Bulletin ILLIN-OIS TsLtxxi^SkJ. Histo]:*3r SvLjr-vey NATURAL iiiSIORr MiiX APR 2 2 1971 lippnoY Fertilization of Establislied Trees: A Report of Field Studies Neely I. Himelick ster R. Crowley, Jr. E OF ILLINOIS KRTMENT OF REGISTRATION AND EDUCATION URAL HISTORY SURVEY DIVISION lANA, ILLINOIS m^ ^tois VOLUME 30, ARTICLE 4 SEPTEMBER, 1970 ILLINOIS ^a^tuira,! Histo]:*3r Swi^^ey SXJLLETIN Fertilization of Established Trees: A Report of Field Studies Dan Neely E. B. Himelick Webster R. Crowley, Jr. ATE OF ILLINOIS EPARTMENT OF REGISTRATION AND EDUCATION ATURAL HISTORY SURVEY DIVISION RBANA, ILLINOIS VOLUME 30, ARTICLE 4 SEPTEMBER, 1970 STATE OF 1L1.INOIS DEPARTMENT OF REGISTRATION AND EDUCATION BOARD OF NATURAL, RESOURCES AND CONSERVATION William H. Robinson, Chairman; Thomas Park, Ph.D., Biology; L. L,. Sloss, Ph.D., Geology; Roger Adams, Ph.D., D.Sc, Chemistry; Robert H. Anderson, B.S.C.E., Engineering ; Charles E. Olmsted. Ph.D., Forestry; W. L. Everitt, E.E., Ph.D., Representing the President of the University oj Illinois; Roger E. Beyler, Ph.D., Representing the President of Southern Illinois VniversitM. NATURAL HISTORY SURVEY DIVISION. Urbana, Illinois SCIENTIFIC AND TECHNICAL STAFF George Sprugel, Jr., Ph.D., Chief Alice P. Campbell, B.A., Secretary to the Chief Section of Economic Entomology William H. Luckmann, Ph.D., Entomologist and Head Willis N. Bruce, Ph.D., Entomologist Wayne L. Howe, Ph.D., Entomologist Stevenson Moore, III, Ph.D., Entomologist, Howard B. Petty, Ph.D., Entomologist, Ex- James E. Applebt, Ph.D., Associate Entomolo- gist Edward J. Armbrust, Ph.D., Associate En- tomologist Marcos Kogan, Ph.D., Associate Entomologist Joseph V. Maddox, Ph.D., Associate Entomolo- gist Ronald H. Meyer, Ph.D., Associate Entom,olo- gist Robert D. Pausch, Ph.D., Associate Entomolo- gist Ralph E. Sechriest, Ph.D., Associate Ento- mologist George L. Godfrey, Ph.D., Assistant Entomolo- gist Clarence E. White, B.S., Assistant Entomoto- ijist Keun S. Park, M.S., Assistant Chem,ist Si'e B. Watkins, Supervisory Assistant Donald E. Kuhlman, Ph.D., Instructor, Exten- sion RoscoE Randell, Ph.D., Instructor, Extension Tim Cooley, M.A., Assistant Specialist, Exten- sion Jean G. Wilson, B.A.. Supervisory Assistant Ketl'RAh Reinbold, M.S., Research Assistant Stephen Roberts, B.S., Technical Assistant Douglas K. Sell, B.S., Technical Assistant Thomas T. Taylor, B.S., Technical Assistant John T. Shaw, Technical Assistant Section of Wildlife Research Glen C. Sanderson, Ph.D., Wildlife Specialist and Head FRANK C. Bellrose, B.S., Wildlife Specialtst Richard R. Graber, Ph.D., Wildlife Specialist Harold C. Hanson, Ph.D., Wildlife Specialist William L. Anderson, M.A., Associate Wild- life Specialist W. W. Cochp^n, Jr., B.S., Associate Wildlife Specialist William R. Edwards, M.S., Associate Wildlife Jack A. Ellis, M.S., Associate Wildlife Spe- cialist Ronald F. Labisky, Ph.D., Associate Wildlife Specialist Stanley L,. Etter, M.S., Assistant Wildlife Specialist Robert E. Greenberg, M.S., Assistant Wildlife Specialist a. Blair Joselyn, M.S., Specialist George B. Rose, Ph.D., Assistant Wildlife Spe- cialist David R. Vance, M.S., Assistant Wildlife Spe- cialist Ronald L. Westemeiee, B.S., Assistant Wild- life Specialist Ronald E. Duzan, Technical Assistant Mary Ann Kjos. Technical Assistant Helen C. Schultz, M.S., Technical Assistant Eleanore Wilson, Technical Assistant Robert D. Crompton, Field Assistant Assistant Wildlife Section of Botdny and Plant Pathology J. Cedric Carter, Ph.D., Plant Pathologist and Head Robert A. Evers, Ph.D., Botanist jQNius L. Forsberg, Ph.D., Plant Pathologist Eugene B. Himelick, Ph.D., Pla/iit Pathologist R. Dan Neely, Ph.D., Plant Pathologist D. F. Schoeneweiss, Ph.D., Associate Plant Pathologist J. IjELand Crane, Ph.D., Assistant Mycologist Walter Hartstirn, Ph.D., Assistant Plant PatJwlogist Betty S. Nelson, Technical Assistant Gene E. Reid, Technical Assistant Section of Faunistic Surveys and Insect Identification Philip W. Smith, Ph.D., Taxonomist and Head Wallace E. LaBerge, Ph.D., Taxonomist Milton W. Sanderson, Ph.D., Taxonomist Lewis J. Stannard, Jr., Ph.D., Taxonomist Robert W. Poole, Ph.D., Assistant Taxonomist John D. Unzicker, Ph.D., Assistant Taxono- mist Donald W. Webb, M.S., Assista/nt Taxonomist Bernice p. Sweeney, Technical Assistant Section of Aquatic Biology George W. Bennett, Ph.D., Aquatic Biologist and Head D. Homer Buck, Ph.D., Aquatic Biologist R. Weldon Larimore, Ph.D., Aquatic Biologist William C. Starrett, Ph.D., Aqttatic Biologist Robert C. Hiltibran, Ph.D., Biochemist William F. Childers, Ph.D., Associate Aquatic Biologist Donald F. Hansen, Ph.D., Associate Aquatic Biologist Richard J. Baur, M.S., Research Assistant Dennis L. Dooley, Technical Assistant Mary Frances Martin. Technical Assistant C. Russell Rose, Field Assistant Warren IT. Brigi-iam, M.S., Junior Technical Assistant Section of Administrative Services Robert O. Watson, B.S., Administrator and Head Supporting Services WiLMA G. Dillman, Property Control and Trust Accounts Robert O. Ellis. Assistant for Operations Lloyd E. Huffman, Stockroom Manager J. William Lusk, Mailing and Distribution Services Melvin B. Schwartz, Financial Records James E. Sergent, Greenhouse Superintend'ent Publications and Public Relations Owen F. Glissendorf, M.S., Technical Editor Robert M. Zewadski, M.S., Associate Technical Editor Shirley McClellan, Assistant Technical Editor Richard M. Sheets, Technical Illustrator Wilmer D. Zehr, Technical Photographer Technical Library Doris F. Dodds, B.A., M.S.L.S., Technical Li- brarian CONSULTANTS ; Parasitology, Norman D. Levine, Ph.D., Professor of Veterinary Parasitology and Veterinary Research, University of Illinois : Wildlife Research, Willard D. Klimstra, Ph D , Professor of Zoology and Director of Cooperative Wildlife Research, Southern Illinois University ; Statistics, Horace W. Norton, Ph.D., Professor of Statistical Design and Analysis, university of Illinois ; Gilbert P. Wai-dbauer, Ph.D., Associate Professor of Entomology, Univer- sity of Illinois, CONTENTS Acknowledgments _.. 235 Review of Literature ..,.. 236 "haracteristics of Study Areas 237 Sites of Fertilizer Plots 237 Soil Characteristics 238 Precipitation Data 240 Tree Species and Spacing 241 VIaterials and Methods 243 Morton Arboretum 246 Natural History Survey Arboretum 249 Sinnissippi Forest 249 Lincoln Trail State Park 250 Crab Orchard Wildlife Refuge 251 Results 251 Morton Arboretum 251 Response to method of application 253 Response to nutrients 253 Response to time of application 255 Response to rate of application 255 Response to source of nitrogen 256 Species response tests 256 Natural History Survey Arboretum 257 Sinnissippi Forest - 257 Lincoln Trail State Park 259 Crab Orchard Wildlife Refuge - 259 Discussion and Conclusions 260 Summary - 262 Literature Cited 263 Index -— - 265 This report is primed by authority of the State of Illinois, IRS Ch. 127. Par. 58.12. It is a contribution from the Section of Botany and Plant Pathology of the Illinois Natural History Survey. (21144—5,000—9-70) "7 Fertilization of Established Trees: A Report of Field Studies Prior to this study thie two senior authors, as plant pathologists, had rec- ommended fertilization as a preventive or corrective control measure for several tree diseases. It was recognized, how- ever, that the procedures for fertilizing established trees had not been thor- oughly subjected to scientific evaluation; more experimental data were needed. While cooperating with the junior author at the Morton Arboretum, Lisle, Illinois, on plant disease studies in 1962 the senior authors learned of an ex- perimental area in the Arboretum which contained uniform, established trees in 100-tree blocks with tree spacing in- tervals optimum for fertilizer trials. In this area a cooperative study was ini- tiated with the Morton Arboretum. Following the early successful at- tempts at measuring growth response to fertilizer applications in 1963 and 1964 at the Morton Arboretum, the senior authors expanded the study with trials at four additional sites in Illinois through 1968. ACKNOWLEDGMENTS First our appreciation is expressed to Dr. J. C. Carter, Head of the Section of Botany and Plant Pathology at the Illi- nois Natural History Survey, for his advice and guidance throughout this study. We also extend our gratitude, for their cooperation during the fertilizer tests in different areas of Illinois, to the following persons who permitted the use of private and public lands: Mrs. C. Philip Miller, owner of Sinnissippi Forest, Oregon, Illinois; Mr. Clarence E. Godschalk, former Director, and Dr. Dan Neely E. B. Himelick Webster R. Crowley, Jr. Marion T. Hall, Director of the Morton