l2 . . V 1!..vi rt!‘tn,1P€.)€ $15.!!!- Oo‘uVlvl. 313.. lovitbllfil li- lilOtitifl t ‘n n I mm“?! lung gig: 1 7?.‘9 ggvsuvglu 9.01219; I»! trifin. .lv bit.-l:r| aliav ....nliO|A1x..|ul. I .. nl A: 0105!!!! Ilv.‘bllv|0l.f'[ " 35 .! ,t.’ l.. ‘.b'..ll..r‘~ '1')» lit; «.,.I||| ' HES‘ STATE UN VERSITY LIBRARIES Immin'iiiiMimi 111 mu I I 3 1293 00891 4347 This is to certify that the dissertation entitled THE INFLUENCE OF CULTIVATION ON SOIL PROPERTIES AND TURFGRASS GROWTH presented by James Arthur Murphy has been accepted towards fulfillment ‘ of the requirements for Ph.D. degreein Crop and Soil Sciences a jor ofessor Date June 11, 1990 MS U is an Affirmative Action/Equal Opportunity Institution 0-12771 A“ _..___._‘ F LIBRARY I Michigan State 4 University x J PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or baton date due. DATE DUE DATE DUE DATE DUE w— I ___ 3;: —‘I ___IL__J jif— W MSU Is An Affirmative Action/Equal Opportunity Institution chM.‘ THE INPLUHNCH OP CULTIVATION ON BOIL PROPERTIES AND TURFGRABS GROWTH BY James Arthur Murphy A DIBBHRTATION Submitted to Michigan state University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences 1990 J21) , 47 "I . — OJ“ 4 ABSTRACT THE INFLUENCE OF CULTIVATION ON SOIL PROPERTIES AND TURFCRASS GROWTH By James Arthur Murphy Traditionally, hollow tine cultivation (HTC) has been limited to spring and/or fall application on golf putting greens due to the demand for use of the turf and a high quality surface. The Toro Company has developed high pressure water injection as a method to deeply cultivate soil while minimizing disturbance of the turf surface. Studies were conducted to determine the effectiveness of water injection (WIC) as a cultivation tool as compared to no cultivation (check) and HTC. The effect of cultivation on soil physical properties and turfgrass growth was evaluated on a ’Penncross’ creeping bentgrass (Agrostis palustris Huds.) green and a ’Cheri’ Kentucky bluegrass (Poa pratensis L.) turf receiving compaction treatment. Under putting green conditions, both HTC and W1C lowered bulk density and increased porosity compared to the check. Soil penetration resistance was reduced by HTC and WIC at the 30 to 60 mm and 40 to 100 m depth zones, respectively. In the Kentucky bluegrass turf, only HTC reduced bulk density and increased total porosity compared to the check. However, the very large macropores (0 to -l kPa moisture potential) were increased with both HTC and WIC. WIC had the greatest improvement in saturated hydraulic conductivity in both studies. Both cultivation methods increased creeping bentgrass yield. There was no effect of WIC on Kentucky bluegrass yield while HTC reduced yield up to four weeks following treatment. Yield reductions were due primarily to the loss of plant crown tissue. Neither HTC nor W1C affected root weights of the Kentucky bluegrass turf, but HTC reduced root weights at the O to 50 and 50 to 100 mm depth zones of the creeping bentgrass green. Minirhizotron root observations (MRO) corroborated the loss of surface rooting with HTC. Below the zone sampled for root weights, MRO found increased rooting in VIC plots in the first year and both HTC and WIC plots in the second year of the putting green study. The minirhizotron method was effective and economical for evaluating root growth dynamics. The reduced level of mechanical stress and surface disruption imposed on turf by WIC indicated that WIC has considerable promise as a year-round cultivation practice. to my father, he will always be missed iv ACKNOVLEDCEHENTS I want to extend my deepest gratitude and thanks to Dr. P. E. Rieke, chairman of my graduate committee, for his unyielding belief in my abilities. I am indebted to Dr. B. E. Branham, Dr. A. J. M. Smucker, and Dr. J2 li.'Vargas, Jr. for their contributions during my graduate program. I would also like to thank my fellow graduate students, especially my wife Stephanie, for the support and friendship which made my education much more fulfilling. Finally, I want to express my appreciation to the The Toro Company of Minneapolis, MN, especially Mr. R. C. Comer, Mr. D. Lonn, Mr. D. Scherbring, and Dr. J. R. Watson, for the motivational and financial support during this research project. The interaction with this group of people took my education beyond the typical academic exercises. TABLE OF CONTENTS Page List of Tables ...................................................... vii List of Figures ...................................................... ix Chapter One: Minirhizotrons for Measuring Creeping Bentgrass Root Development ........................................ 1 Abstract ........................................................ 1 Introduction .................................................... 3 Materials and Methods ........................................... 3 Results and Discussion .......................................... 5 Summary ........................................................ 14 List of References ............................................. 16 Chapter Two: High Pressure Water Injection and Hollow Tine Cultivation of a Compacted Creeping Bentgrass Green .................................................. 18 Abstract ....................................................... 18 Introduction ................................................... 20 Materials and Methods .......................................... 21 Results and Discussion ......................................... 24 Soil Physical Properties ................................. 24 Plant Responses .......................................... 33 Estimated Water Use ...................................... 46 Summary ........................................................ 51 List of References ............................................. 54 Chapter Three: Hollow Tine and Water Injection Cultivation of a Compacted Kentucky Bluegrass Turf ............... 56 Abstract ....................................................... 56 Introduction ................................................... 58 Materials and Methods .......................................... 59 Results and Discussion ......................................... 61 Soil Physical Properties ................................. 61 Shoot Tissue and Thatch/Mat .............................. 65 Rooting .................................................. 65 Clipping Yield ........................................... 68 Stand Density ............................................ 71 Estimated Water Use ...................................... 71 Summary ........................................................ 71 List of References ............................................. 76 vi LIST OF TABLES Correlation of root weight density (RWD), root length density (RLD), and minirhizotron root observations (MRO) at various depth zones; sampled late-May I987 .......... 6 Correlation of root weight density (RWD), root length density (RLD), and minirhizotron root observations (MRO) at various depth zones; sampled mid-October 1987 ....... 7 Soil (0 to 76 mm) bulk density, total porosity, aeration porosity (O to -6 kPa moisture potential), and saturated water conductivity (K Sat) responses to hollow tine (HTC) and water injection (W1C) cultivation of a loamy sand soil ........................................ 25 Soil (76 to 152 mm) bulk density, total porosity, aeration porosity (O to -6 kPa moisture potential), and saturated water conductivity (K Sat) responses to hollow tine (HTC) and water injection (WIC) cultivation of a loamy sand soil ........................................ 27 The influence of hollow tine (HTC) and water injection (WIC) cultivation on soil porosity drained between several moisture potentials in the 0 to 76 mm zone .......... 29 The influence of hollow tine (HTC) and waterinjection (WIC) cultivation on soil porosity drained between several moisture potentials in the 76 to 152 mm zone ........ 31 The influence of hollow tine (HTC) and waterinjection (WIC) cultivation on clipping yield of a compacted creeping bentgrass green mowed at 6 mm ...................... 34 The influence of hollow tine (HTC) and water injection (WIC) cultivation on visual quality of a compacted creeping bentgrass green mowed at 6 mm ...................... 36 The influence of hollow tine (HTC) and waterinjection (VIC) cultivation on the shoot tissue, thatch/mat, and total root weights of a compacted creeping bentgrass green ....................................................... 37 vii The influence of cultivation on root weight densities of a creeping bentgrass green ........................ The influence of cultivation on daily percent root turnover between 19 September and 29 October, 1989... The influence of cultivation on water extraction as estimated by tensiometry and time-domain reflectometry (TDR) in 1989 .......................... The influence of cultivation on soil physical properties at the 0 to 76 and 76 to 152 mm soil zones sampled 1988 and 0 to 76 mm zone sampled 1989 ........ The influence of cultivation on soil porosity distribution between selected moisturepmtentials in the 0 to 76 and 76 to 152 mm soil zone sampled 1988 and 0 to 76 mm soil zone in 1989 ..................... The influence of cultivation on shoot tissue, thatch/mat, and total root weight of Kentucky bluegrass turf sampled in 1988 and 1989 .............. The influence of cultivation on root weight density of a Kentucky bluegrass turf sampled in 1988 and 1989 Effect of hollow tine (HTC) and water injection (WIC) cultivation on visual density estimates of a Kentucky bluegrass turf in 1988 and 1989 ...................... Influence of cultivation on water use of a Kentucky bluegrass turf as estimated by tensiometers between 8:00 and 20:00 h for a 2 or 3 day period ............. Influence of cultivation on water use of a Kentucky bluegrass turf as estimated by time-domain reflectometry from 2 to 5 September, 1989 ............ viii ....... 39 ....... 49 ....... 50 ....... 62 ....... 64 ....... 66 ....... 67 ....... 72 ....... 73 ....... 74 Figure 1.1. LIST OF FIGURES The relationship of root weight density and root length density of a creeping bentgrass green in late-May and in mid-October 1987 ..................................... The relationship of root weight density and minirhizotron observations of a creeping bentgrass green in late-May and mid-October 1987 .................. The relationship of root length density and minirhizotron observations of a creeping bentgrass green in late-May and mid-October 1987 .................. The grand means of minirhizotron observations, root length density, and root weight density at individual depth zones in late-May and mid-October 1987 ............ Influence of cultivation (HTC - hollow tine, WIC - water injection) on penetration resistance of a loamy sand soil sampled 25 July, 1988 ......................... Influence of cultivation (HTC - hollow tine, WIC - water injection) on minirhizotron root observations taken 15 November, 1988 ................................. Influence of cultivation (HTC - hollow tine, WIC - water injection) on minirhizotron root observations at the 48 to 144 mm depth taken 9 August, 1989 .......... Influence of cultivation (HTC - hollow tine, WIC - water injection) on minirhizotron root observations at the 144 to 432 mm depth taken 9 August, 1989 ......... Influence of cultivation (HTC - hollow tine, WIC - water injection) on minirhizotron root observations taken 29 October, 1989 .................................. Influence of cultivation (HTC - hollow tine, WIC - water injection) on daily root turnover along minirhizotrons between 18 July and 30 September, 1988... ix Page .... 9 ....10 ....ll ....13 ....32 ....41 ....42 ....43 ....44 ....45 2.7. 2.8. 3.1. 3.2. Influence of cultivation (MTC - hollow tine, W1C - water injection) on daily root turnover along minirhizotrons between 30 September and 15 November, 1988 ........................................................ 47 Influence of cultivation (HTC - hollow tine, WIC - water injection) on daily root turnover along minirhizotrons between 19 September and 29 October, 1989 ........................................................ 48 Influence of hollow tine (HTC) and water injection (W1C) cultivation on clipping yield of Kentucky bluegrass turf (1988) ....................................... 69 Influence of hollow tine (HTC) and water injection (WIC) cultivation on clipping yield of Kentucky bluegrass turf (1989) ....................................... 