded a 19.8 per cent moisture content two hours after completion of irrigation. Soil samples from the 0-2 and 2-4 inch depths were obtained from each plot at four-day intervals for three weeks. Moisture percentage was calculated on the basis of dry weight of soil after dry- ing in a forced-air oven for 24 hours at 105°C (40.5°F). [11] Table 3 MEAN SOIL MOISTURE PERCENTAGES UNDER BAND WIDTHS OF PETROLEUM MULCH Mean soil moisture percentage Band Width Days after mulch application Mean of readings 12 16 20 over 20-day period inches per cent 7.55 a* 8.18a 9.48b 9.95b 10.50 b 7.36a 7.88 ab 8.48 be 9.02 c 9.73 d 7.60a 8.34 b 8.05 ab 9.94 c 10.44 d 11.10a 3 11.43 ab 6 . 11.92 be 12... 12.39 cd 24 12.75 d * Any two means in vertical order not having letters in common are significantly different at the 5 per cent level by the Duncan test. The mean moisture values for band widths of petroleum mulch are presented in table 3. These data show a nearly linear trend for higher soil moisture re- tention as band width increases during a winter (February) test. Duncan's mulitple range test indicates significant differences only between third-position means. Therefore, with the narrow band widths, significant moisture retention was obtained with a band of approxi- mately 6 inches, whereas in the wider bands, larger increments of width were necessary for significance (approxi- mately 13 inches between 6- and 24-inch bands) . Figure 9 shows that the moisture con- tent was significantly higher at the 2- to 4-inch depth than at the 0- to 2-inch depth. Also, there was a continuing and significant loss of moisture from the soil at progressive sampling dates. These trends in soil moisture are expected in a field study of this type. Similar tests on band widths initiated during summer (July) and fall (Oc- tober) conditions at Riverside showed seasonal differences compared to winter and spring conditions. The drying rate of the soil was so rapid under these warm environments that no significant moisture retention was recorded from any band width of petroleum mulch. 13 " ^^ »2-4 .,•0-2 12 - # ■-""' .-<-• UJ •""'^ O 2 - ^ O « 10 _ »* 9 " 1 1 1 i 20 3 6 BAND WIDTH 24 2 3 4 5 SAMPLING INTERVAL (4 days) Fig. 9. Influence on soil moisture by mulch band widths at two soil depths and at various sampling intervals. [12] I4r 13 12 II 10 9 8 o 2 7 o 6 5 4 3 2- • 500 gal/acre • 375 gal/acre germination emergence inhib 250 gal/acre x x • 125 gal/acre • check 3 4 5 6 7 8 DAYS AFTER IRRIGATION 10 Fig. 10 Pattern of soil moisture depletion or conservation under 6-inch bands of petroleum mulch as influenced by mulch concentration. Results represent a February-March trial at Riverside. Effect of formulation and density of the film on moisture retention. Three formulations of petroleum mulch at rates of 500, 375, 250, and 125 gal/acre (full acre coverage basis) were evaluated for effects on soil moisture using 6-inch wide bands. Changes in both formulation and concentrations in- fluenced the retention of soil moisture. Progressively higher moisture readings were obtained up to the 375 gal/acre rate in each sampling date for a nine-day period (figure 10). The difference in moisture retention between films for the 375 gal and 500 gal/acre rate was not significant. Changes in formulation created differences in the functional properties of petroleum mulch which appear associated with the formation of a continuous film. The greatest proportion of soil mois- ture lost from an open surface is through evaporation. The band of petroleum mulch present on a soil surface is porous, containing numerous pin-sized or larger holes. Yet, in general, these mulch bands are in better moisture condition than nonmulched soils (figure 8) . Considering [13] that the soil is warmer, the better soil moisture under the mulch band ap- parently is caused by the asphalt deposit acting as a barrier against loss of water vapor. This would result directly in a better moisture condition and might also assist in maintaining a continuous moisture column which permits capillary movement of moisture throughout the lower soil levels toward the surface. This moisture effect is evident for only a few days following planting and mulch- ing, but may be important in the emergence of crop