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Published online 24 June 2005
Published in Crop Sci 45:1511-1520 (2005)
© 2005 Crop Science Society of America
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TURFGRASS SCIENCE

Creeping Bentgrass Establishment on Amended-Sand Root Zones in Two Microenvironments

James A. Murphya,b,*, Hiranthi Samaranayakea, Josh A. Honiga, T. J. Lawsona and Stephanie L. Murphya,b

a Dep. of Plant Biology and Pathology, Rutgers, The State Univ. of New Jersey, 59 Dudley Road, New Brunswick, NJ 08901-8520
b Rutgers Cooperative Extension, Rutgers, The State Univ. of New Jersey, 59 Dudley Road, New Brunswick, NJ 08901-8520

* Corresponding author (murphy{at}aesop.rutgers.edu)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Sand-based root zones are commonly used for construction of golf course putting greens. Objectives of this field study were to (i) evaluate sand-based root zone mixtures varying in amendment (fine loam, peat, and inorganic) on the establishment of ‘L-93’ creeping bentgrass (Agrostis stolonifera L.), (ii) compare findings to related published studies, and (iii) repeat the trial in two locations varying in air circulation to assess microenvironmental effect. Eleven root zone mixtures, using predominantly medium-sized sand as the majority component, were replicated four times in a randomized complete block design nested within the two microenvironments. Plots were seeded in May 1998 and establishment was assessed to June 1999. Mixtures with a capillary porosity (–3 kPa water potential) at the high end of, or slightly exceeding, the United States Golf Association (USGA) criterion range (0.15–0.25 m3 m–3) provided more rapid establishment and better turf performance, yet root mass was lowest in these mixtures. Thus, variation in water availability among mixtures appeared sufficient to affect distribution of dry matter between roots and shoots. Mixtures amended to provide greater nutrient retention improved turf establishment; however, low water retention in the inorganic mixtures negated this advantage longer term as irrigation and fertilization shifted from establishment toward a maintenance objective. While shoot response to microenvironment was more limited, total root mass 1 yr after seeding was 24% greater in the open microenvironment than the enclosed, indicating that the initial effect of enclosed microenvironments on growth may go unrecognized during grow-in unless rooting is assessed.

Abbreviations: CEC, cation exchange capacity • DAS, days after seeding • Ksat, saturated hydraulic conductivity • USGA, United States Golf Association


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
THE CONSTRUCTION OF GOLF putting greens that meet USGA recommendations for a root zone mixture is often considered difficult and expensive due, in part, to the availability and cost of suitable materials. Peat has been widely studied and used as an organic amendment to sand in the construction of golf putting green root zones (Kussow, 1987; McCoy, 1992); however, other materials also have been studied, including slag, calcined clay, expanded perlite, and composted soil (Waddington et al., 1974), clinoptilolite zeolite (Ferguson et al., 1986; Nus and Brauen, 1991; Huang and Petrovic, 1995), rice (Oryza sativa L.) hulls, sawdust, calcined clay, and vermiculite (Paul et al., 1970), bark (Baker, 1984), perlite (Baker, 1984; Crawley and Zabcik, 1985), green waste, wood chips, pulp, sewage, and plant residue and fibers (Cook and Baker, 1998), and finer-textured soils (Swartz and Kardos, 1963; Brown and Duble, 1975; Taylor and Blake, 1979; Baker and Richards, 1993). Much of these previous reports emphasized physical properties of root zone mixtures, with more limited information provided on turfgrass response. Identifying combinations of construction materials that result in appropriate physical properties, as well as turfgrass response, would define the range of flexibility in material selection that is available for construction of a putting green root zone and provide useful information to property developers conducting cost–benefit evaluations.