70 CHAPTER ONE Minirhizotrons for Measuring Creeping Bentgrass Root Development ABSTRACT The minirhizotron method has received limited study as a method for in situ evaluation of turfgrass root systems. Forty-five minirhizotrons were installed April 1986 to evaluate the rooting of a 'Penncross’ creeping bentgrass (Agrostis palustris Buds.) putting green and to compare minirhizotron observations to destructive core sampling. Video recording of the minirhizotron tubes and soil sampling were performed late-May and mid-October 1987. Root weight density (RWD) and root length density (RLD) at individual depth zones were significantly correlated at five of six depth zones in May, but only two depth zones in October. No significant correlations were found between RWD and minirhizotron root observations (MRO), and one significant correlation was observed between RLD and MRO at individual depth zones for the tw0 sampling dates. Spatial variation in soil conditions and rooting bemeen the minirhizotrons and soil sampling sites was thought to be the reason for these poor relationships at the small depth intervals examined. When data was combined across all depth zones correlations between RWD and RLD, RWD and MRO, and RLD and MRO were all highly or very highly significant. Seasonal changes in slope indicated that no single relationship between RLD and MRO can be expected. MRO and RWD 2 measurements showed root quantities were greater in May than October. The lack of change in RLD measurements between May and October suggested that RLD may not be sensitive to temporal fluctuations in ”active” root quantity. RLD measurements were thought to be affected by the presence of senescent roots which were not easily distinguished from the active roots during the counting procedure. RWD measurements, although including the same senescent root material, may better reflect changes in active root quantity because the senescent material should lose weight as it slowly decays. Minirhizotron observations offer the advantage of viewing the senescence of roots over time based on discoloration of the roots. Therefore RWD and MRO should be better indices of the active root quantity and distribution. The data indicated that the minirhizotron method provided an acceptable and much less expensive means to characterize the profile distribution of a creeping bentgrass root system. 3 INTRODUCTION Most methods used to study root growth are quite labor intensive and require at least partial destruction of the experimental site (Bohm, 1979). The destruction of field space renders that area useless until reestablished and eliminates the ability for repeated sampling at the same site. To overcome these disadvantages, glass wall methods were developed to observe root growth in situ. McMichael and Taylor (1987) provided a historical overview of the development of the various ”glass wall” methods. Several rhizotron facilities have 'been. constructed. to examine turfgrass root systems (Karnok and Kucharski, 1982; DiPoala et al., 1982; Shearman and Barber, 1987). Rhizotrons are very costly to construct and adequate replication of treatments may be limited by the number of 'viewing compartments (McMichael and. Taylor, 1987). The minirhizotron method has received minimal attention as a method for in situ evaluation of turfgrass root systems (Branham et al., 1986; Hendricks and Branham, 1987). Minirhizotrons offer the advantages of reduced costs and destruction of the experimental site, and greater portability and replication (McMichael and Taylor, 1987). This study evaluated the minirhizotron method as a means of measuring rooting in a ’Penncross' creeping bentgrass (Agrostis palustris Buds.) putting green and compared the minirhizotron method to destructive soil core sampling. MATERIALS AND METHODS The study was initiated in April 1986 on a 5-year old ’Penncross’ creeping bentgrass green (Agrostis palustris Huds.) grown on a modified New Haplul lengt plots insta minim the facii Cidd wall sate at: Clip for 00 Fe Vi ‘nx It 4 loamy sand soil (original soil was a fine-loamy, mixed, mesic, Typic Hapludalf). On 26 and 27 April, 1986 three butyrate tubes of a 0.91 m length and 51 mm i.d. were centrally installed within 3.7 by 4.6 m plots. Fifteen plots were used for a total of 45 minirhizotrons. An installation angle of thirty degrees from horizontal was used to minimize preferential root growth along minirhizotrons. The entry ports of the minirhizotrons were installed facing north and just below the turf surface to minimize exposure to thermal radiation and to facilitate mowing, respectively. Pilot holes were bored with a Giddings probe and lightly brushed to alleviate soil smearing along the wall of the pilot hole. The plot area received 3 passes of 0.68 t water-filled rollers to smooth the surface and ensure soil/tube contact at the surface. Traffic was simulated with compaction treatments performed June through September in 1986 totaling 70 passes and June through August for 54 passes in 1987 utilizing the water-filled rollers. Nitrogen was applied at 9.8 and 14.7 g m'2 in 1986 and 1987, respectively. Phosphorus and potassium were applied to meet soil test recommendations. The green was maintained at a 6 mm cutting height. Pesticides were used as needed to control insects, weeds, and diseases. Minirhizotron root observations (MRO) were made 27 May and 12 Oct., 1987 using the minirhizotron video recording system described by Ferguson and Smucker (1989). The number of active roots in each viewing frame was counted and the frames corresponding closest to the appropriate depth interval (4 frames / 24 -) was summed for a total number of roots observed. Active roots were considered to be those roots white in color and having sharp edges. As roots aged they became R0 5)? 1e Si 111‘ ”I 5 darker in color and began to lose definition as the edges became blurred. Roots of dark color and having blurred edges were considered inactive and not counted. Three soil samples per plot were taken within 3 days of video 2by recording for root length and weight determinations. Each 20 cm 300 mm deep subsample was sectioned into 25 mm intervals over the first 75 mm of depth and then 75 mm intervals over the remaining 225 mm. Roots were separated from soil with the hydropneumatic elutriation system (Smucker et al., 1982) and stored in a 4 degree C cooler until length and weight measurements could be performed. Unfortunately, the 0 to 25, 25 to 50, and six of the 50 to 75 mm samples from the late-May sampling were improperly stored. This improper storage resulted in a marked reduction in root weight density (RWD). Root length density (RLD) was determined using the line-intersect method (Newman, 1966; Tennant, 1975). RLD and RWD represent root length and weight determinations on a soil volume basis. RESULTS AND DISCUSSION The correlations of root weight density (RWD), root length density (RLD), and minirhizotron root observations (MRO) at the various depth zones are presented in Tables 1.1 and 1.2 for the May and October sampling dates, respectively. Generally, correlation of RWD and RLD were very highly significant at individual depth zones for the May sampling. However, the October sampling showed only two depth zones with a significant correlation between RWD and RLD. This could result from a more uniform root morphology and age early in the growing season (May) compared to later in the season (October). Visual observations Table densi' depth Depth ND ( 0 to 25 t: 50 t< 75 t: 150 ' 225 O to 30 t RED Table 1.1. Correlation of root weight density (RWD), root length density (RLD), and minirhizotron root observations (MRO) at various depth zones; sampled late-May 1987. Depth zone (mm) Intercept Slope Correlation RWD (mg cm'3) vs RLD (m cm'3) 0 to 252 1.08 0.75 0.829 *** 25 to 502 0.31 0.82 0.882 *** 50 to 75? 0.51 0.24 0.555 NS 75 to 150 0.17 0.08 0.595 * 150 to 225 0.07 0.10 0.792 *** 225 to 300 0.02 0.32 0.869 *** 0 to 75x 0.07 0.97 0.944 *** 50 to 300w -0.07 0.39 0.954 *** RWD (mg cm’3) vs. MRO (# cm'z) 0 to 252 23.90 -0.93 -0.339 NS 25 to 502 16.55 -l.S6 -O.198 us 50 to 75y 9.57 -1.33 -0.246 NS 75 to 150 4.17 -l.61 -0.344 NS 150 to 225 0.26 0.28 0.121 NS 225 to 300 0.13 0.28 0.155 NS 0 to 75x 9.32 2.17 0.509 ** 50 to 300w -0.17 1.64 0.816 *** RLD (m cm'3) vs. MRO (# cm‘z) 0 to 25 24.17 -0.98 -0 323 us 25 to 50 20.03 -3.31 -0.392 us 50 to 75 10.28 -3.76 -0.278 us 75 to 150 6.27 -14.88 -0.456 us 150 to 225 0.11 -2.43 0.139 us 225 to 300 0.08 1.39 0.287 NS 0 to 300 0.99 4.49 0.847 *** *, ** and *** represent significance at the 0.05, 0.01, and 0.001 probability level, respectively. NS designates not significant. 2, note root weights reduced during storage. y, n~12 x, n~33 (improperly stored samples) w, n-57 (properly stored samples) Tabl dens dept Dept RVD O tc 25: SOt 75 t 150 225 0 tc RED 0U 25 ' 50 ' 75 150 225 0 t 15C 225 *l O n- H NS 7 Table 1.2. Correlation of root weight density (RWD), root length density (RLD), and minirhizotron root observations (MRO) at various depth zones; sampled mid-October 1987. Depth zone (mm) Intercept Slope Correlation RWD (mg cm'3) vs RLD (m cm'3) 0 to 25 4.44 0.04 0.120 NS 25 to 50 1.89 0.17 0.314 NS 50 to 75 0.24 0.56 0.720 ** 75 to 150 0.16 0.21 0.689 ** 150 to 225 0.09 0.11 0.443 NS 225 to 300 0.04 0.14 0.198 NS 0 to 300 0.13 0.53 0.977 *** RWD (mg cm'3) vs. MRO (# cm‘2) 0 to 25 12.95 -0.17 -0.072 NS 25 to 50 0.43 1.52 0.294 NS 50 to 75 -0.11 1.64 0.442 NS 75 to 150 3.55 -2.30 -0.461 NS 150 to 225 0.80 -0.39 -0.069 NS 225 to 300 0.45 -2.13 -0.205 NS 0 to 300 0.74 1.20 0.918 *** RLD (m cm'3) vs. MRO (# cm'z) 0 to 25 14.80 -0.71 -0.088 NS 25 to 50 -2.40 3.37 0.353 NS 50 to 75 1.87 0.98 0.206 NS 75 to 150 2.43 -l.92 -0.116 NS 150 to 225 -0.61 11.68 0.526 * 225 to 300 0.50 -3.88 -0.263 NS 0 to 300 0.48 2.26 0.928 *** *, ** and *** represent significance at the 0.05, 0.01, and 0.001 probability level, respectively. NS designates not significant. founI whil itse subj bra: rela homc act (19: Cut cor 25 deg thi bcn (:0 ob sa an 8 found a large number of white, slender, actively growing roots in May while roots appeared darker, thicker and more contorted in October. The root system of creeping bentgrass is reported to replace itself annually (Beard, 1973). During the growing season, roots are subjected to numerous stresses which can influence root diameter, branching, and mortality, thereby altering root weight and length relationships (Russell, 1977). Spring measurements may reflect a more homogeneously developed root system before climatic and soil stresses act to vary root system weight and length relationships. Hendricks (1988) found similar RLD values under a creeping bentgrass fairway turf. Regression analysis of his data showed RLD was significantly correlated with MRO in the first three 25 m depth zones, but the 0 to 25 mm zone was negatively correlated. No correlations were found at depths below 75 mm in his data. Combining the various depth zones in this study demonstrated a good relationship between RWD and RLD for both sampling dates (Tables 1.1 & 1.2; Figure 1.1). Only one depth zone in the October sampling showed a significant correlation between RLD and MRO, while no significant correlations were observed between RWD and MR0 at individual depth zones for both sampling dates. Most likely, the spatial variation in soil conditions and rooting between the minirhizotrons and actual soil sampling sites was too large for the small depth intervals examined in this study. When root measurements were combined over all depth intervals, RWD and RLD were both significantly correlated with MRO for both the May and October sampling dates (Tables 1.1 6: 1.2; Figures 1.2 6: 1.3). The greater slope for the correlation of RWD and MRO in May (Table 1.1) compared to the October correlation (Table 1.2) suggested a greater 8 7_ o 0 to 25 mm _ o a 25 to 50 mm 6- A 50 to 75 mm - 5_ A 50 to 75 mm _ g (é, o 75 to 150 mm 4" o v 150 to 225 mm" 5- a! 225 to 300 mm— 2- .I 1.. A! A May 1987 _ C) I I I I If I IIIIII 012345678910111213 8- _ .7- o 0 to 25 mm _ a 25 to 50 mm 6- A 50 to 75 mm '- 5_ o 75 to 150 mm o - v 150 to 225 mm 4" as 225 to 300 m " Root length density (m cm-a) October 1987 - I If I I I I I I I I I If 012345678910111213 Root weight density (mg cm'a) Figure 1.1. The relationship of root weight density and root length density of a creeping bentgrass green in late-May and in mid-October 1987. Note: Open circles, squares, and triangles denote data which lost weight due to improper storage of late-May samples. 