seedlings. As an ex- ample, soils drop from the field capacity level of soil moisture to a stage where moisture is at a sufficiently low level as to be a critical factor in seed germina- tion and seedling emergence. In the Riverside soils, this period from field capacity to critical moisture was reached in five to six days without mulch during spring trials. Under mulch, the critical level was delayed for three to four days; that is. moisture was available to the germinating seeds for up to eight to ten days after irrigation (figure 10). This effect is not large enough to greatly re- duce total water requirement to an irri- gated crop, but it does offer benefits dur- ing the early germination and seedling stages. Crop responses The influence of asphalt mulch on the production of vegetables was evaluated in southern California between 1961 and 1968 (Takatori, et al, 1964). Most of the field tests were initiated during February and March. Weather condi- tions during this period are cool and soil temperatures approach the critical mini- mum range for good germination and emergence of warm-season vegetable crops. The width of the petroleum mulch band was standardized at 6 inches and the mulch was applied at the rate of 500 gallons per full acre coverage. The responses of various vegetables Table 4 THE INFLUENCE OF PETROLEUM MULCH OVERLAYS ON VEGETABLE GERMINATION, SEEDLING DEVELOPMENT, AND PRODUCTION* Vegetable Germination Seedling Production Species Variety Early Total Vigor (wt) Early (no.) Total (no.) Beans Beets Cantaloupe Carrots Celery Cucumber Lettuce Onions Peppers Squash Sweet corn Sweet potato Tomato Watermelon Tendergreen Detroit Dark red Holly H.H. 5 P.M.R. 45 Imperator Utah 52-70 Marketeer Great Lakes S Spanish Early Grano Yolo wonder Floral Gem green chili zucchini Golden Bantam Velvet (for shoots p Pearson Imp. W.R. Klondike 88 + + + + + NS + + + + + NS + + + roduction) + + + + + + + NS + + + + + NS + + NS + + NS + + + + + NS -L- + P NS + P + + P P NS + + + NS + NS + NS + * + = significance at 5 per cent level NS = not significant P = possible. No data because of single harv [14] 2 "3 o "3 o 3 o 53.0 28.0 42.0 63.6 4.0 o 62.0 23.0 48.0 71.9* 16.8* i 3 o CM O CM CO O —i 3 § «5 t^ CM OS ©' rji o bo '> M C -a 73 1 o Z 1 e CO CD 00 O CM ^ CO CO 00 CM -h © CO © 00 Ti CO lO t^ CM CM O C C g o "3 o 3 o 55 CO e 30.0 18.0 110.0 128.0 20.0 3 39.0* 15.0 177.0* 157.8* 52.0* '3 3 o 6.2 1.7 51.2 34.5 0.0 1 22.7* 10.5* 129.2* 125.5* 31.7* >> 03 Zucchini Golden Bantam Detroit D red Holly HH 5.. PMR 45 to petroleum mulch are summarized in table 4. Except for pepper variety Floral Gem, celery variety Utah 52-70, and Golden Bantam sweet corn, the rate and total germination for every crop were in- creased with the use of mulch. Where petroleum mulch overlays were not used (control plots) the germination and emergence period extended over a longer period resulting in either a reduced final stand or a stand with young plants of different sizes. This delay in germination was particularly noticeable for canta- loupes, cucumbers and watermelons. In one test, cucumbers failed to germinate without the aid of petroleum mulch be- cause of the existing cold soil tempera- tures. Plant size, measured either by weight or height of the seedlings approximately one month after emergence, was used as an index of seedling vigor. This stage of plant growth corresponds closely to the time when most vegetables are thinned to final stand in a commercial operation. By virtue of an early germination and continued favorable soil temperature under the petroleum mulch soil cover, these plants were larger and more vigorous than plants from the non- mulched control areas during the seed- ling stage of plant growth. For some vegetables the stimulus of early germination and final seedling vigor was manifest throughout the grow- ing season and resulted in increased yields. Zucchini squash and cantaloupes are examples of this type of response (table 5). For other vegetables the initial advantages of earlier germination and increased seedling vigor did not persist throughout the growing season when measured as differences in yield. In many crops the failure to show yield differences may be caused by the cultural practices used in producing the