Material specifications for the construction of putting green root zones are available (Green Section Staff, 1993; Davis et al., 1970; Daniel and Freeborg, 1979); however, the evaluation criteria are primarily limited to physical properties. Amending sand may alter nutritional as well as physical properties of the root zone depending on the amendment properties, amount added, and the properties of the sand being amended (Waddington, 1992). A combination of both nutritional and physical differences among root zone mixtures can confound the understanding of which characteristics are most appropriate for putting greens. A limited number of field studies have assessed the effects of physical properties of sand-based root zones, without the confounding effects of varying nutrition and specific surface, on turf establishment (Nelson and Schroeder, 1984; Neylan and Robinson, 1997; Murphy et al., 2001). Rapid turfgrass establishment on a newly constructed root zone is an important short-term criterion that impacts the timeliness of revenue generation for a golf course and, thus, would be useful to consider in the selection of construction materials.

Potential interactive effects of root zone physical properties and microenvironment on turf establishment have been reported (Murphy et al., 2001); however, the impact of amendments varying in nutritional properties on interactions with microenvironment has not. The objectives of this field study were to (i) examine the effects of root zones varying in amendment type on the establishment of creeping bentgrass turf, (ii) compare these findings with other field reports, particularly reports where physical properties were the primary (i.e., unconfounded) impact on turf performance, and (iii) because the trial was repeated in two microenvironments (locations), assess the potential for root zones to interact with microenvironment.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Root zone plots were constructed in two microenvironments in 1997 using techniques described by Murphy et al. (2001). One microenvironment was open to air circulation; the other was enclosed with obstruction to air circulation and without the effects of shading during summer. Root zone plots measuring 5.2 m2 were constructed 300 mm deep over a gravel-blanket plus tile drainage system (Green Section Staff, 1993) and separated by 30 mil high-density polyethyelene plastic.

Commercially available predominately medium-sized sand meeting the USGA (Green Section Staff, 1993) size guidelines served as the majority component for root zone mixtures (ASTM, 1999a). Root zone mixtures with organic material were constructed at volume ratios of medium sand to sphagnum peat at 19:1, 9:1, and 4:1, and sand to reed sedge peat at 19:1 and 9:1. Additionally, volume mixtures of the medium sand to a fine loam (Table 1) at 39:1, 19:1, and 4:1, to clay-based porous ceramic at 9:1, and to clinoptilolite zeolite charged with ammonium and K at 9:1 were developed. All mixtures in the field were assessed for organic matter by loss on ignition at 360°C (ASTM, 1999b) for 12 h. Laboratory samples of organic-amended sand mixtures were prepared to match organic matter content of field mixtures, and physical properties were determined for all mixtures from four laboratory-packed samples in 51-mm-i.d. by 76-mm-high cores (ASTM, 1997). Saturated hydraulic conductivity (Ksat) was determined under constant head from a 0.5-h flow after 4 h of equilibration flow (Klute and Dirksen, 1986). Air-filled porosity was determined by subtracting capillary porosity at –3 kPa water potential from the calculated total porosity.


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  		Table 1. Particle size distribution of inorganic root zone materials used to construct field plots in two microenvironments.

 
Preplant fertilization applied 9.8, 6.4, and 8.8 g m–2 of N, P, and K, respectively. Plots were seeded with ‘L-93’ creeping bentgrass at 4.9 g m–2 on 31 May 1998. Fourteen postplanting fertilizations were made to all plots between 9 June and 17 Dec. 1998, which applied a total of 24.9, 5.6, and 11.1 g m–2 of N, P, and K, respectively. Additionally, the unamended sand plots required supplemental fertilization, using 46–0–0 N–P–K at 1.5 g m–2 of N on 7 July 1998, to produce sufficient turf growth and survive mowing. Five fertilizations were made to all plots between 7 May and 1 June 1999, which applied a total of 10.5, 1.0, and 4.3 g m–2 of N, P, and K, respectively.

