LIBRARY Midnnguu University "Hts!" This is to certify that the thesis entitled THE EFFECTS OF VERTICAL OPERATING HOLLOW TINE (VOHT) CULTIVATION ON TURFGRASS SOIL STRUCTURE presented by V ‘ J Anthony Martin Petrovic ' has been accepted towards fulfillment of the requirements for Ph.D. degree inEOP and Soil Sciences l p I ' . ' ' Major professor Date July 6, 1979 0-7639 REMOTE STORAGE RES F PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. DATE DUE DATE DUE DATE DUE WW1 l 78 20:: Blue 10/13 p:/C|RC/DateDueForms_2013.:ndd - p95 THE EFFECTS OF VERTICAL OPERATING HOLLOW TINE (VOHT) CULTIVATION ON TURFGRASS SOIL STRUCTURE By Anthony Martin Petrovic A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences. 1979 ABSTRACT THE EFFECTS OF VERTICAL OPERATING HOLLOW TINE (VOHT) CULTIVATION ON TURFGRASS SOIL STRUCTURE By Anthony Martin Petrovic A method of VOHT (vertical operating hollow tine) core cultivation for laboratory and greenhouse experiments was studied. The field VOHT coring unit mechanism of tine movement is periodic in nature. In a laboratory study it was found that increasing the rate of tine movement from 0.5 to 1270 mm/min only increased the pressure required to cause tine penetration a maximum of 0.43 kg/cmz. From the results of a confined compaction test it was concluded that a small pressure increase as noted here would have a negligible effect on soil bulk density. A machine that operates at a constant set rate of movement, such as an InstronR universal testing machine, therefore. can be used for greenhouse and laboratory studies to simulate the field VOHT core cultivator. To determine the effects of VOHT cultivation on soil structure, a method of obtaining bulk density jg_§itg for a volume of soil as small as l.25 x l.25 x 2 mm was developed. The technique of X-ray transmission computed tomography (CT) scanning, an advanced tool used in diagnostic radiology, was studied. CT scanner analysis of samples of Metea fine sandy loam and samples of glass bead-air filled glass Spheres that ranged in bulk density from 0.l4 to l.64 g/cm3 revealed that a positive machine Anthony Martin Petrovic response occurred with increasing density. The minimum effective spatial resolution was determined for materials that varied greatly in density (air to acrylic) and that only had a l% difference in attenuation co- efficients. These resolutions were found to be 1.25 x l.25 x 2.4 mm and 6.4 x 6.4 x 2.4 mm, respectively. Artifacts can occur when the sample container size and composition is not standardized and if large stones and/or long straight holes or channels are present in the sample. Simple methods can be used to correct for such artifacts. Having the technology to accurately measure spatial variation in bulk density in_§itu_for a volume of soil as large as 500 x 500 x 10 mm to as small as l.25 x l.25 x 2 mm will aid researchers in the field of soil science immensely. The effects of VOHT coring on bulk density of a Metea sandy loam soil was examined in laboratory and greenhouse studies. Under laboratory conditions it was found that VOHT coring caused a significant increase bulk density in the soil surrounding the coring hole. The maximum density occurred within 1 to 2 mm from the edge of the coring hole and decreased linearly away from the hole for a distance of lo to 12 mm. Tine size had little effect on the maximum density, however, the larger tines increased the distance of soil away from the coring hole with a higher bulk density. Decreasing the soil moisture content at the time of VOHT coring caused a slight decrease in the maximum density as well as a decrease in the size of the zone of soil with larger bulk density. The relative degree of com- paction caused by VOHT coring was greater in the soil below the coring hole than at the edge of hole. Anthony Martin Petrovic The results from the greenhouse study indicated that VOHT coring caused a similar degree and pattern of compaction as noted previously. Soil at a higher initial bulk density did not show a large level of increased compaction as the lower density soil. After 93 days following VOHT coring, the walls of the coring holes had collapsed. Soil below the coring hole, however was still at a similar compaction level noted at 14 days. In a 2-year field study maintained under putting green conditions, it was found that VOHT cultivation had no short term significant effects on oxygen diffusion rates, turfgrass quality and soil strength. The potential for the long term development of a layer of highly compacted soil just below the depth of cultivation exists. VOHT coring can still, however help reduce surface soil compaction problems on established turfgrass. To my wife Renie and my parents for their love, patience and understanding ii ACKNOWLEDGEMENTS The author wishes to thank Dr. P. E. Rieke, chairman of my guidance committee, for his guidance, encouragement and patience that made my graduate education extremely rewarding. A grateful acknowledge- ment is extended to the members of my guidance committee; Dr. A. E. Erickson, Dr. D. Penner and Dr. J. M. Vargas, Jr. for their assistance in this investigation. The author also wishes to thank Dr. A. K. Srivastava, Mr. J. Siebert and Mr. R. Bay for their assistance. An acknowledgement is also extended to the Golf Course Superintendents Association of America Research Fund and to the Michigan Turfgrass Foundation for their financial support. TABLE OF CONTENTS Page LIST OF TABLES ......................... vi LIST OF FIGURES ......................... vii INTRODUCTION .......................... 1 Chapter I. A VERTICAL OPERATING HOLLOW TINE (VOHT TURFGRASS CORE CULTIVATOR FOR LABORATORY AND GREENHOUSE STUDIES ...... 3 ABSTRACT ....................... 3 INTRODUCTION ..................... 3 MATERIALS AND METHODS ................. 4 RESULTS AND DISCUSSION ................ 6 CONCLUSIONS ...................... 7 LITERATURE CITED ................... 9 II. DETERMINATION OF SOIL BULK DENSITY BY COMPUTED TOMOGRAPHY (CT) SCANNING .................. 14 ABSTRACT ....................... 14 INTRODUCTION ..................... 15 MATERIALS AND METHODS ................. l6 RESULTS AND DISCUSSION ................ 2l SUMMARY ........................ 24 LITERATURE CITED ................... 25 III. SOIL COMPACTION—INDUCING EFFECT OF VERTICAL OPERATING HOLLOW TINE (VOHT) TURFGRASS CULTIVATION, A LABORATORY STUDY ........................... 37 ABSTRACT ....................... 37 INTRODUCTION ..................... 38 iv Chapter Page MATERIALS AND METHODS .................. 39 RESULTS AND DISCUSSION .................. 42 LITERATURE CITED ..................... 49 IV. SOIL COMPACTION INDUCING EFFECTS OF VERTICAL OPERATING HOLLOW TINE TURFGRASS CULTIVATION, GREENHOUSE AND FIELD RESULTS . . . 70 ABSTRACT ......................... 70 INTRODUCTION ....................... 71 MATERIALS AND METHODS .................. 72 RESULTS AND DISCUSSION .................. 76 SUMMARY ......................... 79 LITERATURE CITED ..................... 80 CONCLUSIONS ............................ 85 Table 1.1. 1.2. 11.1. 111.1. 111.2. 111.3. III.4. III.5. IV.T. IV.2. IV.3. IV.4. LIST OF TABLES Page Tine penetration force as a function of tine movement rate for a 6.4 mm tine ............. 12 The effect of compacting pressure on the bulk density of a Metea fine sandy loam soil ......... 13 Mean and standard deviation Of Hounsfield units obtained from computed tomographic (CT) analysis of Metea soil samples at various bulk densities ..... 36 Physical properties of Metea fine sandy loam soil . . . . 65 Coefficients and coefficients of determination (R2)- for multiple regression equations developed from density in the side wall region ............. 66 Coefficients and the coefficients of determination (R2) for multiple regression equations developed from vertical sections below the bottom of the coring hole ....... 67 Parameters used in Equations [2] through [5] to develop density isograms ................ 68 Average reduction in overall soil bulk density following VOHT core cultivation ............. 69 Average increase in soil bulk density following VOHT core cultivation with a 9.5 mm tine. Date shown is the average of 2 replications .............. 82 Average increase in soil bulk density following VOHT core cultivation with a 15.9 mm tine. Data shown is the average of 2 replications ............. 83 Average oxygen diffusion rates (ODR) obtained in the VOHT field study ................... 84 Average penetrometer reading obtained at various points below the soil surface in the VOHT field study . . 85 vi Figure 1.1. 1.2. 11.1. 11.2. 11.3. 11.4. 11.5. 11.6. 11.7. 11.8. 11.9. LIST OF FIGURES Photograph of Instron machine with 6.4 mm tine attached The effect of rate of penetration of a 6.4 mm tine on pressure required to cause tine movement at various depths below soil surface. The lines shown were developed from regression equations found in Table 1.1. Photograph of CT scanner showing the exposed ring of detectors and X-ray source ............... The influence of increasing bulk density of Metea fine sandy loam soil and glass bead-sphere samples on Hounfield units .................... The effect of increasing volumetric water content in Metea sandy loam soil on average Hounsfield units obtained from CT scanner analysis ........... CT image of an acrylic cylinder (A) that contains a series of air-filled hole ranging in size from 2.50 to 0.75 mm in diameter. Note that the arrow in (B) locates the smallest visible holes (1.25 mm) . . CT image of acrylic cylinder that contains various size holes filled with a glycerol: proponal mixture to illustrate low contrast spatial resolution. Note that the arrow locates the smallest visible hole (6.4 mm) ........................ Profile of the nominal 2 and 10 mm beam width settings that contain the full width at half maximum (FWHM) points ......................... CT image of a 21.5 cm (A) and 30.5 cm (8 and C) acrylic water baths .................. CT images of a Metea fine sandy laom soil sample containing a 76 mm long tappered hole (upper diameter of 18 mm, bottom diameter of 16 mm) scanned without (A) and with (8) soil placed back in the hole. Note artifact streaks in (A) created as a result of beam hardening ..................... CT image of 3 stones of various sizes. Note that the small stones (A) have little effect on the surrounding water. The largest stone, however, caused great errors in the water (8) and in the glass beads (E) in the areas of the stone ............. vii Page . IO . ll 27 . 29 . 3O . 32 . 33 . 34 . 35 LIST OF FIGURES (continued) Figure Page III.1. Diagram of cross-section obtained from the CT scanner. Shaded and lettered areas represent the locations of density analysis .............. 51 111.2. Lines of equal bulk density (g/cm3) observed in the uncored soil .................... 52 111.3. Lines of equal bulk density (g/cm3) created by a 6.4 mm VOHT at a soil moisture content of 15.6%, by weight ........................ 53 111.4. Lines of equal bulk density (g/cm3) created by a 6.4 mm VOHT at a soil moisture content of 12.9%, by weight . . . 54 111.5. Lines of equal bulk density (g/cm3) created by a 6.4 mm VOHT at a soil moisture content of 10.9%, by weight . . . 55 111.6. Lines of equal bulk density (g/cm3) created by a 9.5 mm VOHT at a soil moisture content of 15.6%, by weight . . . 56 111.7. Lines of equal bulk density (g/cm3) created by a 9.5 mm VOHT at a soil moisture content of 12.9%, by weight . . . 57 111.8. Lines of equal bulk density (g/cm3) created by a 9.5 mm VOHT at a soil moisture content of 10.9%, by weight . . . 58 III.9. Lines of equal bulk density (g/cm3) created by a 12.7 mm VOHT at a soil moisture content of 15.6%, by weight ......................... 59 111.10. Lines of equal bulk density (g/cm3) created by a 12.7 mm VOHT at a soil moisture content of 12.9%, by weight ......................... 60 111.11. Lines of equal bulk density (g/cm3) created by a 12.7 mm VOHT at a soil moisture content of 10.9%, by weight .......................... 61 111.12. Lines of equal bulk density (g/cm3) created by a 15.9 mm VOHT at a soil moisture content of 15.6%, by weight. . 62 111.13. Lines of equal bulk density (g/cm3) created by a 15.9 mm VOHT at a soil moisture content of 12.9%, by weight. . 63 111.14. Lines of equal bulk density (g/cm3) created by a 15.9 mm VOHT at a soil moisture content of 10.9%, by weight. . 