Arboretum, Lisle, Illinois; Mr. James L. McMillen, Superintendent, Division of Parks and Memorials, Illinois Depart- ment of Conservation, Springfield, Illi- nois; and Mr. T. A. Mehrhoff, Jr., Project Manager, Crab Orchard National Wildlife Refuge, U.S. Fish and Wildlife Service, Carterville, Illinois. Valuable assistance and cooperation in numerous aspects of this research project were provided by Howard W. Fox, Resident Forester and Assistant Professor, University of Illinois, Sin- nissippi Forest, Oregon, Illinois; Leon Cooper, State Park Ranger, Lincoln Trail State Park, Marshall, Illinois; and Robert G. Johnson and Richard J. Johnson, Assistant Project Managers, Crab Orchard National Wildlife Refuge, U. S. Fish and Wildlife Service, Carter- ville, Illinois. Gerald Born, Gary DeBarr, James Schuster, and Robert Slattery, Technical Assistants, Illinois Natural History Sur- vey, assisted the authors with many miscellaneous tasks required in this field study. We are grateful to Dr. L. C. Chad- wick, Professor Emeritus, Department of Horticulture, The Ohio State Uni- versity, and Professor Gordon King, Department of Aboriculture and Park Management, University of Massachu- setts, for their helpful reviews of the manuscript. Also gratefully acknowledged are the efforts of several members of the Illinois Natural History Survey staff who assisted in the preparation and processing of this publication. The photographic work was 235 236 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 done by Wilmer Zehr, Technical Pho- tographer; the illustrations were drawn by Richard Sheets, Technical Illustrator; the manuscript was edited by Owen F. Glissendorf, Technical Editor; and Mrs. Betty A. Nelson, Technical Assistant, assisted in the preparation of the manu- script. REVIEW OF LITERATURE Application of mineral nutrients to soil to stimulate tree growth has been a subject of discussion by arborists for 40 years or more. Most of the pro- cedures used in tree fertilization have been based on field experiences; few have been based on scientific experi- mentation. Forest trees or fruit trees are often used as ornamentals or shade trees. Therefore, experimental results on tree fertilization obtained by foresters and pomologists benefit aborists. A book edited by Childers (1954) reviews the knowledge of mineral nutrients of fruit trees. Since pomologists are mainly in- terested in fruit production, their ex- periences are probably not as relevant as those of foresters. Recent symposia at two universities dealt with the mineral nutrition of forest trees—Duke Uni- versity School of Forestry (1959) and University of Florida ( 1 968 ) . Stoeckeler & Arneman (1960) reviewed the in- formation on fertilizer use in forests. Several hundred papers on forest fertili- zation research are included in the bibliographies of White & Leaf (1956) and Mustanoja & Leaf (1965). Most forestry fertilizer trials have been con- ducted in forest nurseries or with ever- green species, not with established deciduous trees. The number of fertilizer field trials pertinent to the arborist is small. In 1927 and 1928 Jacobs (1929) com- pared fall application with spring appli- cation of fertilizers on American elm and Norway maple street trees. Each species was approximately 5 cm in trunk diameter at a point 1.0-1.2 m above the ground. Jacobs concluded that there was "little difference between fall and spring treatments but a decided benefit from either treatment compared with trees which received no treatment." Beilmann (1936) also recognized the need for data on the effects of fertiliza- tion on shade trees. Although many of his tests did not include control plots, he performed tests on several tree species between 1928 and 1933. He devised a formula for rate of fertilization based on tree height, branch spread, and trunk circumference. Wyman (1936) reported the results of a well-designed 4-year test on nurs- ery-sized pin oaks. He compared results from two combinations of nutrients on two soil types. His fertilizer treatments began the first growing season following planting. During the first three growing seasons, while the trees were becoming established, tree growth was limited. Wyman reported that the fertilization produced a response in twig growth during the second growing season and a response in trunk diameter growth dur- ing the third growing season. Chadwick (1934, 1937, 1940, 1941) measured the annual response of Ameri- can elms to four nutrient combinations and three seasons of application from 1932 through 1940. The elms were planted in 1931. The nutrients were nitrogen (N), nitrogen and phosphorus (NP), and nitrogen, phosphorus, and potassium (NPK) combinations. The fertilizer was broadcast on the soil surface. Chadwick (1941) states, "The inconsistency of the data recorded in- dicate that fertilizer experiments on woody ornamentals out of doors must be of a long-time nature . . . ." His study indicated that fall was as favorable as, or more favorable than, other seasons for application of fertilizers and that NPK or NP combinations of nutrients were more beneficial than N alone. In a test with established Norway maples approximately 4 cm in trunk diameter at 1.4 m height, Chadwick, Sept.. 1970 Neely, Himelick, Crowley: Tree Fertilization 237 Tilford, & Irish (1950) applied NPK mixed with water, air (with an air gun), or peat, on the soil surface and into the soil. They also applied N, P, and K singly and in all possible combinations. Fertilizer treatments were applied in April, 1941 and May, 1947. Growth measurements were made each fall from 1941 through 1948. The results in- dicated that surface applications of fertilizer resulted in a greater diameter increase than other methods of applica- tion and that nitrogen may be considered the limiting element for good growth, but that when nitrogen is coupled with phosphorus a greater stimulation may result. Other results of tree fertilization field studies in the late 1930's or early 1940's include the report by Chandler (1939) who concluded that heavy applications of nitrogen fertilizers increased twig growth of beech and sugar maple by more than 100 percent. Deuber ( 1939) found that it was possible to kill young trees by using extremely heavy rates of fertilizer. Pridham (1938), in continued observation of the pin oak plots fertilized by Wyman, stated that after seven grow- ing seasons the untreated trees were as large as the trees fertilized at planting. He stated that variance in growth due to fertilization at time of planting is much less than the variance in growth due to season, soil, time of planting, and method of planting. Pridham was unable to demonstrate a stimulation of trunk diameter growth of large American elms (1940) or red oaks^(1941) by fertilization. Recent reports of tree fertilization field trials include tests on dogwood by Curlin (1962), sweetgum and oak by Broadfoot (1966), tulip tree by Finn & White (1966), and sugar maple and tulip tree by van de Werken & Beavers (1965). Many nutrients essential to plant growth can enter leaves directly. Pirone (1951 ) reported results from 3 years of testing foliar applications of nutrients on five species of street trees. He noted that the general appearance of trees re- ceiving six foliar sprays was better than that of untreated trees. His chemical analyses of leaves from a small number of London plane trees and pin oaks showed more nitrogen and phosphorus in leaves from the treated trees than in leaves from untreated trees. Preliminary data from the tree ferti- lization field trials at the Morton Arbore- tum test site reported in detail here were published previously by the authors (1965). CHARACTERISTICS OF STUDY AREAS Sil-es of Fer-lilizer Ploh The fertilizer trials on deciduous trees (and two species of evergreens) were conducted at five sites in Illinois. The locations of the fertilizer plots are shown on the map of Illinois (Fig. 1 ). The site of the original test plot was the Morton Arboretum, Lisle, DuPage County. The Morton Arboretum is a privately endowed educational founda- tion, founded in 1922 by Joy Morton. The Arboretum is approximately 25 miles west of Chicago. The second test site was the Illinois Natural History Survey arboretum near Urbana, Champaign County, 1 mile south of the University of Illinois cam- pus. The land is owned by the Univer- sity of Illinois. It was assigned to the Natural History Survey in 1960. The third test site was Sinnissippi Forest, a private plantation and naturally forested area along the east bank of the Rock River, 3 miles southeast of Oregon, Ogle County. Although pri- vately owned by Mrs. C. Philip Miller, Sinnissippi Forest is extensively used for scientific purposes and is managed