crop. For example, the seeding rate for both table beets and sugar beets is normally increased over the amount required for [15] a final stand and the plant population is regulated by thinning to a given stand. When the comparative stand be- tween the treated and nontreated areas was similar, as was the case for table beets (table 5), the advantages of in- creased percentage of germination was negated and no differences in yield were obtained. When a differential in the final stand occurred (sugar beets) the initial treatment effects were reflected in in- creased total production. The greatest effect on yield by use of petroleum mulches appears to relate back to better emergence and particularly better thinned stands associated with early crop responses. Yield differences are more directly related to increased plant populations than to yield differences among individual plants. Therefore, if the plant population has been increased by mulching, resultant yields should be increased. As the industry shifts more toward precision planting, or the posi- tioning of seeds on a plant-to-stand basis, petroleum mulch through its benefits of increased rate and percentage of germi- nation could be a critical fatcor in achiev- ing the desired high plant population. The rate of maturity or earliness of production for many crops may be as important to the grower as total yield. For table beets and onions, the harvest was delayed and the yield determined on a single harvest which minimize the difference in the rate of maturity. In sweet corn, cucumber and squash, where differential harvests were made, a sig- nificant increase in earliness of produc- tion was obtained. In summary, crop responses from pe- troleum mulches were as follows: 1. Petroleum mulch overlays are effec- tive and beneficial for most crops for establishment of a good stand during seasons of the year when weather condi- tions and soil temperatures are in the minimal range for optimum performance. 2. Plants aided by petroleum mulch will generally be larger and exhibit more vigor during the seedling stage than non- mulched plants. 3. For some vegetables, early germina- tion and increased vigor will produce earliness of maturity and increased yields. For other crops, the advantage of higher percentage germination, seed- ling vigor, etc., will be minimized be- cause of cultural practices such as thinning-to-stand. 4. Total yield increases for most vegetable crops relate to increased plant populations due to mulching, rather than to yield differences among individual plants. THE INFLUENCE OF ASPHALT RESIDUES ON VEGETABLES One of the most frequently asked ques- tions regarding petroleum mulches is: "What is the effect of the asphalt residue from petroleum mulches on soil char- acteristics and subsequent crop growth?" To obtain answers to these important considerations, asphalt mulch from three petroleum companies was incorporated into the soil at rates of 500, 1.500, 3,000. [16 1.500 and 6,000 gallons per acre (Taka- tori, et al., 1968) . These quantities simu- late the amount of asphalt that would be added to the soil if a field was mulched for 5. 15, 30, 45 and 60 years, based on an annual application of 100 gallons of actual mulch per acre. The mulch was applied over a 6-month period at a maxi- mum rate of 1.000 gallons per acre per ] Table 6 THE EFFECT OF DIFFERENT AMOUNTS OF PETROLEUM MULCH INCORPORATED INTO THE SOIL ON THE GERMINATION OF 4 VEGETABLE SPECIES*! Material Gallons/acre Crop 500 1,500 3,000 4,500 6,000 1 Grrmination count Tomato 33.8 40.0 48.0 38.0 43.0 37.5 2 38.0 35.0 41.2 42.5 36.2 37.0 3 40.0 42.0 39.2 37.0 X Ave. 37.2a 39.0a 42.9a 39.1 a 39.6a 37.2 a Sweet corn 1 10.5 15.0 14.5 16.2 10.0 11.2 2 12.5 13.0 13.7 10.5 12.5 10.0 3 14.5 11.2 12.5 13.0 Ave. 12.5a 13.0 a 13.5a 13.2a 11.2a 11.1 a Sugar beets 1 37.5 17.5 25.0 17.5 27.5 20.0 2 12.5 20.5 8.0 17.5 18.7 18.8 3 20.0 14.5 12.5 20.5 Ave. 23.3 a 17.5 a 15.1 a 18.5 a 23 . 