Irrigation was applied to facilitate emergence of seedlings; in the absence of rain, one to four waterings per day totaling no more than 16 mm of water were performed until September 1998. Irrigation frequency averaged once every 10 d from September to early December 1998, with 3 to 48 mm of water applied. Irrigation was reinitiated in May 1999, when approximately 7 mm of water was applied every 2 to 3 d.

Mowing was initiated on 4 July 1998 and maintained at 12.5 mm until 1 April 1999, when the height was gradually lowered to 3.2 mm by 25 May 1999. Each root zone treatment was topdressed with the corresponding root zone mixture on 20 July, 19 Sept., and 16 Nov. 1998 at 14.6, 18.2, and 21.8 m3 ha–1, respectively. Plots were core cultivated with 9.5-mm hollow tines to the 63-mm depth in April 1999. Root zone material brought to the surface was reincorporated into the turf canopy, and thatch debris was removed. Coring holes were left open to enhance settling of the plot surface needed for the low mowing height.

Visual ratings of turfgrass establishment, density, spring green-up, and quality were taken using a 1-to-9 scale; 1 being the least desirable characteristic, 9 the best, and 5 being the minimally acceptable rating. Turf cover for each plot was quantified on 22 June and 8 July 1998 via line-intersect counting using 273 intersections over 1.8 m–2. Twelve subsamples per plot from the 0- to 100-mm depth were collected in April 1999 to assess root zone fertility using a 1:1 soil/water solution for pH, and nutrient analysis was performed by direct current plasma spectrophotometry of Mehlich 3 extractions. Nondestructive field measurements of volumetric water content were made with a model 3411-B neutron moisture gauge. Three 32-mm-diam. cores were taken from each plot on 3 June 1999 and sectioned into 75-mm-intervals to sample root mass. Roots were elutriated from core samples (Smucker et al., 1982), decanted in water to remove remnant debris, and recorded for mass after drying at 55°C for 48 h.

Data were analyzed with PCSAS statistical software (SAS Institute, 1985) using the general linear model procedures; experimental design was a randomized complete block with four replications in each microenvironment. Root zone treatments were replicated four times in each microenvironment; replications were nested within the microenvironment (Hicks, 1993). Linear and quadratic contrasts assessed responses to amendment rate for root zones amended with loam, sphagnum peat, and reed sedge peat. Means were separated by Fisher's protected LSD at P ≤ 0.05 (Steel and Torrie, 1980).


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Root Zone Mixture Physical and Chemical Properties
As expected, the loam amendment increased silt and clay content of the sand; the sand-size distribution of the loam mixtures remained similar to the predominately medium-sized sand-base component (Table 1). The porous ceramic clay and clinoptilolite materials were distinctly coarser than the medium sand; however, particle size distribution of mixtures containing these inorganic amendments did not reflect the increased coarseness, which can be attributed to the lower mass of the porous inorganic particles. Organic matter content of the mixtures ranged from 0.8 to 9.2 g kg–1, and peats produced the largest increase in organic matter content of mixtures (Table 2). Organic matter content of mixtures had a positive quadratic response to amending with loam and peats, which indicated greater volume additions of amendments were slightly less effective in increasing organic matter content, by weight, of mixtures than lower volume amending rates. This was probably a result of differences in packing of amendment volumes in the field before mixing with the sand. Organic matter determination by loss on ignition is affected by loss of structural water, carbonate minerals, and some hydrated salts from hydrated aluminosilicates (Nelson and Sommers, 1996), as well as the ammonium contained on the nutrient-charged clinoptilolite; thus, organic matter determination of inorganic mixtures by this method would be confounded.


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  		Table 2. Physical properties and cation exchange capacity (CEC) of root zone mixtures used to construct plots in two microenvironments.

 
The unamended sand and the loam mixtures packed to the highest bulk densities (Table 2). Amending with either peat lowered bulk density as the proportion of peat increased in the mixture (linear response). The 4:1 sphagnum mixture had the lowest bulk density among mixtures, and bulk densities of porous ceramic clay and clinoptilolite mixtures were similar to the 9:1 sphagnum mixture and lower than both reed sedge mixtures. Congruently, relationships among mixtures for total porosity were inverse compared with those for bulk density; hence, the unamended sand and loam mixtures possessed the lowest total porosity.