10 35 o 0 to 25 mm a 25 to 50 mm " A 50 to 75 mm _ a 50 to 75 mm o 75 to 150 mm " p v 150 to 225 mrn_ 'E a 225 to 500 mm o .. =II= _ V May 1987 U) I I I I I I I I I ‘6’ 0123456789101112 e 35 8 O 0 to 25 mm 2 30' D 25 to 50 mm " 3,) 25_ A 50 to 75 mm _ 8 o 75 to 150 mm 20" v 150 to 225 mm o n 15 n 225 to 300 mm 0 - o _ 10- 8 ‘80 o_ 5 .. October 1987 0123456585101'112 Root weight density (mg cm”) Figure 1.2. The relationship of root weight density and minirhizotron observations of a creeping bentgrass green in late-May and mid-October 1987. Note: Open circles, squares, and triangles denote data which lost weight due to improper storage of late-May samples. Observed roots (# cm-z) 11 o 0 to 25 mm a 25 to 50 mm " A 50 to 75 mm _ o 75 to 150 mm v 150 to 225 mm o " a 225 to 300 mm 00 _ [1 o - October 1987 I I I I I I 1 2 3 4 5 6 7 Root length density (m cm-a) Figure 1.3. The relationship of root length density and minirhizotron observations of a creeping bentgrass green in late-May and mid-October 1987. Ma Qt de p: ct be SE at $6 ti. 12 number of roots per unit weight of roots in the spring (Figure 1.2). This would be expected when a root system is in its early stages of annual development and roots have not reached their maximum volume and weight for the season. The slope for the RLD and MRO correlation (Figure 1.3) was considerably larger in May (Table 1.1) than October (Table 1.2) indicating that a single relationship between the two methods does not exist throughout an entire growing season. Figure 1.4 displays graphically the grand means of all three root measurements at the various depth zones for the May and October sampling dates. RWD for the 0 to 25 and 25 to 50 m depth zones were not plotted because of the confounding weight loss during storage of the May root samples. The data show that MRO and RWD were greater in May than October, while RLD did not indicate a decrease in October root quantity. Using a rhizotron, Koski (1983) observed that the seasonal development of root length under a creeping bentgrass turf had two peak periods of activity. The first and greatest period occurred March through June. The second peak of activity occurred during October but was smaller in magnitude. Garwood (1967) observed similar seasonal fluctuations in active root length of several cool-season grasses. In this study, RLD from soil samples would appear to be insensitive to changing active root quantities, while MRO and RWD appeared to be better indicators of active root quantity throughout the growing season. In a perennial turfgrass system, RLD may be a poor index of active roots because it is difficult to distinguish between active and senescent roots during counting. Senescent roots along minirhizotron tubes are not readily visible because their darker color blends into the background color of the soil reducing the chance of being counted. 13 .wme HonouUOIcfia can Anxioumfi ca meson nudge Hmcww>fipcfi um hufimcmv unwwwa uoou can .muflmsow :uwcoa uoou .mcowuw>pmmno couuoufisuficfia mo momma vsmum one .¢.H ouswfim AEEV £58 :8 com com 00. 0 con com 2: o con CON cop o O O I” , IO . M 0 IF 8 .. l—. m. m. m w M I s . 9 9 _mm. wumn kw “m “H. 1?. junvw av 11w“ 1? “H. n? w. .n w. m I u u o we: .6: Im— a. in W.) 1% ,M. w w ) . 5 m cu m .. 1 m c. IV w r [kt 39300 I . rm. 33300 Tm 35300 I me 25.. «lo 0:2. an 1m 05.... ele In .. .. OI bI be sc se If be si pr of me en. in eve Sufi 14 However, RWD may reflect changes in active root quantities because senescent roots lose weight as cell tissue decays and sloughs off. Minirhizotrons and other ”glass wall” methods are considered to be the most suitable method for studying root phenology (Bohm, 1979). SUMMARY Root weight density (RWD) and root length density (RLD) at individual depth zones were significantly correlated in May but not in October. Reasons for the lack of correlation in October might have been due to greater heterogeneity in root morphology and age later in the growing season. Few significant correlations were found between RWD and minirhizotron root observations (MRO) and no correlations were observed between RLD and MRO at individual depth zones. Spatial variation in soil conditions and rooting between the minirhizotrons and soil sampling sites was thought to be the reason for these poor relationships at the small depth intervals examined. When data was combined across all depth zones, correlations between RWD and RLD, RWD and MRO, and RLD and MRO were all highly significant. These results indicated that the minirhizotron method provided an acceptable means to characterize the profile distribution of the root system of a creeping bentgrass green. The minirhizotron method offers the advantage of repeated sampling at the same site, enabling the researcher to observe more easily the seasonal growth dynamics of root systems. These types of observations can assist in evaluating management programs which may affect rooting and subsequently, water use efficiency. 15 Seasonal changes in slope indicated that no single relationship between RLD and PRO can be expected. The lack of change in RLD measurements between May and October suggested that RLD may be insensitive to temporal fluctuations in ”active” root quantity. MRO and RWD demonstrated greater root quantities in May than October and therefore should be better indices of root quantity. The minirhizotron method provides many advantages for root growth research. However, as with all methods there exist limitations. Long term observation of this creeping bentgrass root system found a large accumulation of roots along minirhizotrons at the 0 to 48 mm soil depth zone. Early in the spring it was impossible to determine the total number of roots present because the entire viewing area was full of entwined roots. It was also observed that operator consistency in counting the roots on video was poor between operators, particularly for images containing a large number of roots. Therefore, it is best to have one person for processing video images. LIST OF REFERENCES Bo Br Fe Ca He He Ka K0. Me] NQI 16 LIST OF REFERENCES Beard, J.B. 1973. Turfgrass: Science and culture. Prentice—Hall Inc. Englewood Cliffs, N.J. 658 pp. Bohm, W. 1979. Methods of studying root systems. Springer-Verlag, Inc. New York, NY. 188 pp. Branham, B.E., A.J.M. Smucker, J. Ferguson, P.E. Rieke, and J.A. Murphy. 1986. Examining the turfgrass rootzone with minirhizotrons. p. 131. In Agronomy Abstracts. ASA, Madison, WI. DiPoala, J.M., J.B. Beard, and A. Brawand. 1982. Key events in the seasonal root growth of bermudagrass and St. Augustinegrass. HortSci. 17:829-831. Ferguson, J.C., and A.J.M. Smucker. 1989. Modifications of the minirhizotron video camera system for measuring spatial temporal root dynamics. Soil Sci. Soc. Am. J. 53:1601-1605. Garwood, E. A. 1967. Seasonal variation in appearance and growth of grass roots. J. Br. Grassl. Soc. 22:121-130. Hendricks, M.G., and B.E. Branham. 1987. A comparison of two methods for determining root growth in turf. p. 135. In Agronomy Abstracts. ASA, Madison, WI. Hendricks, M.G. 1988. Management of mixed annual bluegrass and creeping bentgrass stands. M.S. thesis. Michigan State Univ. 103 pp. Karnok, K.J., and R.T. Kucharski. 1982. Design and construction of a rhizotron-lysimeter facility at the Ohio State University. Agron. J. 74:152-156. Koski, A.J. 1983. Seasonal rooting characteristics of five cool season turfgrasses. M.S. thesis. Ohio State Univ. 133 pp. McMichael, B.L., and H.M. Taylor. 1987. Applications and limitations of rhizotrons and minirhizotrons. p. 1-13. In H.M. Taylor (ed.) Minirhizotron observation tubes: Methods and applications for measuring rhizosphere dynamics. ASA Spec. PUbl. No. 50. ASA, CSSA, and SSSA, Madison, WI. Newman, E.I. 1966. A method of estimating the total length of root in a sample. J. Appl. Ecol. 3:139-145. Ru Sh Sn Te 17 Russell, R.S. 1977. Plant root systems: Their function and interaction with the soil. McGraw-Hill Book Company, Ltd. London. 298 pp. Shearman, R.C., and J.F. Barber. 1987. Turfgrass rhizotron construction and design. p. 139. In Agronomy Abstracts. ASA, Madison, WI. Smucker, A.J.M., S.L. McBurney, and A.K. Srivastava. 1982. Quantitative separation of roots from compacted soil profiles by the ° hydropneumatic elutriation system. Agron. J. 74:500-503. Tennant, D. 1975. A test of a modified line intersect method of estimating root length. J. Ecol. 63:955-1001. 18 CHAPTER TWO High Pressure Water Injection and Hollow Tine Cultivation of a Compacted Creeping Bentgrass Green ABSTRACT Traditional core cultivation practices are performed in spring and/or fall to alleviate problems associated with soil compaction on golf course putting greens. Mid-season cultivation is rarely done because of the costs involved with closing the course to play and the objection of players to an uneven putting surface. Short-time pulse injection of highly pressurized water has been introduced as a means to relieve soil compaction while limiting playing surface disturbance. This study evaluated the response of a ’Penncross’ creeping bentgrass (Agrostis palustris Huds.) growing on a loamy sand soil (modified fine- loamy, mixed, mesic, Typic Hapludalf) to hollow tine cultivation (HTC) and high pressure water injection (WIC). Cultivation treatments were applied three and two times in 1988 and 1989, respectively, on a putting green receiving compaction from 0.68 t rollers. WIC was equal or superior to HTC in. improving soil bulk density, porosity, and saturated hydraulic conductivity in the 0 to 76 m depth zone. HTC loosened the surface 30 mm of soil more than WIC, but only WIC provided a significant loosening of the soil from the 60 to 100 m depth. WIC stimulated creeping bentgrass shoot growth after treatment over that 19 achieved with HTC. HTC lowered thatch/mat weight sooner and to a greater extent than WIC. HTC reduced surface (0 to 100 mm) root weights as well as root numbers observed along minirhizotrons compared to the check and WIC plots. Root damage and removal during HTC cultivation. was the reason for this response. Minirhizotron. root observations revealed increased rooting below 200 mm for both HTC and WIC plots compared to the check. Deep rooting was greater in WIC plots than. HTC plots. Increased rooting 'below 200 mm may account for decreased water extraction at the 0 to 100 mm zone in WIC plots with a larger portion of water consumption occurring deeper in the soil. WIC offers the potential for routine cultivation during periods of high site usage and environmental stresses. 2 0 INTRODUCTION Golf course putting greens are subjected to intense levels of traffic which can lead to many problems associated with soil compaction, such as poor water infiltration and percolation, reduced soil aeration, restricted root development, and hard playing surfaces (Madison, 1971). Typically, cultivation practices are performed during the spring and/or fall to relieve soil compaction problems. However, the most severe soil compaction problems occur during mid-season when play and the demand for a quality putting surface are at their highest. The conventional hollow tine cultivation (HTC) technique creates an uneven putting surface because of the removal of turf/soil cores and is not widely used as mid-season cultivation tool. Research regarding the ability of HTC to alleviate soil compaction has been limited and some results are conflicting. Water infiltration rates have increased (Waddington et al, 1974), decreased (Roberts, 1975), or remained unchanged (Byrne et al., 1965; Engel and Alderfer, 1967). Murphy (1986) observed that saturated hydraulic conductivity decreased with cultivation in noncompacted soil and was unaffected by cultivation in compacted soil. HTC has decreased (Murphy, 1986) or increased (Goss, 1984) soil bulk density. Carrow (1988) and Murphy (1986) found HTC reduced penetrometer resistance. Solid tine cultivation (STC) with small diameter tines has greater acceptance as a mid-season cultivation tool but receives considerable criticism for its potential to develop a cultivation pan. Murphy (1986) found STC increased aeration porosity at the 0 to 76 m depth but to a smaller extent than HTC. Murphy and Rieke (1987) reported that penetrometer resistance was decreased in the soil surface, but 21 resistance just below the tine depth suggested a compacted layer was forming with STC compared to HTC plots. Goss (1984) reported increased bulk density and decreased infiltration following STC. HTC has enhanced bermudagrass [Cynodon dactylon (L.) Pers. X C. transvaalensis (Burtt-Davis)] rooting and water extraction, but STC had no effect (Carrow, 1988). A recently developed technique using high pressure water injection shows considerable promise as a tool for mid-season cultivation. This technique uses high velocity streams of water to cut small diameter channels in the soil while minimizing surface disruption. A prototype water injection cultivator was provided by the Toro Company (Minneapolis, MN). This study was designed to compare hollow tine cultivation (HTC) and high pressure water injection cultivation (WIC) based on the ability to improve soil physical conditions and turf growth of a ’Penncross’ creeping bentgrass (Agrostis palustris Huds.) putting green. MATERIALS AND METHODS The study was initiated on a 5-year old ’Penncross’ creeping bentgrass green maintained at a 6 mm cutting height and grown on a modified loamy sand soil (original soil was a fine-loamy, mixed, mesic, Typic Hapludalf). Compaction was initiated on 16 June, 1986 with water-filled rollers (approximately 50 kPa). The entire plot area received 70 passes of compaction between 16 June and 16 Sept., 1986; 54 passes between 18 June and 31 Aug., 1987; 120 passes between 8 Apr. and 7 Oct., 1988, and 120 passes between 6 Apr. and 29 Sept., 1989. 