PRES 5 Eee CNEL ped POEL rd ong ps i dttestit eee {5 58 Pf te rT ie, ia duis wots SSI SS) Pet ae v. tach 6-00-81 Seth asia z SHAS my V4 5 a 6 STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION NATURAL HISTORY SURVEY DIVISION EXPERIMENTAL FIELD STUDIES ON SHADE TREE FERTILIZATION E. B. Himelick Dan Neely Webster R. Crowley, Jr. Illinois Natural History Survey OCT 5 1965 LIBRARY EXPERIMENTAL FIELD STUDIES ON SHADE TREE FERTILIZATION MUCH OF THE PUBLISHED INFORMATION con- cerning response of trees to the addition of nutrient ele- ments comes from the fields of pomology and forestry, very little from arboriculture. In orchards, the response is usually measured in yields of fruit, which may or may not be related to tree growth. The fertilization studies in forestry have been directed toward improving the growth of seedlings in the nursery or of young trees in plantations. The responses may be quite different from those of estab- lished trees in lawn areas. Recent reviews of field studies on nutrient response in forest trees were prepared by Stoeckeler & Arneman (1960) and the Duke University School of Forestry (Anon. 1959). Foliar application and foliar absorption of nutrients is a relatively new field; this research was reviewed by Boynton (1954) and by Wittwer & Teubner (1959). The fertilization studies in pomology and forestry have little direct application for the arborist and the homeowner, who are interested in maintaining aesthetic appeal of shade trees by improving the color, promoting more vigorous growth, or restoring the condition of trees that have been weakened by disease, insect attack, or unfavorable environ- mental conditions. Early research on fertilization of shade trees was con- ducted for 2 years on American elm and Norway maple by Jacobs (1929) in Kent, Ohio. Jacobs applied a 5.75-8-3 fertilizer to established street trees approximately 2 inches in diameter. His results indicated little difference in benefits between fall and spring treatments but a decided benefit from either treatment. Beilman (1934) reported studies on shade tree feeding at the Missouri Botanical Garden in St. Louis. His recom- mendations are based on observations of response to appli- cations of various fertilizer treatments over several years rather than on controlled, replicated experiments. He con- cluded that the fertilizer formulation 10-8-6 is best for shade trees, which “cannot be over-fed; they require large amounts of food.” Wyman (1936) reported a study on nursery-size pin oaks transplanted into a field maintained under lawn condi- tions. He compared ammo-phos (15-30-0 and 11-46-0) and ammonium sulfate by placing the fertilizers in holes 10 inches deep and 12 inches from the tree trunks on both stony clay and silty clay loam soils. Three years of data show that both fertilizers materially increased tree growth. The ammo-phos produced a greater response than ammoni- This paper is published by authority of the State of Illinois, IRS Ch. 127, Par. 58.12. It is a contribution from the Section of Applied Botany and Plant Pathology of the Illinois Natural History Survey. Dr. E. B. Himelick and Dr. Dan Neely are Associate Plant Pathologists with the Illinois Natural History Survey. Mr. Webster R. Crowley, Jr., is Head of Applied Re- search at the Morton Arboretum, Lisle, Illinois E. B. Himelick, Dan Neely, and Webster R. Crowley, Jr. um sulfate on both soil types; in 2 of the 3 years, the response was greater on the silty clay loam soil than on the other type. Chadwick (1935, 1937, 1940) contributed considerable information on shade tree fertilization practices through his study of a block of 500 American elms, Ulmus ameri- cana L. He recorded 7 years of data (1933-1939) on the results from 12-6-4, 6-6-4, ammonium sulfate, and a mix- ture of ammonium sulfate and superphosphate (or an approximate equivalent) applied in the spring, summer, and fall to the soil surface over the entire area beneath the spread of the branches. Chadwick's study indicated that fall was as favorable as, or more favorable than, other seasons for application of fertilizers and that complete fer- tilizers were more beneficial than nitrogen alone. Chadwick et al. (1950) in a test on Norway maples, Acer platanotdes L., evaluated various methods of fertiliz- ing shade trees. The trees, averaging 1.5 inches dbh at the start of the experiment, had been planted in the test plot in the fall of 1935. They were fertilized in 1941 and again in 1947. Trunk diameters were recorded annually, the last time in 1948. The greatest increase in diameter resulted from surface application of a complete fertilizer to a mulch, 2 to 3 inches deep, of rotted stable manure around each tree. The complete fertilizer alone (without peat or stable manure) produced better results when applied to the surface than when placed in holes made by a drill or crow- bar. There were no significant differences between the other methods of application: fertilizer applied with air or water, or both air and water, in drilled holes, or fertilizer placed in holes made with a crowbar. In plots from which one or more of the nutrient elements had been omitted, nitrogen was considered the limiting element; when phosphorus was added to nitrogen, a greater stimulation resulted than from nitrogen alone. Pirone (1951) reported experiments in New York City with foliar application of nutrients to more than 300 street trees of five species. He noted that the general appearance of treated trees was better than that of un- treated trees. His chemical analyses of leaves from a small number of London plane trees and pin oaks showed more of both nitrogen and phosphorus in leaves from the treated trees than in leaves from the untreated trees. He concluded that both nitrogen and