by a University of Illinois resident forester. The fourth test site was the Lincoln Trail State Park, approximately 3 miles south of Marshall, Clark County. The park is managed by the Illinois Depart- ment of Conservation and has a resident 238 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 SINNISSIPPI FOREST, OREGON MORTON ARBORETUM, LISLE NATURAL HISTORY SURVEY ARBORETUM, URBANA LINCOLN TRAIL STATE PARK. MARSHALL CRAB ORCHARD NATIONAL WILDLIFE REFUGE, CARTERVILLE Fig. I. — The five tree fertilization test sites in Illinois. ranger. In addition to the natural wooded area surrounding a man-made lake, the park contains numerous decid- uous and evergreen tree plantations. The fifth fertilizer test site was the Crab Orchard National Wildlife Refuge, southeast of Marion, Williamson County. The Refuge is managed by the U.S. Department of the Interior, Fish and Wildlife Service. One of the nu- merous resident employees is a forester. Soil Characterisfics In the fertilizer plots in this study at five sites, 10 soil types are represented. The following descriptive information concerning the soil types was primarily obtained from University of Illinois Agricultural Experiment Station Bulletin 725 by Fehrenbacher, Walker, & Wascher (1967). Loess is the most extensive parent material of Illinois soils. It is a silty material deposited by wind during glacial times. In Illinois, because of the pre- vailing westerly winds, loess is thickest just east of the sources at the Mississippi and Illinois River Valleys. It thins in a regular manner with distance away from the sources. Glacial drift is also a major source material for Illinois soils. This material was deposited after having been moved by glaciers. The drift de- posits are subdivided into glacial out- wash, which consists of stratified gravel, sand, silt, or clay deposits, and glacial till, which is unstratified. Sept., 1970 Neely, Himelick, Crowley: Tree Fertilization 239 Surface soil color is a reasonably good guide to the organic matter content of Illinois soils—the darker the soil the greater the organic matter content. In general, dark-colored soils developed under grass or prairie vegetation and light-colored soils developed under trees or forest vegetation. The degree of soil development refers to the extent of weathering and change the parent materials have undergone in the formation of the soil. In strongly developed soils the soil profile contains horizons or layers with well differenti- ated properties of color, texture, and structure. At the Morton Arboretum the trees in the fertilizer tests were on Andres, Beecher, Markham, and Morley silt loams. Andres silt loam is a dark-colored grassland soil with moderate develop- ment. It formed in silty clay loam glacial till with a mantle of less than 0.5 m of loess or glacial drift. The till is calcareous at 0.5-1.0 m depth. It has a slope of 1-3 percent. The surface soil is a black to very dark brown silt loam 25-40 cm thick with fine crumb to granular structure. The subsurface soil is a very dark brown loam 8-15 cm thick with weak structure. The subsoil is a gray and brown clay loam 30-50 cm thick with imperfect water perme- ability. Markham, Morley, and Beecher soils developed from the same parent ma- terial as Andres. These, however, are lighter colored, moderately developed soils formed under forest or mixed forest and prairie vegetation. Markham has a slope of 3-8 percent. The surface soil is a very dark grayish brown silt loam with granular structure 15-20 cm thick. The somewhat lighter colored subsurface soil has weaker structure and is 5-12 cm thick. The subsoil is brown silty clay loam 0.5-1.0 m thick with moderately slow to slow permeability. Morley has a slope of 4-12 percent. It is quite similar to Markham except that it has a slightly lighter colored and thinner surface soil layer, only 5-12 cm thick, and a thicker subsurface soil layer 8-20 cm thick. Beecher has a slope of 1-4 percent. It is somewhat poorly drained, since sur- face runoff is slow to medium and sub- soil permeability moderately slow to slow. Otherwise, it is similar to Mark- ham. The surface soil layer is 15-25 cm thick and the subsurface soil layer 8-20 cm thick. There are distinct mot- tles throughout the subsoil. At Sinnissippi Forest the fertilizer plots are on Plainfield sand. The Plain- field soils are on nearly level to sloping glacial outwash plains and stream ter- races and on sloping to steep morainic areas (2-15 percent slope). They have formed in sandy drift with high quartz and low weatherable mineral content. The soils are excessively drained with surface runoff slow to medium and permeability very rapid. The surface horizon is a dark grayish brown sand 15-25 cm thick and medium acid. The subsoil layer is yellowish brown sand 30-45 cm thick and strongly acid. The soil in the Natural History Sur- vey aboretum is Flanagan silt loam. It is a dark, moderately developed, grass- land soil with a slope of 1-3 percent. It is an imperfectly drained soil that formed in 1.0-1.5 m of loess overlying calcareous loam glacial till. The surface soil is a black to very dark gray silt loam 15-25 cm thick with moderately good structure and medium acidity. The subsurface soil is a dark brown, heavy silt loam 18-30 cm thick. The subsoil is a mottled, brownish, silty clay loam that has moderate permeability and is 75-100 cm thick. The soil types at Lincoln Trail State Park and Crab Orchard Wildlife Refuge are of similar origin. The four types in- volved are Stoy, Weir, Bluford, and Wynoose silt loams. All are light-col- ored, strongly developed soils of south- ern Illinois that formed under forest vegetation. 240 Illinois Natural History Survey Buli etin Vol. 30, Art. 4 Stoy and Weir formed in loess 1-3 m thick on Illinois drift (largely till) or from more than 2 m of loess on bedrock residuum. Stoy has a slope of 1-4 per- cent. The surface soil is a dark brown friable silt loam with weak crumb struc- ture, strongly acid, and 12-18 cm thick. The subsurface soil is pale brown and 25-35 cm thick. The subsoil is a gray and brown silty clay loam with slow water permeability. Weir has a slope of 0-2 percent. Soil profile depths and colors are similar to those of Stoy. The subsoil contains slightly more clay. Drainage is poor to very poor with run- off slow to medium and permeability slow. Wynoose and Bluford are very strongly developed soils that formed in 0.5-1.2 m of loess on Illinois glacial drift (largely till) and their subsoil hori- zons usually extend into the till. Wy- noose is quite similar in topography, profile, texture, structure, and reaction to Weir. Bluford is similar to Stoy in these same characteristics. Data on the available plant nutrient supply as determined by soil tests were obtained from untreated soils from the five test sites. Soil samples collected at the Morton Arboretum from the upper 30 cm of soil and at the Survey arbore- tum from the upper 15 cm of soil were tested in 1965. Soil samples from the Crab Orchard Refuge, Lincoln Trail State Park, and Sinnissippi Forest plots were collected from the upper 15 cm of soil and tested in 1968. Averages of the soil test data from the tree fertilizer plots are given in Table 1. Additional properties of these soil types are also included in the table. Precipitation Data Along with soil fertility, a factor that greatly influences the growth of trees is soil moisture. The precipitation data from the U.S. Weather Bureau collect- ing stations nearest the fertilizer test sites give an indication of the abundance or sparsity of soil moisture throughout the growing season. The precipitation data collecting sta- tions were relatively close to the five fertilizer test sites. The collecting sta- tions were located 4 miles northwest of the Morton Arboretum until June 1966 when the station was moved to the Ar- boretum, 1 mile north of the Survey arboretum, 15 miles east of Sinnissippi Forest, 4 miles northeast of Lincoln Trail State Park, and 4 miles northeast Table I. — Soil test data for the soils at the fertilizer test sites. Sept., 1970 Neely, Himelick, Crowley: Tree Fertilization 241 Table 2. — Precipitaiion data per quarter year from U.S. Weather Bureau collecting stations nearest the five fertilizer test sites during those years tests were in progress. Location and Growing Season 242 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 Q. palustris Muench. Evergreen Trees Pin oak „. .. Finus resmosa Ait. Tilia amencana L. r^^ -^ Basswood p ,^^^^ L. T. cordata Mill. Loblolly pine Littleleaf linden Ulnius parvijolia Jacq. Trees in 26 of the 29 test plots were Chinese elm in plantations. Within each plot these Table 3. — Age, spacing distance, percentage survival, and size of