22 Cultivation treatments were initiated on 9 July, 1988 in a randomized complete block design with five replications. Additional cultivation treatments were applied on 19 Aug. and 3 Oct. , 1988, and 14 Aug. and 2 Oct., 1989. The treatments consisted of (i) no cultivation (check), (ii) hollow tine cultivation (HTC), and (iii) high pressure water injection cultivation (WIC). HTC was performed with a TORO greens aerator equipped with 13 mm hollow tines. WIC was applied using 19.3 to 22.1 MPa line pressure through thirteen injection nozzles (orifice of 1.2 mm i.d.) spaced 76 mm apart. Soil brought to the surface with both cultivation methods was removed with a flat shovel followed by brushing. Three minirhizotron tubes of 91 cm length and 51 mm i.d. were installed in each plot on 26 and 27 April, 1986 at an angle of 30 degrees from the soil surface. Minirhizotron tube entry ports were mounted subsurface to facilitate normal turf maintenance and compacting operations and faced north to minimize exposure to thermal radiation. Video recording of roots was performed on several dates in 1988 and 1989 using the system described by Ferguson and Smucker (1989). Cultivation holes created during treatment application were no closer than 160 mm to the soil exit point of the minirhizotron tubes. The number of active roots in each viewing frame was counted. The root counts were summed over four frames for a total number of roots observed at 24 m depth intervals. Active roots were considered to be those roots white in color and having sharp edges. As roots aged they became darker in color and began to lose definition as the edges became blurred. Roots of dark color and having blurred edges were considered inactive and not counted. Root counts became very high and difficult 23 to accurately count in 1988 along the first 48 mm (eight frames) of the minirhizotrons. By 1989, the viewing area along the surface 48 mm of the minirhizotrons was often totally covered with roots. Because of the inability to obtain accurate root counts information will not be reported for the first 48 mm of depth along the minirhizotrons. Nitrogen was applied at 98, 146, 317, and 171 kg ha.1 in 1986, 1987, 1988, and 1989, respectively. Nitrogen rates were high in 1988 because of the longer than normal growing season experienced that year. Fertility applications were made on 29 Apr., 20 May, 4 June, 26 June, 19 July, 12 Aug. , 1988, and 9 May, 14 June, 31 July, 23 Aug., 22 Sept., 1989. Potassium and phosphorus were applied according to soil test recommendations. Pesticides were applied as necessary to control insects and diseases. Irrigation was used to maintain soil moisture potential below -30 kPa, except for drydown periods used to evaluate moisture loss as affected by treatment. Clippings were collected and weighed for the growth periods of 15 to 19 Aug., 23 to 26 Aug., 26 to 31 Aug., and 26 Sept. to 1 Oct., 1988, and 22 to 27 May, 6 to 11 July, 3 to 9 Aug., 30 Aug. to 4 Sept., 4 to 21 Sept., and 4 to 29 Oct., 1989. Water extraction was estimated by tensiometry (Gaussoin et al., 1990) from 6 to 9 Aug., 1989. Two tensiometers were installed in each plot for the 10 to 50 mm and 90 to 140 mm soil depth zones. Time- domain reflectometry (Topp and Davis, 1985) was utilized as a measure of water extraction during 6 to 9 Aug. and 18 to 21 Sept., 1989. Two pairs of waveguides were installed in each plot for the 0 to 100 and 0 to 200 m depth zone. Water use from the 100 to 200 m depth zone was determined by subtraction. 24 Sampling for root, thatch/mat, and shoot tissue weights was performed November 1988, and July and November, 1989. The term thatch/mat will be used to describe the approximately 15 mm thick layer of organic matter between the soil surface and the green shoot tissue. This layer included organic material which was unmixed (thatch) and well-mixed (mat) with soil. Soil cores 102 mm in dia. and 200 mm in depth were excavated. $011 was sectioned into 0 to 50, 50 to 100, and 100 to 200 mm intervals. Soil and roots were separated ‘by the hydropneumatic elutriation method (Smucker et al., 1982). Thatch and shoot tissue were sectioned from the soil cores and frozen. until washing with the elutriation system could be performed. All samples were dried overnight at 60° C and weighed. Soil core sampling was achieved using 76 i.d. by 76 mm high cores. Samples were taken at the 0 to 76 and 76 to 152 mm soil depth zones for bulk density, soil porosity, and saturated hydraulic conductivity determinations in November, 1988 and 1989. Only 0 to 76 mm samples were excavated in August 1989. Analysis of variance was performed on all data and means were separated using Fisher’s protected LSD procedure at the 0.05 level of probability (Steel and Torrie, 1980). RESULTS AND DISCUSSION 52W Data for cultivation effects on soil density, aeration porosity, total porosity, and saturated hydraulic conductivity are presented in Table 2.1. After 3 treatments (November 1988), HTC and WIC lowered soil bulk density, and increased aeration porosity and total soil porosity in the 0 to 76 mm soil zone. Aeration 25 Table 2.1. Soil (0 to 76 mm) bulk density, total porosity, aeration porosity (0 to -6 kPa moisture potential), and saturated water conductivity (K Sat) responses to hollow tine (HTC) and water injection (WIC) cultivation of a loamy sand soil. Bulk Total Aeration Density Porosity Porosity K Sat November 1988 (5 weeks after treatment) Mg m'3 —— m3 100 m'3 — mm hr'l Check 1.83 29.3 7.3 21 arc 1.78 31.4 9.2 23 VIC 1.77 32.2 9.6 46 LSD (0.05) 0.03 0.79 2.0 us August 1989 (46 weeks after treatment) Check 1.84 29.6 3.8 ND HTC 1.80 30.9 4.8 ND WIC 1.81 30.8 4.7 ND LSD (0.05) 0.026 0.8 0.8 November 1989 (7 weeks after treatment) Check 1.83 29.6 7.4 10 HTC 1.77 32.2 9.0 21 WIC 1.75 32.3 9.0 29 LSD (0.05) 0.05 1.3 NS 11 ND denotes not determined. NS denotes not significant. 26 porosity was measured as the amount of water drained between 0 and -6 kPa moisture potential. WIC was more effective in increasing total porosity of the soil compared to HTC. Data taken prior to treatment in 1989 (August 1989) showed that the improved soil conditions measured in the previous year (November 1988) were beginning to diminish (Table 2.1). Others have observed short-lived soil responses to cultivation treatment (Roberts, 1975; Lee, 1989). Two additional cultivation treatments in 1989 resulted in density and porosity values similar to those observed in 1988. Although aeration porosity was increased, saturated hydraulic conductivity was not significantly affected by cultivation in 1988. The nonsignificant effect of cultivation was due to considerable variability, particularly with WIC soil. While excavating the soil samples, WIC channels were observed to be variable in depth of penetration with some channels extending beyond the 76 mm depth. This inconsistency of depth was thought to account for the lack of significance in 1988 conductivity data. By November 1989, conductivity was significantly improved with WIC compared to check plots (P<0.05). Conductivity was increased with HTC compared to the check at the 0.10 level of probability. In the 76 to 152 mm soil zone, total soil porosity was found to increase after 3 WIC treatments compared to the check and HTC plots in November 1988 (Table 2.2). Most likely, this response was a result of the slightly greater depth of penetration (soil channels created) with WIC compared to HTC. Channels were typically 50 to 70 mm deep with HTC and 80 to 100 mm with WIC. However, an increase in total porosity was not observed in November 1989. No other soil responses were detected 27 Table 2.2. Soil (76 to 152 mm) bulk density, total porosity, aeration porosity (0 to -6 kPa moisture potential), and saturated water conductivity (K Sat) responses to hollow tine (HTC) and water injection (WIC) cultivation of a loamy sand soil. Bulk Total Aeration Density Porosity Porosity K Sat November 1988 (5 weeks after treatment) Mg m'3 —— m3 100 m'3 — mm hr'1 Check 1.85 27.3 9.0 8 HTC 1.84 27.6 9.5 9 WIC 1.83 28.4 10.1 10 LSD (0.05) NS 0.67 NS NS November 1989 (7 weeks after treatment) Check 1.84 28.1 8.7 15 HTC 1.86 27.7 8.1 10 WIC 1.84 28.0 8.8 17 LSD (0.05) NS NS NS NS NS denotes not significant. 28 in the 76 to 152 mm soil zone in 1988 and 1989. Table 2.3 presents soil porosity distribution for the 0 to 76 mm soil depth zone as determined by the water drained between various water potential ranges. Moisture release data was used to evaluate porosity distributions for each cultivation treatment. Each ten-fold increment in moisture potential was considered an endpoint for a particular pore size range. For this discussion 0 to -l kPa represents the very large macropores, -1 to ~10 kPa represents the medium-sized macropores, -10 to -100 kPa represents intermediate sized pores (mesopores), and -100 kPa to oven-dry (OD) represents the very fine pores (micropores). Cultivation resulted in an increased quantity of the very large macropores (0 to -1 kPa) in the 0 to 76 mm soil zone, with both HTC and WIC being of similar effectiveness in November 1988 and 1989. The 0 to -1 kPa porosity levels measured in August 1989 showed that both HTC and WIC treated plots had lost some porosity within this range and WIC was no longer significantly greater than the check soil. This data substantiated the previously mentioned loss in treatment effect during the non-treatment period of October 1988 to August 1989 (Table 2.1). Neither HTC nor WIC changed the volume of mesopores or micropores. Murphy (1986) feund that hollow and solid tine cultivation decreased the -l to -10 kPa macropore region and increased the amount of micropores in the 0 to 76 mm depth zone. This was concluded to be a compactive effect on the soil which reduced soil water conductivity. During the course of this study, neither HTC nor WIC resulted in any soil response which would indicate the‘ development of severely compacted zones or layers. 29 Table 2.3. The influence of hollow tine (HTC) and water injection (WIC) cultivation on soil porosity drained between several moisture potentials in the 0 to 76 mm zone. Water Potential Range (-kPa) o to 1 1 to 10 10 to 100 100 to 00* November 1988 (5 weeks after treatment) m3 100 111'3 Check 2.0 7.4 5.1 14.8 HTC 4.1 7.0 5.3 15.0 WIC 3.8 8.2 5.3 14.9 LSD (0.05) 0.4 NS NS NS August 1989 (46 weeks after treatment) Check 1.9 7.4 4.5 15.8 HTC 2.8 6.9 4.7 16.5 WIC 2.4 7.5 4.9 16.0 LSD (0.05) 0.6 NS NS NS November 1989 (7 weeks after treatment) Check 1.9 7.1 5.3 15.4 HTC 3.6 6.8 5.7 16.1 WIC 3.4 7.2 6.0 15.7 LSD (0.05) 0.6 NS NS NS *, OD - Oven dry 105° C. NS denotes not significant. 