1 a 19.4 a Turnips 1 305 192 228 250 225 228 2 262 245 210 210 235 222 3 230 168 228 240 Ave. 265 a 201 b 222 b 233 b 230 b 225 b * Within each row any two means not having letters in common are significantly different at the 5 per cent level by the Duncan test. t Number of plants/ 10 ft row. % Material 3 was not tested at rates above 3,000 gal/acre. month. The material was exposed on the soil surface for 30 days before incorpora- tion into the soil. Sweet corn, tomatoes and sugar beets were planted the first season (April 1967). The second season the entire test area was planted to turnips and followed with a crop of cantaloupes. All five plant species grew vigorously and appeared normal, with no visual symptoms ob- served throughout the growing season that would indicate asphalt toxicity. The germination count for four of the crops is presented in table 6. Except for tur- nips, no differences in germination rates among treatments were obtained. The germination count for the asphalt- treated plots was less than for the non- treated control for the turnip crop; how- ever, this was caused by planting diffi- culties which necessitated replanting rather than by asphalt levels in the soil. No differences in yield were obtained among treatments for the five plant species tested in this study. Soil samples were collected periodic- ally throughout the test. The asphalt con- tent of the soil was determined by spectrophotometric analysis of solvent extracts of the soil by Douglas Oil Com- pany, Paramount, California. The rela- tive asphalt content of the soil at various time intervals during the test is given in table 7. Just prior to the initial planting, the asphalt content of the soil was .053, .081, .139, .156 and .316 g/100 g of soil for treatment rates of 500, 1,500, 3,000, 17] Table 7 THE DEGRADATION OF ASPHALT CONTENT IN THE SOIL Sample Date Amount of materia applied gal/acref Control 500 1,500 3,000 4,500 6,000 grams/ 100 grams of soil Nov. 1966 Dee. 1966... .009 .039 .008 .014 a* .018 a .017a .082 .091 .042 .053 ab .035 a .039 b .178 .098 .081 be .046 a .086 be .155 .139cd .053 a .099 cd .156 d .114 b .112 cd Jan. 1967 Apr. 1967 Jan. 1968 Sept. 1968 .316e .123 b 120d * Any two means not having letters in common for a given sampling date are significantly different at the 5 per cent level by the Duncan test. t Petroleum mulch applied over a 6-month period at a maximum rate of 1,000 gal/acre/month. 4,500 and 6,000 gallons per acre, re- spectively. The nonmulched control soil indicated a background level of .014 g/100 g soil. As shown in table 7, the asphalt content progressively increased with increasing amounts of petroleum mulch applied. The differences in asphalt content in soils from the control and the 500 gallon treatments were not signifi- cant, suggesting that the asphalt was degraded during the 6-month period be- tween application and the first planting date. Soil samples collected nine months later (January, 1968) showed that the asphalt content of the soil for all treat- ments up to the 3,000 gallon per acre rate had decreased to the comparable background reading of the controls. At the higher concentrations (4,500 and 6,000 gallons per acre), the asphalt con- tent was reduced to approximately one- half the original preplant level. Twenty months after the first applica- tion of petroleum mulch, the field was reworked and sampled on the flat ground surface. All of the treated plots showed traces of asphalt residues; however, the Table 8 THE INFLUENCE OF VARIOUS AMOUNTS OF ASPHALT RESIDUE ON THE INFILTRATION RATE OF THE SOIL* Material Sampling time interval Amount of petroleum mulch applied gal/acre 500 1,500 3,000 4,500 6,000 minutes 30 60 120 30 60 120 30 60 120 inches of water /hour 1 .126 .171 .252 .272 .412 .680 .199 .291 .466 .304 .453 .614 .205 .317 .400 .254 .385 .507 .223 .298 .607 .388 .668 1.080 .305 .483 .843 .281 .414 .718 .465 .735 1.120 .373 .574 .916 .170 .255 .395 .701 1.152 1.650 .435 .703 1.022 .177 2 .229 .315 .727 1.147 1.640 .452 .688 .977 Tests made 9 months after petroleum mulch was incorporated and after the removal of one crop. [18 quantities were small. The data suggest that under normal agricultural use, little or no asphalt accumulation should occur by repeated seasonal applications. The four vegetables and sugar beets were not susceptible to asphalt toxicity for the amounts utilized in this test, which would suggest that most crops are not highly susceptible to asphalt mulches. Soil additives frequently alter some physical characteristics of the soil. The infiltration rate of water