The relatively coarse particle size distribution of the porous ceramic clay and clinoptilolite amendments (Table 1) produced mixtures with greater volume of large interparticle pore space, and thus a high air-filled porosity (>0.21 m3 m–3) compared with other mixtures (Table 2). Mixtures amended with peat had air-filled porosities ranging from 0.154 to 0.186 m3 m–3; a positive linear rate response was found for sphagnum mixtures. The lowest air-filled porosities were observed in the unamended sand and the 19:1 and 4:1 loam mixtures, which did not meet the lower limit for air-filled porosity (0.15 m3 m–3) suggested by the USGA (Green Section Staff, 1993).

Capillary porosity had a positive linear rate response to amending with loam and sphagnum, while amending with reed sedge did not have a significant rate effect. Mixtures with porous ceramic clay and clinoptilolite ranked lowest for capillary porosity and were statistically lower than the higher amending rates of loam, sphagnum, and reed sedge mixtures. Others have reported better water retention of mixtures using peat compared with porous inorganic amendments (Bigelow et al., 2004; McCoy and Stehouwer, 1998; Waltz et al., 2003). Bigelow et al. (2004) reported that capillary porosity of very narrow grades of fine, medium, and coarse sand was not significantly increased when mixed with clinoptilolite at 9:1 (v/v). Similarly, they found that increases in capillary porosity of sand mixed with porous ceramic clay at 9:1 occurred only in the relatively coarse sands, that is, very narrow grades of medium and coarse size sand, and these increases in capillary porosity were rather small compared with 9:1 mixtures with sphagnum peat. Li et al. (2000) reported that porous ceramic clay added to a sand–peat root zone increased water retention and availability; however, their conclusion was based on gravimetric data which may be confounded by the differences in bulk density that were also evident in their study. Huang and Petrovic (1995) concluded that an additional amendment would be needed in combination with the sand–clinoptilolite mixture to increase water retention and meet USGA guidelines. Ok et al. (2003) indicated that clinoptilolite mixed with medium-fine sand had either no effect or a small increase in capillary porosity. Field measurements of water content in our study indicated that porous ceramic clay and clinoptilolite mixtures had greater water retention than unamended sand plots; however, the increased water content was small compared with the increased water content observed in 4:1 sphagnum and 9:1 reed sedge peat mixtures (Table 3).


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  		Table 3. Field water content of root zones in two microenvironments as determined by a surface neutron probe.

 
Saturated hydraulic conductivity of most mixtures achieved values categorized as accelerated (300–600 mm h–1) by the USGA (Green Section Staff, 1993), yet most mixtures had air-filled porosities within the lower third of the acceptable range (0.15–0.30 m3 m–3) or below the minimum acceptable value. Moreover, most mixtures were either near the maximum acceptable capillary porosity value of 0.25 m3 m–3, as suggested by the USGA, or exceeded it. This inconsistency among USGA indexes probably arises from the change to higher water potential (from –4 to –3 kPa) used to delineated air-filled and capillary porosity of samples (ASTM, 1997) without changes in the critical range values used to interpret testing results (Green Section Staff, 1993).

Increasing the amending rate of loam, sphagnum, and reed sedge decreased Ksat of the mixture; the response was quadratic for loam and linear for both peats. The lowest Ksat values were observed with loam mixtures; the 39:1 mixture achieved the normal range of the USGA guidelines, while neither the 19:1 nor 4:1 loam mixtures met the minimum value of 150 mm h–1. The porous ceramic clay mixture exceeded the accelerated range maximum for Ksat, probably because of a greater amount of large interparticle pore space created by the coarse particle size of the amendment. Li et al. (2000) found that porous ceramic clay increased Ksat when mixed with a sand–peat mixture. Waddington et al. (1974) reported that calcined clay, a granular inorganic amendment, increased air porosity and was highly effective in increasing soil permeability of compacted mixtures. The appreciable silt content of the clinoptilolite amendment (Table 1) probably tempered the effect of coarseness in that mixture, producing a Ksat in the accelerated range. Huang and Petrovic (1995) found that clinoptilolite particles < 0.047 mm reduced Ksat in mixtures with medium-sized sand.