30 Soil porosity data for the 76 to 152 mm zone showed WIC increased total soil porosity in November 1988 (Table 2.2). This increase in soil porosity occurred primarily in the very large macropore region, 0 to -1 kPa (Table 2.4). The porosity response to WIC at this soil depth demonstrated the benefit of deeper penetration, improving soil conditions below that achieved with HTC. No treatment responses were detected in this soil zone for the 1989 sampling. The lack of response to WIC at the 76 to 152 mm depth zone in 1989 was thought to be due to soil variation. During soil core sampling in 1989, a large number of stones were observed at the 76 to 152 mm zone in many of the plots. Only a few plots in 1988 were observed to have such a soil condition. The greater occurrence of stones may have limited water injection penetration and/or increased variability in the soil parameters measured. Figure 2.1 shows soil strength values recorded on 25 July following 9 July cultivation treatment in 1988. HTC reduced soil strength at the 30 mm depth compared to the noncultivated plots. Between 40 and 60 mm both HTC and WIC provided similar reductions in soil strength compared to the noncultivated plots. From 70 to 100 mm, only the WIC treatment resulted in a significant reduction in soil strength compared to the check plots. Thus, WIC provided a significant loosening of this compacted loamy sand to the 100 mm soil depth while HTC influence was limited to the 60 mm depth. Penetration resistance data also demonstrated WIC was not as disruptive (less loosening) in the soil surface 30 mm compared to HTC. Carrow (1988) reported that HTC was the most effective of five cultivation treatments in lowering penetration resistance. 31 Table 2.4. The influence of hollow tine (HTC) and water injection (WIC) cultivation on soil porosity drained between several moisture potentials in the 76 to 152 mm zone. Water Potential Range (-kPa) 0 to 1 1 to 10 10 to 100 100 to 00* November 1988 (5 weeks after treatment) m3 100 m’3 Check 1.7 8.8 3.7 13.1 HTC 1.8 9.2 3.7 12.9 WIC 2.0 9.7 3.7 13.0 LSD (0.05) 0.2 NS NS NS November 1989 (7 weeks after treatment) Check 1.9 7.8 3.6 14.8 HTC 1.8 7.2 3.5 15.2 WIC 1.9 8.0 3.8 14.3 LSD (0.05) NS NS NS NS *, OD - Oven dry 105‘ C. NS denotes not significant. 32 .wme .masn mu woadamm HHom comm Samoa a mo mocmumamou cowucuuosmm co Aaowuuonca nouns n 0H3 .ocau 30HH0£ I oemv coaum>auanu mo moamafimsH .H.N ouawwm AEEV £88 :8 oo. om on on cm on 0* on ON In _ _ _ . . _ . .N 0.; I 0.5 ole .. xomzo are H In m. 1:? .J «u . 8 ) W A d D ( 1m 88 .22. mm 30.8 on. n 6.6m . 33 W Clipping yield data on 26 August demonstrated that WIC and HTC increased shoot growth immediately following treatment compared to check plots in 1988 (Table 2.5). HTC and WIC increased growth 16% and 422, respectively compared to the check. This difference in yield between HTC and WIC was attributed to the removal of crown tissue with HTC. Penetration resistance data (Figure 2.1) showed HTC resulted in more surface loosening (disruption) compared to WIC. Most likely, greater disruption. with HTC also imposed. more mechanical injury stress to the turf than WIC. Yield data on 31 August showed that only WIC had significantly greater clipping yield compared to the check plots. Shoot growth enhancement with both HTC and WIC declined with time and became equivalent to the check plots prior to the 3 October treatment date in 1988. Clipping yields on 27 May, 1989 showed growth on WIC plots was greater than the check plots during early spring growth. During a period of high growth rate in. July 'no treatment differences were observed. On 9 August both HTC and WIC increased growth compared to the check. Compaction stress may have become great enough during this time to limit growth and cause a response in cultivated plots. Alderfer (1954) reported that cultivation of a heavily compacted Kentucky bluegrass turf did not increase growth. Roberts (1975) found cultivation of a Kentucky bluegrass turf reduced clipping yield. Sampling dates in September and October, 1989 showed no growth responses to cultivation (Table 2.5). This lack of response to cultivation treatment may be a result of the slow growth rates observed during this period. Table 2. 5. 34 The influence of hollow tine (HTC) and water injection (WIC) cultivation on clipping yield of a compacted creeping bentgrass green mowed at 6 mm. Check HTC WIC LSD (0.05) Check HTC WIC LSD (0.05) 1988 Clipping Yields 8/19 8/26 8/31 10/1 8 m'2 day'1 2.8 1.9 1.9 1.2 2.7 2.2 2.3 1.3 2.8 2.7 2.6 1.2 NS 0.2 0.4 NS 1989 Clipping Yields 5/27 7/11 8/9 9/4 9/21 10/29 8 m'2 day'1 1.62 3.6 2.2 1.7 0.6 0.2 1.8 3.7 2.5 1.7 0.7 0.2 1.9 3.7 2.5 1.8 0.6 0.2 0.26 NS 0 2 NS NS NS 2, Only 4 replications were available for 5/27 sampling. NS denotes not significant. Treated 9 July, 19 Aug., and 3 Oct., 1988 and 14 Aug. and 2 Oct., 1989. Nitrogen applied 29 Apr., 20 May, 4 June, 26 June, 19 July, and 12 Aug., 1988, and 9 May, 14 June, 31 July, 23 Aug., and 22 Sept., 1989. 35 Table 2.6 shows the effect of cultivation treatment on visual quality in 1988 and 1989. WIC increased creeping bentgrass quality on these compacted plots by late August while HTC did not improve quality until late September in 1988. WIC had better quality in November compared to both HTC and check plots, and HTC plots were of better quality than check plots. It is important to note that two treatment applications (9 July and 19 August) were required before any improvement in quality could be observed in this study. Thus soil cultivation does not necessarily have an immediate impact on quality in a turfgrass system. Quality ratings in 1989 showed that WIC plots had the best ratings throughout the season with three of the five dates being significantly better than the check. HTC received a better rating compared to the check on only one date; WIC was better than HTC on two dates. Table 2.7 gives the shoot, thatch/mat, and total root weights measured in 1988 and 1989. Neither HTC nor WIC treatment had an effect on shoot tissue weight in November of 1988 and 1989. However, shoot tissue weight was found to be greater in cultivated plots compared to check plots in July 1989. This increase in shoot tissue was greater in WIC plots than HTC plots. Shoot tissue may have increased with cultivation only in July 1989 in response to reduced compaction stress during a period when other stresses, such as temperature and moisture, may be additive to the compaction stress. Thatch/mat data supported the conclusion of crown tissue removal and injury. HTC resulted in lowering the amount of thatch compared to noncultivated and WIC plots. The 17! decrease in thatch/mat weight observed in November 1988 with HTC corresponded well: with the 36 Table 2.6. The influence of hollow tine (HTC) and water injection (WIC) cultivation on visual quality of a compacted creeping bentgrass green mowed at 6 mm. 1988 Quality Ratings 7/20 8/28 9/11 9/30 11/8 (9-ideal and 6-acceptable) Check 8.2 7.1 7.5 7.0 5.0 HTC 8.0 6.9 7.2 7.5 5.5 WIC 8.6 7.9 7.8 7.6 6.1 L.S.D.(0.05) NS 0.76 NS 0.35 0.46 1989 Quality Ratings 5/27 7/10 8/3 10/7 11/1 (9-ideal and 6-acceptab1e) Check 6.0 7.6 7.2 6.0 5.8 HTC 7.4 6.8 6.9 7.0 6.0 WIC 8.0 8.2 8.1 7.0 7.1 LSD (0.05) NS NS 0.8 0.6 0.5 NS denotes not significant. Treated 9 July, 19 Aug., and 3 Oct., 1988 and 14 Aug. and 2 Oct., 1989. Nitrogen applied 29 Apr., 20 May, 4 June, 26 June, 19 July, and 12 Aug., 1988, and 9 May, 14 June, 31 July, 23 Aug., and 22 Sept., 1989. 37 Table 2.7. The influence of hollow tine (HTC) and water injection (WIC) cultivation on the shoot tissue, thatch/mat, and total root weights of a compacted creeping bentgrass green. Shoot Thatch/ Total Tissue Mat Root Weight November 1988 (4 weeks after treatment) kg In"2 Check 0.246 1.25 0.534 HTC 0.223 1.04 0.466 WIC 0.205 1.31 0.518 LSD (0.05) NS 0.18 0.065 July 1989 (40 weeks after treatment) Check 0.196 0.70 0.469 HTC 0.216 0.76 0.397 WIC 0.230 0.65 0.431 LSD (0.05) 0.013 NS 0.046 November 1989 (6 weeks after treatment) Check 0.232 1.47 0.633 HTC 0.211 1.06 0.477 WIC 0.223 1.28 0.600 LSD (0.05) NS 0.16 0.065 NS denotes not significant. 38 calculated 13% area affected by three HTC treatments with 13 mm dia. tines (4.62 per treatment). Smith (1979) partially attributed the reduction in thatch organic matter to the physical removal via cultivation. No treatment differences in thatch/mat weight were observed in July 1989. Thatch/mat weights in July 1989 dropped compared to the November 1988 weights suggesting that the washing technique used for the July 1989 samples differed in some way. Thatch/mat weights in November 1989 again showed that HTC reduced this material compared to the check plots. Surprisingly, WIC also showed significantly lower thatch/mat weight compared to the check. Apparently, WIC inhibited the accumulation of organic material in the thatch/mat zone. Total root weight (TRW) was reduced with HTC compared to the check on all three sampling dates (Table 2.7). HTC lowered TRW compared to WIC by November 1989. The reduction in rooting following HTC was limited to the 0 to 50 m depth zone for the November 1988 and July 1989 sampling dates (Table 2.8). However, after a total of five HTC treatments, root weight density (RWD) was significantly decreased in both the 0 to 50 and 50 to 100 mm depth zones compared to the check and WIC plots. WIC resulted in significantly lower RWD compared to the check on only one date (July 1989) at 0 to 50 mm. There is likely some injury to roots which occurs with any effective cultivation method including WIC. These data demonstrated that HTC resulted in considerably more damage to the surface root system than WIC. Root weight data indicated that large increases in surface root development during the fall did not occur following summer and fall cultivation. Large increases in surface rooting due to cultivation may 39 Table 2.8. The influence of cultivation on root weight densities of a creeping bentgrass green. Root Weight Density Zone (mm) 0 to 50 50 to 100 100 to 200 November 1988 (4 weeks after treatment) kg 111'3 Check 7.95 1.95 0.39 Hollow Tine 7.02 1.73 0.29 Water Injection 7.76 1.84 0.38 LSD (0.05) 0.91 NS NS July 1989 (40 weeks after treatment) Check 6.99 1.87 0.26 Hollow Tine 5.63 1.71 0.29 Water Injection 6.29 1.82 0.26 LSD (0.05) 0.67 NS NS November 1989 (6 weeks after treatment) Check 10.30 1.80 0.28 Hollow Tine 7.63 1.46 0.23 Water Injection 9.54 1.86 0.30 LSD (0.05) 1.40 0.29 NS NS denotes not significant. 40 result in the spring when the initiation rate of new roots is greatest. Koski (1983) found the greatest length of active creeping bentgrass roots occurred during March through June. Minirhizotron root observations (MRO) made on 15 Nov., 1988 (Figure 2.2), and 9 Aug. (Figure 2.3) and 29 Oct., 1989 (Figure 2.5) corroborated the root weight data and are representative of MRO videotaped on other dates during this study. MRO demonstrated that HTC reduced root numbers in the upper 100 to 150 mm of the soil profile. WIC did not result in a consistent lowering of root numbers within this zone. Root numbers below the depth (200 mm) evaluated by the soil sampling method showed that WIC increased root numbers below 260 mm in November 1988 (Figure 2.2), from 144 to 384 mm in August 1989 (Figure 2.4), and from 220 to 408 mm in October 1989 (Figure 2.5) compared to the check. HTC did not result in such a response until August 1989, and any increase was of a smaller magnitude compared to WIC. Carrow (1988) has observed increased rooting below 200 mm after cultivation of a compacted bermudagrass turf. Examination of the root turnover along minirhizotrons yields root growth information concerning where roots are appearing and disappearing within the soil profile (Ferguson and Smucker, 1989). Root turnover between 18 July and 30 Sept., 1988 demonstrated that both HTC and WIC resulted in a loss or a smaller increase in root numbers in the upper 168 mm of the profile compared to the check (Figure 2.6). However, WIC resulted in a large increase in rooting at the 264 to 360 mm depth zone. The third HTC treatment in 1988 resulted in a loss of roots between 30 September and 15 November at numerous depths 41 00¢ .wwaH .uonao>oz ma :oxmu macaum>pomno uoou couuonwnufiafia n 0H3 .ocfiu soHHos u oemv coaum>aufiso mo mocmaawcH .N.~ ouswam AEEV £88 :8 so AsOAuoomafi Houm3 0ch 0mm own 0mm com on. 00— IUIIIIIUUITIIIITIIIIITIIIIIUIIUITUIIIIIIITTI wmmp .>oz mp 0.3 I 0...: Ole xoon film to n 52 2 22. m 866: ( we JeqwnN) $1001 pe/uesqo :- 42 .awma .umoms< o coo—mu sun—op ea .1: on we 05 um macaumtomoo uoou souuouanuwcwa no Acowuooncw nouns n 33 6:3 3030: u 3.5 coauozufiso mo oocosHmcH .m.~ ouswfim AEEV £58 :3 0: cm. 2t: om. _ . p _ b D D b 1 mm? .62 m ( we JaqwnN) $3,001 pe/uasqo I I I I I l l I I I O O) Q I\ (D ID V V’) N '- O F 0.; Ta .. B: 0.6 ... xomzo elm mmmr E ucoEuoob 3 not; 43 .mme .umewe< m coxmu Sodom 35 «me on «ea onu um muowum>hmmno uoou couponanuwcfia so AGOfiuoohaH noumz n 0H3 .ocfiu aoHHos u oemv coaum>fiuaeo mo cosmeamcH .