phosphorus can be absorbed directly by leaves and are of benefit when applied as foliar sprays. The investigation reported here was initiated to com- pare and evaluate current shade tree fertilization recom- mendations concerning formulations and methods of ap- plication. It is expected to form the basis for future shade tree research relating soil fertility and tree vigor to certain physiological and pathological diseases. EXPERIMENTAL PROCEDURES IN TREE FERTILIZATION The experimental area (Fig. 1) used in our tests of shade tree fertilization was located on the grounds of the Morton Arboretum near Lisle, Illinois. This area is ap- proximately 25 miles west of Chicago. It has a 2% to 4% slope to the south and 7 to 14 inches of topsoil. The soil is Classified as Andres silt loam (293). An Illinois soil survey report (Wascher et al. 1962) characterized this soil as follows: “Andres is high in or- ganic matter, medium to slightly acid, low in available phosphorus, and about medium in available potassium. Water-holding capacity is high but moisture movement within the silty clay loam till is somewhat slcw.” In a representative profile of Andres silt loam, the surface soil is black to very dark brown friable loam to silt loam, fine crumb to granular structure; 10 to 16 inches thick. The subsurface soil is very dark brown to very dark grayish-brown friable loam to silt loam; weak, very fine subangular blocky structure; 3 to 6 inches th’. The subsoil is very dark grayish-brown to yellowish-brown firm clay loam to sandy clay loam with a few small pebbles; weak, medium subangular blocky structure; neutral; 12 to 20 inches thick. Soil samples collected in November, 1964, from 15 sites in the check areas at 12- and 24-inch depths were analyzed by the Department of Floriculture at the Uni- versity of Illinois using the Bray method. From samples taken at the 12-inch depth, the pH readings averaged 6.81; the phosphorus averaged 14.5 and the potassium 189 pounds per acre. At the 24-inch depth, the pH readings 3 averaged 6.96; the phosphorus averaged 7.2 and the potas- sium 131 pounds per acre. Samples taken in the fall of 1963 at a 6-inch depth averaged 32 pounds of nitrogen per acre. In 1964, the nitrogen analysis at the 12-inch depth ranged from a high of 13 pounds per acre down to a trace. Three species of trees growing on the experimental avea were used in the tests: pin oak (Quercus palustris Muench.), white ash (Fraxinus americana L.), and honey locust (Gleditsia triacanthos L. var. inermis Pursh). The trees had been planted in square blocks with 15- to 20-foot spacing distances between trees and 25 feet between blocks. Each block originally contained 100 trees of a single species. The oak and ash had been transplanted to the experimental area in 1956, the locust in 1957. When transplanted, the oaks were 1 to 3 feet tall, the ashes 4 to 6 feet tall, and 4 the locusts 3 to 4 feet tall. Twelve oaks were planted on the area in 1958 to replace oaks that had died. Since sev- eral locusts were missing, it was necessary to use trees in two blocks to obtain the desired number for the test. All blocks had been planted with Kentucky bluegrass, Poa pratensis L., and a sod had been maintained with occa- sional mowing each summer. In the spring of 1963 when the fertilizer tests were started, the oaks averaged 1.64 inches dbh and 10 feet tall, the ashes 2.94 inches dbh and 14 feet tall, and the locusts 1.74 inches dbh and 10 feet tall. Four methods of application and several fertilizers were used in 16 different combinations (Table 4), each com- bination designated as a treatment. Each block of trees Fic. 1.—Part of plot of pin oak trees in the experimental area used for the investigation reported here. test plots located at the Morton Arboretum, Lisle, Illinois. This is one of the four The picture was taken in April, 1965. 4 was divided into plots, each plot containing five contiguous trees. Each plot received one of the 16 treatments. The treatments were selected at random but in such a way that five trees of each species received one of the 16 treatments. Eighty trees of each species were treated. The remaining trees (14 oak, 12 ash, and 10 locust) received no treatment and served as controls. Several materials were used as sources of nutrient ele- ments in the fertilizer treatments. Ammonium nitrate (33.5-0-0) and urea (45-0-0) were used as sources of nitrogen. When the dry form of NPK was needed, a com- mercial 10-10-10 farm fertilizer was used. When a solu- tion of N, P, and K was required, a commercial water- soluble 23-19-17 (Ra-Pid-Gro) was used. Source materials for the water-soluble fertilizer were urea, ammonium phos- phate, potassium phosphate, and potassium nitrate. When P and K were used in dry form, superphosphate (0-45-0) and muriate of potash (0-0-60) were mixed. For soluble P and K_ treatments, potassium mono-H — phosphate (K,HPO,) was used. The minor elements added were contained in Peters Trace Element Mix. This mix, pre- pared from soluble compounds, contained the following minor elements: Mn 9.0%, Fe 6.0%, Cu 3.0%, Zn 3.0%, B 2.0%, Mo 0.5%, and Mg 0.4%. The type and amount of fertilizer applied to the soil per tree is given in Table 1. The type and amount of fertilizer used per 100 gallons of spray for foliage applica- tion is given in Table 2. The amount of nitrogen added to the soil was maintained at 6 pounds of N per 1,000 square feet. Although the per cent of phosphorus and potassium varied slightly in the various fertilizers, an at- tempt was made to add these elements to the soil at the rate of 6 pounds each of P,O, and K,O (2.64 pounds of P and 4.98 pounds of K) per 1,000 square feet. The 1963 soil treatments and the first foliar spray were made on May 14, 15, and 16. The second foliar spray was applied June 20 and the third on July 23. In 1964, each tree received the same treatment it had received in 1963. The soil treatments in 1964 were made on April 22, 23, and 24. The foliar sprays were applied May 20, June 24, and July 24. A nail was driven into the xylem of each tree approxi- mately 3 feet above the ground, so that it was possible to measure the trunk growth rate at the same tree height on different dates. The original circumference measurements were taken on May 13, 1963. Additional measurements were made October 2, 1963, and October 7, 1964. Because callus growth formed around each nail, the final two meas- urements on all trees were made one-fourth inch above the nails. A visual determination of foliage greenness was made once each summer. Each tree was given a rating of 1 to 5, TABLE 1.