All amendments were capable of increasing cation exchange capacity (CEC) when mixed with medium sand, and increasing the amending rate enhanced the effect (Table 2). The clinoptilolite mixture had the highest CEC; however, the CEC of all mixtures were considered low, that is, <4 cmolc kg–1 (Carrow et al., 2001). Before planting, pH of root zone mixtures ranged from 6.4 to 7.2 and declined to a range of 5.5 to 6.5 by April 1999, which are the common soil pH values under golf course turf in the northeastern United States. The lowering of pH was probably due to the predominate use of ammoniacal fertilizer in this trial.

As expected, loam mixtures had increasingly greater nutrient content as amending rate increased for all measured nutrients except B, which decreased slightly (Table 4). Increased Ca and Mg content in sphagnum and reed sedge mixtures were found as amendment rate increased, whereas P content declined. It is not clear why extractable P declined at greater amendment rates of peat; however, it is plausible that a loss of P from root zones occurred through clipping removal. This form of P loss could have been greater from root zones with higher amendment rates of peat, which had better turf performance (i.e., greater shoot growth) as discussed below. Boron content increased linearly in reed sedge mixtures. Porous ceramic clay and clinoptilolite mixtures contained more P, K, Ca, and Mg, and less B than unamended sand; the clinoptilolite mixture had greater Mn content.


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  		Table 4. Nutrient content at the 0- to 100-mm depth zone of root zone mixtures growing creeping bentgrass in two microenvironments; sampled April 1999.

 
Turf Responses in 1998
The root zone treatment effect on visual ratings of bentgrass establishment was consistent across both microenvironments (no interaction) during the initial 60 d (Table 5), and described more of the total variation in the ANOVA than microenvironment (data not shown). Bentgrass establishment through 60 days after seeding (DAS) was better on amended root zone mixtures compared with unamended sand. Turf established most rapidly on the clinoptilolite mixture as would be expected with a nutrient-charged amendment. Ok et al. (2003) observed better establishment of creeping bentgrass on sand amended with nutrient-charged clinoptilolite compared with the same unamended sand and a coarser sand–peat mixture. Improved creeping bentgrass establishment has been observed in field trials using noncharged clinoptilolite (Ferguson et al., 1986; Nus and Brauen; 1991). Increasing amendment rates of loam, sphagnum, and reed sedge improved the rate of establishment. An acceptable establishment rating (5 or higher, which indicated turf would withstand mowing) was observed at 17 DAS on the clinoptilolite mixture, 20 DAS for the 4:1 sphagnum and loam mixtures, 24 DAS for the porous ceramic clay, 9:1 reed sedge and sphagnum mixtures, 28 DAS for the 19:1 loam mixture, and 34 DAS for the 19:1 reed sedge and sphagnum mixtures and the 39:1 loam mixtures. Acceptable establishment ratings were not observed on the unamended sand until 41 DAS; note unamended sand received an additional 1.5 g m–2 of N at 37 DAS to promote sufficient growth and enable turf to survive mowing. Despite this additional N fertilization, creeping bentgrass establishment on the unamended sand rated lowest through 60 DAS.


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  		Table 5. Establishment ratings of ‘L-93’ creeping bentgrass seeded 31 May 1998 on root zones in two microenvironments.