trees in plantations at the five fertilizer lest sites, and the type ot soil in which the trees were growing. /Site, Test, and Tree Species Planting Distance Initial'^ Year Between Planting Trunk of Trees, Survival, Diameter, Soil Type Planting m Percent cm Morton Aboretum Method White ash Honey locust Pin oak Time Pin oak Bate White ash Species response Basswood Norway maple Red maple Sugar maple Red oak Swamp white oak White oak NHS Arboretum Species response Green ash Chinese elm Hawthorn Littleleaf linden Norway maple Sinnissippi Forest Method Green ash Red pine Sycamore Black walnut Lincoln Trail Method Loblolly pine Persimmon Sweet gum Sycamore Tulip tree Crab Orchard Species response Pecan Sweet gum Black walnut 1956 Sept , 1970 Neely, Himelick, Crowley: Tree Fertilization 243 trees were of the same age, had a uni- form spacing between trees, and within a narrow range had a uniform size. The spacing distances in the different plots varied^from 1.2 to 15.3 m (4-50 ft.) between trees. Uniform spacing was a primary factor in selecting test plots and sites; however, in most plots not all the trees originally planted were surviving when the testing began. In three of the test plots, the trees were in naturally re- generated stands. Table 3 lists the tree species used at each of the five sites and gives the planting date, the original spacing between trees, the percentage of tree survival, tree size when testing be- gan, and the soil type. MATERIALS AND METHODS In this study the initial tests were aimed specifically at determining what nutrients would stimulate a growth re- sponse in established trees when applied in various ways. Sixteen fertilizer treat- ments were used and each treatment consisted of a different combination of fertilizer and method of application. Later tests were designed to give more limited data that would confirm or fail to confirm the results obtained from the initial tests by utilizing additional species of trees growing in different soil types and locations. The nutrient elements used in varying amounts and combinations in these tests were the macronutrients nitrogen, phos- phorus, and potassium and the micro- nutrients manganese, iron, copper, zinc, boron, molybdenum, and magnesium. The combinations of nutrient elements were: nitrogen alone (N), phosphorus and potassium (PK), nitrogen, phos- phorus and potassium (NPK), and ni- trogen, phosphorus, potassium, and micronutrients (NPK4-). Several materials were used as sources of nutrient elements. Ammonium nitrate (33.5-0-0), urea (45-0-0). ammonium sulfate (21-0-0), and ureaform (38- 0-0) were used as sources of nitrogen. When the dry form of NPK was needed. a commercial 10-10-10 or 12-12-12 farm fertilizer was used. When an NPK solution was required, a commercial water soluble 23-19-17 fertilizer (Ra- Pid-Gro') was used. The source ma- terials in Ra-Pid-Gro are urea, am- monuim phosphate, potassium phos- phate, and potassium nitrate. When P and K were used together in dry form, triple superphosphate (0-45-0) and muriate of potash (0-0-60) were mixed. For the soluble PK treatments, the source material was potassium mono-H phosphate (K,HPOj. The combination of micronutrients used was that of Peters Trace Element Mix-, which contains micronutrients as follows (percentages): Mn 9.0, Fe 6.0, Cu 3.0. Zn 3.0. B 2.0, Mo 0.5, and Mg 0.4. The quantity of nutrient elements per unit area of soil was constant through- out the tests at all five sites regardless of tree size, tree species, tree spacing, or soil type. (The one exception was the rate of nitrogen test on white ash at the Morton Arboretum.) The nitrogen fertilizers were applied at the rate of 29.3 g of elemental N per square meter (6 lb N per 1,000 sq ft). The phosphate fertilizers were applied at 12.9 g of ele- mental P per square meter (6 lb PjO,^ per 1,000 sq ft ). The potassium fer- tilizers were applied at 24.3 g of ele- mental K per square meter (6 lb K.O per 1,000 sq ft). The amounts of fer- tilizer source materials used in the soil treatments are given in Table 4. Foliar fertilization was tested only at the Morton Arboretum. The three water-soluble nutrient sprays applied to the foliage included nitrogen alone, NPK, and NPK plus micronutrients. The amounts of fertilizer source materials used in the foliar treatments are given in Table 5. Fertilizers were applied to the soil by three methods: (i) broadcast on the soil around the trees, (ii) placed as dry fer- tilizers into holes made in the soil, and 244 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 Table 4. — Nutrient source materials used to fertilize the soil, and rates of usage at the five fertilizer test sites. Source Material Rate of Usage, g/sqm Elemental Nutrients, g/sqm Ammonium nitrate (33.5-0-0) Ammonium sulfate (21-0-0) Urea (45-0-0) Ureaform (38-0-0) Triple superphosphate (0-45-0) Muriate of potash (0-0-60) Potassium mono-H-phosphate Commercial 10-10-10 Commercial 12-12-12 Water soluble 23-19-17 Trace element mix 87.4 Sept., 1970 Neely, Himelick, Crowley: Tree Fertilization 245 Rg. 2. — The push-f-, lawn spreader was used apply bands of ferfiii; alongside rows of trees Urbana. Fig. 3. — The cyclone type lawn spreader was used to apply fertilizer to the soil surface at Lisle, Oregon, Marshall, and Carterville. was made to fill or close the holes fol- lowing the distribution of the fertilizer. Injection of liquid fertilizers into the soil was tested in the single-tree plots at the Morton Arboretum. Enough fer- tilizer solution to treat 15 trees was pre- pared. Fifty-seven liters (15 gal) of solu- tion were used per tree with this volume evenly divided into 14 injection sites. It was injected 45-60 cm (18-24 in) deep with a soil needle (Fig. 7) and a ^ / 246 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 Fig. 5. — The soil profile tube which removes cores of soil from the upper 10-14 inches of soil was used to make holes in the soil at Lisle. hydrauli: sprayer with an agitator using 10 kg per sq cm (150 lb per sq in) pressure. The volume of fertilizer used at each injection site was regulated by opening the soil needle valve for a pre- determined number of seconds. Four of the injections were made on the four sides of the tree approximately 0.75 m from the tree trunk and the remaining ten injections were made in a circle ap- proximately 1 .4 m from the trunk. Foliar fertilization was tested on the single-tree plots at the Morton Arbore- tum. Fertilizer solutions were prepared in amounts to treat 15 trees. The quan- tities of nutrients applied per tree in foliar treatments were much less than the quantities used in soil applications. The trees were sprayed with a hydraulic sprayer until the solution began to drip from the foliage. No attempt was made to prevent runoff onto the soil. Foliar sprays were applied each year during May, June, and July at approximately monthly intervals. They were applied between 8 a.m. and 12 noon on days having little or no wind. Each tree re- ceived 6-8 liters of solution each appli- cation. In all of the fertilizer tests the growth responses were determined by measuring the tree trunks approximately 1 m above the soil. The circumference of each tree was measured with a steel tape at the start of each test and at the end of each growing season. Trees were measured to the nearest 0.005 ft (1.5 mm) in cir- cumference. The height at which the trunk was measured was permanently marked with tree marking paint or with a nail at one or more points around the tree. The following sections present specific information concerning the different fertilizer tests at the five sites. Morton Arboretum With one exception the trees at the Morton Arboretum were in two areas — the experimental area, which is along the northern boundary of the Arboretum and was once pasture, and the forestry plots, which are in the approximate center of the Arboretum and are sur- rounded by a natural stand of forest trees. The exception was a natural stand of large white oaks immediately adja- cent to the experimental area. The three species growing in the ex- perimental area were pin oak, white ash, and honey locust. They had been planted in square blocks with 4.5 or 6.0 m spacing distances between trees and 7.5 m between blocks. Each block contained 100 trees of a single species. The oaks and ashes were planted in 1956, and the locusts in 1957. When planted, the oaks were 0.3-1.0 m tall, the ashes 1.3-2.0 m tall, and the locusts 1.0-1.3 m tall. All blocks had been Sept.. 1970 Neely, Himelick, Crowley; Tree Fertilization 247 &-- t Fig. 6. — A punch bar made from a car axle was used to prepare holes In the soil at Lisle, Oregon, Mar- shall, and Cartervllle (left). Fig. 7. — A soil needle at- tached to a hydraulic pump with a hose was used to inject water-soluble fertiliz- ers Into the soil at Lisle. planted with Kentucky bluegrass, Poa pratensis L., and a sod was maintained with occasional mowing each summer. White ash, pin oak, and honey locust trees were used in a method test. Each block of trees was divided into plots. Each plot contained five contiguous trees and received one of 16 treatments. Eighty trees of each species were treated. Several trees (14 oak, 12 ash, and 10 locust) received no treatment and served as controls. The 16 treatments included am- monium nitrate and urea each applied dry to the soil on the surface and in holes, in the soil in solution, and as a spray to the tree foliage; NPK and NPK plus micronutrients applied to the soil in holes and in solution and to the tree foilage; and PK applied to the soil in holes and in solution. The treatment each tree received in 1963 was repeated in 1964 and 1965. Soil treatments were made on May 14, 15. and 16, 1963; on April 22 and 23, 1964; and on April 28 and 29. 