—Soil treatments and the rates of application to trees in experimental plots at the Morton Arboretum, Lisle, Illinois, 1963 and 1964. Fertilizer, Elemental Nutrients, Plot Fertilizer Grams Per Tree Amount Per Tree 1,2,3 Ammonium nitrate (33.5-0-0) 812 272g N SIGN Urea (45-0-0) 605 272g N 15 Superphosphate (0-45-0) 605 120g P + muriate of potash (0-0-60) 454 226g K 16 Potassium mono-H-phosphate 544 972 P; 244 2K 9 Commercial 10-10-10 2,724 272g N; 120g P. 226g K 10 Water soluble 23-19-17 1,185 272g N; 99g P. 167g K 12 Commercial 10-10-10 2,724 272g N; 120g P; + Peters Trace Element Mix 85 226g K + minor elements 13 Water soluble 23-19-17 1,185 272g N; 99g P; + Peters Trace Element Mix 85 167g K; + minor elements TABLE 2.—Foliar treatments and amounts used per 100 gallons of spray on trees in experimental plots at the Morton Arboretum, Lisle, Ilinois, 1963 and 1964, Fertilizer, Elemental Nutrients, Plot Fertilizer Grams Per 100 Gallons* Amount Per 100 Gallons 4 Ammonium nitrate (33.5-0-0) 1,557 5222 N 8 Urea (45-0-0) 1,158 5222 N 11 Water soluble 23-19-17 2,270 5222 N; 190g P. 320g K 14 Water soluble 23-19-17 2,270 222 N: 190g P; + Peters Trace Element Mix 340 320g K + minor elements * Oak and locust received approximately 1.5 gallons of spray per tree and ash approximately 2 gallons of spray per tree for each application. a en ee a. ae he based on the following scale: 1, yellow green; 2, light green; 3, green; 4, moderately dark green; and 5, dark green. The 1963 color ratings were made on September 9 and the 1964 ratings on July 24. Each recorded rating was the average of the ratings made by two observers. Precipitation data (Table 3) were obtained from the nearest weather station, at Wheaton College, about 3 miles from the experimental area. In both 1963 and 1964, rain- fall was below average. This shortage was evident during the fall and winter. Spring and summer rainfall was near or above normal. Four currently used methods of fertilizing established trees were included in the tests: surface broadcasting, TABLE 3.—Precipitation data from the Wheaton College weather station, Wheaton, Illinois. Jan. April July Oct. Feb. May Aug. Nov. Year March June Sept. Dec. Total 1963 4.05 10.44 10.30 3.61 28.40 1964 435 9.90 12.42 3.85 30.52 Normal* 6.03 ive) 9.68 6.62 33.44 *Normal is an average of approximately 80 years of data taken from records of weather stations located in the Northeast Climatological Division of Tllinois. Fic. 2.—Electric drill being used to make holes in which dry fertilizer is placed in the soil around trees. The electric-drill method of making holes is more rapid than the punch-bar method, but it requires a heavy-duty drill and a source of electricity. It is especially useful when the soil is dry. 5 placement of dry fertilizer in holes made in the soil, injec- tion of fertilizer solutions into the soil, and foliar feeding. Surface Broadcasting of Fertilizers Since the penetration of phosphorus and potassium into the soil is limited, only nitrogen was tested by surface broadcasting. One of two readily available nitrogen sources, ammonium nitrate and urea, supplied in the pellet form, was broadcast on the soil surface around each tree. The fertilizer required for each tree was weighed and broadcast by hand as uniformly as possible within a circu- lar area having a radius of 514 feet. The area treated was approximately 100 square feet. Most of the root system of each of the treated trees was assumed to be included in this area. Natural rainfall was depended upon to carry the ammonium nitrate and urea into the soil. Placement of Dry Fertilizers in Holes Five fertilizers were evaluated by being applied, in dry form, in holes made in the soil. The fertilizers used were ammonium nitrate, urea, PK, NPK, and NPK plus minor it — rT Fic. 3.—Punch-bar being used to make holes in which dry fertilizer is placed in the soil around trees. elements. In 1963, the soil was sufficiently dry at the time of treatment to require that the holes be made with a drill or a soil profile tube. For the large amounts of NPK or NPK plus minor elements needed, holes 2 inches in diame- ter were made with an electric drill (Fig. 2). For the smaller amounts of N or PK fertilizers required, holes were made with a soil profile tube three-fourths inch in diameter. In 1964, the soil was wet at the time of treat- ment and the punch-bar method of making holes was used (Fig. 3 and G6). The amount of fertilizer for each tree was weighed and distributed equally in 18 holes around each tree (Fig. 4); 6 each hole was 12 to 15 inches deep. Six of the holes were made in a circle having a radius of approxima ely 21 feet. The remaining 12 holes were distributed in a circle having a radius of 414 feet, sufficient to include most of the root system of the treated tree. After the fertilizers had been applied, no attempt was made to fill the holes, and no supplemental watering was done. Injection of Liquid Fertilizers The five kinds of fertilizers applied in holes were ap- plied also by the soil injection method. Solutions of the five fertilizers were injected 18 to 24 inches deep with a soil needle (Fig. 5 and 6) and a hydraulic sprayer at 150 pounds pressure. The volume of fertilizer used at each injection point was carefully regula*ed by opening the soil needle valve for a predetermined number of seconds. Fif- teen gallons of a fertilizer solution were used per tree. The 15 gallons of liquid fertilizer were evenly divided among 14 injection points about each tree. Four injections were made on four sides approximately 2! feet from the tree trunk, and the remaining 10 injections were made in a Fic. 4.