into the soil was determined nine months after the mulch was incorporated and after the first crop was removed from the test area. Under field conditions these data were difficult to determine because of the extreme variability among samples within treat- ments as well as among replications. In general, there was a trend for increased infiltration rate of water into the soil with the addition of petroleum mulch. The average rate of percolation for the various treatments and materials is given in table 8. Each figure represents an average of 24 determinations. With the exception of the 500 gal/acre rate for Material 2, the average water infiltra- tion rate for the mulched plots was in- creased over the nonmulehed plots. THE INFLUENCE OF PETROLEUM MULCH OVERLAYS ON HERBICIDE PERFORMANCE Petroleum mulch stimulates the germina- tion of weed seeds as well as seeds of crop species. Trials were initiated to evaluate the effectiveness of herbicides in combination with petroleum mulch under furrow irrigation. The following three factors were considered: (1) whether the combination with petroleum mulch modified crop response to the herbicide; (2) whether the combination enhances weed control ; and (3) whether petroleum mulch could serve as a method of herbicide incorporation, i.e., whether a surface application of herbicide covered by petroleum mulch would be equivalent to the standard (under semiarid condi- tions with furrow irrigation) mechani- cally incorporated nonmulch method of herbicide application. Herbicides Herbicides used in trials 1 and 2 EPTC CIPC CDEC Diphenamid Herbicides used in trials 3 and 4 Alanap CDEC CIPC EPTC Bensulide Diphenamid Dacthal Benefin Trifluralin The effect of petroleum mulch alone on the emergence of the weed population is shown in table 9. Trials 1 and 2 (February and April, 1964) were dupli- cate tests initiated on different dates, as were trials 3 and 4 (April, 1965) . When temperatures were cool (Trial 1) pe- troleum mulch stimulated weed seed germination as expected. Trials 2, 3, and 4 were installed when temperatures of the nonmulehed soil were sufficient for weed seed germination, and little or no difference was obtained between mulch and nonmulehed treatments. Because of this variability in temperature, results of each trial must be interpreted separately, [19] Table 9 THE EMERGENCE OF WEEDS FROM CONTROL PLOTS OF 4 HERBICIDE TESTS Trial Date application Rainfall during trial Time after appli- cation Grass weeds Broadleaf weeds Mulch No mulch Mulch No mulch 2/27/64 4/14/64 4/1/65 4/27/65 inches 2.7 0.4 4.7 0.0 weeks 3 4 2 3 5 2 4 Number Number 1 2 3 79.9 68.8 32.0 46.0 195.0 236.0 207.0 42.1 54.4 32.5 40.0 92.0 241.0 181.0 47.1 29.6 47.4 38.8 85.0 209.0 171.0 4.4 5.3 17.2 22.8 94 4 296.0 198.0 Table 10 THE EFFECT OF HERBICIDES, MULCH OVERLAYS, AND MECHANICAL INCORPORATION ON WEED CONTROL AND GERMINATION OF VARIOUS VEGETABLES Trial No. EPTC CIPC CDEC Diphenamid Crop Mulch No Mulch Mulch No Mulch Mulch No Mulch Mulch No Mulch S i S I S I S I S I S I S i S i Grass 1 a a d a+ b a a a c b d a+ a a a a 2 a a d b+ d a+ d a+ a a d a+ d a+ d a+ 1 2 a a a a d d d b d+ d d d b d a b a a d+ c d d c a+ a c a a a d a a+ Corn 1 a a a a a+ d d+ d a a a a a a a+ c 2 a a a a a+ d d+ d a b a a a b a a Cucumber 1 d d d d c+ d d d b+ d a+ d b b a+ d 2 d d c d d c d d d d a+ d d d c d Onion 1 d d 1) a b+ d d+ d a+ d b+ d b b a b 2 d d a+ d d d a+ d a a a+ d a+ d a+ d Tomato 1 a a d d d d d d b a d d a a d d 2 d d a+ d d d d d d a d d a a d a+ Symbols: a = 90-100 per cent control of weeds or percentage of stand of vegetable species b = 80-90 per cent control of weeds or percentage of stand of vegetable species c = 70-80 per cent control of weeds or percentage of stand of vegetable species d = 60 per cent or less control of weeds or percentage of stand + = significant differences at 5 per cent level of probability S = surface applied herbicide I = incorporated herbicide [20] and it is difficult to compare data be- tween trials. The relationship of herbicides, mulch overlays, and mechanical incorporation on weed control and emergence of vari- ous vegetables is shown in table 10. In general, weed control was enhanced by mechanical incorporation both with and without petroleum mulch. The most