64 viii INTRODUCTION Soil compaction is a major problem associated with high use recreational areas such as golf course putting greens. Extensive foot and vehicular traffic can result in an increased compaction and an associated reduction of water movement into the soil, in poorly aerated soil conditions, and in a high soil mechanical impedence of root growth. The overall turfgrass quality is usually lower under compacted soil con- ditions. In addition, maintenance requirements are substantially larger under compacted soil conditions. Common practices used to alleviate surface compaction on established turfs are traffic control measures and cultivation. Types of Cultivation include slicing, spiking, coring and deeper subaerification. Several forms of core cultivation are spoon, drum and vertical operation hollow tine (VOHT). The overall effects of VOHT coring on reducing the level of surface compaction, however are not clearly understood. The design of the coring tines are such that the hole made in the soil by coring is substantially larger than the cylinder or core of soil removed. The soil surrounding the coring hole must therefore be compressed to compensate for this size difference. Research on the effects of VOHT coring on soil structure has been 1) limited by natural soil variability under field condition, 2) somewhat limited by the lack of a suitable laboratory coring machine, and 3) to a large extent by the current soil physical analytical methodology. The Objectives of the investigations were to: (l) devise a method to simulate the field VOHT coring operation for use in laboratory and greenhouse studies; (2) develop an analytical technique that can measure soil bulk densities jfl_situ for a volume of soil 2 mm or less; (3) study the effects of VOHT cultivation on soil structure as influenced by tine size, soil moisture content, and initial degree of soil compaction. CHAPTER 1 A VERTICAL OPERATING HOLLOW TINE (VOHT) TURFGRASS CORE CULTIVATOR FOR LABORATORY AND GREENHOUSE STUDIES ABSTRACT The mechanism of tine movement for a field VOHT (vertical operating hollow tine) core cultivator is periodic in nature. A laboratory study was conducted to determine if the rate of tine penetration has an appreciable effect on the force needed for penetration. Increasing rate of tine movement was found to have a slight effect on increasing force and pressure of tine penetration. However, the increase in pressure was small and should have a negligible effect on soil parameters such as bulk density. The Instron universal testing machine, which can be operated at a set rate of movement was found to simulate the field VOHT core culti- vator and can, therefore, be used for laboratory and greenhouse studies. INTRODUCTON Compaction is a major problem associated with high use recreational turfgrass areas such as athletic fields, parks and golf courses. Common ' methods used to combat soil compaction are soil modification with sand and/or other coarse aggregates, traffic control and cultivation (1). Core cultivation, in particular the vertical operating hollow tine (VOHT) method, is widely used on golf course putting greens. Little, if any, research has been published on the effects of VOHT core cultivation on soil structure and plant growth. The field VOHT coring machine has an oscillating speed of tine movement. This presents a problem of duplication of the technique for research studies since such mechanisms are both difficult and costly to construct. Units that have a constant speed driving head, such as the Instron universal testing machine, are commonly found in agricultural engineering and civil engineering laboratories. The objective tested in this research were to determine 1) the effects of tine movement speed on the force required to cause tine penetration into the soil and 2) if the Instron machine would simulate the field core cultivator for use in greenhouse and laboratory studies. MATERIALS AND METHODS The speed of tine movement of a VOHT coring machine, in this case a Ryan's GreensaireR aerifier model A-5, was measured during operation in the field. At an engine speed of 300 rpm, the crank-rod-tine assembly rotated 237 rpm. The total vertical tine displacement was 11.4 cm. The maximum velocity of 85,070 mm/min occurred at 90° of crank rotation. An Instron universal testing machine, model TM (see Fig. 1.1.), was used to study tine penetration force as a function of tine velocity under laboratory conditions. Velocities selected were 0.51, 5.1, 51, 254, 510 and 1270 mm/min. 1270 mm/min is the maximum attainable speed for this unit. Force required to cause tine penetration was monitored on a load cell and was plotted against distance of tine penetration with a chart recorder. The soil used was an air dried surface Metea fine sandy loam (loamy, mixed, mesic Arenic Hapludalf) passed through a 1.00 mm sieve. This soil contained 73% sand, 18.6% silt and 8.4% clay, and 1.1% organic matter; Aluminum cylinders, 7.36 cm 1.0. by 12.7 cm long, were covered at one end with two layers of cheese cloth and filled with uncompacted soil. The initial bulk density was 1.30 g/cm3. The packed cylinders were placed on 1 bar porous ceramic plates, saturated for 24 hours with tap water, and then equilibrated at a potential of 0.33 bar in pressure extraction containers for 3 days. The moisture content by weight ranged from 10 to 11%. Compaction was applied three times to the upper surface at a pressure of 2.8 bar. A hydraulic compacting frame, similar to that described by Tanabe and Murdock (7) was used for compacting. The bulk density following compaction was 1.55 g/cm3. The Instron machine, fitted with a 6.4 mm 1.0. coring tine, was used to core 3 replicates at each of the 6 speeds (previously listed) to a depth of 7.6 cm. The tine size referred to was that of the manufacturer; however, the actual measured 1.0. was 7.0 mm. Prior to the coring treat- ments, one sample handled in the manner described above was cored so as to fill the tine with soil. Subsequently, the tine contained soil from the previously cored sample thus simulating the natural sequence observed in the field. The general shape of the tine consisted of 3 succeedingly larger truncated cones with the uppermost cone connected to a short cylinder. The external cone diameters each reached a maximum at 1.5, 50.6 and 73.6 mm above the tine tip. The external surface area (cm2) of the tine exposed to the soil at 20, 40, 60 and 76 mm from the tip was calculated and used to convert force of penetration (kg) into pressure (1 bar = 0.98 kg/cmz). A completely random design was utilized in this study. Regression equations describing force of tine penetration as a function of rate of tine movement at 20, 40, 60 and 76 mm in the depth of penetration were developed on a Tektronics mini-computer, model 4050, that contained Plot 50: statisticsR software. The compactability of this soil as related to the compaction (load) pressure was determined by a confined compression test. Acrylic cylinders, 5.1 cm 1.0. by 7 cm long, were filled with soil to give an average initial bulk density of 1.45 g/cm3 i 0.01. Subsamples of soil were taken during packing on which the gravimetric moisture content was determined (dried at 105 C for > 24 hours). The air dry density was then converted to the oven dry equivalent. Each sample received a surface application of tap water to bring the moisture content to 11% by weight and then placed in a desiccator and sealed for 4 days. A weight loss of approximately 0.5% occurred during this period due to water evaporation into the atmosphere within the desiccator. Loading pressures of 0.70, 2.76 and 4.55 bar were used to compact samples by the procedure described previously. The change in bulk density was determined by measuring the decrease in the height component of the volume occupied by soil. Five replications of each of the pressure treatments were arranged in a completely random design. RESULTS AND DISCUSSION The effect of tine movement rate on force required to cause tine penetration is shown in Table 1.1. Increasing the speed generally resulted in a slight increase in force of tine penetration at each depth. However, this effect was minimal at speeds of 50 mm/min or greater. It was estimated from the regression equations shown in Table 1.1. that an increase in the speed of tine movement from 1270 mm/min to the maximum observed for the field unit (85,070 mm/min) would result in only a slight rise in force. The plots of rate verses force of penetration showed no abrupt decrease in force, indicating that shear failures were not induced by speeds in this range. The shape of the coring tine, a truncated cone, is similar to cone- type penetrometers used to measure soil strength. The effect of the rate of penetrometer probe penetration on the resistance of soil to penetration has been found to be inconsistent. Gerard, et a1. (5), Voorhees, et al. (8), and Waldron and Constantin (9) have observed an increase in pene- tration resistance with an increase in rate. However, others have found no effect (2,3) or a slight decrease (4). Changing the speed of tine movement in this case from 0.5 to 1270 mm/min was found to change tine penetration pressure less than 1 order of magnitude (Fig. 1.2.). Pressure differences of such a small degree would appear to have very little impact on bulk density. As seen in Table 1.2., increasing the compacting pressure from 0.70 bar to 4.55 bar resulted in an increase in bulk density of only 8.7%. This would correspond to a 1.3% increase in density for each order of magnitude increase in compacting pressure. This finding was very consistent with that observed by Reaves and Nichols (6). They found that the bulk density of a Decatur silty clay loam soil increased 1.3 to 2.3% (depending on moisture content) per magnitude of increase in load pressure for the pressures ranging from 0.18 to 4.23 bar. CONCLUSIONS The rate of tine movement was found to have a small effect on the force (or pressure) needed to cause tine penetration into the soil. The oscillating rate of tine penetration observed in the field VOHT coring machine, therefore, should have a negligible effect on the bulk density of this soil. The Instron unit, which operates at a set constant rate Of penetration would simulate the field VOHT cultivator and can be used in laboratory and greenhouse studies. LITERATURE CITED Beard, J. B. 1973. Turfgrass: science and culture. Prentice-Hall, Inc., Englewood Cliffs, N.J. 658 pp. Blanchar, R. W., C. R. Edmonds and J. M. Bradford. 1978. Root growth in cores formed from fragipan and B2 horizons of Hobson soil. Soil Sci. Soc. Am. J. 42:437-440. Bradford, J. M., D. A. Farrell and W. E. Larson. 1971. Effect of soil overburden pressure on penetration of fine metal probes. Soil Sci. Soc. Am. Proc. 35:12-15. Cockroft, 8., K. P. Barley and E. L. Greacen. 1969. The penetration of clay by fine probes and root tips. Aust. J. Soil Res. 7:333-348. Gerard, C. J., H. C. Mehta and E. Hinojosa. 1972. Root growth in a clay soil. Soil Sci. 114:37-49. Reaves, C. A. and M. L. Nichols. 1955. Surface soil reaction to pressure. Agric. Eng. 36:813-816. 820. Tanabe, M. J. and C. L. Murdoch. 1974. A modified shop press for use in soil compaction studies. Soil Sci. Soc. Am. Proc. 38:681-682. Voorhees, W. 8., D. A. Farrell and W. E. Larson. 1975. Soil strength 33d aeration effects on root elongation. Soil Sci. Soc. Am. Proc. :948-953. Waldron, L. J., and G. K. Constantin. 1970. Soil resistance to a slowly moving penetrometer. Soil Sci. 109:221-226. Fig. 1.1. Photograph of Instron machine with 6.4 rrm tine attached. TINE PENETRATION PRESSURE,(bor1 [\D «b I N N I N C) I bo l 'm I Its in L Fig. 1.2. 11 DEPTH,mm 0 20 A 40 0 60 A 76 so t- l l l l l O 1 2 3 4 5 Log (RATE) (mm mm") The effect of rate of penetration of a 6.4 mm tine on pressure required to cause tine movement at various depths below soil surface. The lines shown were developed from regression equations found in Table 1.1. 12 Table 1.1. Tine penetration force as a function of tine movement rate for a 6.4 mm tine. Tine movement Depth of tine penetration, mm rateffi 20 40 60 76 mm/min ------------------- kg ------------------ 0.51 6.0 a* 10.1 a 16.2 a 25.0 a 5.1 6.9 ab 11.2 ab 16.7 a 24.3 a 51 7.1 bc 12.1 bc 18.4 bc 27.2 a 254 7.5 bc 12.2 bc 18.5 bc 26.3 a 510 8.0 c 13.1 c 20.3 c 30.3 b 1270 7.9 c 12. 7 c 19.2 c 27.0 a 85,070 10.9+ 13.1+ 21.7+ 32.5+ *Values within columns followed by the same letter are not significantly different at the 5% level. +Estimated values are from the following equations. 20 3mm, v= 0.9293 log x - 0.33309 (log x)2 + 0.067298 (log x13 + 6.32, r2 = .742**; 40 mm, Y= 1.18996 log x - 0.131865 (log x)2 + 10. 41. r2 = .748**; 60 mm, Y= 1. 08267 log x + 16. 34, r2 = .637**; 76 mm, v= 0. 82554 109 x + 0.158699 (log X)2 24.62, r2 = .342*, where Y is force of tine penetration and X is tine movement rate. 13 Table 1.2. The effect of compacting pressure on the bulk density of a Metea fine sandy loam soil. Compacting pressure, bar 0+ 0-7 2-76 4.55 *Values followed by the same letter are not significantly different at the 1% level. +Initial bulk density. CHAPTER 11 DETERMINATION OF SOIL BULK DENSITY BY COMPUTED TOMOGRAPHIC (CT) SCANNING ABSTRACT Current soil bulk densitometric techniques have poor 3-dimensi0nal spatial resolution. The X—ray transmission computed tomography (CT) scanner is on advanced tool in diagnostic radiology used to obtain a non- destructive cross-sectional representation of the human body with a spatial resolution of 2x2x2 mm or less. The machine response is known for materials with linear attenuation coefficients near water. Information on machine response at the upper limit of the measurement range where soil is located was determined. Scanner analysis of soil and glass bead-air filled sphere samples, that varied in bulk density from 0.14 to 1.64 g/cm3, revealed that a positive linear response occurred with increasing density. High and low contrast spatial resolution was found to be 1.25 x 1.25 x 2.4 mm and 6.4 x 6.4 x 2.4 mm, respectively. Loss of data can occur as a result of certain machine artifacts, however, many of these can be avoided by relatively simple methods. Thus, the CT scanner can be used for determinations of soil bulk density jn_situ with a fine 3-dimensional spatial resolution which offers promise to the field of soil science in the areas of compaction, soil management and cultivation research. 