—Diagram illustrating the placement of holes around an experimental tree fertilized by the dry-fertilizer-in-holes method. by a hardened steel axle on which are welded a foot rest and a handle. The soil needle is like types available commercially. FG. 5.—Hydraulic injection of liquid fertilizer at 150 pounds pressure through a soil needle. Fic. 6.—Punch-bar (left) and soil needle designed and used the authors of this publication. The punch-bar is made of 7 the NPK source, and Ra-Pid-Gro with additional minor elements added was used as the NPK plus trace elements. All of these materials are water soluble. Because of possible foliage burn, the amount of material applied as a spray was necessarily less than that used for the soil applications. Ra-Pid-Gro was used at the rate of 5 pounds per 100 gallons of water currently recommended for foliar applica- tion. For the NPK plus minor elements, three-fourths pound (340 grams) of Peters Trace Element Mix per 100 gallons of spray was added to Ra-Pid-Gro. The concen- tration of N used was the same in all of the foliar treat- ments. The spray solution was applied to the foliage with a hydraulic sprayer (Fig. 7) until the solution began to drip from the foliage. No effort was made to prevent run- off to the soil. Three foliar sprays, the first one the third week of May, were applied at approximately 1-month inter- vals each year of the experiment. All of the foliar sprays were applied between 8 AM and 12 noon on days having little or no wind. Fic. 7.—Foliage application of a liquid fertilizer. A hydraulic sprayer is used in this operation. The solution was applied until it EXPERIMENTAL RESULTS OF TREE FERTILIZATION began to drip from the foliage. : ; F ; The increases in circumference of the experimental circle approximately 414 feet from the trunk. The 225 shade trees given the various fertilizer treatments tested gallons of liquid fertilizer required for each treatment during 1963 and 1964 are shown in Table 4. Each cir- (three tree species, five trees each) were prepared in a cumference figure shown for the treated trees is the average 300-gallon hydraulic sprayer tank having an agitator. obtained from five contiguous trees in a plot. The circum- ference figure for each control group is an average for un- Foliar Applications of Fertilizers treated trees of the species represented: 14 pin oaks, 12 In a series of foliar applications, ammonium nitrate white ashes, 10 honey locusts. The totals for the 2 years was compared with urea, and NPK alone was compared were analyzed statistically, and significant differences be- with NPK plus trace elements. Ra-Pid-Gro was used for tween treatments at the 1% and 5% levels were noted. TABLE 4.—Average increases in growth of three deciduous hardwoods following various fertilization treatments at Lisle, Illinois, 1963 and 1964. Each average for treated trees represents five contiguous trees in a plot. The averages for untreated (control) trees are based on 14 pin oaks, 12 white ashes, and 10 honey locusts. Circumference Increase (0.001 Foot) Application Pin Oak White Ash Honey Locust Fertilizer Plot Method 1963 1964 Total 1963 1964 Total 1963 1964 Total NH,NO; 1 Surface 127 167 294** 132 129 261** 139 166 S05 2 Holes 135 173 308** 94 118 212 80 116 196* 3 Solution 145 172 SBT fea 105 107 212 123 176 299** 4 Foliar 92 135 227 105 85 190 63 56 119 Urea 5 Surface 129 165 294** 95 108 203 128 148 276" * 6 Holes 131 176 307** 105 110 215 65 97 162 7 Solution 120 152 PAT ips 130 143 213" 111 137 248* * 8 Foliar 94 116 210 92 92 184 54 50 104 NPK 9 Holes 109 161 270* 108 109 217 73 88 161 10 Solution 166 203 369* * 127 134 ZO 85 102 187 * 11 Foliar 82 122 204 80 70 150 49 19 98 NPK + trace 12 Holes 107 200 307=* 97 118 215 76 100 176 elements 13 Solution 127 166 293°** 109 121 230* 106 118 224*°* 14 Foliar 69 119 188 97 103 200 56 52 108 PK 15 Holes 9) 117 208 82 83 165 i8 50 98 16 Solution 90 112 202 71 64 135 56 53 109 Controls 17 No treatment 84 116 200 88 78 166 69 67 136 Least significant difference at the 5% level > )p a 63.9 19.3 Least significant difference at the 1% level 13.5 85.0 65.6 * Significant at the 5% level. ** Significant at the 1% level A summary of the results from four different methods of applying nitrogen-containing fertilizers to the experi- mental shade trees is given in Table 5. These data were obtained by averaging data from the nitrogen-containing treatments listed in Table 4. Data from treatments 15 and 16, in which only P and K were used, are not included in TABLE 5.—Average increases in growth of three deciduous hardwoods during a 2-year period of nitrogen fertilization treat- ments at Lisle, Illinois, 1963 and 1964. Circumference Increase (0.001 Foot) Method of Pin White Honey Application Plot Oak Ash Locust Surface application 1,5 294 232 291 Dry in holes 2,6,9,12 298 215 174 Solution injection 3,7,10,13 313 244 240 Foliar spray 4,8,11,14 207 181 107 No treatment 1 200 166 136 TABLE 6.