¢.N ouemqm AEEV £58 :8 one cow can con 0mm com on — _ . _ _ _ _..ol 1 .05 I I _..o I 1N6 1. Inoo 1 led .. A. 1nd 83 .92 m A .. r 10.0 0.3 I I 0...: ale 4 15.0 xouro elm mmmw E «co—Soot 3 corn. I md ( we .quwnN) SlOOJ pemesqo 44 .mwma .uonouoo mu :oxwu maowum>hmmno uoou couuonwnuacaa do Asoauoomcfi nouns n 0H3 .mcwu onHos u camv coaum>auaeo mo oucoeamcH .n.~ euewam AEEV £58 :8 00¢ 00¢ 0mm. own 0mm OQN om _. onw P cm... 1 Infiltifll-H n 10.0 I . 5.3! t I _ I T I I’:‘I.:r.I4HHJIv i n //.I.- l .. Ind m /. _. ... fl h I 10... H .6 /. . H T 83 e 0 mu .» In; T u H 0.; I. to N I ... 1 B: To . I . . 3.025 I me< 4; peacock __ . o N :- ( we JeqwnN) $100.1 pe/uesqo 45 .won .Hopaoudom on was Sana wH awesome ecouuoufisuwcaa macaw um>ocueu uoou haamw so AaOHuooHCa umum3 I 0H3 .ocfiu 3oHHon n Dewy coauw>fiuaeo we moaoeamcH .o.~ gunman AEEV £88 :8 om...V 00..V 09... com. omN DON on P CO — on _ _ . _ . . owl. I‘' I .3, _ :3 I C) U) I I 8 (,fDP z_w .quwnN) .Ierwm 1003 .. new. .38 on B 22. 9 ..on. T WOON .. 0.; Ta I on: 61.0 92 mp omw xowzo film 32.. m pounce... : com. 46 (Figure 2.7). WIC produced a gain in rooting at many depths above 288 mm for this observation period. WIC plots lost roots between 288 and 384 mm reflecting the greater number of roots present in this zone earlier in the season. HTC plots lost roots from 19 Sept. to 29 Oct., 1989 in the upper 144 mm while WIC plots tended to gain roots in this zone (Figure 2.8). During this period, root turnover data below 144 mm tended to be erratic, but did show that WIC resulted in a gain of roots at many depths while HTC produced a loss of roots. As a result of the larger number of deep roots present in WIC plots, the percent of roots lost in HTC was much greater than that observed in WIC plots (Table 2.9). Estimted Water; Egg. Water extraction data as estimated in 1989 by tensiometry and time domain reflectometry (TDR) is presented in Table 2.10. Water use estimated by tensiometry suggested that WIC plots used less water from the surface 76 mm in August compared to the noncultivated checks. Water use at the 76 to 152 m depth did not differ among treatments. Water use estimated by the TDR method did not support the tensiometry data in August 1989. Water use estimated by the TDR method in September demonstrated that WIC plots lost less water compared to the checks during this measurement period. Carrow (1988) reported greater water extraction between 200 and 600 mm following cultivation treatment of a compacted bermudagrass turf. Rooting of the bermudagrass turf was also increased within this depth zone. Although no data was taken below 200 mm in this study, the lower water use observed in the surface 100 mm suggests that an increase in water utilization deeper in the soil profile may have occurred. 47 .wwaH .umoaw>oz ma can Honsmudom om assauon mcouuonasuficfia macaw Ho>o=u=u uoou Sagan co ACOfiuoonaw Houm3 u 0H3 .ocwu Boaaon u oamv coauc>auaeo we moaoefimsH .n.N ouewwm AEEV £68 __6m 05. cm... 0mm can 0mm cam on. co. on _ _ O O - 5 - _ . N - . .... .. m. lM'-..t‘.L 0 1 (I J .I : I c u u u u : L n Ina nu .. w .8 m \N/ I loop n new. .82 m. 2 How on W I mom. 9 Id .. ..oow w. z 0.3 I ”.00 n c D. .. 2: 61. one. a. .63 .w xoon are be: m peace; (\._. 48 .ommH .uooouoo am one umoewudom oH coo3uoo mcouuonwsuwcfia mcoflm uo>ocueu uoou wagon so Aa0fiuoohca nouns u 0H3 .ocfiu 30HHon u uamv coaum>auaeo mo woaoechH .w.~ ouewfim AEEV £96 :8 one om... omn own omu omu on. oop on _ _ o fiOOmuI HG m r $2 .60 mm 3 3mm 2 a. 15.7 1. \ m .. .. Icon... w a O A .. ..oouI m 1N7 I u c IOOFI m .. ..o W 1 I .. 15. w. z 0.; I P .. B: 61. to u loom .m xomzo E 02:; peace... (x... con 49 Table 2.9. The influence of cultivation on daily percent root turnover between 19 September and 29 October, 1989. Hollow Water Check Tine Injection Depth mm 2 day"1 72 -0.08 -0.70 -0.05 96 -0.56 -0.87 -0.45 120 -0.70 -l.00 0.00 144 -0.38 -l.02 0.20 168 -0.90 -0.85 -l.04 192 -l.40 -1.08 -0.52 216 0.24 1.92 -0.98 240 -0.51 ~0.33 -0.22 264 -l.84 -0.58 0.83 288 -l.56 -l.l7 0.18 312 -l.77 -0.60 -0.37 336 -l.77 -1.32 -0.56 408 0.00 -0.77 -1.32 432 0.00 0.00 0.00 Total -15.13 -9.97 -1.59 Average -0.95 -0.62 -0.10 50 Table 2.10. The influence of cultivation on water extraction as estimated by tensiometry and time-domain reflectometry (TDR) in 1989. Tensiometry TDR 8/6 to 8/9 8/6 to 8/9 9/18 to 9/21 Depth Zone 0 to 152 mm 0 to 200 mm Check 12.7 13.3 7.9 HTC 11.3 14.9 5.7 WIC 11.0 14.8 4.9 LSD (0.05) NS(1.5) NS NS(2.7) Depth Zone 0 to 76 mm 0 to 100 mm Check 8.6 5.4 2.2 HTC 7.7 5.4 1.7 WIC 7.0 5.2 0.8 LSD (0.05) NS(1.4) NS 1.0 Depth Zone 76 to 152 mm 100 to 200 mm Check 4.1 7.8 5.7 HTC 3.6 9.4 4.0 WIC 4.0 9.5 4.1 LSD (0.05) NS NS NS NS denotes not significant. Values in parentheses are the LSD at the 5.02 probability level but did not meet Fisher's protected LSD requirement. 51 Minirhizotron observations showed an increase in rooting below 200 mm on WIC plots which lends support to the idea of deeper soil water extraction (Figures 2.1, 2.3, 6: 2.4). One reason for the discrepancy in TDR during August was unfamiliarity with the operation of the TDR which may have resulted in considerable operator error. Comparison of the tensiometry and TDR data showed that the TDR method estimated greater water extraction in the deeper portions of the profile relative to the surface profile. Water extraction by the tensiometer method showed the opposite. Total water use was similar for the two methods suggesting that the shorter probes (100 mm) used in the TDR method may have yielded inaccurate data. It should be noted that comparison of the two methods is confounded by the different depth zones for each type of measurement. SUMMARY Analysis of soil physical properties demonstrated that water injection cultivation (WIC) was equal or superior to hollow tine cultivation (HTC) in improving bulk density, total soil porosity, aeration porosity, and saturated hydraulic conductivity in the 0 to 76 m depth zone. Total soil porosity was increased slightly in 1988 at the 76 to 152 mm zone with WIC compared to HTC and check plots. Increased soil porosity resulted from the very large pores created by cultivation, i.e., coring holes and injection channels. Saturated hydraulic conductivity was increased with WIC compared to the check. HTC did not have a significant effect on conductivity in the two years of treatment. HTC was more effective in loosening the surface 30 mm of 52 soil compared to WIC. However, below the 60 m depth only WIC provided a significant loosening of the soil down to the 100 m depth. WIC stimulated creeping bentgrass shoot growth of a compacted putting green over that achieved after conventional HTC. An immediate shoot growth increase following WIC would allow for faster recovery of putting greens from compaction stress relative to HTC treatment. Mechanical injury to turf and roots and loss of crown tissue following HTC would place an additional stress on the turf, which may slow the recovery time of the turf to improved soil conditions. WIC had no measurable effect on thatch/mat weight after three treatments while HTC decreased thatch/mat weight after one season. WIC did not reduce thatch/mat levels in a single growing season. The impact on long term thatch accumulation with continued WIC remains a question, even though a reduction in thatch/mat weight was evident after five treatments over two seasons. HTC reduced total root weight compared to the check and WIC plots. Root damage and removal during cultivation was the reason for this response to HTC. Minirhizotron root observations (PRO) supported the conclusion of reduced rooting following HTC and to a limited extent following WIC. Reduced injury to the root system should enable the turf to respond more quickly to the improved soil conditions following cultivation. Minimizing the amount of mechanical injury stress incurred by the turf during cultivation should be important when considering cultivation during and prior to periods when environmental stresses are high (e.g., treatment of isolated dry spot in putting greens). PRO below the soil zone sampled for root weight revealed increased rooting for both HTC and WIC plots compared to the check. 53 This deep rooting response was greater in WIC plots than HTC plots. Increased rooting below 200 mm may help explain the decreased water extraction at the 0 to 100 mm zone in WIC plots. The presence of deep roots may have distributed water consumption over a larger soil volume (depth), thus minimizing surface water consumption. The data demonstrated WIC produced soil responses simiLmr to HTC. However, 'WIC appeared. to .alter soil properties deeper in the soil profile while reducing the amount of surface disturbance. HTC resulted in considerable disruption of the turf surface which damaged and removed plant tissue. WIC should be a very beneficial cultivation method during periods of high demand for recreational use and environmental stresses. LIST OF REFERENCES 54 LIST OF REFERENCES Alderfer, R.B. 1954. Effects of soil compaction on bluegrass turf. Penn. State College Turf. Conf. 23:31-32. Byrne, T.G., W.B. Davis, L.J. Booker, and L.F. Werenfels. 1965. A further evaluation of the vertical mulching method of improving old golf greens. Calif. Agric. 19:12-14. Carrow, R.N. 1988. Cultivation methods on turfgrass water relationships and growth under soil compaction. 1988 U.S.G.A. Green Section Turfgrass Summary. p. 14. Engel, R.B., and R.B. Alderfer. 1967. The effect of cultivation, topdressing, lime, nitrogen, and wetting agent on thatch development in 1/4-inch bentgrass turf over a ten-year period. New Jersey Agric. Exp. Stn., Bul. 818:32-45. Ferguson, J.C., and A.J.M. Smucker. 1989. Modifications of the minirhizotron video camera system for measuring spatial and temporal root dynamics. Soil Sci. Soc. Am. J. 53:1601-1605. Gaussoin, R.E., J.A. Murphy, and B.E. Branham. 1990. A vertically installed, flush-mounted tensiometer for turfgrass research. HortSci. 25(8):928-929. 6055, R.L. 1984. Aerification - A comparison of shattercore versus hollow tine. p. 46-48. In R.L. Goss (ed.) Proc. 38th Northwest Turf Conf. 17-20 Sept. Koski, A.J. 1983. Seasonal rooting characteristics of five cool season turfgrasses. M.S. thesis. Ohio State Univ. 133 pp. Lee, D.K. 1989. Effects of soil cultivation techniques on rooting of Kentucky bluegrass sod. M.S. thesis. Mich. State Univ. 62 pp. Madison, J.B. 1971. Principles of turfgrass culture. Van Nostrand Reinhold Co., New York, N.Y. 420 pp. Murphy, J.A. 1986. The effect of hollow and solid tine cultivation on soil structure and turfgrass root growth. M.S. thesis. Mich. State Univ. 61 pp. 55 Murphy, J.A., and P.E. Rieke. 1987. Hollow and solid tine coring research. p. 28-33. In P.E. Rieke and M.T. McElroy (ed.) 57th Annual Mich. Turf. Conf. Proc. Lansing, MI. 12-14 Jan. 1987. Roberts, J.M. 1975. Some influences of cultivation on the soil and turfgrass. M.S. thesis. Purdue Univ. 60 pp. Smith, G.S. 1979. Nitrogen and aerification influence on putting green thatch and soil. Agron. J. 71:680-684. Smucker, A.J.M., S.L. McBurney, and A.K. Srivastava. 1982. Quantitative separation of roots from compacted soil profiles by the hydropneumatic elutriation system. Agron. J. 74:500-503. Steel, R.C.D., and J.H. Torrie. 1980. Principles and procedures of statistics. Second Ed. McGraw-Hill, New York, NY. 633 pp. Topp, G.C., and J.L. Davis. 1985. Measurement of soil water content using time-domain reflectometry (TDR): A field evaluation. Soil Sci. Soc. Am. J. 49:19-24. Waddington, D.V., T.L. Zimmerman, G.L. Shoop, L.T. Kardos, and J.M. Duich. 1974. Soil modification for turfgrass areas. Penn. Agric. Exp. Stn. Progress Rep. No.337. 