1965. FoHage treatments were made on May 6, June 20, and July 23, 1963; on May 20, June 24, and July 24, 1964; and on May 18, June 9, and July 15. 1965. Annual growth of the trees was measured for 6 years. The initial measurement was made on May 13, 1963 and the subsequent growth meas- urements were made on October 2, 1963, October 7, 1964, October 14, 1965, September 28, 1966, October 19, 1967, and October 16. 1968. One block of pin oaks in the ex- perimental area was used in a time of application test. Sixteen treatments were used, each treatment applied to five 248 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 trees selected at random. Ten trees were untreated and served as controls. In all treatments nitrogen fertilizers were applied to the soil surface. The nitrogen fertilizer source materials were ammonium nitrate, ammonium sulfate, urea, and ureaform. Each tree received 29.3 g of elemental N per square meter (6 lb per 1,000 sq ft) per year. Each source material was applied (i) full rate in April; (ii) Vi rate in April and Vi rate in June; (iii) Vz rate in April, Vi rate in June, and Vz rate in October; or (iv) full rate in October. Each tree received the same treatment for 3 con- secutive years; on April 23, June 24, and October 6, 1964; April 27, June 9, and October 14, 1965; and April 26, June 8, and September 27, 1966. Annual growth was measured for five seasons. The initial tree measurement was made on May 7, 1964 and growth measurements were made on the same days as those reported above for the method test. One block of white ash trees in the experimental area was used in a rate of application test. Each tree was treated individually with a random selec- tion for treatment throughout the block. There were 16 treatments with each treatment applied to five trees. Fifteen trees were untreated and served as con- trols. All treatments were nitrogen ferti- lizers applied to the soil surface. The nitrogen source materials were ammoni- um nitrate, ammonium sulfate, urea, and ureaform. The rates of application were Vi, 1, IVi, and 2 times the rates shown in Table 4. Fertilizers were applied on April 22, 1964 and April 27, 1965, each tree receiving the same treatment for 2 consecutive years. Annual growth was measured for 4 years. The initial trunk measurements were made on April 22, 1964 and subsequent measurements were made on October 7, 1964, October 14, 1965, September 28, 1966, and October 19, 1967. The remaining fertilizer test at the Morton Arboretum was the species re- sponse test. The trees in this test (with the exception of the white oaks) were in the forestry plots. They were crowded, relatively small, 40-year-old trees. Rela- tively uniform groups of approximately 20 trees of each of six species were selected for the test. Table 6. — Tree species, fertilizer +reatments, and fertilizer amounts used per year In species response tests at the Morton Arboretum. Tree Species Sept., 1970 Neely, Himelick, Crowley: Tree Fertilization 249 The area was divided into two plots. Ammonium nitrate was broadcast over tiie soil surface of one plot. The other plot served as an unfertilized control. Plot sizes and fertilizer amounts are given in Table 6. The trees were treated for 3 consecutive years, on April 20, 1964, April 27, 1965, and April 26, 1966. Initial tree measurements were made on April 20, 1964 and annual growth measurements were made on October 7. 1964, October 14, 1965, September 28, 1966, and October 10, 1967. Natural History Survey Arboretum The test in the Natural History Sur- vey arboretum was a species response test in a field that had previously been cultivated. The trees were planted, in nursery-type rows, 2 or 3 years before the test began and were just becoming established. A lawn-type bluegrass sod was present. Ammonium nitrate was applied in 0.6-m wide bands to the soil surface along each side of rows of five species of trees. Alternating 5-tree plots in a row were treated or left untreated with one border tree between plots. No adjacent rows were treated. The trees were treated for 3 consecutive years, on April 16, 1964, May 13, 1965, and May 10, 1966. The amounts of fertilizer ap- plied are given in Table 7. Initial tree measurements were made on May 8, 1964, and the growth measurements were taken on October 12, 1964, Octo- ber 5, 1965, and October 5, 1966. Sinnissippi Forest At Sinnissippi Forest the test plots were in plantations established in open fields that once were farmed. The green ash and sycamore plots were in experi- mental plantations of approximately 0.4 hectare ( 1 acre ) . The red pine and black walnut were in larger plantations. In the ash and pine plantations shading restricted the growth of competing vege- tation. Weeds were present in the syca- more and walnut plantations. Each species was divided plots of 10-12 trees with one, two, or more rows of trees separating the plots. This method test compared (i) nitro- gen on the surface, (ii) NPK on the sur- face, (iii) NPK in soil holes, and (iv) no treatment. The ashes received an addi- tional treatment of PK on the surface. The fertilizer treatments and the amounts applied are given in Table 8. The plots were treated on May 5 and 6, 1965, April 28, 1966, and April 18, 1967. Initial tree measurements were made Table 7. — Tree species, feriilizer treatments, and fertilizer amounts used per year in species response tests at the Natural History Survey arboretum. Tree Species Amount of Number Plot Plot Fertilizer TreatmetU * 250 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 Table 8.— Tree species, fertilizer treatments, and •fertilizer amounts used per year in method tests at Sinnissippi Forest. Sept.. 1970 Neely, Himelick, Crowley: Tree FER^lLIz.^TION 251 Table 10. — Tree species, fertilizer treatments, and fertilizer amounts used per year response tests at Crab Orchard National Wildlife Refuge. 252 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 throughout the study. As with all bio- logical data, there were variations be- tween trees, plots, treatments, species, and years during the testing period. The annual growth determinations in the method test are given in tabular form—the pin oak data in Table 1 1 , the white ash data in Table 12, and the Table II. — Trunk diameter growth of pin oaks in the method-of-application fertilizer plot at •he Morton Arboretum. Five trees per treatment were fertilized In 1963, 1964, and 1965. Sept., 1970 Neely, Himelick, Crowley: Tree Fertilization 253 honey locust data in Table 13. A more condensed and digested version of the data from the 3 species is presented in Table 14, showing the percentage in- creases of treated over untreated trees. Response to Method of Applica- tion.—Nutrients applied to the fohage of trees stimulated growth much less than soil-applied nutrients. Trees re- ceiving foliar applications grew slightly more or no more than the trees receiving no treatment. The oak and ash trees that received foliar nutrients grew more than untreated trees, while the treated honey locusts grew less than untreated trees (Table 14). The differences in growth between untreated trees and foliar-treated trees were probably due to plot variability rather than treatment response. Statistically, the results from foliar treatments were not significantly better than the results from no treatment (Himelick, Neely, & Crowley 1965). Stimulation of growth, if present, may have resulted, in part, from the uptake of nutrients that dripped from the fo- liage onto the soil. All methods of applying fertilizer lo the soil stimulated tree growth. Neither surface application, dry fertilizer in soil holes, nor injection of soluble fertilizers into the soil was significantly better than any other soil application method, while all three produced significantly better growth than occurred with foliar fertili- zation and in untreated controls. Minor variations in growth response did occur between the three soil methods of fertili- zation. During the 3 years fertilizers were applied, the locusts responded best to surface applications, and the oaks and ashes responded best to solution in- jection (Table 14). The method of plac- ing dry fertilizers in soil holes was slightly less effective than the other soil methods. Trees treated in this manner, however, tended to show more of a residual response the year following treatment than trees fertilized by surface application or solution injection. Response to Nutrients.