14 INTRODUCTION Bulk density is widely used to characterize soil structure and compaction phenomena. Current methods of determining soil bulk density include the direct sampling by extraction of soil cores (17) or clods (l); jg_situ radiation methods such as single beam (25) and dual beam (5) gamma ray attenuation measurements, neutron scattering analysis (9); and to a lesser extent, by the analysis of shear- and compressional-wave propagation through column samples (22). Studies involving modeling of soil mechanical processes (i.e., com- paction, tillage and cultivation) in which fine 3-dimensional spatial resolution is required are limited by contemporary soil densitometry technology. Spatial resolution persists as the principal limitation of soil densitometry. Values obtained with cores or clads represent the gross average density of the sample and give little or no information concerning internal variation. Radiation techniques have improved on l-dimensional resolution in the range of 0.5 mm (8). Resolution in orthogonal directions, however, is several centimeters. In addition, errors can occur in gamma ray densitometry if density within the beam path is not homogenous or if it fluctuates in a non-linear fashion (19). The field of diagnostic radiology has been faced with a similar problem in attempting to obtain an accurate, non-destructive, low-radiation- dose, three-dimensional internal representations of the human body. Roentgen's discovery of the X-ray in 1895 and subsequent development of radioactive sensitive film and fluorosc0pic screen resulted in the con- ventional X-ray shadowgram. Much information is lost, however, when a 3-dimensional object is superimposed on a 2-dimensional detector. With recent advances in X-ray physics, detector technology and mathematical reconstruction theory, the X-ray Transmission Computer 15 16 Tomography (CT) scanner has emerged. The first usable CT scanner system was developed in 1969 by Hounsfield (14) and units became available com- mercially in 1972. The advantage of the CT scanner over other radiographic processes is that a cross section of linear attenuation coefficients (u) is obtained with a recordable radiation adsorption difference as low as 0.1% and a 2-dimensional resolution of 2 mm square or less. There are numerous extenSive review articles on the physics, mathematics, and design of different CT scanners with extensive bibliographies such as Brooks and DiChiro (2,3) McCullough and Paine (18), Swindle and Barret (23) and Ter-Pogossian et a1. (24). Current CT scanner designs are focused on the medical imaging application of body tissues. Hence, instrument performance has been optimized for X-ray absorptions near that of water (0 : 0.2 cm']) and of subjects of roughly circular cross section (ie. the cranium or abdomen). The typical u for soils, however, lies near the upper limit of the measurement range of the instrument. Moreover, soil cores that are scanned in a vertical orientation would have a rectangular shaped cross-section. The objectives of the research reported here are to investigate the limitations, precision, linearity and resolution of CT scanner for determination of soil bulk density. MATERIALS AND METHODS Instrumentation An American Science and Engineering, Inc. CT ScannerR housed at the Michigan State University Clinical Center was used for these studies. This scanner is a fourth generation type which employs a divergent X-ray fan beam that rotates inside the stationary ring of 600 scintillation 17 detectors partially shown in Fig. 11.1. The beam is collimated to form a 50° sector with a variable thickness of 2 to 10 mm. Bismuth germanate scintillation detectors are spaced at 0.6° intervals around the beam path. Either 6 or 12 second scan times may be selected. During a 12 second scan, each detector measures 1200 ray paths (projection) as the X-ray source rotates through the 90° in which that detector is illuminated. A two-dimensional mapping of absorption values into a 512 x 512 element array [0 (x,y)] is reconstructed from the projection data acquired during a scan. The array is graphically displayed as an image on a high—resolution cathode ray tube monitor (see Figure 11.4). As in most current commercial CT scanners, a reconstruction algorythm, called the convolution method of filtered—backprojection, generates the u (x,y) (4,13). Image recon- struction utilizes a specialized extensive computer system to produce the resultant array in about 60 seconds. Depending upon the selected mathematical scaling, the effective size of the 512 x 512 matrix of picture elements (pixels) comprising the image range from 0.25 mm square to 1.00 mm square area in the actual image plane. Hence, an individual pixel value can represent the absorption value of a volume element from 0.25 x 0.25 x 2 mm up to l x l x 10 mm. Objects up to 50 cm in diameter can be imaged. As displayed, the brightness of a pixel is proportional to its numerical value In (x,y)]: the larger the u(x,y) value, the brighter the pixel. To portray the array effectively, the operator interactively selects the mean value (window level) and the range (window width) of absorption values. Several software features assist the operator in printing out or plotting the numerical pixel values within interactively selected areas (known as a curson). The size and location of the cursor 18 can be controlled. Average pixel values and standard deviations are available instantly by cursor manipulation. The instrument output is not in the conventional u units of cm'], but rather in a standardized number scale known as Hounsfield units (H). The linear scale is defined by two points: the absorption values of air and water being -1000 H and 0 H, respectively. Each H represents a 0.1% change in the absorption coefficient (u). Machine Response Studies Response characteristics evaluated were as follows: linearity in response versus density changes for Hounsfield units ranging from ~800 H to +800 H; spatial resolution; effective slice thickness or beam width; and beam hardening effect as influenced by sample size and density. Samples of various proportions of glass beads and hollow glass spheres were used to study the linearity of scanner response with varia- tions in bulk density. Aluminum cylinders 7.36 cm 1.0. by 12.5 cm deep with a side wall thickness of 1.3 mm were filled with mixtures of glass beads 0.2 mm diameter (BallontiniR impact beads, Potter Industries, Inc.) and glass bubbles 0.1 mm diameter (MicrospheresR, 3M, Inc.) to attain bulk densities of 0.04, 0.8, 1.0. 1.21, 1.32 and 1.55 g/cm3. To facili- tate uniform mixing, a small amount of distilled water was added to each mixture. Each sample was allowed to air dry, then scanned in 2 orienta- tions and the results averaged. Spatial resolution involves the ability to distinguish two objects contained in the zone of analysis. Objects that differ greatly in u (high contrast) and objects that only vary slightly (10w contrast) were used to determine the spatial resolving power of this scanner. High-contrast spatial resolution was examined by a test procedure 19 devised by an American Association of Physicists in Medicine (AAPM) for CT scanners (15). The test consists of scanning a 15 cm diameter acrylic cylinder containing a pattern of air-filled square holes with side dimensions of 0.75, 1.00, 1.25, 1.50, 1.75, 2.00, and 2.50 mm. Distance between holes was the same as the hole width for a given size. The acrylic block was centered in a 21.5 cm diameter acrylic water tank. Low contrast resolution was determined from a sample that contained holes that had a 1% difference in u from the surrounding material. A 21.5 cm diameter acrylic cylinder, with holes filled with a fluid contain- ing 50% glycerol to 50% propanol, was scanned. Slice thickness or effective beam width is specified as the full width at half-maximum (FWHM) of the response across the slice orthogonal to the image plane (15). Again, the AAPM (15) recommendation for effective slice thickness determination was followed. A 0.5 mm thick by 25 mm long strand of aluminum positioned at 45° relative to the image plane was scanned. The resulting image depicts the effective beam profile. The FWHM points for 2 and 10 mm width beams were determined from this image. Beam hardening or spectral shift is a phenomenon in which unequal filtration of the polychromatic X-ray beam occurs as the beam penetrates a sample. Photons of lower energy are more readily absorbed by photo- electric interactions as they pass thru material than higher energy photons. -So as an X-ray beam passes through material it "hardens", becoming higher in effective energy. Attempts can be made physically and mathematically (7,16) to correct for this phenomenon, however, beam hardening artifacts do occur under certain conditions. The degree of beam hardening is related to the size, density and atomic number of the sample. Two acrylic cylinders with diameters of 21.5 cm and 30.5 cm 20 were filled with water and used to demonstrate the effect of size on this type of artifact. Zones of drastically changing density can also cause beam hardening artifacts. A sample of Metea fine sandy loam soil (refer to next section on soil preparation) was placed in a 7.36 cm 1.0. by 12.5 cm long aluminum cylinder. A slightly tapered hole, 76 mm long with an upper diameter of 18 mm and bottom diameter of 16 mm, was made in the sample. The sample was scanned and then rescanned after refilling the hole with loosely packed soil. To determine the effects of stones on density of the adjacent soil, three stones varying in size were placed in aluminum cylinders containing water and glass beads were scanned. Soil Studies To evaluate CT scanner response to a soil, samples consisting of a Metea fine sandy loam (loamy, mixed mesic Arenic Hapludalf) were prepared and scanned. The first experiment involved scanning 12 soil samples of known bulk densities ranging from 1.28 to 1.64 g/cm3 and obtaining the mean absorption value (H) over the sample cross section. The soil, at a moisture content of 6.0-7.5% by weight, was passed through a 1.00 mm sieve and packed into 3.2 cm 1.0. by 4 cm high acrylic cylinders. Samples were oven dried at 105 C for 24 hours prior to scanning. The effect of soil moisture content on the scanner response for a given dry bulk density was studied. Soil was placed in 7.36 cm 1.0. x 12.7 cm long aluminum cylinders to a dry equivalent bulk density of 1.30 9/cm3 , saturated with tap water for 24 hours, and equilibrated to potentials of -9.5, -15, -35 and -100 cbar in pressure plate extraction equipment for 2 days. Three replicates of each moisture content were included. 21 The machine was calabrated for a 21.5 cm diameter acrylic water bath which set H for water at 0 :_5. A water filled aluminum cylinder used in these studies also had a mean H value for water of 5 H. All samples were scanned with the X-ray source operated at 125 keV and 30 mA. The 12 second scanning mode was employed with a nominal 10 mm wide X-ray beam. RESULTS AND DISCUSSION Machine Response Understanding the performance of the CT scanner in the range of Hounsfield units (H) greater than +400 has not been well documented (15). As seen in Fig. 11.2., the CT scanner's response to increasing density in the glass bead—sphere samples was linear. Each unit rise in bulk density (mg/cm3) corresponded to a 1.15 H increase. Scanner analysis of Metea soil samples (Fig. 11.2.) also revealed that the machine responded in a linear fashion to changing density. The standard deviations found in Table 11.1. and regression equation in Fig. 11.2. were used to explain the density resolving power of the CT scanner for the Metea soil. Standard deviations (o) of the soil samples ranged from 9 to 50 H while the measurement of a uniform field of tap water yielded a o of 3.5. Hence, the variation in the density and/or composition of these carefully prepared soil samples dominated over the variation of the measurement technique. A change in soil density of 3.8 mg/cm3 would cause a 5 H change in absorption which is considered as the lower limit of density resolution with this machine. Improvements in density resolution can be made by employing longer scan times, higher energy X-ray beams, small sample size and wider slice thicknesses. 