ap- parent instance of benefit from a mulch overlay is shown with EPTC. Because of the volatility of EPTC, the mulch overlay was apparently effective in preventing volatilization, and hence its performance was equal whether surface-applied under mulch or incorporated. In contrast to these results, without mulch EPTC was rather ineffective when applied to the surface as compared to mechanical in- corporation (grass weed control, trials 1 and 2) . In the one instance where mulch- surface herbicide application was sig- nificantly better for weed control than herbicide incorporation (Trial 1, CIPC), the percentage of stand for both treat- ments was below 60. The importance of rainfall as a factor in influencing herbi- cide performance is clearly shown in comparing some of the results between trials 1 and 2. In trial 1 (2.7 inch rain- fall), Diphenamid performed equally well whether mechanically incorporated Table 11 THE EFFECT OF SURFACE APPLIED HERBICIDES WITH MULCH OVERLAYS, AND NONMULCH MECHANICAL INCORPORATED HERBICIDES, ON WEED CONTROL AND GERMINATION OF VARIOUS VEGETABLES Tri- al No. EPTC CIPC CDEC Diphenamid Crops Mulch Surface No mulch Incorp. Mulch Surface No mulch Incorp. Mulch Surface No mulch Incorp. Mulch Surface No mulch Incorp. Grass 1 a a b a c a+ a a 2 a b d -- a+ a a d -- a+ 3 a b b a b d b c 4 c a c -- a-f d 1) a+ -- d Broad- 1 a+ d d -- a+ a c a a leaf.... 2 a b d — b+ a a c a+ 3 d b d c b b d d 4 c b d c a a d d Corn 1 a a a+ d a a a+ c 2 a a a+ -- d a a a a Cucum- 1 d d c+ -- d b+ -- d b-f d ber 2 el d d d d d d d Onions . 1 d -- a+ b+ -- d a+ -- d 1) b 2 (1 d d-f d a+ d a+ d Toma- 1 a+ d d d b+ -- d a+ d toes .... 2 (1 d d d d d a a Lettuce 3 b+ d I) a a+ -- d a a Canta- loupe 4 d d b+ -- d c+ d b+ -- d Symbols: a = 90-100 per cent control of weeds or percentage of stand b = 80-90 per cent control of weeds or percentage of stand c = 70-80 per cent control of weeds or percentage of stand d = 60 per cent or less control of weeds or percentage of stand -i significant difference at 5 per cent level [21] or not, with and without a mulch overlay, whereas in trial 2 (0.4 inch rainfall) the surface application (both with and with- out mulch) was ineffective. In the first trial, there was enough rainfall to effec- tively incorporate Diphenamid and in the later trial there was not. No added crop injury was incurred as a result of using a herbicide-mulch combination over that with herbicide alone. In most instances, surface applica- tion was less toxic (also gave less weed control) than the incorporation treat- ment. This condition occurred in both mulch combinations and in nonmulch treatments. The comparison of surface applied herbicides with mulch overlays, and non- mulched mechanical incorporated herbi- cides on weeds and vegetables is shown in table 11. Although differences were dependent on the herbicide, in general, the nonmulch incorporated herbicide gave the best weed control. This was particularly noticeable for CIPC. As stated above, with the more volatile herbicides such as EPTC, the data indi- cates that a surface application covered with mulch can be as effective as me- chanical incorporation without mulch. Similar results were reported by Mills, etal. (1968). As in table 10, the crops showed equal or greater tolerance to herbicides applied on the surface with a mulch overlay, than mechanically incorporated without mulch, except for one instance with onions treated with EPTC. From the data available, the general recommendation for weed control in petroleum mulch operations would be to select the most effective herbicide for the crop, apply it in the method for best weed control results, and overlay the soil sur- face with a band of petroleum mulch for temperature and moisture response for the crop. GENERAL CONSIDERATIONS FOR A SUCCESSFUL MULCHING OPERATION Successful results from petroleum mulch depend upon considerations of the fol- lowing: Production areas. Localities which have clear, sunny days during the early planting season will produce best results from petroleum mulching. Types of crops to be mulched. Best results are obtained with warm season crops seeded during cool seasons. Soil preparation. A smooth, fine- textured soil surface, free of clods, debris and uneven areas will