—Average increases in growth of three deciduous hardwoods during a 2-year period of soil fertilization treatments at Lisle, Illinois, 1963 and 1964. (Trees given foliar applications are not included. ) Circumference Increase (0.001 Foot) Pin White Honey Fertilizer Plot Oak Ash Locust NH.NOs il pes) 306 228 267 Urea 5,6,7 291 230 229 NPK 9,10 320 239 174 NPK -+ trace elements 12,13 300 AP) 200 PK 15,16 205 150 104 No treatment 7) 200 166 136 Table 5. The amount of N applied per tree was the same for each method of application except the foliar spray. Trees given the foliar spray did not make substantially greater growth than the unfertilized trees (Table 5). Growth differences between these two groups of trees were no greater than would be expected from normal biological variation. The three methods of soil application appeared to be about equally effective on pin oak. On white ash, the solution injection method produced a noticeably greater response than the hole method of soil application. On honey locust, the surface application produced the greatest response. Of the three methods of soil application, surface application produced the greatest amount of total growth on trees of the three species combined. The precipitation that occurred from April through September in both 1963 and 1964 (Table 3) was adequate to carry the surface- applied fertilizer into the soil. The response of the experimental shade trees to five fertilizers applied to the soil is summarized in Table 6. The data were obtained by averaging data from the soil treatments included in Table 4. Growth of only those trees receiving nitrogen treatments was significantly better than growth of the untreated trees. The application of phosphorus and potassium to the soil did not bring about a significant growth response; nor did a combination of phosphorus, potassium, and nitrogen produce a response that was significantly greater than that produced by nitro- gen alone. The addition of minor elements to NPK pro- duced no significant growth response. Ammonium nitrate and urea appeared to be about equally effective as nitrogen sources. The addition of nitrogen to the soil resulted in TABLE 7.—Color ratings (1 to 5)+ of three deciduous hardwoods following various fertilization treatments at Lisle, Illinois, 1963 and 1964. Each color rating for treated trees represents the average for five contiguous trees in a plot. Method of Pin Oak White Ash Honey Locust Fertilizer Plot Application 1963 1964 1963 1964 1963 1964 NH,NOs 1 Surface A So Rts 4.3* 4.9** 432% 4.6** 72 Holes 3.8 yin 3.8 4.3* 3.8 3.9* 3 Solution 4.0* 4.4** 3.6 4.0 4.0* 502* 4 Foliar 2.8 3.4 31) Bal 3D 3.3 Urea 5 Surface 4.0* 3.4 3.5 3.2 4.8** 5.08* 6 Holes 4.0* 3.4 3.4 3.4 4.0* SU hot 7/ Solution 3:2 3.5 3.7 4.1 4.0* 4.8** 8 Foliar 2.8 4.9** 3.4 4.1 3.0 3.5 NPK 9 Holes 3.8 4.5** 3.8 4.1 3.6 4.0** 10 Solution 4.8* 5.0" 3.9 4.2* 3.9F 0S 11 Foliar 3.0 3.5 3.0 Bee. 3.4 3.4 NPK + trace 12 Holes 4.2** 50s" 303 4.0 Ae 43%* elements 13 Solution 4.8** Ae 3.7 4.3* re Road 4.3** 14 Foliar 3.2 3.6 3.6 3.8 33 32 PK 15 Holes 3.0 4.6** 33 3.7 3.3 3.7 16 Solution 3.2 3.6 3.0 3.7 3.0 33 Controls 17 No treatment 3.1 3.5 3.5 3.2 3.3 3.2 Least significant difference at the 5% level 0.73 0.58 0.78 0.91 0.56 0.54 Least significant difference at the 1% level 0.97 0.77 1.04 1.21 0.75 0.72 ; Color rating 1, yellow green; 2, light green; 3, green; 4, moderately dark green; 5, dark green. * Significant at the 5% level. ** Significant at the 1% level. Sy TABLE 8.—Color ratings (1 to 5)7¥ of three deciduous hardwoods during a 2-year period of fertilization treatments at Lisle, Illinois. Each color rating for treated trees represents the average for five contiguous trees in a plot. Method of Pin Oak White Ash Honey Locust Application Plot 1963 1964 1963 1964 1963 1964 Surface 115) 43 4.1 ahs, 4.1 4.6 4.8 Holes 2,6,9,12 4.0 44 3.6 4.0 3.9 4.3 Solution 3,7,10,13 4.2 4A a7 4.2 4.0 4.8 Foliar 4,8,11,14 3.0 3.8 3.4 3.6 ah) 3.4 No treatment 17 Spl 3.5 2h) ee she) a? 7 Color rating: 1, yellow green; 2, light green; 3, green; 4, moderately dark green; 5 dark green. TABLE 9.—Color ratings (1 to 5)* of three deciduous hardwoods during a 2-year period of fertilization treatments at Lisle, Illinois. Each color rating tor treated trees represents the average for five contiguous trees in a plot. Pin Oak White Ash Honey Locust Pertilizer Plot 1963 1964 1963 1964 1963 1964 NH.NOs 15255 4.1 4.6 3:9 4.4 4.0 4.5 Urea 5,6,7 ahy/ 3.4 3.5 3.6 43 4.9 NPK 9,10 4.3 4.8 3.9 4.2 3.8 4.5 NPK + trace 12,13 45 4.9 3.6 4.2 4.2 4.3 elements PK 15,16 ay) 4.1 3.2 3.7 3.2 3.5 No treatment 17 ap 3.5 3.5 3.2 3:3 Sie + Color rating: 1, growth that, measured by circumference increase, was con- siderably greater than growth of the controls: 52% greater in the pin oak, 39% greater in the white ash, and 73% greater in the honey locust. The color data for the fertilizer treatments of the three tree species in the 1963 and 1964 tests are shown in Table 7. These data were analyzed statistically. The color re- sponse to the various methods of treatment is presented in Table 8. Nitrogen fertilizers applied to the soil surface, in holes made in the soil, or as solutions injected into the soil, produced a foliage color that was significantly darker than foliage color of the trees receiving no treatment. Dur- ing the 2-year test, the solution injection and surface broadcast methods appeared slightly better than the soil- hole method. The foliage color of the trees receiving foliar fertiliza- tion was not significantly better than the foliage color of the untreated trees. In the first year of the experiment, no difference in color of foliage could be detected between the trees receiving foliar treatments and the untreated trees. In the second year, the foliage of all three tree species receiving foliar fertilization appeared slightly darker in color than foliage of the