22 The slope of the linear regression lines shown in Fig. 11.2. varied slightly between the glass bead-sphere and Metea soil studies. This probably occurred as a result of a difference in atomic composition between the two systems. When density and photon energy are held constant, p is a function of the effective atomic number of the absorbing material (24). Variation in volumetric moisture content (6) in the Metea soil was detected by the CT scanner (see Fig. 11.3.) A change in 6 resulted in a corresponding linear change in H. It should be pointed out, however, that a large variation in u occurred in these samples. Standard deviations ranged from 62 to 128 H in this case. It is apparent the further research is needed to clarify the capability of the CT scanner in determinating volumetric soil moisture content. High contrast resolution, in this case air (-1000 H) to acrylic (: + 125 H), is shown in Fig. 11.4. The CT scanner was able to clearly detect air-filled holes of 2.50, 2.00, 1.75, 1.50 and 1.25 mm in diameter. Holes of 1.00 were slightly visible but not seperated while 0.75 mm holes were not visible. Therefore, a 1.25 x 1.25 mm area in the image plane is considered the resolving power of this machine. The ability to differentiate zones of material that have only a small difference in u is vital in soil research. Fig. 11.5. contains the CT image of the low contrast sample. A region as small as 6 mm can be detected for a difference in u of 1% as shown here. Low contrast resolu- tion is noise-limited since structures are hidden in the image grain. The beam width determines the resolution in the direction perpen- dicular to the image plane. Fig. 11.6.contains the beam profile plots at nominal settings of 2 and 10 mm. Effective beam width (slice thickness) 23 is determined by the location of the full width at half maximum (FWHM) point on the beam profile and was found to be 2.4 and 7.6 mm for the 2 and 10 mm beams, respectively. The beam hardening artifact can be a potential problem in soils research. The size of the sample has a small but pronounced effect on the image obtained. Water has an H value set at 0, however, the center value in the 21.5 and 30.5 cm diameter water baths were +9.6 and -17.2 H, respectively (Fig. 11.7. A and B). The scanner can be calibrated for a particular size object which in this case was about a 25 cm diameter water bath. In addition, a variation of 7.4 H occurred between the center and edge of the 30.5 cm sample (Fig. 11.7 A and C). This difference is related to the length travelled by the X-ray beam through an absorber. The longer the path of travel the greater the likelihood that lower energy photons will be absorbed which will increase the effective energy of the beam. It should be pointed out that in experiments involving comparisons of CT images, the size and composition of the sample container should be standardized to avoid an artifact of this nature. Errors introduced by the container can be readily seen by scanning it filled with water. A zone of drastically changing density, such as an air-filled hole or a stone in soil, can cause the destruction of information due to beam hardening and mathematical anomalies. In the example where a long straight zone containing a large density gradient (Fig. 11.8A), lines or streaks developed in the plane of symmetry at the density gradient interface. Filling the air-filled hole with loose unpacted soil eliminated the streaks (Fig. 11.88). 24 Fig. 11.9. contains a series of CT images of different size stones in different media. It was found that only the large wedged shape stone (22 mm high by 15 mm at the base) had an appreciable negative effect on surrounding water beyond the interface region. The streaking was still evident when this stone was placed in the more dense glass beads (density similar to soil). (See Fig. 11.9C.) Many of the basic studies that have developed the fundamental concepts of compaction processes in soil have used less accurate indirect methods of analysis. These methods include strain gauge pressure cells (20,21), displacement of pins in a grid system (6,10,11), and the extrac- tion of large soil cores (12) to obtain the gross average bulk density in a profile. It is likely that the addition of objects (strain gauges or pins) or the core sampling operation could have had some influence on the results of these studies. SUMMARY Studies were conducted to determine the limitations and precision of the CT scanner for soil bulk density determinations. The machine response was found to be linear with respect to increasing bulk density over a range of densities from 0.14 to 1.64 g/cm3. High and low contrast spatial resolution were 1.25 x 1.25 x 2.4 mm and 6.4 x 6.4 x 2.4 mm, respectively. Information can be lost due to artifacts that occur when size and compo- sition of the sample container varies, when large stones are present and when a long straight air filled hole or channel is in the sample. Having the technology to accurately measure spatial variation in bulk density jn_§itg_for a volume of soil as large as 500 x 500 x 10 mm. to as small as 1.25 x 1.25 x 2 mm will aid researchers in the field of soil science immensely. 10. ll. 12. 13. 25 LITERATURE CITED Brasher, B. R., D. P. Franzmeier, V. Valassis, and S. E. Davidson. 1966. Use of saran resin to coat natural soil clods for bulk density and water retention measurements. Soil Sci. 101:108. Brooks, R. A., and G. DiChiro. 1975. Theory of image reconstruction in computed tomography. Radiology 117:561-572. Brooks, R. A., and G. DiChiro. 1976. Principles of computer assisted tomography in radiographic and radioisotopic imaging. Phys. Med. Biol. 21(5):689-732. Chase, R. C., and J. A. Stein. 1978. An improved imaged algorithm for CT scanners. Medical Physics 5(6):497-499. Corey, J. C., S. F. Peterson, and M. A. Wakat. 1971. Measurement of attenuation of Cs and Am gamma rays for soil density and water content determinations. Soil Sci. Soc. Am. Proc. 35:215-219. Dexter, A. R., and D. W. Tanner. 1972. Soil deformations induced by a moving cutting blade, an expanding tube and a penetrating sphere. J. Agric. Eng. Res. 17:371-375. Duerinckx, A. J. and A. Macovski. 1978. Polychromatic streak artifacts in computed tomography images. J. Comput. Assist. Tomogr. 2:481-487. Gardner, W. H., G. S. Campbell, and C. Calissendorff. 1972. System- atic and random errors in dual gamma energy soil bulk density and water content measurements. Soil Sci. Soc. Am. Proc. 36:393-398. Gardner, W., and D. Kirkham. 1952. Determination of soil moisture by neutron scattering. Soil Sci. 73:391-401. Gill, W. R. 1968. Influence of compaction hardening of soil on penetration resistance. Trans. ASAE 11:744-745. . 1969. Soil deformation by simple tools. Trans. ASAE . and C. A. Reaves. 1956. Compaction patterns of smooth rubber tTres. Agric. Eng. 37:677-680. 684. Herman, G. T., A. V. Lakshminarayana, and A. Naparstek. 1977. Recon- struction using divergent-ray shadowgrams. (In) Reconstruction tomography in dia nostic radiology and nuclear medicine. Ter- Pogissian et a1. Ieds.). University Park Press. Baltimore. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26 Hounsfield, G. N. 1972. A method of and apparatus for examination of a body by radiation such as X or gamma-radiation. British Patent No. 1283915, London. (Filed Aug., 1968). Judy, P. F., S. Balter, D. Bassano, E. C. McCullough, J. T. Payne, L. Rothenberg. 1977. Report Number I, AAPM task force on CT scanner phantoms: Phantoms for performance valuation and quality assurance of CT scanners. American Association of Physicists in Medicine, Chicago, Illinois. Kijewski, P. K., and B. E. Bjarngard. 1978. Correction for beam hardening in computed tomography. Med. Phys. 5(3):209-214. Lutz, J. F. 1947. Apparatus for collecting undisturbed soil samples. Soil Sci. 64:399-401. McCullough, E. C., and J. T. Payne. 1977. X-ray-transmission computed tomography. Med. Physics 4(2):85-98. Nofziger, D. L. 1978. Errors in gamma-ray measurements of water content and bulk density in nonuniform soils. Soil Sci. Soc. Am. J. 42:845-850. Reaves, C. A., and M. L. Nichols. 1955. Surface soil reaction to pressure. Agric. Eng. 36:813-816. 820. , and A. W. Cooper. 1960. Stress distribution in soils under tractor loads. Agric. Eng. 41:21,22,31. Rickman, R. W. 1970. Soil structure evaluation with audiofrequency vibration. Soil Sci. Soc. Am. Proc. 34:19-24. Swindell, W. and H. H. Barrett. 1977. Computerized tomography: taking sectional X-rays. Physics Today 30(12):332-4l. Ter-Pogossian, M. M. Phelps, and G. L. Brownell (eds.). 1977. Reconstruction tomography in diagnostic radiology and nuclear medicine. University Park Press. Baltimore. Vomocil, J. A. 1954. Ig_situ measurement of soil bulk density. Agric. Eng. 39:651-654. 27 Fig. 11.1. Photograph of CT scanner showing the exposed ring of detectors and X—ray source. HOUNSFIELD UNITS (HI, GLASS DEAD-SPHERE Fig. 28 800- 1800 0 GLASS DEAD-SPHERE 400 _ A NETEA SOIL . 700 0' 9600 -400- 1500 '800 " -1 400 . . . j 0.2 0.4 0.6 018 140 1:2 1.4 1.6 BULK DENSITY (g/cm31 11.2. The influence of increasing bulk density of Metea soil and glass bead-sphere samples on Hounfield units. HOUNSFIELD UNITS (HI, METEA SOIL 29 880 r so 860 T 840 F 820L 800 - HOUNSFIELD UNITS (HI .4 00 CD I 1‘0 12 1'4 1'6 18 20 WATER CONTENT (cm3/cm3) Fig. 11.3. The effect of increasing volumetric water content on average Hounsfield units obtained from CT scanner analysis. m s u CLINICRL can gLIcE - 958E . NL 40 mm 300 Fig. 11.4. ....O «— 222?. B C O O O O ' ”9 '- CT image of an acrylic cylinder (A) that contains a series of air-filled hole ranging in size from 2.50 to 0.75 mm in diameter. Note that the arrow in (B) locates the smallest visible holes (1.25 mm). 31 Fig. 11.5. CT image of acrylic cylinder that contains various size holes filled with a glycerol: proponal mixture to illustrate low contrast spatial resolution. Note that the arrow locates the smallest visible hole (6.4 m). 32 1 BCMD 2mm 10mm 70C> Y J SCKJ- SCK) U 4(X)’ 3CK3- nouns FIELD UNITS (HI, 2mm SETTING 2CM3- 1 100 aiaiaisaaaiaiaaaa WIDTH,mm Fig. 11.6. Profile of the nominal 2 and 10 m beam width settings that contain the full width at half maximum (FWHM) points. ZCM) H30 HOUNSFIELD UNITS (HI, 10mm SETTING 33 CLINICRL CENTER M S U H. S. U. CLINICAL CENTE . .... . :1 a . . .. . ...I.v. win flr.uh.fid%hfl L...w..,r....m:......? .. ..~ ...w~H«\THm. . .P'r.’ v4.5 ..¢ . . \I 4.! nté a... \ . .thuu JCU~Z~JU D m (A) and 30.5 cm (B and C) acrylic f a 21.5 c 1.7. CT image 0 water baths. 1 Fig. 34 CCNTER Fig. 11.8. CT images of a Metea fine sandy loam soil sample containing a 76 mm long tapered hole (upper diameter of 18 mm, bottom diameter of 16 mm) scanned without (A) and with (B) loose soil placed back in the hole. Note artifacts streaks in (A) created as a result of beam hardening. 35 CT image of 3 stones of various sizes. Note that the small stones (A) have little effect on the surrounding water. The lar est stone, however, caused great errors in the water (8)1 and in the glass beads (C) in the areas around the stone. 36 Table 11.1. Mean and standard deviation of Hounsfield units obtained from computed tomographic (CT) analysis of Metea soil samples at various bulk densities. Hounsfield units Soil bulk density Mean Standard deviation g/cm3 """""""" H """"""" 1.277 465 18.7 1.305 509 18.0 1.327 543 19.0 1.405 610 21.0 1.429 658 21.2 1.434 647 18.7 1.500 667 11.6 1.570 789 21.3 1.598 796 13.0 1.613 798 13.7 1.614 805 9.0 1.636 780 50.5 Tap water 0 3.5 CHAPTER III SOIL COMPACTION - INDUCING EFFECT OF VERTICAL OPERATING HOLLOW TINE (VOHT) TURFGRASS CULTIVATION, A LABORATORY STUDY ABSTRACT The effects of vertical operating hollow tine (VOHT) turfgrass cultivation on soil bulk density, as influenced by tine size and soil moisture content, were examined under laboratory conditions. Samples of a Metea sandy loam surface soil were screened, compacted and equili- brated to moisture potentials of -9.5, -15 and -35 cbar. Tine sizes of 6.4, 9.5, 12.7 and 15.9 mm in diameter were used to core samples to a depth of 76 mm. A crosssectional array of soil bulk density values immediately following cultivation was obtained by X-ray transmission computed tomographic analysis. In general, VOHT coring caused a large increase in bulk density in the soil surrounding the coring hole. The bulk density reached a maximum within 2 rrm of the coring hole and decreased linearly away from.the hole for a distance of 10 to 12 mm. Beyond this point there was no difference in bulk density between the cored and uncored samples. Varying the tine size had little effect on the maximum density observed. The larger tines did, however, cause an increase of 3.3 mm in the distance away from the side of the coring holes that had higher bulk density. Decreasing the soil moisture content was found to decrease the 37 38 maximum density and the thickness of the zone of soil with higher density at the side wall region of the coring hole for the 6.4 and 9.5 mm tines. This was not true for the 12.7 and 15.9 mm tines. The density of the soil below the coring hole was not influenced to a large degree by variations in tine size and/or moisture content. The relative degree of increased soil bulk density (compaction) caused by VOHT cultivation was larger in the soil below the coring hole than at the side walls. A bulk density gradient was very evident in the uncored samples. It is the assumption of many researchers that surface compacted disturbed samples like these have a uniform density profile. It is apparent that this may not be the case. INTRODUCTION Turfgrass cultivation involves mechanical methods of selectively tilling established turf without destroying the sod characteristics (1). VOHT (vertical operating hollow tine) core cultivation is primarily used on putting greens and tees to alleviate surface compaction, reduce thatch levels, and/or remove unwanted soil layers. However, evidence to support these uses is both limited and conflicting. Engel and Alderfer (4) found that during a 10 year field study under putting green conditions core cultivation had no significant effect on thatch reduction, water penetration, or overall turfgrass quality, and caused a slight increase in oxygen diffusion rate. Murray and Juska (8) observed, however, that coring reduced both thatch accumulation and leaf spot damage and improved the turf quality of common Kentucky bluegrass (Egg pratensis L.). Others have found that water infiltration rates were 39 unaffected (2), reduced (13) or increased (16) by VOHT cultivation. The degree to which a soil will compact is related to its moisture content. Reaves and Nichols (11) and Soehne (14) observed that soil bulk density increased in response to an applied pressure when the moisture content increased from air dry to the lower plastic limit (LPL). The LPL is defined as the minimum moisture content at which the soil particles are sufficiently lubricated so that an applied pressure will cause a perminant change in their size and shape. The objectives of the research reported here were to determint if 1) VOHT coring causes compaction in the cultivation zone and 2) if the degree of soil compaction is related to tine size and soil moisture content at the time of coring. MATERIALS AND METHODS The Metea fine sandy loam soil (loamy, mixed, mesic Arenic Hapludalf) utilized in this investigation had the physical properties shown in Table 111.1. The organic matter content of this soil was 1.1%. Following the procedures used by Tanabe and Murdoch (15), this soil was found to have saturated hydraulic conductivity of 0.13 cm/hour (after 24 hours with a 1 cm hydraulic head) at a bulk density of 1.62 g/cm3. Air dried soil was passed through a 1.00 mm sieve and packed into 7.36 cm 1.0. by 12.7 cm long aluminum tubing. The initial bulk density was 1.29 g/cm3. The samples were then equilibrated to a -33 cbar poten- tial for 3 days and compacted on the upper surface with a hydraulic, compacting ram at a pressure of 2.8 bar. The density following compaction was 1.55 g/cm3. The specific procedure used was similar to that of a previous study (10). 40 The samples were then placed on 1 bar porous ceramic plates, saturated for 1 day in tap water, and equilibrated to a potential of -9.5, -15 or R machine -35 cbars for 2 days in pressure plate extractors. The Instron (10) was used to core each sample at a vertical penetration rate of 51 mm/min to a depth of 76 mm. The force required to cause tine penetration was monitored during the operation. Four sizes of Ryan'sR Greensaire tines used were designated as 6.4, 9.5, 12.7 and 15.9 mm 1.0. However, the actual inside diameters at the lower lip of the tines as measured were 7.0, 7.4, 9.8 and 12.7 mm, respectively. Thus the dimensions designated by the manufacturer are quite different from the actual inside diameters at the smallest point. The 12 soil moisture potential-tine size treatments were replicated 3 times. Three uncored samples, equilibrated at -35 cbar potential, were included for comparison. Samples were oven dried for at least 24 hours at 105 C prior to density analyses. After equilibration, several samples at each moisture potential were sectioned at 2 cm intervals and moisture contents were determined. Moisture content was found to vary by less than 1% by weight within the soil columns. Prior to the coring treatments, one sample handled in the manner described above was cored so as to fill the tine with soil. Subsequently, the tine contained soil from the previously cored sample thus better simulating the natural sequence observed in the field. Bulk density for the region of soil surrounding the coring hole was determined by the x-ray transmission computed tomography (CT) scanning technique (9). Loose oven dried soil was lightly packed into the coring holes to avoid artifacts (9) at the bottom of the samples. The poly- cromatic X-ray beam generated was at a photon energy of 125 keV at 30 mA to at re IE 41 for a 12 second scan. Each sample was positioned so that the 4 mm wide x-ray beam vertic- ally bisected the coring hole (see Fig. 111.1.). Raw data was obtained at various points adjacent to the hole left after coring. Eight horizontal rectangular sections from the center of the sample 30 mm wide, were taken from the following intervals below the soil surface: 0-8, 10-18, 20-28, 30-38, 40-48, 50-58, 60-68 and 70-73 mm. Vertical variation within each interval was small thus the data were averaged in the vertical direction. Five vertical sections of data, 2 mm wide by 12 mm long, were obtained below the coring hole. Fig. 111.1. shows the diagram of the zones selected for data analysis. The vertical sections as seen in Fig. 111.1. referred to the following location: a, the center of the coring hole; b, mid point between a and edge of coring hole (c); and d, approximately midway between c and the outer edge of soil affected by the coring operation (e). The distance between these sections varied depending on tine size. It was found that the raw data only varied slightly in the horizontal direction (2 mm) of these sections. The data were therefore averaged horizontally over this region. The output from the CT scanner is in Hounsfield units. Based on the results of a previous study (9), in which 12 samples of this soil at bulk densities ranging from 1.28 to 1.64 g/cm3 were scanned, the following equation was used to convert Hounsfield units into bulk density: Y = 0.00108X + 0.747 r2 = 0.969** [1] where Y is bulk density and X is Hounsfield units. A comparison of the density plots between uncored and cored samples revealed that a distance of 10 to 12 mm away the coring hole was affected 42 by VOHT coring. Multiple regression equations were developed from data obtained in the horizontal and vertical section described above. A TektronieR minicomputer, model 4050, with Plot 50: StatisticR software, using a forward model selection process, generated the equations and corresponding statistical analyses. RESULTS AND DISCUSSION Density Equations Equations developed to describe density in the cultivation zone were divided into two regions. For the horizontal sections of soil (referred to as the side wall zone), density was a function of per cent soil moisture by weight (X1), force of tine penetration in kg (X2), and horizontal distance away from the edge of the coring hole in mm (X3). Two general forms of equations found were: Y = ax1 + bx2 + ex3 + d [2] Y = eX1 + fXZ + 9 ln X3 + h [3] Thetcoefficients and the coefficients of determination (R2) for the side wall zone equations are shown in Table 111.2. Soil density in the vertical sections below the coring hole was found to conform to the following general equation: _ 2 3 . Y - ax1 + bx2 + cx3 + dx3 + ex3 + fX3 + 9x3 + hx3 + i [41 where Y is bulk density, X1 is percent soil moisture by weight, X2 is the average force of tine penetration caused by the lower lip of the tine in kg and X3 is the vertical distance below the bottom of the coring hole in mm. An exception to this equation occurred for the 6.4 mm tine at 3.6 and 6.6 mm distances away from the edge of the coring hole C0 Cy 43 (refer to vertical sections d and e in Fig. III.l.). In this case, density followed the equation: Y = ax1 + bx2 + c ln(X3 + 1) + i [5] Table 111.3. contains the coefficients and the coefficients of determin- ation (R2) for these equations. The equation describing density within the uncored soil was Y = 0.0015x 2 3 1 2 2 (R2 = .700**) [6] - 0.0076X - 0.00274X + 0.000318X2 + 1.6311 where Y is bulk density, X1 is the horizontal distance away from the center of the sample in mm and X2 is the vertical distance below the soil surface in cm. The regression coefficients shown in Tables 111.2 and 111.3. con- tained enough significant figures to estimate bulk density to the third 3) ‘ decimal place (mg/cm Bulk Density Isograms The effects of VOHT cultivation on soil bulk density are shown in Figs. 111.3 through 111.4. Equations [2] through [5], with coefficients found in Tables 111.2 and 111.3 and parameters listed in Table 111.4 were used to develop the isograms. The parameters used in these equations were soil moisture content (X1), force of tine penetration (X2) and distance away from coring hole (X3). Each figure contains a diagram of the external surface of the tine which would correspond to the hole remaining following cultivation. Points were joined by smooth curves. Fig. 111.2 contains density plots for the uncored soils. In the side wall zone, the lines of equal density generally were contoured parallel to the coring hole. Exceptions occurred near the cylinderical areas of the hole (upper l to 2 cm) for the 9.5, l2.7, and 44 l5.9 mm tines. Density was observed to decrease linearly away from the hole in a horizontal direction for the first cm. Beyond this point density was comparable to that of the uncored soil. Dexter and Tanner (3) studied the effects of vertical penetration of a l4.3 mm thick rectangular blade into a moist loamy sand. They observed a very similar pattern of equal lines of percent volumetric compression of this soil which conformed to the shape of the blade. In addition, they noted that the amount of compression decreased in a linear fashion with distance away from the blade. Gill (6) also found that compaction, as measured by soil displacement, decreased linearly away from the depression made in the soil by wedge-shaped tools. The lines of equal density in the zone of soil below the lower lip and the bottom of the tine revealed that two areas of compaction occurred during VOHT coring. The first was region normal to the surface of the lower lip of the tine in which the lines were arranged in a bulb or arch- like pattern. The second area was located below the bottom of the tine from the edge to the center point of the tine. In this case the equal density lines were parallel to the bottom edge of the hole. Studies involving stress distribution caused by blunt-shaped probes (5,ll) have shown that lines of equal stress conform to these general types of configurations. The 9.5 mm tine caused a slight variation in the equal density for the region below the coring hole in that the greatest density occurred midway between the edge of the tine and the center of the hole. (location b in Fig. 111.1.) The soil moisture content at the time of cultivation was found to significantly affect density in the side wall region for 6.4 and 9.5 mm tines (coefficients a and e in Table 111.2.). In each case, the maximum m " '.g.._r '. . Mm“ Y‘ “‘wi" I.” ""33" h”.' :q' ~ .‘fii 45 density occurred at the LPL and became slightly smaller with drier soil conditions. This effect of moisture content on the compactability of a soil has been observed by others (ll,l4). Soil moisture content did not, however, consistently influence density in the soil below the coring hole (coefficient a in Table III.3.). Varying the tine size had little effect on the magnitude of density observed. Tine size did, however, influence the area of soil that had a high bulk density. As stated earlier, this soil had a low saturated hydraulic conductivity (D.l3 cm/hr) at a bulk density of l.62 g/cm3. A density of 1.62 g/cm3 , therefore, was set as a base above which density could severely restrict saturated water flow. In the side wall region, increasing the tine size from 9.5 to l5.9 mm caused the zone of soil with density of 3_l.62 g/cm'3 to expand from 6 to 9.3 mm in length away from the hole (at l0.9% moisture content). In the area of soil below the coring hole this zone (3.1.62 g/cm3) ranged from 9 to l2 mm and was independent of the tine size and the soil moisture content. In general, the region of soil below the coring hole had a slightly larger maximum density and a wider zone of density 3_l.62 g/cm3 than the side wall area. When compared to the same locations in the uncored soil, the maximum densities were 9% higher in the side wall area and l7% higher below the hole than in the uncored soil. The difference in magnitude of compaction between the side region and the region below the coring hole could be explained in part by the density gradient observed in the uncored soil (Fig. 111.2). Reaves and Nichols (ll) found that increasing the density of a soil a given amount at a specific load pressure is proportional to the degree the soil is already compacted. 