—In this test on oak, ash, and locust trees, there was no positive growth response to fer- tilization with phosphorus and potas- Table 13. — Trunk diameter growth of honey locusts in the method-ot-applica+ion fertilizer plot at the Morton Arboretum. Five trees per treatment were fertilized in 1963, 1964. and 1965. 254 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 Table 14. — Percent annual trunk diameter growth increase of treated trees over that ot untreated trees In the method-of-appllcatlon fertilizer plots in the Morton Arboretum. Trees were fertilized in 1963, 1964. and 1965. Sept., 1970 Neely, Himelick, Crowley: Tree Fertilization 255 persisted for only 1 or 2 years after fertilization ceased. In 1968, the third year after fertilization ceased, the treated trees grew less than the untreated trees (Table 14). Competition for light, water, or nutrients between trees in the fertil- ized plots may have limited the growth in 1967 and 1968. The branches be- tween trees in many of the fertilized plots began to touch in 1967, and this was not true in the untreated plots. Response to Time of Application. —Data for comparing the effect of fer- tilizing trees during different seasons of the year were derived from one block of pin oaks treated with surface application of four nitrogen fertilizers. The annual growth measurements of trees treated at the various seasons are given in Table 15. A summary of this data expressed as percentage increases in growth of treated over untreated trees is given in Table 16. The greatest growth stimulation wai obtained by applying all of the nitrogen in April. Trees receiving a portion or all of the nitrogen in June or October grew less than trees receiving all of the nitrogen in April. Trees fertilized in October grew more than untreated trees. Unfortunately, the trees treated in October were at a disadvantage in two ways. They were not fertilized in Octo- ber of 1963; therefore, all fertilizers were not available during the same growing seasons. Also, the fertilized pin oaks were competing for space during 1966 and this factor may have limited the increased response to fertilizers dur- ing 1966 and subsequent years. Trees fertilized in April and June responded well to fertilizers in 1964 and 1965, while trees fertilized in October re- sponded well only in 1965 (Table 16). Response to Rate of Application. —Data for comparing the response to varying rates of application of nitrogen fertilizers were obtained from one block of white ash trees treated with surface applications of four nitrogen fertilizers. The growth measurements of the trees are given in Table 17. Data from this test, although more variable than data from previously dis- Table 15. — Trunk diameter growth ot pin oaks in the tinne-of-application fertilizer plot at the Morton Arboretjnn. Five trees per treatment were fertilized in 1964, 1965, and 1966. 256 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 Table 16.— Percent annual trunk diameter growth increase of treated trees over that of untreated trees In the pin oak tinne-of-application fertilizer plot in the Morton Arboretum. Trees were fertilized in 1964, 1965, and 1966. Sept., 1970 Neei.y, Himelick, Crowley: Tree Fertilization 257 Table 18. — Trunk diameter growth of trees in the species response fertilizer plots at the Morton Arboretum. Trees were fertilized in 1964, 1965. and 1966. Species 258 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 Table 19. — Trunk diameter growth of trees in ihe species response fertilizer plots at the Natural History Survey arboretum. Trees were fertilized in 1964, 1965, and 1966. Species Sept., 1970 Neely, Himelick, Crowley: Tree Fertilization 259 response between surface and soil hole methods of application. There was a tendency for fertilizers applied in holes to give slightly less response than surface-appHed fertilizers during the first year of treatment and to give slightly more response as a residual action in the year following application. Lincoln Trail State Parle Fertilized trees in every plot at Lincoln Trail State Park grew more than the untreated trees. Loblolly pines and tulip trees grew moderately well without fertilizers during the period of this test but the persimmon, sweet gum, and sycamore trees grew slowly. The amounts of growth of treated and un- treated trees are given in Table 2 1 . The four deciduous species responded with greater percentage increases in growth than did the loblolly pines. The treated persimmons and sycamores grew about three times as fast as untreated trees. The increased growth of treated over untreated trees was about 60 per- cent for tulip trees, about 40 percent for sweet gums, and about 30 percent for loblolly pines. The trees fertilized with NPK did not consistently grow more than the trees receiving only N. Among the sweet gums and tulip trees, one plot of trees receiving NPK grew more than, while another grew less than, trees receiving N alone. Persimmons receiving NPK grew more than those receiving only N. Syca- mores receiving NPK grew less than those receiving N alone. One method of application at Lincoln Trail State Park was not consistently better than another. The sweet gums and tulip trees receiving NPK on the surface grew more than comparable trees fertilized with NPK in holes, while the reverse was true with sycamores. There was a tendency for the trees treated with NPK on the surface to respond more than trees treated either with NPK in soil holes or N on the surface. Crab Orchard Wildlife Refuge The three species of trees at Crab Orchard Wildlife Refuge—sweet gum, pecan, and black walnut—all responded favorably to fertilization. The amounts of growth of the treated and untreated trees are given in Table 22. Particularly Table 21.— Trunk diameter growth of trees in the nnethod-of-treatment fertilizer plots at Lincoln Trail State Park. Trees were fertilized in 1966, 1967, and 1968. 260 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 Table 22. — Trunk diameter growth of trees In the species response fertilizer plots at Crab Orchard National Wildlife Refuge. Trees were fertilized in 1966, 1967, and 1968. Sept., 1970 Neely, Himelick, Crowley: Tree Fertilization 261 the amount of soil moisture available. Trees must have an established root sys- tem before trunk diameter measure- ments will indicate growth stimulation due to fertilization. Shoot growth of many trees occurs during a relatively short period early in the growing season with possible recurrent flushes of growth later in the season. In other trees, how- ever, shoot growth may occur over a longer period of time. Shoot growth has not been as well correlated with climatic factors as has trunk growth. The obvi- ous difficulty of accurately determining the height of large trees, and the large number of measurements required for adequately sampling shoots on large trees, prohibited the use of these means of measuring tree growth in this study. The results of this study on the re- sponses of established trees to fertilizers do not indicate the need for radical changes from current practices in fertil- izing trees. However, the results do give a good means of comparing time, rate, and method of fertilizer applications, and the nutrients that may stimulate growth response. In our tests at five sites in Illinois, significant growth response was obtained only from nitrogen. This is not surpris- ing, because nitrogen is the element that most frequently stimulates the growth of other plants. Moreover, an optimum supply of nitrogen is often lacking in most soils of inorganic origin. The soils at the five test sites repre- sented sandy soils, fertile deep topsoils of prairie origin, fertile shallow topsoils of forest origin, and infertile shallow topsoils with heavy clay subsoils. Re- gardless of soil type, nitrogen stimulated growth in deciduous trees. Other nu- trients, although they were available in relatively low quantities in some of the soils, failed to stimulate growth