provide the re- quired continuous asphalt film for maxi- mum temperature and moisture re- sponses. Mulch concentration and band wiflth. Spray mulch at a concentration of approximately 400-500 gallons per full acre coverage (see concentration chart, figure 3) as a 6-inch band directly centered over the seed row. Dual spray nozzles per row, one spraying forward and one rearward provides best soil coverage. Weed control. Petroleum mulches stimulate germination and growth of weed species, so that herbicides recom- mended for the crop should be used in conjunction with the mulching operation. Handling of the mulch product. Follow the recommendations of the mulch supplier for proper spray equip- ment and procedures, and for handling and storage of the petroleum product. [22] ACKNOWLEDGMENTS Robert Dunning, S. Fugimoto, Miles 0. Hall, Orval D. McCoy, James I. Stillman, Fred L. Whiting. Douglas Oil Company, Standard Oil Company of New Jersey, and Union Oil Company. LITERATURE CITED Cannell, G. H., and C. W. Asbell 1964. Prefabrieation of mold and construction of cylindrical electrode-type re- sistant units. Soil Sci. 97: 108-12. Cannon, M. D. 1965. Thermal environments under synthetic strip mulches. Amer. Soc. Agr. Eng. Trans. 8 (3): 374-76. Frost, K. R. 1966. Shallow strip tillage in seedbed preparation. Amer. Soc. Agr. Eng. Trans. 9(4): 456-57. Frost, K. R. 1968. Application of asphalt-emulsion for early seed germination. Div. Petroleum Chem.. Amer. Chem. Soc, Symposium on New Uses of Asphalt. Preprints 13(4):C53-C58. Honma, S., F. McArdle, J. Carew, and D. H. Dewey 1959. Soil and air temperature as affected by polyethylene film mulches. Quart. Bui. Michigan Agr. Exp. Sta. 40(4) : 834-42.' Lippept, L. F., F. H. Takatori and F. L. Whiting 1964. Soil moisture under bands of petroleum and polyethylene mulches. Proc. Amer. Soc. Hort. Sci. 85: 541-46. Lippert, L. F., F. H. Takatori and M. 0. Hall 1968. Performance of asphalt mulch in relation to surface condition and tempera- ture of the soil. Div. Petroleum Chem.. Amer. Chem. Soc. Symposium on New Uses of Asphalt. Preprints 13(4) : C59-C63. Mills, C. L., A. R. Hamson and C. F. Williams 1968. Effects of combinations of asphalt mulch overlay with selected herbicides on vegetable crops. Div. Petroleum Chem., Amer. Chem. Soc. Symposium on New Uses of Asphalt. Preprints 13(4) : C68-C75. Scudder, W. T., and J. F. Darby 1964. Equipment for the application of plastic and petroleum resin mulches. Proc. Florida State Hort. Soc. 76: 208-13. Takatori, F. H., L. F. Lippert, and F. L. Whiting 1964. The effect of petroleum mulch and polyethylene films on soil temperature and plant growth. Proc. Amer. Soc. Hort. Sci. 85: 532-40. Takatori, F. H., L. F. Lippert, and R. L. Dunning 1968. The influence of asphalt mulch residue accumulation on the soil on vegetable production. Div. Petroleum Chem., Amer. Chem. Soc. Symposium on New Uses of Asphalt. Preprints 13(4) : C64-C67. [23] Waggoner, R. E., P. M. Miller, and H. C. Deroo 1960. Plastic mulching, principles and benefits. Connecticut Agr. Exp. Sta. Bui. 634: 44p. Williams, C. F., A. R. Hamson, and T. A. Reeve 1968. The effects of petroleum mulches on the emergence of vegetable seedlings. Div. Petroleum Chem., Amer. Chem. Soc, Symposium on New Uses of Asphalt. Preprints 13(4) : C76-C83. ABSTRACT The results of many laboratory and field studies with petroleum mulch on soil temperature, soil moisture, crop response, and weed control are summarized. Soil temperature effects were diurnal with large increases during the day and little or no retention of heat during the night. The evaporation rate of the soil was reduced with mulching films. The germination rate and stand for most crops were favorably influenced when grown during periods of adverse weather conditions. The degrada- tion rate of asphalt at concentrations recommended for agricultural use was rapid. A description of petroleum mulch, spray equipment soil preparation, and general considerations for a successful mulching operation have been included. To simplify this information, it is sometimes necessary to use trade names of products or equip- ment. No endorsement of named products is intended nor is criticism implied of similar products not mentioned. 'Sm-3,'71(P214lL)J.F.