46 It is interesting to note the density gradient that was present in the uncored soil (Fig. 111.2). In this case, a pressure was applied to the upper surface of the sample. The result was that compaction, as indicated by higher bulk density, occurred not only at the upper surface but also at the sides and at the bottom of the container. Numerous studies in the past have examined compaction effects on soil physical properties and/or on plant growth in which surface compaction has been applied to disturbed confined samples. It is apparent that a compaction gradient similar to the one observed here could have developed and may have had a significant effect on the results of these studies. Generalized Discussion The hole remaining after coring is substantially larger than the core of soil removed. Thus it is not surprising that VOHT coring caused some compaction in the cultivation zone as observed in this study. The weight of soil removed during VOHT coring was used to calculate the overall reduction in bulk density for the entire sample of soil (see Table 111.5). The field VOHT coring machine has a normal tine spacing of 5l mm. This would represent on the average an area of El x 51 mm for each coring tine. Extrapolating the data in Table 111.5 to the field tine spacing for a similar sample depth (105 mm) and coring depth (76 mm), VOHT coring would cause an overall reduction in bulk density of l.3, l.l, 2.0 and 3.4% for the 6.4, 9.5, 12.7 and 15.9 mm tines, respec- tively. The difference observed here is related to the 1.D. of the tine at the lower lip which corresponds to the diameter of the core of soil removed. 47 As shown here, VOHT cultivation caused a maximum increase of 9 to 17% in bulk density for the soil adjacent (sidewall and below) to the coring hole. Thus, even though an overall reduction in bulk density (or increase in total porosity) for this soil would occur following VOHT coring, the net initial effect on water flow, aeration and overall turfgrass quality may be negligible due to the increased compaction in the zone of soil surrounding the coring hole. It should be emphasized that the results found here only reflect a single cultivation treatment. Repeated coring to the same depth over a period of years could lead to the development of a highly compacted layer of soil just below the depth of cultivation. This would be similar to the plow sole formation observed in other agricultural operations. There are conditions, however, under which improvements in the overall soil physical condition in the rooting zone would be expected to occur following core cultivation. In general, an area that contains an undesirable layer (or layers) within the depth of cultivation would show a positive response to VOHT coring. This layer may be either a zone of highly compacted soil or material that differs widely in texture or composition from the surrounding soil mass. To a large degree, these conditions may help explain the lack of response observed by others. The field test area in the Engel and Alderfer (4) study involved an uncompacted Nixon loam soil that had a naturally high water infiltration rate (NIR). Byrne et. al. (2) found that holes 2.5 cm in diameter by l5 cm deep, back filled with a coarse top soil mixture, resulted in an increase in WIR, whereas VOHT coring to a more shallow depth had no effect. In the 48 case (l3) where WIR was reduced following VOHT coring a small increase in bulk density in the 5 cm below the coring hole was reported. This would suggest that the compaction inducing effect of VOHT coring resulted in the lower NIR he observed. 10. ll. 12. l3. l4. 49 LITERATURE CITED Beard, J. B. 1973. Turfgrass: Science and culture. Prentice—Hall, Inc. Englewood Cliffs, N.J. 658 pp. Byrne, T. 6., w. B. Davis, L. J. Booher, and L. F. Werenfels. 1965. Vertical mulching for improvement of old golf greens. Cal. Agr. 19(5):12-l4. Dexter, A. R., and D. u. Tanner. 1972. Soil deformation induced by a moving cutting blade, an expanding tube and a penetrating sphere. J. Agric. Eng. Res. 17:371-375. Engel, R. E. and R. B. Alderfer. 1967. The effect of cultivation, topdressing, lime, nitrogen and wetting agent on thatch development in l/4-inch bentgrass turf over a ten-year period. New Jersey Agr. Exp. St. Bull. 818:32-45. Gill, w. R. 1968. Influence of compaction hardening of soil on penetration resistance. Trans. ASAE 11:741-745. . 1969. Soil deformation by simple tools. Trans. ASAE 12:234-239. . and C. A. Reaves, 1956. Compaction patterns of smooth rubber tires. Agric. Eng. 37:677-680, 684. Murray, J. J.and F. V. Juska. 1977. Effect of management practices on thatch accumulation, turf quality and leaf spot damage in common Kentucky bluegrass. Agron. J. 69:365-369. Petrovic, A. M., J. Siebert and P. E. Rieke. l9__. Determination of soil bulk density by computed Tomographic (CT) scanning (to be submitted to Soil Sci. J.). Petrovic, A. M., A. K. Srivistava and P. E. Rieke. l9__. A vertical operating hollow tine (VOHT) turfgrass core cultivator for laboratory and greenhouse studies (to be submitted to Agronomy Journal). Reaves, C. A., and A. w. Cooper. 1960. Stress distribution in soils under tractor loads. Agr. Eng. 41:20,21,3l. Reaves, C. A., and M. L. Nichols. 1955. Surface soil reaction to pressure. Agric. Eng. 36:813-816, 820. Roberts, J. M. 1975. Some influences of cultivation on the soil and turfgrass. M. S. Thesis. Purdue University. Soehne, w. 1958. Fundamentals of pressure distribution and soil compaction under tractor tires. Agric. Eng. 39:276-281, 290. 15. 16. 50 Tanabe, M. J., and C. L. Murdock. 1974. A modified shop press for use in soil compaction studies. Soil Sci. Soc. Am. Proc. 38:681-682. Naddington, D. V., T. L. Zimmerman, G. L. Shoop, L. T. Kardos and J. M. Duich. 1974. Soil modification for turfgrass areas. Pennsylvania Agr. Exp. Sta. Progress Report No. 337. 96 pp. 51 / E 3? Es LIJ C2) 8- . obcde IO- 2 4 6 HORIZONTAL DISTANCE (cm) Fig. 111.1. Diagram of cross-section obtained from the CT scanner. Shaded and lettered areas represent the locations of density analysis. DEPTH (cm) 0 52 DISTANCE FROM CENTER OF SAMPLE (mm) IO 20 310 L64 Fig. 111.2. Lines of equal bulk density (g/cm3) observed in the uncored soil. 53 DISTANCE FROM CENTER OF TINE (mm) 0 IO 15 DEPTH (cm) Fig. 111.3. Lines of equal bulk density (g/cm3) created by a 6.4 mm VOHT at a soil moisture content of 15.6%, by weight. DISTANCE FROM CENTER OF TINE (mm) 0 IO 15 L60 DEPTH (cm) Fig. 111.4. Lines of equal bulk density (g/cm3) created by a 6.4 mm VOHT at a soil moisture content of 12.9%, by weight. 55 DISTANCE FROM CENTER OF TINE (mm) IO I5 I O 3 . . l.64 L60 DEPTHIch Fig. 111.5. Lines of equal bulk density (g/cm3) created by a 6.4 mm VOHT at a soil moisture content of 10.9%, by weight. O DEPTH (cm) 56 DISTANCE FROM CENTER OF TINE (mm) l5 Fig. 111.6. Lines of equal bulk density (g/cm3) created by a 9.5 mm VOHT at a soil moisture content of 15.6%, by weight. 57 DISTANCE FROM CENTER OF TINE (mm) 0 I5 DEPTH Ich Fig. 111.7. Lines of equal bulk density (g/cm3) created by a 9.5 mm VOHT at a soil moisture content of 12.9%, by weight. 58 DISTANCE FROM CENTER OF TINE (mm) 0 ‘ S... - IO 15 DEPTH Ich Fig. 111.8. Lines of equal bulk density (g/cm3) created by a 9.5 mm VOHT at a soil moisture content of 10.9%, by weight. 59 DISTANCE FROM CENTER OF TINEImm) o 5 IO 15 DEPTH (cm) L62 Fig. 111.9. Lines of equal bulk density (g/cm3) created by a 12.7 mm VOHT at a soil moisture content of 15.6%, by weight. 60 DISTANCE FROM CENTER OF TINE (mm) 0 5 IO 15 00000000000000000000000000000 OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOO 0000000000000000000000000000 0000000000000000000000000000 OOOOOOOOOOOOOOOOOOOOOOOOOOOO DEPTH (cm) Fig. 111.10. Lines of equal bulk density (g/cm3) created by a 12.7 mm VOHT at a soil moisture content of 12.9%, by weight. 61 DISTANCE FROM CENTER OF TINE 1mm) 0. 5 IO 15 L64 DEPTH 1cm) L60 Fig. 111.11. Lines of equal bulk density (g/cm3) created by a 12.7 mm VOHT at a soil moisture content of 10.9%, by weight. 62 DISTANCE FROM CENTER OF TINE 1mm) 0 5 IO 15 20 Fig. 111.12. Lines of equal bulk density (g/cm3) created by a 15.9 mm VOHT at a soil moisture content of 15.6%, by weight. DEPTH (cm) 63 DISTANCE FROM CENTER OF TINE 1mm) 0 5 IO 15 20 OOOOOOOOOOOOOOOO 00000000000000000 0000000000000000 OOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOO 0000000000000000 ................. ................ 000000000000000 00000000000000 ....... O. C C I a I O 00000000000000 OOOOOOOOOOOOOOO 00000000000000 OOOOOOOOOOOOOOO OOOOOOOOOOOOOO OOOOOOOOOOOOOOO OOOOOOOOOOOOOO OOOOOOOOOOOOOOO OOOOOOOOOOOOOO OOOOOOOOOOOOOOO OOOOOOOOOOOOOO 000000000000000 OOOOOOOOOOOOOO OOOOOOOOOOOOOOO OOOOOOOOOOOOOO OOOOOOOOOOOOOOO OOOOOOOOOOOOOO OOOOOOOOOOOOOOO 00000000000000 OOOOOOOOOOOOOOO OOOOOOOOOOOOOO 000000000000000 OOOOOOOOOOOOOOO 000000000000000 OOOOOOOOOOOOOO OOOOOOOOOOOOOOO 000000000000000 OOOOOOOOOOOOOOO 000000000000000 000000000000000 OOOOOOOOOOOOOOO OOOOOOOOOOOOOO ............... 00000000000000 OOOOOOOOOOOOOOO OOOOOOOOOOOOOO OOOOOOOOOOOOOOO OOOOOOOOOOOOOO OOOOOOOOOOOOOOO OOOOOOOOOOOOOO OOOOOOOOOOOOOOO 00000000000000 OOOOOOOOOOOOOOO OOOOOOOOOOOOOO OOOOOOOOOOOOOOO 00000000000000 OOOOOOOOOOOOOO OOOOOOOOOOOOOO OOOOOOOOOOOOOO 00000000000000 OOOOOOOOOOOOOO .............. OOOOOOOOOOOOOO 0000000000000 00000000000000 0000000000000 OOOOOOOOOOOOOO IIIIIIIIIIIII 0000000000000 OOOOOOOOOOOOO OOOOOOOOOOOOO 0000000000000 OOOOOOOOOOOOO OOOOOOOOOOOOO IIIIIIIIIIIII OOOOOOOOOOOO OOOOOOOOOOOOO oooooooooooo OOOOOOOOOOOOO cccccccccccc Fig. 111.13. Lines of equal bulk density (g/cm3) created by a 15.9 mm VOHT at a soil moisture content of 12.9%, by weight. 64 DISTANCE FROM CENTER OF TINE 1mm) O 5 10 I 5 20 ................................... I'..' T F L74 ES 0 "’ IJO 1.66 1.62 I 5... G. LLJ O 9 1 1 1 Fig. 111.14. Lines of equal bulk density (g/cm3) created by a 15.9 mm VOHT at a soil moisture content of 10.9%, by weight. 65 Rp.op mp uwsPP cwumm_a cmzo4+ o_-m.pp m.mp-m.mp +m_-~_ e.w m.w_ mu o.op m.mm m.P~ o.m m.o ¢.N mm mp m.m xm_u u__m ccmm mo.-—. _.-mm. m~.im. m.i_ Fim NA Leno- «meucmuoa umeugepwom mwmxmmc< quwcmzumz Es .mmcmg «NPm uzmwmz x3 .mmcmc ucmucou mgzamwoz mwmapocu teem .Pwom stop xucmm mcwm mmbmz mo mmmuemgoca _mowmagm ._.-H mpnmh 66 may do «mum mgu ace» xazm mucmam.t m. .x .»S.meee J.ae a. > meme: ; + mxe. N xe + .xe 1 > .m-oc acpgou .uu:o~.gog m. mx use co.uoguwcma on.“ ma oULOL m. 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I 11- 111111 111111 1 II 1 15:1 mm 111M911--211111:D1--11.-1 1;;M:1111119111mw11--111,-- c u a a muouunwu__om muzmewbeOU UUCQfime .:o_ame ._a3 mu_m may :. xu_mcmv ace. cmao.m>mc m:o_um=:m :o_mmmeame m_a_a.:a Cc. Axxv :o_uo:pscoumu Lo mu:m_u_bbmou was mucm.u.~uoou .~.___ o-ac_ 67 .o—on oc.10u any to couaoo us» xo—on mucoum.v .ou.uLu> 0:» a. nu new .o=.u oz» Co 3.. Lyxop on» an vomaou co_uocuocva we.» we coco; mmocu>o “.mx 33¢on 33 “can con a. —x .hucmcuv .23 a. r 01.0...) — + onxz + mnxo + tax» + nnxo + ~nxv + nxu + ~xm + :0 a > ”cozgco 053028 2.3 5 3:32:08- _u>.Sdaaaee ._e>a_ um we. J, we“ a. 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M19861 To ..am~.o m.~._ 1 1 m1o_x_mo.m1 1n1opxoo~e._ .m~__o.c1 n~.o.o Leo.O1 .1o,xm n.m 11mmw.o m~o., 1 1 11.1o_xmann..1 .1n1o_xmm.m.n .1Noo~o.o1 .1Loeo.o uno.o n1o_xo.o c ..~_m.o 03m._ 1 ..m1o,.~_...n .1n1o_.~_.m~._1 11omooe_o.o 1.4m.o_.o1 .1eom~.o «mo.o n1o.xo._ ~.n1 11aeo.c o~n._ 1 1 11e1opxom~o._1 .1n1o.x~_~..m 11maaeo.o1 11mmm_.o n_.o o..o.o ..o1 2: E :— ofio.o cem._ 1 1 1 1 1 .1o_xo.~ m1o_xo.m n1o_xm~.~ n.~ ..o~o.o Nmo.. 1 1 m1o.x~ao.n1 .1opxwo.o __ooo.o1 o__o.o «mo.o1 n1o_xo.m m.” .1.m~.o o~o.. 1 1 .m1o_xn.e1 11n1o_xm.~.. ..oem_o.O1 11womo.o ~.o.c1 n1o.e~.~ o 11ee~.o N~S.. 1 11m-o_xno°.. 11m1o_x~noc...1 ..m__m_o.o ..m_no..c1 .1.¢n~.o “no.9- «1°.xm._ m.~1 ...L~.o ~_~._ .m1o_xo~oo._1 .m1o_.mmeo.m .1n1o.xmoo__.o1 11em~o.o.o ..o~sm_.o1 1.ao~n.c ._n_.01 ”10.xo.e1 a..- SSERG h~_.o mom._ 1 1 1 1 1 n1o_x_.a1 .no.o n1o.x_.~ o.» .1_.~.o ooe._ 1 1 1 1 1 11mneo.o1 .1~..o 11mo~o.o o.n 1.mom.c 0.0.. 1 1 .m1o_xnoo.~1 11n1o_xom¢.~ 1..~o_o.o1 w-o.o Neo.o .1n1o_ee.a o ..~q~.c mmo.. 1 11m1n_xmm... ..n-o_..ooe._1 11e~e~_o.o 1.,Noo.o1 11.x“..o n1o.xm.m1 e1c.xo._1 ..~1 11Laa.o oem._ 1 11m-o_e~o.. .1n1o_xmo.o._1 11-_o~o.o .._—mo_.o1 .._a-.o 11oeo.O1 .1o_xo.m1 a..- ac.” 2: ..o 1251 ~¢ . e o e a o u a e a.wu wmwuau muco.u.»»oou afluwaWHMMm.v .22 9.28 2: Co 8:8 one 1300 mcozuon ”3.31.2. 601C Boo—0‘50 2.53250 covnmogovg 033—2.. .5» AN: cozocvctouuu yo 3:33:25 0.: we: 3:33:02” 61—: 2a: 68 Table 111.4. Parameters used in Equations [2] through [5] to develop density isograms. Tine penetration force, X2 3:11“ m°15i3;; (X1) 6.4 0156 $1212.?m 15.9 -mm- -%- ------------ kg ------------ O-8 15.6 8.1+ 9.7 11 8 16.4 0-8 12.9 12.1 12.8 15.7 22.9 0-8 10.9 17.5 20.4 25.6 32.8 lO-lB 15.6 6.0 7.9 9.6 13.3 10-18 12.9 9.1 10.2 13.1 19.1 10-18 10.9 13.3 16.1 20.5 27.3 20-28 15.6 4.7 6.3 7.7 10.7 20-28 12.9 7.1 8.4 10.3 15.3 20-28 10.9 10.3 13.2 16.3 22.0 30-38 15.6 3.7 5 1 6.1 8.6 30-38 12.9 5.6 6 6 8.2 11 9 30-38 10.9 7.9 10.7 12.8 17.2 40-48 15.6 2.9 4.1 4.8 6.7 40-48 12.9 4.1 5.2 6.4 9.2 40-48 10.9 6.2 8.5 9.9 13.2 50-58 15.6 2.3 3.2 3.6 5.2 50-58 12.9 3.4 4.1 5.0 6.9 50-58 10.9 4.7 6.6 7.7 10.0 60-68 15.6 1.7 2.3 2.6 3.8 60-68 12.9 2.4 3.2 3.6 4.9 60-68 10.9 3.4 4.6 4.9 7.0 70-73 15.6 0.9 1.3 1.5 2.2 70-73 12.9 1.6 2.1 2.2 2.9 70-73 10.9 2.3 2.9 2.9 3.9 76-88 15.6 0.16 0.38 0.69 0.55 76-88 12.9 0.33 0.47 0.70 0.78 76-88 10.9 0.59 0.71 0.60 0.72 +Average of 3 values obtained from study. 