untreated controls. However, the response to foliar fertilization was not nearly as marked as the response obtained from any one of the three soil fertilization methods. A comparison of the color responses to the various fertilizers tested is presented in Table 9. Only those trees receiving fertilizer treatments containing nitrogen had leaves that were significantly darker green in color than leaves of the untreated controls. There was little or no yellow green; 2, light green; 3, green; 4, moderately dark green; 5 dark green. color response to phosphorus and potassium applied to the soil. The addition of phosphorus and potassium to nitrogen sources did not produce a color response that was greater than that produced by nitrogen alone. The addition of minor elements to NPK produced no measurable color response. Ammonium nitrate as a source of nitrogen ap- peared to give a darker green color to leaves of oak and ash than did urea; on locust, urea appeared more effective than ammonium nitrate in producing the darker color. TOXICITY OF FERTILIZERS TO BLUEGRASS Because some of our experiments showed that surface applications of nitrogen fertilizers constituted a practical and economical method for fertilizing established shade trees, we conducted additional experiments to determine the rates at which these applications could be made without injuring the grass that is commonly found under and around such trees. Wyman (1936) reported a 2-year test on the applica- tion of ammonium sulfate (20-0-0) to a lawn at rates as high as 20 pounds of N per 1,000 square feet. He found that on dormant Kentucky bluegrass, when precipi- tation was ample, no injury resulted from ammonium sul- fate applied at rates of 10 pounds of N per 1,000 square feet and no serious injury at rates as high as 16 pounds. After the grass had started to grow, 4 pounds of N per 1,000 square feet were applied without injury to grass; 10 pounds per 1,000 square feet caused considerable burn- ing but left some grass green. In tests at the Morton Arboretum, we observed no injury to the Kentucky bluegrass, Poa pratensis L., growing 10 beneath the oak, ash, or locust trees treated by surface application with urea or ammonium nitrate at the rate of 6 pounds of N per 1,000 square feet. Also, we observed no injury to grass when the fertilizer was applied dry in holes or injected into the soil in solution. Since such variables as time of application, rate of application, and the presence or absence of moisture droplets on the grass blades were not investigated in the Morton Arboretum tests, we included these variables in a series of fertilizer toxicity tests on a lawn near Urbana, Illinois, in the spring and summer of 1964. The lawn of a farm residence 1 mile south of Urbana was used in this study. The lawn was predominantly Ken- tucky bluegrass. It had no history of previous fertiliza- tion. The grass was regularly cut throughout the test to a height of approximately 3 inches. Rain provided the only source of water except in one of the tests in which the grass was sprinkled to simulate a heavy dew. A lawn fertilizer spreader, 20 inches wide and typical of the push type commonly used by homeowners (Fig. 8), was cali- brated to spread 3 pounds of N per 1,000 square feet of soil surface for each of the five fertilizers used in this test. The five fertilizers applied were ureaform, urea, 10-10-10, ammonium nitrate, and ammonium sulfate. Each fertilizer was applied at rates of 3, 6, 9, and 12 pounds of N per 1,000 square feet on April 15, May 15, and July 30 in bands 20 inches wide and 20 feet long. The 6-pound rate required two applications at the 3- pound rate; the 9-pound rate required three applications; and the 12-pound rate required four applications. An additional test was made on May 15 and July 30 to com- pare the effect of applying fertilizers to wet grass. For this test, a strip of lawn 10 feet long was sprinkled with water immediately prior to applying the 20-inch-wide band of fertilizer. Fic. 8.—Surface application of dry fertilizer. A common lawn fertilizer spreader may be used in applying fertilizer to either grass or trees. Observations were made 4 and 7 days after each appli- cation, and the phytotoxicity of each application was rated on a scale of 0 through 7 (Table 10). No injury was recorded for the April 15 applications. Some injury re- sulted from several of the May 15 and July 30 applications. Ureaform caused no observable injury at any time, or in any amount used, on either dry or wet grass. Urea used TABLE 10.—Phytotoxicity ratings (1 to 7)? of five fertilizers applied to Kentucky bluegrass at Urbana, Illinois, 1964. Pounds of N Per Applied to Dry Grass Applied to Wet Grass Fertilizer Per Cent N 1,000 Square Feet April 15 May 15 July 30 May 15 July 30 Ureaform 38.0 12 0 0 0 0 0 9 0 (0) 0 0 0 6 0 0 0 0 0 3 0 0 0 0 0 Urea 45.0 12 0 2 0 4 0 9 0 l 0 3 0 6 0 0 0 1 0 3 0 0 0 0 0 10-10-10 10.0 12 0 2 0 7 4 9 0 0 0 6 2 6 0 0 0 >} 2 3 0 0 0 4 0 NH.NOs 33.5 12 0 3 6 7 6 9 0 2 6 5 6 6 0 0 i 4 rT 3 0 0) 2 2 2 (NH,) SO, 21.0 12 0 2 0 6 2 9 0 2 0 6 2 6 0 0 0 j 2 3 0 0 0 0 0 + Phytotoxicity ngs based on injury to Kentucky bluegrass: 0, none; 1, very slight; 2, slight; 3, slight to moderate; 4, moderate; 5, moderate oO severe; 6, severe; 7, very severe. at the rate of 6 pounds of N per 1,000 square feet caused no injury when applied on dry grass and only very slight injury when applied on wet grass. The 10-10-10 formula- tion caused no injury when applied on dry grass at rates of 9 pounds or less of N per 1,000 square feet; at even 3 pounds of N on wet grass it caused some injury. Both ammonium nitrate and ammonium sulfate were safely applied in the spring at 6 pounds of N per 1,000 square feet. Ammonium nitrate applied in July, when the