when added as fertilizers. The four sources of nitrogen used in these tests were equally beneficial. Am- monium nitrate, ammonium sulfate, and urea release nitrogen rapidly in the soil, making it readily available for plant use. Ureaform releases nitrogen more slowly. It is less effective in the first year of application but has a greater residual influence than the other nitrogen sources tested. Soil surface, soil hole, and solution injection were almost equally effective methods of applying nitrogen fertilizers. There is a great difference, however, in the economic aspects of application by these three methods. Solution injection is slow and expensive because it requires soluble fertilizers and a hydraulic sys- tem for injection. Placing dry fertilizer in soil holes is slow, difficult, and ex- pensive because it requires extensive time and manpower to prepare the soil holes and distribute the fertilizer. Broad- casting on the surface is fast, easy, and relatively inexpensive. It requires only a lawn fertilizer spreader and a nitrogen fertilizer. In this study the growth response to foliar fertilization was extremely slight. The color response given in the prelim- inary report (Himelick, Neely, & Crow- ley 1965) was just as slight. Soil appli- cations of fertilizers gave significant growth and color responses, while foliar applications did not. The rate of application of nutrients used in these tests was an empirical figure. It was based on area of soil, not size of trees. Nitrogen at the rate of 29.3 g per sq m (6 lb per 1,000 sq ft) of soil area is commonly used for fer- tilizing established shade trees. Arborists placing dry fertilizers in holes use this rate commercially, and have found it nontoxic to trees and grass. Our results confirm the usefulness of the rate. The trees fertilized with one-half this rate grew less than half as much as the trees fertilized at this rate. The trees fertil- ized with additional nitrogen grew more, but the additional growth was insuffi- cient to justify changing the recommen- dations. Higher rates of nitrogen applied to the surface during summer months were toxic to grass (Himelick, Neely, & Crowley 1965). Spring applications of nitrogen were 262 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 more effective than summer and fall ap- plications. The distinct advantage of April over October applications ob- tained in this study is not in agreement with the research of Jacobs (1929) or Chadwick (1941). There is little in the results of this study on which to base recommenda- tions on frequency of fertilization. In most of our tests, the trees were fertil- ized for 3 consecutive years. The amount of additional growth due to fertilization was relatively uniform each year with little or no cumulative effect. Within 2 years after fertilization ceased, the treated trees were growing at the same rate as the untreated trees. Although 20 species of deciduous trees were included in this study, it is difficult to reach conclusions concerning the inherent capabilities or genetic limi- tations of tree species in response to fertilization. At four of the five sites the slow-growing tree species gave the greatest percentage increases in growth when fertilized, but they did not neces- sarily produce a greater volume of wood than the faster-growing trees. The slow- growing trees were the smaller trees at these sites. Tree size and tree competi- tion rather than tree species more likely influenced the degree of response to fer- tilization. At no time during the 6 years of this study was there injury to grass or under- story plant material following surface application of N or NPK fertilizers. The fertilized understory plants became darker green and grew larger than com- parable unfertilized plants. Fertilized trees grew more than unfertilized trees even with the additional competition from weeds and bluegrass turf. In Illinois there usually is an adequate supply of rainfall during the months of April, May, and June. During the period of these tests, rainfall in April, May, and June usually amounted to 25-35 cm (10-14 inches) at each of the five tree fertilization test sites (Table 2). Periods of drought are more common during the other 9 months of the year. During one 3-month period rainfall totals may be two or three times greater in one year than in the same period of the previous year. Annual variations in tree growth are partly determined by the amount of soil moisture present. Due to variability in frequency and intensity of rainfall and variability in soil characteristics, it is very difficult to determine soil moisture content from rainfall data. In an at- tempt to associate amounts of rainfall with tree growth, two correlations were found. There was little divergence of pin oak, white ash, and honey locust trees in the method test at Morton Arboretum from the pattern of little growth in 1963, increased growth in 1964, increased growth in 1965, de- creased growth in 1966, increased growth in 1967, and decreased growth in 1968. Both the amount of rainfall from October through March, prior to the growing season, and the amount from June through August, during the growing season, were correlated with the trunk diameter growth of trees (Fig. 8). These correlations were found to exist on many species of trees at all five sites in this study. Recommendations for shade tree fertilization to arborists and homeowners were prepared by Neely & Himelick (1966). The recommendations were based primarily on this study with addi- tional information gleaned wherever pos- sible from experiments in aboriculture, pomology, forestry, and agronomy. SUMMARY The responses of established trees to applications of fertilizers at five sites in Illinois were determined by annual trunk circumference measurements. As many as 16 treatments (each of the treatments a different combination of fertilizer and method or time or rate of application) were used on 20 species of deciduous trees and 2 species of evergreens. Four methods of application were used: sur- face broadcasting, placement of dry I Sept., 1970 Neely, Himelick, Crowley; Tree Fertilization 263 200 - 160- 120 80- 40- NITR06EN UNTREATED 1963,64,65 264 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 Horticultural Science Proceedings for 1936, 34:664-668. 1940. Fertilization of woody orna- mental plants. Ohio Agricultural Experi- ment Station Bimonthly Bulletin 25:89-96. . 1941. Fertilization of ornamental trees, shrubs, and evergreens. Ohio Agri- cultural Experiment Station Bulletin 620. 29 p. -. Paul E. Tilford. and Charles F. Irish. 1950. A study of some methods of fertilizing shade trees. American Society for Horticultural Science Proceedings for 1949, 55:519-526. Chandler, Robert F., Jr. 1939. The influ- ence of nitrogenous fertilizer applications upon the growth and seed production of beech and sugar maple trees. Arborist's News 4:17-19. Childers. Norman F. (editor) 1954. Miner- al nutrition of fruit crops. Horticultural Publications, Rutgers University, New Brunswick, New Jersey. 907 p. CuRLiN, J. W. 1962. Dogwood responds to nitrogen fertilization. Journal of Forestry 60:718-719. Deuber, Carl G. 1939. Tests of the capacity of shade trees to utilize fertilizers. Bartlett Tree Research Laboratories (F. A. Bartlett Tree Expert Company, Stamford, Connecti- cut) Bulletin 3:3-19. Duke University School of Forestry. 1959. Mineral nutrition of trees, a symposi- um. Duke University School of Forestry Bulletin 15. 184 p. Fehrenb.acher, J. B., and R. T. Odell. 1959. Williamson county soils. Illinois Agricultural Exijeriment Station Soil Re- port 79. 72 p. , G. O. Walker, and H. L. Wascher. 1967. Soils of Illinois. Illinois Agricultural Experiment Station Bulletin 725. 47 p. Finn, Raymond F., and Donald P. White. 1966. Commercial fertilizers increase growth in a yellow-poplar plantation. Jour- nal of Forestry 64:809-810. Himelick. E. B., Dan Neely, and Webster R. Crowley, Jr. 1965. Experimental field studies on shade tree fertilization. Illinois Natural History Survey Biological Notes 53. 12 p. Jacobs, Homer L. 1929. Fertilization of shade trees. Part 1 : Fall vs. spring fertiliza- tion. Davey Tree Expert Company (Kent, Ohio) Research Department Bulletin 4. 28 p. Mustanoja, Karl J., and Albert L. Leaf. 1965. Forest fertilization research, 1957- 1964. Botanical Review 31:151-246. Neely, Dan, and E. B. Himelick. 1966. Fertilizing and watering trees. Illinois Natural History Survey Circular 52. 20 p. PiRONE, P. P. 1951. Foliage application of nutrients. National Shade Tree Conference Proceedings 27:23-35. Pridham, a. M. S. 1938. Growth of pin oak (Quercus palustris) — Report of seven years' observation. American Society for Horticultural Science Proceedings for 1937, 35:739-741. . 