69 Table 111.5. Average reduction in overall soil bulk density following VOHT core cultivation. Bulk density reduction Soil moisture potential, -cbar Tine size 9.5 15 35 - mm - ------------ mg/cm3 ------------ 6.4 14.3 bcde* 11.3 cde 10.0 de 9.5 13.0 bcde 9.7 de 8.3 e 12.7 17.3 bcd 20.0 bc 21.0 b 15.9 31.7 a 32.0a 31.3 a *Values with columns or rows followed by the same letter are not significantly different at the 5% level. CHAPTER IV SOIL COMPACTION INDUCING EFFECTS OF VERTICAL OPERATING HOLLOW TINE (VOHT) TURFGRASS CULTIVATION, GREENHOUSE AND FIELD RESULTS ABSTRACT VOHT (vertical operating hollow tine) turfgrass cultivation is a common cultural practice used on putting greens. Little research has been published on the effects of VOHT coring on soil structure. In a 2-year field study conducted on a Metea sandy loam soil that was maintained under putting green conditions, VOHT coring was found to have no consistent effect on oxygen diffusion rates, turfgrass quality and soil strength. Results from a greenhouse study conducted under similar conditions as the field experiment, revealed that VOHT coring caused a large increase in soil bulk density surrounding the coring hole for 9.5 and 15.9 mm diameter tines. The degree of increased density from coring was greater on a soil with a lower initial bulk density than on a more highly com- pacted soil. The sides of the coring holes had not collapsed after 14 days but did collapse 93 days after coring. The degree of compaction observed below the coring hole was similar at 14 and 93 days following coring, indicating that repeated VOHT coring could induce the development of a compacted soil layer below the depth of coring. The benificel effects from the reduction in surface compaction caused by VOHT coring should, however, outweigh the potential problems associated 70 71 with the long term development of a compacted layer below the depth of coring. INTRODUCTION Vertical operating hollow tine (VOHT) turfgrass cultivation is a common management practice used on putting greens. The objectives of VOHT coring are to alleviate surface soil compaction problems, remove unwanted soil layers near the surface and to help reduce thatch accumu- lation. However, limited research has been published in support of these objectives. Murray and Juska (10) found that coring reduced thatch levels, whereas Engel and Alderfer (7) observed that thatch accumulation was not signifi- cantly reduced by coring. Water infiltration rates have been found to be unaffected (4), reduced (15) or increased (16) following VOHT cultivation. As noted in an earlier section, Petrovic et al. (13) found that VOHT coring caused a large increase in bulk density in the soil surrounding the coring hole in a moderately compacted soil under laboratory conditions. That research did not determine what the effects of the growing turf plants, other natural processes such as soil wetting and drying cycles, and a soil at a higher degree of compaction would have on the results they observed. The degree to which a soil will compress is related to both the soil moisture content and the extent to which the soil is already compressed. This theory developed by Doner (6) and confirmed by Reaves and Nichols (14) states that an increment increase in compression of a non-plastic granular medium at a specific compacting pressure is proportional to the soil moisture content and to the degree the soil is already compressed. The amount of compression (compaction) increases with increasing soil moisture content from air dry to the lower plastic limit (LPL). The amount of 72 compression is reduced, however, when soil moisture content increases past the LPL. The LPL is defined as the minimum moisture content at which the soil particles are sufficiently lubricated so that an applied pressure will cause a perminant change in their size and shape (2). The objectives of the research reported here were to examine the effects of VOHT coring, under both greenhouse and field conditions on soil structure and turfgrass quality as influenced by l) the degree of soil compaction and 2) the soil moisture content at the time of coring. MATERIALS AND METHODS Field Study A VOHT field cultivation study was conducted at the Michigan State University Soil Science Research Farm at East Lansing on a Metea fine sandy loam soil (loamy, mixed, mesic Arenic Hapludalf). The soil was found to have 73% sand, 18.6% silt, 8.4% clay, 1.1% organic matter, a pH of 6.9 and LPL at 16.1% by weight. The sand content was further character- ized by wet sieving analysis with the following results: 2.4% > 2 mm; 0.8% from 2-1 mm; 3.0% from l-O.5 mm; 21.5% from 0.5-0.25 mm; 35.3% from 0.25-0.1 mm and 10% from 0.1-0.053 11111. In June 1976, the experimental site was seeded to Penncross creeping bentgrass (Agrostis palustris Huds.). A_cutting height of 6.4 mm was maintained throughout the study. Total N, P205, and K20 applied in 1976 were 171, 49 and 49 kg/ha, respectively. VOHT coring treatments were initiated in 1977 on 2.7 x 4.6 m main plots arranged in a randomized complete block design. Each main plot was split with half of each plot receiving frequent compaction applications. Three replications of each treatment were included. 73 Coring treatments with a Ryan'sR Greensaire aerfier, model A-5, consisted of using 9.5 and 12.7 mm diameter tines to core plots at soil moisture potentials of 0, -10 and -33 cbar. An uncored plot was included for comparison. Coring treatments were applied on July 26 through July 29 and on October 7 through 13 in 1977 and in 1978 on May 31 through June 6 and on October 12 through 18. At the time of coring, soil moisture potentials were monitored by tensiometers placed 7.6 to 10.2 cm below the turf surface and were main- tained within the following limits: 0-1, -10 :_1.5 and -33 :_8 cbar. Soil samples taken at the depth of the tensiometer placement during the coring operation revealed that the 0, -10 and -33 cbar moisture potentials corresponded to moisture contents by weight of 23 to 19.5%, 18-15% and 12 to 9%, respectively. Compaction treatments that averaged twice weekly were initiated on July 28 and May 5 and were terminated on October 31 and October 26 in 1977 and 1978, respectively. One pass with a Ryan'sR water-filled vibrating power roller, that had 12 golf soils with spikes adhered to the roller surface, comprised the compaction treatments. The total amount of N, P205, K20 applied in 1977 and 1978 were 147, 31, 37 and 171, 37, 48 kg/ha, respectively. Fungicides were applied as needed to control diseases. Supplemental irrigation was used as needed to prevent wilt. Penetrometer readings, oxygen diffusion rates (DDR5) and bulk density analyses were used to characterize soil structural changes resulting from VOHT coring. A depth monitoring penetrometer (5) was used to take 10 readings per plot at locations equidistant from the center of the coring holes. The measurements were made on October 28, 1978. Soil moisture content at 74 the time of the penetrometer measurements was 20.7% :_1.2, by weight. ODR's were determined by the platinum microelectrode technique (8) on August 9 and 21, 1978 when the soil moisture potential was within 1 cbar of saturation. Twenty readings per plot were made with electrodes placed 5 cm deep equidistant from the center of surrounding coring holes. Two soil core samples, 7.36 cm 1.D. x 12.5 cm deep were taken from each plot on November 24-25, 1978 for computed tomographic (12) bulk density analyses. Greenhouse Study The experiment was conducted during the period of January 26 through May 24, 1979. Surface soil was collected adjacent to the field plots having the physical and chemical properties as described previously. The soil was air dried and passed through a 1.00 mm sieye. The experimental design used was a 5x22 factorial with 3 replicates arranged in randomized complete blocks. The first factor included tine sizes of 9.5 and 15.9 mm in diameter that were used to core samples at -9.5 and -33 cbar soil moisture potentials. An uncored sample, equili- briated at -33 cbar potential, was included for comparison. The second factor involved 2 levels of bulk density. Half of the samples were packed into 7.7 cm 1.0. x 15.2 cm deep plastic tubing to a bulk density of 1.55 g/cm3. The second group had an additional 2 cm section of plastic tubing attached to the upper surface. Thirty days after sodding, compaction was applied to the sodded surface over a 3 day period to decrease the column height by 2.0 cm (added section was removed). The bulk density of these samples was increased to 1.70 g/cm3. Sampling dates of 14 and 45 days following cultivation comprised the third factor. 75 Each pot received a plug of soil-less sod on January 20 that had been taken earlier from the field study plots. Electric trimming shears were used to mow each plot 3 times weekly at a height of 8 mm :_2. Clippings were removed. Based on soil tests, no phosphorus was required and prior to sodding, 96 kg/ha of potassium sulfate was added to the pots and thoroughly mixed throughout the soil. Ammonium nitrate was applied at the rate of 24.4 kg/ha on Feburary 9 and 24, March 20 and April 24. Chlorothalnil was applied to control diseases at weekly intervals at the rate of 7.84 1/ha using a small hand atomizer. Watering was done on a set daily bases by an overhead misting system. A soil moisture content of 12 to 17% by weight was maintained in this way throughout the study. Minimum temperature was set at 18 C and a 14 hour daylight period was utilized by the addition of supplimental flourescent lighting. VOHT coring was done by the Instron method (11) to a depth of 76 mm at a vertical tine movement rate of 254 mm/min. Half the samples were cored on March 16, the other half on May 10. To achieve soil moisture potentials of -9.5 and -33 cbar, the samples were placed on 1 bar ceramic plates, saturated in tap water for 24 hours and placed in pressure plate extractors for a 1 day period. At this time the soil moisture contents were 17 to 15% (LPL) and 12 to 10% at the —9.5 and -33 cbar potentials, respectively. A count of the number of shoots per pot was taken on March 21 through 23 on the samples that were to be treated on May 10. These samples reflect a difference in soil bulk density that was very evident at this point. 76 The experiment was terminated on May 24 at which time all samples were oven dried at 55 C for at least 3 days. A vertical cross-section of soil bulk density values were taken directly at the center of the coring hole (or center of uncored sample) by the computed tomographic technique (12). Earlier research conducted under laboratory conditions (13) revealed that the zones of greatest induced compaction caused by a 9.5 and 15.9 mm tines were 2 and 4 cm below the soil surface at the sides of the coring hole, respectively. Also, it was found that the 9.5 and 15.9 cm tines caused the greatest compaction midway between the edge and center of the tine and directly below the edge of the coring hole, respectively. These same locations were selected for bulk density analysis in this study. For the region of soil at the sides of the coring hole, a horizontal section 8 mm high x 30 mm wide, at 2 and 4 cm below the soil surface for the 9.5 and 15.9 cm tines, respectively, was used for bulk density comparisons. Below the coring hole, bulk density was obtained in 2 mm wide by 12 mm long vertical section at location described above. RESULTS AND DISCUSSION VOHT Greenhouse Study A highly significant reduction in shoot density occurred with an increase in bulk density. Shoot densities were 14.9 and 11.6 shoots/cm2 at bulk densities of 1.55 and 170 g/cm3, respectively. The effects of VOHT coring on the soil bulk density at selected regions in the cultivation zone are shown in Tables 1V.1 and IV.2. The data are for only 2 replicates and represent the change in density that occurred when compared to the same locations in the uncored soil. 77 In general, the edges of most of the coring holes were intact 14 days (May 10) following cultivation but had totally collapsed after 93 days. (March 16) The maximum density occurred within 2 mm of the hole and density decreased rapidly with distance away from the hole. This was consistent with what was found in an earlier study (13). Increases in bulk density of less than 100, 100 to 200 and > 200 mg/cm3 wwere assumed to be slight, moderate and severe increase in compaction, respectively. The initial soil bulk density had a marked effect on the degree to which VOHT coring caused an increase in bulk density in the soil surrounding the coring hole. At the lower bulk density of 1.55 g/cm3, both tine sizes caused severe to moderate increases in compaction in the soil below the coring hole, whereas, at the higher bulk density of 1.70 g/cm3, compaction was only moderate to slight. This would be predicted from the findings of Doner (6) and Reaves and Nichols (14). The soil moisture content influenced the degree of compaction induced by the 15.9 mm tine. At the lower bulk density the 15.9 mm tine caused a severe increase in compaction below the coring at the -9.5 cbar potential; however, when the soil was drier (-33 cbar) there was only a moderate level of compaction. Others (6,14) have observed the degree of compaction is less when the soil is drier. The amount of compaction induced at the sides of the coring hole by VOHT cultivation was more evident at 14 days (May 10) following coring than after 93 days (March l6)./ In contrast,the soil below the coring hole was observed to be at the same relative degree of compaction at both 14 and 93 days following coring. 