soil was dry, caused injury at all application rates. However, all the fertilizer burn was temporary. No burn from any treatment was evident on October 1. The probable explanation for lack of injury from the first (April 15) fertilizer applications may be found in precipitation data for the area. Rain fell on 5 of the 7 days following the April 15 applications; precipitation recorded by the Urbana weather station for these days totaled 5.92 inches. Rain fell on 3 of the 7 days following the May 15 application; precipitation totaled 0.10 inch. No precipitation occurred during the 7 days following the July 31 application. Rainfall following heavy applications of fertilizer may reduce the phytotoxic effect of the fertilizer. Under normal lawn conditions, the fertilized area should be heavily watered with a lawn sprinkler. Under the conditions of this lawn fertilization test, it appeared that most nitrogen-containing fertilizers can be safely broadcast on dry Kentucky bluegrass at the rate of 6 pounds of N per 1,000 square feet. Moderate burn of grass blades may occur when fertilizer is applied at this rate on wet grass. Higher rates of application are possible if fertilization is followed within a few hours by precipitation sufficient to wash the fertilizer off the leaf blades. Supple- mental watering would undoubtedly lessen the amount of injury that might occur following heavy applications of N. Even in plots receiving the heaviest applications of fer- tilizers, all signs of burning disappeared a month after the fertilizer had been applied. DISCUSSION Recommendations for fertilization of shade trees should specify time of fertilization, type and amount of fertilizer to be used, and method or methods of application. Time of fertilization and amount of fertilizer are variables not investigated in our tree study reported here. All of our fertilizer treatments were applied in the spring. All of our experimental trees received fertilizer at the rate of 6 pounds of N, P.O,, or K,0 per 1,000 square feet of area. This rate was selected since it is approximately equivalent to the amount of fertilizer commonly recom- mended for established shade trees and is a rate known to be nontoxic to grass and trees when the fertilizer is ap- plied dry in holes. Formulas that have been used for determining the amount of fertilizer to be applied are varied, and some of them are difficult for the average arborist to follow. One of these formulas employs the sum of the following: the height of the tree in feet, the branch spread in feet, and the trunk circumference in inches 1 foot above the soil il line. The total of these figures is the number of pounds of 10-8-6 fertilizer to apply in holes. The most common formula now used is based on the diameter of the tree trunk at breast height. Trees of 6 inches dbh or larger receive one-half pound of nitrogen per inch of trunk diame- ter; smaller trees receive one-fourth pound of nitrogen per inch of trunk diameter. Another formula specifies 3 pounds of a balanced fertilizer per inch of trunk diameter. Wikle (1963), in a discussion of shade tree fertiliza- tion, emphasized the large differences between various application rates that are based on trunk diameter. He recommended that the rates be based on the area of soil to be treated, not on trunk diameter. We agree with his recommendation. The basic reason for application of fer- tilizer is to supplement the nutrients naturally available in the soil occupied by the tree roots, which, for most species, extend at least as far as branch spread. Such a recommendation greatly simplifies the problem of deter- mining the amount of fertilizer to be applied. The answer to the question, “Should I or shouldn't I fertilize this tree?” depends on the answers to a number of other questions. What is the soil type? Has the char- acter of the soil type been changed by previous manage- ment practices? Will the use of nitrogen in a fertilizer give a measurable growth response? Will the addition of other soil elements to the fertilizer give additional growth response? Is the tree of such an age and species that it will respond to the use of fertilizer? Will increased soil fertility resulting from use of fertilizer prevent or at least retard tree decline or dieback from certain physiologi- cal or pathological diseases? Much research must be done before these questions can have adequate answers. To some of the questions, research already reported has given only partial answers, and, to other questions, conflicting answers. Our use of nitrogen-containing fertilizers on pin oak, white ash, and honey locust in northern Illinois resulted in an increase in tree circumference that was 39% to 73% greater than the increase for untreated trees. To what extent certain other tree species will respond to fertilizers containing nitrogen or other nutrient elements can be determined only through additional controlled experimenta- tion. In our northern Illinois tests, significant growth response was obtained from nitrogen and from no other nutrient element. In Ohio and New York tests, growth response was reported from use of nitrogen and additional growth response when phosphorus was added to nitrogen. The method used in applying fertilizers is especially important because it determines to a great extent the cost of the operation and the ease with which it is accomplished. The drilled hole method and the solution injection method are relatively expensive, for they require considerable time and expensive equipment. The punch-bar method requires a great amount of labor and time. The surface broadcast method is fast and requires only that equipment already owned by most gardeners or arborists. In our tests, the tree response to nitrogen applied to the soil