96 pp. 56 CHAPTER THREE Hollow Tine and Water Injection Cultivation of a Compacted Kentucky Bluegrass Turf ABSTRACT A regular core cultivation program is frequently recommended on general turf sites receiving high levels of traffic. Few studies have evaluated cultivation of general turf subjected to regular compaction stress. This study was initiated on a six-year-old ’Cheri’ Kentucky bluegrass (Poa pratensis L.) turf growing on a sandy loam soil (fine- loamy, mixed, mesic, Typic Hapludalf) to evaluate cultivation with vertically operating hollow tines (HTC) and pulse injection of highly pressurized water (WIC). A prototype of the commercial water injection unit was furnished by the Toro Company, Minneapolis, MN. Compaction stress was applied with a water-filled vibrating roller (51 kPa static pressure). Soil bulk density was decreased and aeration porosity was increased with HTC, but not by WIC. WIC increased saturated hydraulic conductivity more than HTC due to the deeper channels created with WIC. Clipping yield was decreased by HTC on several dates in 1988 and 1989 following treatment application. WIC had no effect on clipping yield. Thatch/mat weights were reduced after two years (six treatments) of both HTC and WIC. HTC reduced thatch/mat weight more than WIC, but this was offset by a loss in stand density with HTC. WIC appeared to 57 be a less damaging cultivation practice than HTC and should be a better cultivation technique for improving soil water movement when turf will not tolerate excessive mechanical injury and be slow to recover. 58 INTRODUCTION Core cultivation is often recommended as a routine cultural practice to improve turfgrass growth and soil conditions on general turf areas subjected to regular compaction stress. Core cultivation research on general turf has been limited primarily to evaluation of thatch control, turfgrass quality, and water infiltration. Core cultivation of a ’Meyer' zoysiagrass (Zoysia japonica Steud.) turf reduced turf quality and thatch (Weston and Dunn, 1985). Carrow et a1. (1987) reported that core cultivation once and twice a year reduced stand density but did not lower thatch accumulation of a ’Tifway’ bermudagrass [Cynodon dactylon (L.) Pers. X C. transvaalensis (Burtt- Davis)] homelawn turf. Murray and Juska (1977) observed core cultivation had no impact on common Kentucky bluegrass (Poa pratensis L.) thatch during the first five years, but after the sixth year thatch-organic matter weight was reduced and turf quality increased with core cultivation. Cultivation. with spoon tines lowered the quality of a Colonial bentgrass (Agrostis tennis) turf receiving minimal traffic (Engel, 1951a). Engel and Alderfer (1967) found water infiltration was unaffected with spoon type cultivation. A limited number of studies have evaluated cultivation on general turf sites under compacted conditions. Engel (1951a) reported that spoon tine cultivation (eight applications over three seasons) did not affect the quality of a golf course fairway comprised of Kentucky bluegrass and annual bluegrass (Poa annua L.). Based on pasture work, Engel (1951b) speculated that cultivation may be harmful to Kentucky bluegrass turf. Core cultivation was reported to enhance recovery of ’Merion’ Kentucky bluegrass following simulated foot traffic (Cordukes, 59 1968). Core cultivation of a heavily compacted Kentucky bluegrass turf decreased runoff but did not increase turf growth compared to noncultivated plots. (Alderfer, 1954). Byrne et a1. (1965) found no change in infiltration of a compacted putting green following core cultivation; only coring holes dug manually to 150 mm improved infiltration. Core cultivation has increased water infiltration rates (Waddington et al., 1974) of compacted soils, particularly soils with large sand volumes. High pressure water injection has recently been introduced as a new method to cultivate compacted turf soils. A prototype high pressure water injection unit was provided by the Toro Company, Minneapolis, MN. This study compared water inflection and hollow tine cultivation as a routine management practice on a ’Cheri’ Kentucky bluegrass turf subjected to compaction stress. MATERIALS AND METHODS The study was initiated on a six-year-old ’Cheri’ Kentucky bluegrass turf growing on a sandy loam soil (fine-loamy, mixed, mesic, Typic Hapludalf). Compaction treatments were initiated in July 1987 and performed throughout the study with a vibrating water-filled roller (50 kPa); 120 passes between 27 July and 31 Aug. 1987; 132 passes between 10 Apr. and 30 Sept. , 1988; and 134 passes between 29 Apr. and 1 Oct., 1989. Cultivation treatments consisting of no cultivation (check), hollow tine cultivation (HTC), and high pressure water injection cultivation (WIC) were arranged in a randomized complete block design with three replications. HTC was performed with a TORO greens aerator 60 equipped with 13 mm hollow tines reaching maximum depth of 75 mm. WIC was applied using 19.3 to 22.1 MPa line pressure through 13 injections nozzles spaced 76 mm apart which cut small diameter channels to an average 110 m depth. Cultivation treatments were applied on 6 July, 10 Aug., and 28 Sept., 1988; and 7 Aug., 12 Sept., and 7 Oct., 1989. Soil brought to the surface with HTC was removed with a flat shovel. All plots were then leaf-raked to remove remaining debris. No soil was brought to the surface with WIC. Nitrogen was applied at 142 and 134 kg ha'1 in 1988 and 1989, respectively. Dates of application were 5 July, 16 Aug., and 5 Oct., 1988, and 6 May, 10 July, 23 Aug., 1989. Phosphorus and potassium were applied according to soil test recommendations. Supplemental irrigation was applied to avoid wilt. 2 swath, dried, and weighed Clippings were collected from a 1.4 m for selected growth periods in 1988 and 1989. Soil moisture use was estimated by tensiometer in 1988 and 1989, and time-domain reflectometry (Topp and Davis, 1985) in 1989. Two tensiometers per plot were installed in the 25 to 75 mm and 100 to 150 mm soil depth zones. Volumetric water contents were interpolated from soil moisture characteristic curves developed from 76 mm i.d. soil cores taken from the 0 to 76 and 76 to 152 mm soil depth zones. Two waveguides for the time-domain reflectometry (TDR) measurements were installed in each plot at the 0 to 100 and 0 to 200 m depth zones. Measurements for the 100 to 200 mm were determined by subtraction. TDR volumetric water contents were calculated using the equations of Topp and Davis (1985). Sampling for shoot tissue, thatch/mat, and roots was performed November 1988, and June and November 1989. Shoot tissue was considered to be any aerial tissue above the depth in the canopy where green color 61 was no longer found. Thatch/mat consisted of the material below the shoot tissue harvest down to the soil depth where rhizomes were no longer present (25 mm). Root material was sampled from the soil below the thatch/mat layer. Soil cores 102 mm in dis. were excavated. The first 25 mm of the core, comprised of the thatch/mat zone, was cut from the core. The soil was sectioned into 0 to 50, 50 to 100, and 100 to 200 mm soil depth intervals. Shoot, thatch/mat, and root tissue were separated from any soil present using a hydropneumatic elutriation method (Smucker et al., 1982), dried overnight at 60° C, and weighed. Soil sampling was performed November 1988, and August and November 1989 using 76 i.d. by 76 mm high cores. Samples were taken at the 0 to 76 and 76 to 152 mm soil depth zone (below the 25 mm thatch/mat zone) for bulk density, soil porosity, and saturated hydraulic conductivity measurements. Analysis of variance was performed on all data and means were separated using Fisher’s protected LSD procedure at the 0.05 level of probability (Steel and Torrie, 1980). RESULTS AND DISCUSSION 8 a t Table 3.1 presents soil bulk density, total porosity, aeration porosity (0 to -6 kPa), and hydraulic conductivity data for the different sampling dates and depth zones in 1988 and 1989. After the initial three treatment applications in 1988, soil bulk density was decreased, and total porosity and aeration porosity were increased with HTC compared to noncultivated plots, while WIC had no measurable effect. Since WIC removed no soil, neither density nor overall porosity measurements were affected on these plots 62 Table 3.1. The influence of cultivation on soil physical properties at the 0 to 76 and 76 to 152 mm soil zones sampled 1988 and 0 to 76 mm zone sampled 1989. Bulk Total Aeration Density Porosity Porosity K Sat October 1988 (3 weeks after treatment) Mg m'3 -—— m3 100m'3 ——— mm hr'1 0 to 76 mm zone Check 1.66 a+ 37.7 b 6.4 b 11 b Hollow Tine 1.60 b 39.6 a 8.4 a 24 ab Water Injection 1.64 ab 38.1 b 6.7 b 41 a 76 to 152 mm zone Check 1.67 a 35.4 a 7.2 a 7 a Hollow Tine 1.68 a 35.1 a 7.0 a 15 a Water Injection 1.69 a 34.7 a 6.6 a 7 a August 1989 (47 weeks after treatment) 0 to 76 mm zone Check 1.67 a 35.3 b 4.4 a nd Hollow Tine 1.65 a 36.2 a 5.2 a nd Water Injection 1.65 a 35.8 ab 4.7 a nd November 1989 (6 weeks after treatment) 0 to 76 mm zone Check 1.64 a 35.8 5.6 b 13 a Hollow Tine 1.63 a 36.9 a 7.0 a 16 a Water Injection 1.63 a 36.2 ab 5.9 b 41 a + Within each column and depth zone, numbers with the same letter are not significantly different based on Fisher’s protected LSD at the 0.05 level of probability. nd designates not determined. 63 receiving compaction. However, porosity distribution measurements (Table 3.2) showed both HTC and WIC increased the very large macropores (O to -l kPa) within the 0 to 76 mm zone. HTC was better at increasing this range of porosity because of the removal of soil. Hydraulic conductivity increased 273% following WIC and 118% with HTC compared to noncultivated checks sampled November 1988. The deep channels cut with WIC had a dramatic influence on conductivity. Random measurement of 20 channels cut with WIC in each plot on 6 July, 1988 showed the depth ranged from 60 to 175 mm and averaged 110 mm. Soil data in August 1989 (prior to 1989 treatments) showed that improvements in density and porosity achieved with HTC and WIC had dissipated. This response illustrates the need for a regular cultivation program on turf where routine traffic re-compacts the soil. Others have observed that the improvement in soil density and macroporosity following cultivation was lost after treatment (Roberts, 1975; Lee, 1989). After continued cultivation treatment in 1989, total and aeration porosity were increased with HTC compared to noncultivated and WIC plots (Table 3.1). WIC had no effect on these measurements compared to the check plots due to the lack of soil removal. Porosity distribution in November 1989 showed the large macropores (O to -1 kPa) were greater after three additional HTC and WIC treatments compared to the checks (Table 3.2). A significant decline in the remaining macroporosity (1 to 10 -kPa) was found suggesting that HTC and WIC were resulting in some compaction effects in the O to 76 mm soil zone. 64 Table 3.2. The influence of cultivation on soil porosity distribution between selected moisture potentials in the 0 to 76 and 76 to 152 mm soil zones sampled 1988 and 0 to 76 mm soil zone in 1989. Moisture Potential Ranges (- kPa) 0 to 1 1 to 10 10 to 100 100 to OD October 1988 (3 weeks after treatment) 0 to 76 mm zone m3 100 m'3 Check 3.5 0+ 3 7 a 3.5 a 26.9 b Hollow Tine 5.4 a 3 9 a 3.1 a 27 l ab Water Injection 4 3 b 3 2 a 3.0 a 27 7 a 76 to 152 mm zone Check 3 l a 5.2 a 3 8 a 23.2 a Hollow Tine 3 2 a 4.8 a 3 5 a 23.5 a Water Injection 3 2 a 4.3 a 3 6 a 23.5 a August 1989 (47 weeks after treatment) 0 to 76 mm zone Check 2.3 a 3.9 a 4.2 a 25.0 a Hollow Tine 2.9 a 4.1 a 4.0 a 25.1 a Water Injection 2.6 a 3 7 a 4.6 a 24.9 a November 1989 (6 weeks after treatment) 0 to 76 mm zone Check 2.5 c 4.1 a 2.8 a 26.4 a Hollow Tine 4.5 a 3.2 b 2.8 a 26.3 a Water Injection 3.7 b 3.1 b 3 2 a 26.2 a + Within each column and depth zone, numbers with the same letter are not significantly different based on Fisher's protected LSD at the 0.05 level of probability. 65 Hydraulic conductivity, although not significant in November 1989, still remained highest in the WIC plots. Hydraulic conductivity was highly variable in November 1989 due to considerable earthworm activity in all plots. Numerous soil cores had to be discarded and some re- excavated to avoid obvious earthworm activity. No effect of cultivation was observed in 76 to 152 m depth zone sampled November 1988. No soil measurements were made in the 76 to 152 mm zone in 1989. oot is ue nd a t Both HTC and WIC had no consistent effect on shoot and thatch/mat weight until November 1989 (Table 3.3). Weston and Dunn (1985) observed cultivation required two years of treatment to affect thatch depth of ’Meyer’ zoysiagrass turf. Shoot tissue of the Kentucky bluegrass turf in this study was decreased with HTC compared to noncultivated plots, in November 1989. WIC had no effect on shoot tissue compared to check plots. By November 1989, HTC and WIC decreased thatch/mat weight by 24 and 152, respectively compared to noncultivated plots. This decrease in thatch/mat weight illustrates the mechanical removal and injury of plant tissue within the thatch/mat zone via cultivation. Smith (1979) partially attributed decreased thatch to the physical removal by mechanical cultivation. The loss in shoot tissue with HTC suggested that HTC was more damaging to the turf than WIC. 39.9.2138... No influence on root growth was observed on any sampling or depth zone (Tables 3.3 and 3.4). This may have been due in part to the thickness of the thatch mat zone (approximately 25 mm). The data show that HTC had a marked influence on thatch/mat weights indicating HTC has a considerable effect at the surface. At maximum tine 66 Table 3.3. The influence of cultivation on shoot tissue, thatch/mat, and total root weights of Kentucky bluegrass turf sampled in 1988 and 1989. Shoot Total Root Tissue Thatch/Mat Weight November 1988 (4 weeks after treatment) kg 111'2 Check 0.36 1.29 0.11 Hollow Tine 0.28 1.23 0.12 Water Injection 0.34 1.26 0.12 LSD (0.05) NS NS NS June 1989 (32 weeks after treatment) Check 0.19 0.94 0.19 Hollow Tine 0.16 0.86 0.22 Water Injection 0.16 0.78 0.19 LSD (0.05) NS NS NS November 1989 (4 weeks after treatment) Check 0.34 1.08 0.11 Hollow Tine 0.27 0.82 0.12 Water Injection 0.30 0.92 0.12 LSD (0.05) 0.05 0.14 NS NS denotes not significant. 