78 VOHT Field Study The effects of VOHT coring on oxygen diffusion rates (ODR's) are shown in Table IV.3. All ODR‘s were well above the 15 g 02 x 10"8cm’2 1 standard at which root growth of certain turfgrass species has been min found to be limited by ODR ( 9). It is apparent that even at or near saturated soil moisture conditions, cultivation and supplemental compaction had no consistent effects on ODR. Lack of improvement in ODR resulting from VOHT cultivation rated here might be attributed to the short duration of this study. Engel and Alderfer ( 7) noted that VOHT cultivation caused a 20% increase in ODR in the tenth year of a field study. Compaction has been shown to reduce ODR (9). This would indicate that the level of compaction of this soil was not great enough to cause a reduction in ODR. Penetrometer readings (see Table 1V.4), used to measure soil strength, showed a marked increase from the compaction treatments consistent with what others have found (1,3). The VOHT coring did not significantly influence soil strength at the 5% level. However, at the 10% level, VOHT coring with a 12.7 mm tine at a soil moisture potential of -10 cbar caused an increase in soil strength in the 6 to 10 cm depth below the turf surface. This increase in soil strength would indicate that a compacted layer of soil was developing below the depth of cultivation by repeated VOHT coring. This compacted layer would confirm the results observed in the greenhouse study and in a previous laboratory experiment (13). Since the overall turfgrass quality was not significantly influenced by VOHT coring the data are not reported. Compaction did cause a slight reduction in quality midway through the second summer. Murray and Juska (10) observed that coring caused an increase in Kentucky bluegrass (Egg 79 pratensis. L) quality, whereas Engel and Alderfer (7) found no effect on Penncross creeping bentgrass. It is evident that a positive quality response from core cultivation is dependent on both the species of turfgrass used and the conditions of the turf and soil. SUMMARY It is evident that a moderately compacted soil, in this case at a bulk density of 1.55 g/cm3, would show a greater degree of compaction induced by VOHT coring than in a more highly compacted soil. The compaction created at the sides of the coring hole would appear to have little long term negative effect on overall turfgrass quality. However, the zone of compaction created in the soil below the coring hole by VOHT cultivation was still present after 93 days. This could pose a long term problem since VOHT coring is often done 2 times a year, occasionally more often, and could lead to the development of a compacted layer of soil below the depth of coring. This could result in the impedence of water movement, gas exchange and root growth below this zone. Still the benifits of VOHT coring may very well out-weigh the potential problems associated with a compacted layer of soil below the cultivation depth. 10. 11. 12. 8O LITERATURE CITED Barley, K. P., D. A. Farrell, and E. L. Greacin. 1965. The influence of soil strength on the penetration of a loam by plant roots. Aust. J. Soil Res. 3:69-79. Baver, L. D., W. H. Gardner, and W. R. Gardner. 1972. Soil Physics. John Wiley and Sons, Inc., New York. 498 pp. Bradford, J. M., D. A. Farrell, and W. E. Larson. 1971. Effect of soil overburden pressure on penetration of fine metal probes. Soil Sci. Soc. Am. Proc. 35:12-15. Byrne, T. G., W. B. Davis, L. J. Booher, and L. F. Werenfels. 1965. Vertical mulching for improvement of old golf greens. Cal. Agr. 19(5):12-14. Davidson, D. T. 1965. Penetrometer measurements. In_C. A. Black (ed.) Methods of soil analysis. Agronomy 9:472-484. Doner, R. D. 1936. A theory of arch action in granular media. Agric. Eng. 17:299-304. Engel, R. E., and R. B. Alderfer. 1967. The effect of cultivation, topdressing, lime, nitrogen and wetting agent on thatch development in l/4-inch bentgrass turf over a ten-year period. New Jersey Agr. Exp. Stn. Bull. 818:32-45. Lemon, E. R., and A. E. Erickson. 1952. The measurement of oxygen diffusion in the soil with a platinum electrode. Soil Sci. Soc. Am. Proc. 16:160-163. Letey, J., W. C. Morgan, 5. J. Richards, and N. Valoras. 1966. Physical soil amendments, soil compaction, irrigation and wetting agents in turfgrass management 111. Effects on oxygen diffusion rate and root growth. Agron. J. 58:531-535. Murray, J. J., and F. V. Juska. 1977. Effect of management practices on thatch accumulation, turf quality and leaf spot damage in common Kentucky bluegrass. Agron. J. 69:365-369. Petrovic, A. M., A. K. Srivestava, and P. E. Rieke. l9__, A vertical operating hollow tine (VOHT) turfgrass core cultivator for laboratory and greenhouse studies (to be submitted to Agronomy Journal). Petrovic, A. M., J. Siebert and P. E. Rieke. l9 . Determination of soil bulk density by computed tomographic (CTT scanning (to be submitted to Soil Sci. Soc. Am. J.). 13. 14. 15. 16. 81 Petrovic, A. M., P. E. Rieke, and A. E. Erickson. 19__, Soil compaction-inducing effect of vertical operating hollow tine (VOHT) turfgrass cultivation, a laboratory study (to be submitted to Agron. J. or Soil Sci. Soc. Am. J.). Reaves, C. A., and M. L. Nichols. 1955. Surface soil reaction to pressure. Agric. Eng. 36:813-816, 820. Roberts, J. M. 1975. Some influences of cultivation on the soil and turfgrass. M.S. Thesis. Purdue University. Waddington, D. V., T. L. Zimmerman, G. L. Shoop, L. T. Kardos, and J. M. Duich, 1974. Soil modification for turfgrass areas. Pennsylvania Agr. Exp. Sta. Progress Report No. 337. 96 pp. 82 1 mm1 ON1 oH1 Nm on on no m.m1e.N eH mm on.“ ow we we mm mm me NN ON1 N eH mm oN.~ 1 mm mm No mm moH mmfi mm m.m1m.N mm mm ON.“ NHH Na NN NNN mmfi mHH NNH an N mm mm oN1~ 1 cm cw no we“ omN men mNN m.m1o.N «H mm mm.“ Nm mm moH NHN Na mm NHH No N ea mm mm.~ 1 Ho mu emH qua mmN oNN mo“ m.m1m.N mm mm mm1fi Hm No es QHH mag mNN mm mm N mm mm mm1H 1 oq1 «1 c1 mm NoH mmfi g1 m.w1o.N eH m1m oN.H Ne mm on ow Hm oHH mNH MNH1 N ea m.a ou.H 1 cm Hm cog eN mmH mHN mm m1w1o.N mm m1m oN1H Ne Ne Ne om MN we NHH on N mm m.m oN.H 1 No an we“ mmfi mVN meN «ma w.m1o.N ea m1m mm.“ 0N N- mm~ mm“ me mNH NON Na N «H m1m mm.~ 1 MN mm MN“ moH nmN oNN mvH m.w1o.N mm m1m mm.H mm mm mm mm mm om mm «H +N mm m1m mm1H 11111111111111111111 m 1111111111111111111111111 1 msu\ 2 so Luau mEU\m m,- w- pr m 8 CI .41 o 88;... :91. 13:8 32.33 .928 55 «upon mcwgou mo wave soc» mucmpmwo zopmn mcpzop—ow wgzumwos span swede asap! FLem rememem .m:o_»muppamg N No wmmew>m mg» mp czosm mama .m:_u EE m.m a saw: cowum>wupau wgou on> mcvzoppow xummcmu xpan pvom :- mmmmgucw ommsm>< ._.>_ apne- 83 mmH mud 1 0N1 mN mo oNH NmH m.m1o.N ¢~ mm 0N1H H1 N1 m1 m1 HH1 oH1 mfi mm c ea mm 0N1H 1 No mm mmH we mmH mafi Nmfi m1w1o.N mm mm om.H on Nm mN mmH NNH «HN mHH mmN1 v mm mm ON.“ 1 NN mm «m “HH eoN mNN omH m.m1m.N «H mm mm.~ ow ms HN mm «a oNH mm mH e ea mm mm.H 1 mm m mm NNH NON NON oefi w1w1m.N mm mm mm.“ He mm Hm mm cog mNH on em e mm mm mm1~ 1 Nm1 mH Hm mm mm“ Nwfi mm m1m1m1N ea m1m ON.H HH mm HH em emH mofi mHN mN1 c ¢~ m.m oN.H 1 me No NHH om mNH em mm m.m1m.N mm m.m oN.H mm Nu am ow mm mm He mN1 e mm m.m ON.H 1 mm mm mHH em“ mmN mmN eHH m1w101N eH m.m mm.H co co mag Ne" Nmfi NmN moN NH1 e cfi m1m mm1H 1 HNH wNH mmfi mo“ NNN NNN «HN w.m1m.N mm m.m mm.“ Nw mm mN ow we «HH MNH mfiH e mm m.m mm.” 1111111111111111111111 mso\ms 1111111111111111111111 Eu Lma81 mEU\m 2 NH 2 b w e w o 88.5... :8 3.28 33:38 .3355 SE .m—o; mchou No mmvw soc; mucmpmwa zopma mcwzoppo» mgaum_os x_:a £88 £8 :8 25.5 .mcowumUVPng N No mmmcm>m on» my czozm came .62?“ as m.mH m ;»_3 coppm>wu_:o mcoo Azo> ozwzoppoL Aupmcmu span Prom cw mmmmcucv mmmem>< .N.>~ mpawh 84 Table 1V.3 Average oxygen diffusion rates (ODR) obtained in the VOHT field study. Soi1 Tine moisture Measurement date size ,potential Compaction1 879/78 8/21/78 mm -cbar 902x10"8 cm"2min'1 O - + 24.0* 24.7 0 - - 25.3 20.5 9.5 O + 28.0 25.2 9.5 O - 30.4 21.0 9.5 10 + 28.8 22.9 9.5 10 - 2911 23.0 9.5 33 + 25.8 22.2 9.5 33 - 27.5 24.0 12.7 0 + 26.7 21.7 12.7 0 - 22.9 19.7 12.7 10 + 25.0 21.9 12.7 10 - 26.8 20.7 12.7 33 + 24.0 19.8 12.7 33 - 30.3 22.7 1 +/- refer to with and without compaction treatments. * Each value represents an average of 60 readings. 85 Table 1V.¢L Average penetrometer reading obtained at various points below the soil surface in the VOHT field study. 5011 Tine moisture Distance below soil surface, cm size potential Compaction‘I 2 6 8 10 12.7 mm -cbar ----------------- bar -------------- 0 - + 31.2* 33.4 33.8 33.4 '32.7 0 - - 23.6 26.7 27.8 27.5 27.0 9.5 o + 25.6 30.9 32.1 33.2 30.5 9.5 o - 19.9 24.1 26.4 26.5 26.6 9.5 10 + 28.5 35.8 36.8 36.3 34.2 9.5 10 - 18.8 26.1 29.2 29.9 29.5 9.5 33 + 29.7 33.2 33.3 32.1 31.0 9.5 33 - 22.5 27.0 28.6 28.9 27.9 12.7 0 + 29.3 34.7 35.5 37.7 34.0 12.7 0 - 20.6 26.0 27.8 28.2 27.0 12.7 10 + 33.0 38.6 38.9 38.5 35.3 12,7 10 - 23.1 34.0 37.2 37.9 35.1 12.7 33 + 28.9 34.0 34.9 34.6 31.2 12.7 33 - 20.3 25.4 28.1 28.6 27.7 mean + 29.5a* 34.4 a 35.1 a 34.8 a 32.7 - 21.2 b 26.9 b 29.3 b 29.6 b 28.7 *Values within columns followed by the same letter are at the 1% level. + +/- refers to with and without compaction treatments. ¢Each value represents an average of 30 measurements. not significant a b 10. 11. 12. 13. CONCLUSIONS The following were the conclusions drawn from these investigations: The Instron universal testing machine was found to simulate the field VOHT coring unit and can be used for laboratory and greenhouse studies; Increasing the rate of tine movement with the Instron machine in laboratory studies had only a slight effect on increasing the force required for tine penetration; Using the Instron machine, the increase in force associated with an increase in tine movement rate should have a negligible effect on soil bulk density; The CT scanner at the Michigan State University Clinical Center responded in a linear fashion to increasing bulk density of a Metea fine sandy loam soil and glass beads-glass air-filled samples; High and low contrast spatial resolution of thes CT scanner was 1.25 x 1.25 x 2.4 mm and 6.4 x 6.4 x 2.4 mm, respectively; Loss of information can result from beam hardening artifacts during CT analysis, however, procedures were found to reduce the effects of such artifacts; The CT scanner can be used effectively to determine soil bulk density in situ with a fine 3- dimensional spatial resolution and can have wide application to the field of soil science research; VOHT coring caused a large increase in bulk density in the soil surrounding the coring hole in a laboratory study; Soil bulk density was at a maximum within 2 mm from the coring hole and decreased linearly away from the hole for a distance of 10 to 12 mm, beyond which no compaction was apparent; Varying the tine size had only a slight effect on the maximum density observed; however. the largest tine size (15.9 mm) did cause an increase of 3.3 mm in the thickness of the soil away from the hole which had a higher bulk density after coring; Soil that was drier at the time of VOHT coring had a smaller maximum density and smaller thickness of the zone of higher density at the sides of the coring hole for only the 6.4 and 9.5 mm tines; Density below the coring hole was not influenced to a large extent by variations in tine size and/or soil moisture content; The relative degree of increased compaction caused by VOHT coring was less at the sides of the coring hole than below the coring hole; 85 14. 15. 16. 17. Under greenhouse conditions, VOHT coring caused a large increase in bulk density in the soil surrounding the coring hole which was still present 14 days following cultivation; At 93 days following VOHT coring, the zone of increased bulk density was only present in soil below the coring hole since the side walls had collapsed; VOHT coring caused a smaller increase in bulk density in the soil surrounding the coring hole in soil that had a higher initial bulk density, thus a soil with a high bulk density (highly compacted) will be less susceptible to a compacting influence with VOHT coring; VOHT coring had little effect on oxygen diffusion rates, turfgrass quality and soil strength in a 2-year field study. 86 "IIIIIIIIIIIIIIIIIIIIIT