surface was comparable to the response to nitrogen placed in the soil. 12 Foliar applications of nutrients for tree fertilization ap- pear to have only limited usefulness. In our tests, trees given the foliar spray did not make substantially greater growth than unfertilized trees, and the color of the foliage of the treated trees was not significantly better than that of unfertilized trees. Several considerations favor shade tree fertilization. The cost of the fertilization is negligible in comparison with the high aesthetic value homeowners place upon their trees. Lawns are not injured by the fertilization; in fact, the growth of grass is stimulated by the use of fertilizers applied at rates required to obtain good growth in trees. Trees of some species that have few desirable qualities other than that they grow rapidly are now planted by some homeowners and municipalities because quick replacement of shade is demanded. With additional information on shade tree fertilization, it should be possible to make greater use of some tree species that heretofore have not been used extensively because they are considered slow- growing. Some of these species may be used as replace- ments of American elms killed by the Dutch elm disease. Slow-growing tree species having otherwise desirable char- acteristics may be planted and, through fertilization, stimu- lated to grow faster. ACKNOWLEDGMENTS Acknowledgments are made to staff members of the Illinois Natural History Survey: Dr. J. Cedric Carter, who, as Plant Pathologist and Head of the Section of Applied Botany and Plant Pathology, provided administrative su- pervision and made a critical review of the manuscript. James S. Ayars, Technical Editor, edited the manuscript, Wilmer D, Zehr, Assistant Technical Photographer, made most of the photographs for this publication, Dr. J. L. Forsberg, Plant Pathologist, made others, and William L. Taylor, Assistant Technical Editor, prepared the drawing for Fig. 4. Webster R. Crowley, Jr., provided Fig. 1. Special thanks are given to Gary L. De Barr, Research Assistant, for assistance in a portion of the field work, and to Mrs. Betty Nelson, who typed the manuscript. The manuscript has benefited from the reviews of Dr. J. B. Gartner, Professor of Floriculture, Horticulture Depart- ment, University of Illinois, and Dr. S. W. Melszed, Pro- fessor of Soil Chemistry, Agronomy Department, Univer- sity of Illinois. ABSTRACT Fertilization experiments were carried out in 1963 and 1964 on pin oak, white ash, and honey locust in block plantings established for 7 years at the Morton Arboretum, Lisle, Ilinois. Sixteen fertilizer treatments (each of the treatments a different combination of fertilizer and method of application) were used on each tree species. Four methods of application were used: surface broadcasting, placement of dry fertilizers in holes made in the soil, in- jection of liquid fertilizers into the soil, and spraying of foliage. The following nutrient elements or combinations of elements were used: N, PK, NPK, and NPK plus minor or trace elements. The addition of nitrogen to the soil at the rate of 6 pounds per 1,000 square feet resulted in tree circumference increases greater than the increases in untreated controls: 39% greater in white ash, 52% greater in pin oak, and 73% greater in honey locust. The application of phos- phorus and potassium to the soil did not bring about a significant growth response; nor did a combination of phosphorus, potassium, and nitrogen produce a response that was significantly greater than that produced by nitro- gen alone. The addition of minor elements to NPK produced no significant growth response. The three methods of soil application appeared to be about equally effective, with minor variations among the tree species. Surface application produced the greatest amount of total growth on trees of the three species con- sidered together. Foliar sprays did not produce a sub- stantially greater growth than the growth of unfertilized controls. LITERATURE CITED ANONYMOUS. 1959. Mineral nutrition of trees, a symposium. Duke Univ. School Forest. Bul. 15. 184 p. BEILMAN, A. P. 1934. How to feed a shade tree. Missouri Bot. Garden Bul. 22:113-126. (Article signed merely A.P.B.) BOYNTON, DAMON. 1954. Nutrition by foliar application. Ann. Rev. Plant Physiol. 5:31-54. CHADWICK, L. C. 1935. The fertilization of shade trees in the nursery. Amer. Soc. Hort. Sci. Proc. for 1934, 32:357-360. . 1937. Fertilizer trials with shade trees in the nursery. Amer. Soc. Hort. Sci. Proc. for 1936, 34:664—668. . 1940. Fertilization of woody ornamental plants. Ohio Agr. Exp. Sta. Bimonthly Bul. 25:89-96 , PAUL E. TILFORD, AND CHARLES F. IRISH. 1950. A study of some methods of fertilizing shade trees. Amer. Soc. Hort. Sci. Proc. for 1949, 55:519-526. Jacosps, HOMER L. 1929 Fertilization of shade trees. Part I: Fall vs. spring fertilization. Davey Tree Expert Co. (Kent, Ohic) Res. Dep. Bul. 4. 28 p. PIRONE, P. P. 1951. Foliage application of nutrients. National Shade Tree Conf. Proc. 27:23-35 STOECKELER, JOSEPH H., AND HAROLD F. ARNEMAN. Fertilizers in forestry. Advances in Agron. 12:127-195. WASCHER, H. L., P. T. VEALE, AND R. T. ODELL. 1962. Will County soils. Ill. Agr. Exp. Sta. Soil Rep. 80. 108 p. WIKLE, JACK. 1963. Some comments and questions on soil improvement and fertilization for shade trees. Arborist's News 28 (8-9) :61-69. WitTwer, S. H., AND F. G. TEUBNER. 1959. Foliar absorption of mineral nutrients. Ann. Rey. Plant Physiol. 10:13-32. WYMAN, DONALD. 1936. Growth experiments with pin oaks which are growing under lawn conditions. Cornell Univ. Agr. Exp. Sta. Bul. 646. 23 p. 1960. (L0814—6M—4-65) cfs 14 eS a) eee oe ee Sn baa sot a Sas Sigs: : . UR tees : a* . ; : re x Cary oN gC RAL EAD has: ee Sie