1940. Response of mature American elm to ammonium sulfate as a fertilizer. American Society for Horticultural Science Proceedings for 1939, 37:1075-1076. . 1941. Response of red oak to fertili- zation with ammonium sulfate. American Society for Horticultural Science Proceed- ings 39:439. Stoeckeler, Joseph H., and Harold F. Arneman. I960. Fertilizers in forestry. Advances in Agronomy 12:127-195. Symposium on Forest Fertilization (April 1967 at Gainesville, Florida). 1968. For- est fertilization— theory and practice. Tennessee Valley Authority National Fer- tilizer Development Center, Muscle Shoals, Alabama. 306 p. Wascher, H. L., P. T. Veale, and R. T. Odell. 1962. Will county soils. Illinois Agricultural Experiment Station Soil Re- port 80. 108 p. Van de Werken, Hendrik, and James T. Beavers. 1965. The effect of nitrogen on shade trees for lawns. Tennessee Farm & Home Science. Progress Report 54 (April, May, June 1965), p. 19-20. White, Donald P., and Albert L. Leaf. 1956. Forest fertilization. A bibliography, with abstracts on the use of fertilizers and soil amendments in forestry. Syracuse University College of Forestry Technical Publication 81. (World Forestry Series Bulletin No. 2). 305 p. Wyman, Donald. 1936. Growth experiments with pin oaks which are growing under lawn conditions. Cornell University Agri- cultural Experiment Station Bulletin 646. 23 p. INDEX A Acer plalanoiJes. 236. 241 riibrum. 241 sacchaiuin, 241 Application of nutrients methods [see foliar feeding and soil fer- tilization) rates [see rates of fertilization) times [see seasons of application) Ash green, 241 white. 241. 246 Basswood, 242 Broadcast applications. 244. Field trial requirements, 260 Foliar feeding, 237. 243, 246. 253. 261 Fra.xiiius aniericana. 241, 246 pennsyhanica. 241 Gledilsia liiacuiiihos, 241. 246 Growth correlation of with rainfall. 262 measurement of. 246. 251. 260-261 H Hawthorn. 241 Hole treatments with dry fertilizers. 244, 261 Honey locust. 241, 246 Carya illinoeiisis, 241 Color response data. 260. 261 Competition for nutrients, 255, 257. 260. 262 Crab Orchard National Wildlife Refuge precipitation data. 240-241 soil characteristics, 239 test site description, 238, 251 tree species tested. 242 CniloevKs o.xyacaiuha. 241 Diospyios virginianii. 241 Dry fertilizers broadcast applications. 244, 261 hole treatments with, 244, 261 I Injection of liquid fertilizers, 245-246. 261 Jiiiihins nii;ni. 241 L Leaf color. 260 Lincoln Trail State Park precipitation data. 240 soil characteristics. 239 test site description. 237-238. 250-251 tree species tested. 242 Linden. 242 Liquid fertilizers, 245-246. 261 Liquidainhar styiacifiua. 241 Liriodendiim liilipijeia. 241 Elm. 236. 242 Equipment for fertilizer application. 244. 245- 246 Fertilizers dry [see broadcast applications und hole treatments) liquid. 245-246. 261 methods of application [see foliar feed- ing and soil fertilization ) rates of application [see rates of fertiliza- tion) source materials, 243 times of application [see seasons of ap- plication) M Maple Norway. 236. 241 red. 241 sugar. 241 Methods of fertilization [see foliar feeding and soil fertilization ) Morton Arboretum precipitation data, 240 soil characteristics. 239 test site description, 237. 246 tree species tested, 242 N Natural History Survey Arboretum precipitation data, 240 265 266 Illinois Natural History Survey Bulletin Vol. 30, Art. 4 soil characteristics. 239 test site description, 237, 249 tree species tested, 242 Nutrient elements tested (see fertilizers, source materials) Oak pin, 236, 242, 246 red, 241 swamp white, 241 white, 241 Pecan, 241 Persimmon, 241 Pine loblolly, 242 red, 242 Piniis resinosa, 242 tacda, I'^l Platanus occidcntalis, 241 Qiiercus alba, 241 bicolor, 241 palustris, 236, 242, 246 rubra, 241 Rates of fertilization, 243, 244, 248, 255-256, 261 Residual fertilizer, 254 Seasons of application, 247-248, 255, 261- 262 Sinnissippi Forest precipitation data, 240 soil characteristics, 239 test site description, 237, 249 tree species tested, 242 Soil fertilization, 253, 261 Source materials for nutrients micronutrients, 243, 254 nitrogen, 243, 254, 256, 261 phosphorus, 243, 253-254 potassium, 243, 253-254 Sweet gum, 241 Sycamore, 241 T Tilia americana, 242 cordata, lAl Tree growth {see growth) Tulip tree, 241 U Ulinits parvifolia, 242 Rainfall, correlation of with tree growth, 262 Ra-Pid-Gro, 243 Walnut, 241 Some Publications of the ILLINOIS NATURAL HISTORY SURVEY BULLETIN Volume 28, Article 3.—A Comparative Study of Bird Populations in Illinois, 1906-1909 and 1956-1958. By Richard R. Graber and Jean W. Graber. October, 1963. 146 p., 4 frontis., 32 fig., bibliogr., index. Volume 29, Article 1.—A Biological Investi- gation of the Fishes of Lake Chautauqua, Illinois. By William C. Starrelt and Ar- nold W. Fritz. March, 1965. 104 p., frontis., 40 fig., bibliogr., index. Volume 29, Article 2.—Stocking and Sport Fishing at Lake Glendale (Illinois). By Donald F. Hansen. July, 1966. 54 p., fron- tis., 9 fig., bibliogr., index. Volume 29, Article 3.—Hybridization of Four Species of .Sunfishes (Centrarchidae). By William F. Childers. September, 1967. 55 p., frontis., 2 fig., color plate, bibliogr., in- dex. Volume 29, Article 4.—The Thrips, or Thysa- noptera^of Illinois. By Lewis J. Stannard. May, 1968. 338 p., frontis., 310 fig., bib- liogr., index. Volume 30, Article 1.—^Largemouth Bass and Other Fishes in Ridge Lake, Illinois, 1941- 1963. By George W. Bennett, H. Wick- liffe Adkins, and William F. Childers. Sep- tember, 1969. 67 p., 10 fig., bibliogr., in- dex. Volume 30, Article 2. — Dynamics of One- Species Populations of Fishes in Ponds Subjected to Cropping and Additional Stocking. By D. Homer Buck and Charles F. Thoits III. March, 1970. 97 p., 10 fig., bibliogr., index.^ BIOLOGICAL NOTES 57.—Man's Effect on the Fish and Wildlife of the Illinois River. By Harlow B. Mills, William C. Starrett, and Frank C. Bellrose. June, 1966. 24 p., 16 fig., bibliogr. 58.—The Life History of the Slough Darter, Etheostoma gracile (Pisces, Percidae). By Marvin E. Braasch and Philip W. Smith. June, 1967. 12 p., 8 fig., bibliogr. 59.—^Tables for Estimating Ages and Birth Dates of Cottontail Rabbits with Sugges- tions for Handling Lenses. By William R. Edwards. December, 1967. 4 p., 2 fig. 60.—Use of Feather Minerals as Biological Tracers to Determine the Breeding and Molting Grounds of Wild Geese. By Har- old C. Hanson and Robert L. Jones. Feb- ruary, 1968. 8 p., 2 fig., bibliogr. 61.—Waterfowl Migration Corridors East of the Rocky Mountains in the United States. By Frank C. Bellrose. June, 1968. 24 p., 6 fig., bibliogr. 62.—Nightlighting; Its Use in Capturing Pheasants, Prairie Chickens, Bobwhites, and Cottontails. By Ronald F. Labisky. Octo- ber, 1968. 12 p., 8 fig., bibliogr. 63.—Selected Minerals in Soils, Plants, and Pheasants: An Ecosystem Approach to Un- derstanding Pheasant Distribution in Illinois. By Robert L. Jones, Ronald F. Labisky, and William L. Anderson. December, 1968. 8 p., 1 fig., bibliogr. 64.—^The Value of In Vitro Fungicide Tests. By Dan Neely. January, 1969, 8 p., bibliogr. 65.—Trends in Pheasant Abundance in Illi- nois: 1958 to 1968. By Ronald F. Labisky. May, 1969. 8 p., 4 fig., bibliogr. 66.—^Tree and Shrub Hosts of Verticillium albo-atrum. By E. B. Himelick. July, 1969. 8 p., bibliogr. 67.—Concentrations of Chemical Elements in Pheasant Tissues. By William L. Anderson and Peggy L. Stewart. April, 1970. 15 p., bibliogr. CIRCULAR 46.—Illinois Trees: Their Diseases. By J. Cedric Carter. June, 1964. (Third printing, with alterations.) 96 p., frontis., 89 fig. 49.—The Dunesland Heritage of Illinois. By Herbert H. Ross (in cooperation with Illi- nois Department of Conservation). August, 1963. 28 p., frontis., 16 fig., bibliogr. 51.—Illinois Trees: Selection, Planting, and Care. By J. Cedric Carter. August, 1966. 123 p., frontis., 108 fig. 52.—Fertilizing and Watering Trees. By Dan Neely and E. B. Himelick. December, 1968. (Second printing.) 20 p., 9 fig., bibliogr. 53.—Dutch Elm Disease in Illinois. By J. Cedric Carter. October, 1967. 19 p., fron- tis., 17 fig. List of available publications mailed on request No charge is made for publications of the Illinois Natural History Survey. A single copy of most publications will be sent free to anyone requesting it until the supply becomes low. Costly publications, more than one copy of a publication, and publications in short supply are subjects for special correspondence. Such correspondence should identify the writer and explain the use to be made of the publication or publications. Addrett orders and correspondence to the Chief, Illinois Natural History Survey Natural Resources Building, Urbana, Illinois 61601