 
Excluding the porous ceramic clay and clinoptilolite root zone mixtures, a capillary porosity of 0.243 m3 m–3 or lower (Table 2) was associated with slower turf establishment. Murphy et al. (2001) reported better turf establishment on mixtures with capillary porosity of 0.25 m3 m–3 or higher; the mixtures in that study were not confounded by differences in nutrient retention. Field measurements also indicated there was a direct relationship between field measurements of root zone water content (Table 3) and initial turf establishment, except for the clinoptilolite mixture. Others have made similar observations on the positive impact of greater water retention on turf establishment under field conditions (Bigelow et al., 2001b; Carlson et al., 1998; Neylan and Robinson, 1997; Nelson and Schroeder, 1984).

Greater initial turf establishment on mixtures containing porous ceramic clay or clinoptilolite was probably more a result of the greater retention of nutrients (Table 4) than water, since water retention data indicated these mixtures had either no effect (Table 2) or only a small increase (Table 3) in water retention compared with unamended sand. The clinoptilolite contained a synthetic apatite as well as appreciable ammonium and K on exchange sites (Ming and Allen, 2001). Huang and Petrovic (1994) and Ferguson and Pepper (1987) reported increased ammonium retention in sand amended with noncharged clinoptilolite, and Bigelow et al. (2001a) observed lower ammonium loss in leaching studies with porous ceramic clay. Others have reported greater retention of other nutrients in mixtures containing porous ceramic clay (McCoy and Stehouwer, 1998; Li et al., 2000) and nutrient-charged clinoptilolite (Ok et al., 2003). The majority of fertilizer N in this field trial was applied in the form of ammonium. Thus, it is probable that the improved turf establishment on porous ceramic clay and clinoptilolite amended sand mixtures as well as other mixtures with higher CEC was attributable to better nutrient retention, most notably ammonium nitrogen.

Turf cover measurements (Table 6) on 22 June and 8 July (22 and 38 DAS, respectively) corroborated visual ratings of turf establishment. The unamended sand, 39:1 loam, and 19:1 peat mixtures had the least turf cover on 22 June, while the clinoptilolite mixture had the greatest turf cover. On both dates, better turf cover was found as the amending rate of loam and both peats increased. The unamended sand had the least cover compared with all mixtures on 8 July. Turf cover was consistent across microenvironments and no effect of microenvironment was apparent.


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  		Table 6. Turf cover, density, green-up, and quality of ‘L-93’ creeping bentgrass on root zones in two microenvironments during establishment in 1998 and 1999.

 
Assessments of turf density (August) and quality (October) in 1998 continued to indicate turf performance was best on the clinoptilolite mixture and poorest on the unamended sand (Table 6). Increasing amending rate of both sphagnum and reed sedge improved density and quality (linear responses), resulting in high turf density and quality on the 4:1 sphagnum and 9:1 reed sedge mixtures, but less than that on the clinoptilolite mixture. Increasing the amending rate of loam was beneficial to turf density and quality up to the 19:1 mixing ratio; increasing loam to 4:1, however, was detrimental to density and of no further benefit to quality (i.e., quadratic responses). Turf density on the porous ceramic clay plots was not different from unamended sand plots in August, while turf quality on the porous ceramic clay plots was slightly better in October.

Turf Responses in 1999
While most establishment data in 1998 indicated the porous ceramic clay mixture improved turf response, this mixture produced turf responses in spring 1999 that were either no better or poorer than the unamended sand (Table 6). Similarly, the superior 1998 establishment data for the clinoptilolite mixture were in striking contrast to the turf responses observed in 1999. The clinoptilolite mixture, along with the porous ceramic clay and 4:1 loam, had poorer turf green-up than unamended sand in April 1999. Turf quality on the clinoptilolite mixture was only slightly better than unamended sand in April and similar to the unamended sand in May. Ok et al. (2003) observed turf quality on clinoptilolite amended sand become similar to unamended sand during the third year after seeding. Increasing the amending rate of both sphagnum and reed sedge improved green-up and quality in 1999, resulting in the best green-up and turf quality on the high amendment rates of sphagnum (4:1) and reed sedge (9:1) mixtures. Turf response to loam mixtures differed from the peat mixtures. Detrimental turf responses were initially observed on 4:1 loam plots compared with unamended sand in spring 1999; however, turf quality improved on 4:1 loam plots compared with unamended sand by May 1999. The 39:1 and 19:1 loam mixtures were either similar to or slightly better than the unamended sand plots.