67 Table 3.4. The influence of cultivation on root weight densities of a Kentucky bluegrass turf sampled in 1988 and 1989. Root Weight Density Zones (cm) 0 to 5 5 to 10 10 to 20 November 1988 (4 weeks after treatment) kg 111'3 Check 1.38 0.35 0.19 Hollow Tine 1.57 0.36 0.19 Water Injection 1.57 0.39 0.21 LSD (0.05) NS NS NS June 1989 (32 weeks after treatment) Check 2.68 0.60 0.26 Hollow Tine 2.74 0.65 0.26 Water Injection 2.54 0.63 0.27 LSD (0.05) NS NS NS November 1989 (4 weeks after treatment) Check 1.50 0.36 0.14 Hollow Tine 1.69 0.43 0.15 Water Injection 1.62 0.46 0.14 LSD (0.05) NS NS NS NS denotes not significant. 68 penetration, only the surface 50 mm of soil would be affected with HTC. Since full tine penetration is not always reached due to stones and varying soil strength, the depth of soil affected on average would be less than 50 mm. The depth of penetration with HTC appeared to be inadequate to have any influence on root weight. Engel (1951a) found spoon tine cultivation (eight treatments over three seasons) had no statistically consistent effect on rooting of a golf course fairway turf, although root weight was 82 greater in cultivated plots compared to noncultivated plots. Carrow (1988) observed increased rooting of bermudagrass at the 200 to 600 m depth as a result of cultivation. MM. HTC significantly lowered clipping yield compared to WIC and noncultivated plots on 5 and 31 Aug. , 1988 (Figure 3.1). A similar response was observed on 25 July and 24 Aug., 1988 (P<0.10). Decreased clipping yield with HTC supports the conclusion that HTC injures the turf by physically removing plant tissue. WIC did not decrease clipping yield. Decreased yield during spring green-up was evident on HTC plots sampled 13 May, 1989 (Figure 3.2). However, HTC plots recovered quickly when growth increased in the spring and subsequent yields equaled WIC and check plots. Following the 7 August and 12 September treatment applications in 1989, HTC again decreased clipping yield compared to the check (Figure 3.2). Reductions in clipping yield appeared to be of greater duration in 1988 than 1989 (up to four weeks following HTC treatment). This may have resulted from the extreme high temperature stress which occurred in 1988 coupled with the injury and plant removal associated with HTC. Roberts (1975) reported lower clipping yield of ’Merion’ Kentucky bluegrass following core cultivation . 69 .mwma .uonEmuamm mm was .umsms< OH .hash o vmfiaaam mums muamaummua coauomnEou mmmm e no N oumoavsfi when vaaom .muao>m .muau mmmumeHn hxosucmx mo camwh wcaddwao so aowuw>auasu ADsz coauooficw nouns was Aoamv wcau soHHon mo mucosamnu .H.m muswfim mmmp mum OD< IS... mN PN me 2. m P RN NN hp NF B N mN 0N mp — — b - c 71.51%; 6 o s [0.0 'hflflflm1lllllll.a ”H“ ..l/, hflflfl .U .lhu6P / w.) 1n; #H ION a 1m.N 6 ..o.n . Ind O; I God 10.? 0...: ole cowl. nouoouotocoz n ._. ..mé v32.5 nlm co_uoo=aa< z n 4 $3.9m... I Eon ..otm 06 (..Kop .411 6) plau BUIdduo 70 '1 .amma .uonouoo n was .uopamuqom NH .um=m=< n vowaanm whoa musmaumoua .mucm>o aofiuodeoo mama 0 damaged“ mama cfiaom .musu mmwuwosan exosusmm mo mama» mafiaawao so coaum>fiuaso AUHEV soauomflnfi umum3 use Aoemv mafia soHHos mo mucosamaH mmmp .50 mum OD< 153122. >< NN NP nu mp .vN 1 MN m— co_uoo__ao< z n .8903 u Eon ..otm 2 no.0 10.0 10.. In.— ION ..mN 106 Ind :06 msv .N.m 666666 (Mop 6w 5) PIS'A 5U1dduo 71 W Stand density ratings were not affected by cultivation treatment until September 1989 (Table 3.5). September and October 1989 ratings showed HTC plots had lowered stand densities compared to noncultivated and WIC plots. Most likely, shoot growth during this period was not great enough for HTC plots to recover from damage caused during treatment in 1989. Weston and Dunn (1985) and Carrow (1987) observed lower quality and density following core cultivation of ’Meyer’ zoysiagrass and ’Tifway’ bermudagrass turf, respectively. Engel (1952) reported that cultivation improved turf quality only in areas with severe thatch accumulation. W Water use estimates by tensiometry (Table 3.6) and time-domain reflectometry (Table 3.7) did not indicate any increase or decrease in water utilization as a result of cultivation treatment. Carrow (1988) has reported increased water utilization following cultivation treatment on bermudagrass. Possibly the methods used for estimating water use in this study were not precise enough to detect differences between treatments. Also, rainfall events and the limited range of soil moisture sensing with tensiometry resulted in rather short periods of measurement which might not have been long enough to detect differences. The water use rates in this study were low compared to other reported values (Feldhake et al., 1983), but high humidity and heavy dew formation were prevalent during these measurement periods . SUMMARY Hollow tine cultivation (HTC) had a pronounced effect on soil physical properties, such as decreased bulk density and increased Table 3.5. Effect of hollow tine (HTC) and water injection (WIC) 72 cultivation on visual density estimates of a Kentucky bluegrass turf in 1988 and 1989. 1988 1989 8/10 9/28 10/18 8/7 9/8 10/14 Density (9-dense, 6-acceptab1e, l-no turf) Check 8 0a 8.0a 8 0a 7.7a 8 7a 7.3a HTC 7 7a 7.7a 7 3a 7.7a 6 7b 5.7b WIC 8.7a 7 3a 8 0a 7.7a 8 3a 7.7a + Within each column, numbers followed by the same letter are not significantly different based on Fisher’s protected LSD test at the 0.05 level of probability. Treatments were applied 6 July, 10 Aug., and 28 Sept., 1988, and 7 Aug., 12 Sept., and 7 Oct., 1989. 73 Table 3.6. Influence of cultivation on water use of a Kentucky bluegrass turf as estimated by tensiometers between 8:00 and 20:00 h for a 2 or 3 day period. July 1988 July 1989 21 to 23 26 to 28 6 to 7 mm 0 to 76 mm zone Check 3 6 a+ 3.2 a 2 8 a Hollow Tine 3 1 a 3.1 a 2 6 a Water Injection 2 4 a 2.7 a 2 7 a 76 to 152 mm zone Check 3 1 a 3.2 a 2 3 a Hollow Tine 2 7 a 2.5 a 2 0 a Water Injection 2 5 a 2.7 a 1 8 a 0 to 152 mm Check 6.7 a 6.4 a 5.1 a Hollow Tine 5.7 a 5.6 a 4.6 a Water Injection 4 9 a 5 4 a 4.5 a + Within each column and depth zone, numbers followed by the same letter are not significantly different based on Fisher’s protected LSD test at the 0.05 probability level. Treatments were applied 6 July, 10 Aug., and 28 Sept., 1988, and 7 Aug., 12 Sept., and 7 Oct., 1989. 74 Table 3.7. Influence of cultivation on water use of a Kentucky bluegrass turf as estimated by time-domain reflectometry from 2 to 5 September, 1989. Depth Zone (mm) 0 to 100 100 to 200 0 to 200 mm Check 4.7 a+ 2.0 a 6.7 a Hollow Tine 5.9 a 0.5 a 6.4 a Water Injection 4.3 a 2.5 a 6.8 a + Within each column, numbers followed by the same letter are not significantly different based on Fisher’s protected LSD test at the 0.05 probability level. Treatments were applied 6 July, 10 Aug., and 28 Sept., 1988, and 7 Aug., 12 Sept., and 7 Oct., 1989. 75 porosity compared to water injection cultivation (WIC). However, WIC resulted in better water conductivity than HTC illustrating the benefit of deeper cultivation channels with WIC. Even though soil properties were improved with HTC, clipping yield of the Kentucky bluegrass turf was reduced up to four weeks following HTC treatment. This response was attributed to the removal of plant tissue during HTC and appeared to be more pronounced during 1988, a year of high temperature and low rainfall. WIC had no effect on clipping yield of this turf. Shoot tissue and thatch/mat weights were not affected until after the second year of treatments. Both HTC and WIC lowered thatch/mat weight while only HTC lowered shoot tissue. Decreased shoot tissue on HTC plots was reflected in a decline in stand density on HTC plots. Root weight was not measurably affected by either HTC or WIC. Estimated water use also failed to show any influence of HTC or WIC treatment. The data suggested that an aggressive program of core cultivation can be used to improve soil physical conditions and reduce thatch/mat accumulation as observed at the end of the second year. However, these benefits may be offset by the injury imparted during core cultivation which can lead to a decline in stand density and quality. This may be of greatest importance on turfs which are dormant or growing slowly due to environmental stress. Water injection cultivation appears to be a superior cultivation. method to improve soil water movement during periods where the turf may not recover quickly from mechanical injury caused by HTC. LIST 01" REFERENCES 76 LIST 0? REFERENCES Alderfer, R.B. 1954. Effects of soil compaction on bluegrass turf. Penn. State College Turfgrass Conf. 23:31-32. Byrne, T.G., W.B. Davis, L.J. Booker, and L.F. Werenfels. 1965. A further evaluation of the vertical mulching method of improving old greens. Calif. Agric. 19:12-14. Carrow, R.N. 1988. Cultivation methods on turfgrass water relationships and growth under soil compaction. 1988 U.S.G.A. Green Section Turfgrass Summary. p.14. Carrow, R.N., B.J. Johnson, and R.N. Burns. 1987. Thatch and quality of Tifway bermudagrass turf in relation to fertility and cultivation. Agron. J. 79:524-530. Cordukes, W.E. 1968. Compaction. The Golf Superintendent. 36:20-24. Engel, R.E. 1951a. Studies of turfgrass cultivation. Ph.D. diss. Rutgers Univ. 100 pp. Engel, R.E. 1951b. Some preliminary results from turf cultivation. Rutgers Univ. Annual Short Course in Turf Management. 19:17-22. Engel, R.E. 1952. Turf cultivation. Rutgers Univ. Annual Short Course in Turf Management. 20:9-11. Engel, R.E., and R.B. Alderfer. 1967. The effect of cultivation, topdressing, lime, nitrogen and wetting agent on thatch development in 1/4-inch bentgrass turf over a ten-year period. New Jersey Agric. Exp. Stn., Bul. 818:32-45. Feldhake, C.M., R.E. Danielson, and J.D. Butler. 1983. Turfgrass evapotranspiration. I. Factors influencing rate in urban environments. Agron. J. 75:824-830. Lee, D.K. 1989. Effects of soil cultivation techniques on rooting of Kentucky bluegrass sod. M.S. thesis. Mich. State Univ. 62 pp. 77 Murray, J.J., and F.V. Juska. 1977. Effects of management practices on thatch accumulation, turf quality and leaf spot damage in common Kentucky bluegrass. Agron. J. 69:365-369. Roberts, J.M. 1975. Some influences of cultivation on the soil and turfgrass. M.S. thesis. Purdue Univ. 60 pp. Smith, G.S. 1979. Nitrogen and aerification influence on putting green thatch and soil. Agron. J. 71:680-684. Smucker, A.J.M., S.L. McBurney, and A.K. Srivastava. 1982. Quantitative separation of roots from compacted soil profiles by the hydropneumatic elutriation system. Agron. J. 74:500-503. Steel, R.C.D., and J.H. Torrie. 1980. Principles and procedures of statistics. Second Ed. McGraw-Hill, New York, NY. 633 pp. Topp, G.C., and J.L. Davis. 1985. Measurement of soil water content using time-domain reflectometry (TDR): A field evaluation. Soil Sci. Soc. Am. J. 49:19-24. Weston, J.B., and J.H. Dunn. 1985. Thatch and quality of Meyer zoysia in response to mechanical cultivation and nitrogen fertilization. Proc. Fifth Int. Turfgrass Res. Conf. pp. 449-458. Waddington, D.V., T.L. Zimmerman, G.L. Shoop, L.T. Kardos, and J.M. Duich. 1974. Soil modification for turfgrass areas. Penn. Agric. Exp. Stn. Progress Rep. No.337. 96 pp. HICHIGRN STRTE UNIV. LIBRQRIES llHIIIWIIIHIIIMIMIIlllllllllllmlllflIIIWIHHIIIHI 31293008914347