Irrigation was not reinitiated until 13 May 1999, and it is plausible that water retention of mixtures had an impact on turf responses in spring 1999. Water retention greater than that provided by the porous ceramic clay and clinoptilolite mixtures (i.e., 4:1 sphagnum and 9:1 reed sedge) appeared to be necessary for improved turf performance, since the porous ceramic clay and clinoptilolite mixtures had similar or better nutritional content than peat mixtures (Table 4) but lower water retention (Tables 2 and 3) and poorer turf green-up and quality in 1999 (Table 6). Bigelow et al. (2004) reported that clinoptilolite and porous ceramic clay mixed with narrowly graded sands did not increase available water holding capacity as estimated by pressure plate water extraction methods in the laboratory. Thus, improved nutritional characteristics of these low-water retention mixtures that were an asset under the frequent irrigation during seedling establishment were probably negated by relatively low water availability in those plots when irrigation was more limited in spring 1999. Moreover, the greater ability to retain nutrients, particularly ammonium, probably became less important as fertilization was decreased toward a maintenance program level over time (30.2 g m–2 of N during 6 mo after seeding and 15.7 g m–2 of N from 6 to 12 mo after seeding) and ammonium was depleted from the charged clinoptilolite. The most consistent and best turf performance during the first year of establishment was observed on 4:1 sphagnum and 9:1 reed sedge mixtures compared with all others root zone treatments; these better mixtures had >0.25 m3 m–3 of capillary porosity as well as increased CEC. Others have reported greater water retention with sand–peat mixtures compared with other sand–amendment mixtures (Baker, 1984; Nus and Brauen, 1991). Bigelow et al. (2001b) observed better establishment of turf on a sand–peat mixture compared with sand amended with porous ceramic clay and noncharged clinoptilolite. It is not clear why green-up on the 4:1 loam mixture was poor; possibly the low Ksat of this mixture limited the intake of precipitation during the winter, which resulted in low water availability during green-up. These grow-in responses suggest that consideration must given to the potential for longer term turf response, or lack thereof, when considering the use of these inorganic amendments or high amendment rates of loam to enhance initial establishment. Further study of long-term turf responses to these mixtures is needed to more completely address this issue.

Turf green-up and quality was generally better in the enclosed microenvironment compared with the open microenvironment (Table 6). Higher soil temperatures at the 50-mm depth in 9:1 sphagnum plots have been observed in the enclosed microenvironment during summer months (data not shown). Thus, it is feasible that greater soil warming in the enclosed microenvironment during spring could have hastened green-up.

Root Zone Interactions with Microenvironment
While interactions between root zones and microenvironment (location) were detected (Table 6), these interactions were inconsistent over time (data not shown). Thus, meaningful interpretations of the interactions involving specific root zone treatments were not evident. The significant interactions generally indicated that one or more root zone treatments (most often sphagnum peat mixtures, but not a specific amending rate) performed better in the enclosed microenvironment than the open microenvironment, while other treatments were similar across microenvironments. No root zone treatment had consistently poor turf performance in the enclosed microenvironment than the open microenvironment.

Root Mass Response
While shoot growth responses in 1999 were generally better in the enclosed microenvironment compared with the open microenvironment, root mass measured 1 yr after seeding indicated 24% more total root mass in the open microenvironment than the enclosed (Table 7). Root mass also was significantly greater at all depth zones except the 0- to 75-mm depth for turf grown in the open microenvironment compared with the enclosed. Sixty-nine percent of the total root mass was found in the 0- to 75-mm depth in both microenvironments, similar to the findings of Murphy et al. (2001).


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  		Table 7. Root mass of ‘L-93’ creeping bentgrass after 1 yr of establishment on root zones in two microenvironments, sampled 3 June 1999.

 
Greatest total root mass was found in the unamended sand, 39:1 and 19:1 loam, 19:1 sphagnum, porous ceramic clay, and clinoptilolite mixtures. An increased amending rate of loam and either peat in the root zone mixture decreased the total root mass linearly. The lowest total root mass was found in mixtures having high amendment rates: 4:1 loam, 9:1 and 4:1 sphagnum, and 9:1 reed sedge mixtures. The lowest total root mass measured (4:1 sphagnum) was 25% less than the highest (unamended sand). Roots were observed at all depth zones for all mixtures, and the relative differences in total root mass response among root zone treatments were generally evident in root mass assessed at all four 75-mm depth zone intervals. The lowest root mass in the 0- to 75-mm depth zone was observed in the 4:1 loam mixture and was 21% percent less than the highest root mass found in the unamended sand. The lowest root mass in the 75- to 150-, 150- to 225-, and 225- to 300-mm depth zones was found in the 4:1 sphagnum mixture, which was 54, 60, and 46% less than the greatest root mass measured at the respective zone. Higher amending rates with sphagnum reduced (linear) root mass at all depth zones compared with lower amending rates. A similar response was evident with reed sedge and loam amendment, except at the 150- to 225-mm zone. The 39:1 loam and clinoptilolite mixtures consistently had the greatest root mass at all depth zones.

Thus, there was a relationship of lower root mass with mixtures having greater water storage, yet these mixtures also consistently produced high turf quality. Similarly, Murphy et al. (2001) observed that finer-textured and, consequently, wetter sand root zones resulted in lower root mass at depths below 75 mm and better turf quality the first year of establishment. These findings indicate that variation in water availability can be sufficient to impact distribution of dry matter between root and shoots, as discussed by Russell (1977), on sand-based putting green root zones.


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Creeping bentgrass turf responded during grow-in to varying root zone mixture properties within as well as outside the criteria ranges suggested by the USGA. Mixtures having a capillary porosity (–3 kPa water potential) at the high end of, or slightly exceeding, the USGA criterion range can provide better turf performance during grow-in, resulting in more rapid turf establishment. Mixtures with higher CEC will also improve turf performance during grow-in; however, concurrent low water retention potential in a mixture will offset this advantage as irrigation and fertilization objectives shift away from establishment toward a maintenance goal. Turf responses indicated that root zone mixtures with air-filled porosity as low as 0.099 m3 m–3 and Ksat < 60 mm h–1 can limit longer-term turf performance. Initial effects on performance of a putting green turf due to microenvironment may go unrecognized unless efforts are made to assess rooting of turf during grow-in. Thus, turf managers should periodically assess rooting within the first year of establishment to identify putting greens that have potential for poor turf performance due to microenvironment; differences in rooting may be more apparent at depths below 75 mm. No root zone treatment offset the detrimental effect of microenvironment on rooting during establishment (i.e., no interaction). Longer-term study of turf responses to these root zone mixture parameters is needed to verify the persistence of responses, especially considering some of the better turf responses occurred on mixtures with capillary porosities that exceeded the currently accepted maximum value suggested by the USGA.


   ACKNOWLEDGMENTS
 
This work was supported by the New Jersey Agricultural Experiment Station, State and Hatch Act funds, Rutgers Center for Turfgrass Science, and other grants and gifts. Additional support was received from the United States Golf Association, Tri-State Turf Research Foundation, Golf Course Superintendents Association of America, New Jersey Turfgrass Foundation, and Golf Course Superintendents Association of New Jersey.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
New Jersey Agricultural Experiment Station Publication No. D-12180-22-05.

Received for publication April 7, 2004.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 


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