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                                         Maxim J. Schlossberg
  Pennsylvania State University, 116 ASI Bldg., University Park, PA, 16802 USA email:
                                            David R. Moody
 Pennsylvania State University, 116 ASI Bldg., University Park, PA, 16802 USA email:
                                           Andrew S. McNitt
  Pennsylvania State University, 116 ASI Bldg., University Park, PA, 16802 USA email:
                                          Michael A. Fidanza
    Pennsylvania State University, Berks Campus, Reading, PA, 19610 USA email:

Utility is often the most important function of a turfgrass system, making internal drainage and compaction
resistance the priority deliverables of modern root zone design. For this reason, primary minerals having
sand-sized diameters predominate in constructed turfgrass root zones. Unfortunately, not all properties of
sand-based root zones are desirable; as their rapid percolation rates inversely relate to specific surface
area, while quartz and calcitic minerals comprise the bottom tier of cation exchangers. To counteract
these less desirable traits, amendments can be added at volumetric rates of 5—20% to enhance both
water retention and cation exchange capacity (CEC) of sand-based root zones. Soil amendments, either
of the organic (peat moss, compost, and polyacrylamides) or inorganic (calcined clay, diatomaceous
earth, and zeolites) variety, are commonly implemented for this purpose.

The rapid generation of biomass by healthy perennial turfgrass systems provides copious quantities of
detritus to soil, and subsequently direct contributions to soil OM (SOM) levels. Though particulate SOM
has long been recognized as the primary source of non-polar compounds and/or hydrophobic waxes in
soil, researchers have recently identified specific microbial population dynamics, primary substrate
influence (Hallett et al., 2001), and management-related physical processes that govern SOM
transformation and subsequent release of these problematic hydrophobic compounds (Figure 1;
Schlossberg et al., 2005). It is likely these compounds first avoid hydration by grouping into energy-saving
micelle configurations, then later by bonding to available mineral solid phases, or by joining established
hydrophobic coatings and/or amorphous organic aggregates possessing chemistry similar to their own.
This fateful combination of turfgrass and a surface area-limited mineral fraction is well associated with the
development of organic coatings, hydrophobic
                                                               Sand Mineral Fraction Contact Angle ()

aggregates, and ultimately, severe soil water repellency         85
(SWR) in the uppermost layer of sand-based root zones.
                                                                                                          83       Compacted
Considering the increasingly frequent practice of sand-                                                   81
based root zone amendment; improved accuracy in
predicting the effects amendment formulation have on
root zone SWR development could prove valuable to                                                         77
turfgrass managers and soil consultants alike. Thus, the                                                  75
objective of this laboratory study is to determine the
influence of root zone amendment (by type and rate) on                                                    73
SWR development in sand-based root zones, and
                                                                                                               0   100      200       300         400   500
identify interactions between SWR development and                                                                        Days after sodding (DAS)
imposed      hydration/dehydration     cycling   (irrigation                              Figure 1. Effects of maturity and compaction
frequency) over the initial root zone maturation period.                                  treatment on the contact angle of sands
                                                                                          collected from the 0-3 cm depth of creeping
This laboratory incubation/study was initiated July 2004,                                 bentgrass (Agrostis palustris L.) root zones.
in a constant temperature/humidity chamber (Lunaire
Environ. Inc., Williamsport, PA, USA) at the Penn State Univ. University Park Campus. Four root zone
amendments were selected to represent a general array of available products in most US regions. The
four amendments used were: Profile, a calcined illite clay (Profile Products LLC, Buffalo Grove, IL, USA);
Sunshine-Pro, a sphagnum peat moss (Sun Gro Hortic., Vancouver, BC, Canada); Dakota reed sedge
peat moss (Dakota Peat & Equip., Grand Forks, ND, USA); and a biosolid compost (AllGro Inc.,
Columbus, NJ, USA). Each amendment was volumetrically formulated with USGA-spec sand in both
80:20 and 90:10 sand:amendment (v:v) combinations. An unamended USGA sand was included as a
control mixture. Each of the nine volumetric root zone mixtures were prepared individuallly for every
experimental unit. The volume components were spiked with 1-g ground, dried creeping bentgrass root
mass, then thoroughly agitated in a mixer. Each prepared root zone (~150 cm ) was then transferred into
a 10-cm length of polyvinyl chloride (PVC) pipe (schedule 40, 5.1-cm ID), with one end previously sealed
by a cheesecloth double-layer and vinyl screening (20-mesh). Last, a dedicated column tamper
compacted each root zone to a firmness typical of a well-trafficked putting green (ASTM Intl., 1998).

 Once at standard compaction, columns were placed in a dilute nutrient solution bath and saturated slowly
 from the bottom over a 72-h period. The columns were then set on racks to gravitationally drain, before
 sets of nine replications (representing each root zone formula) were randomly assigned to each of three
                                                  incubation bins (Figure 2). The three incubation bins
                                                  were maintained under identical temperature (22-23 C)
                                                  and ventilated conditions, yet by forced-air having
                                                  different atmospheric vapor pressure (hourly mean
                                                  values: 1.78, 2.19, and 2.45 kPa). This purposeful
                                                  ‘incubator-effect’ imposed three distinct hydration/
                                                  dehydration frequency treatments, independent of time
                                                  and temperature. Surplus root mix (of each formula) was
                                                  analyzed in duplicate for gravimetric water content at
                                                  300-kPa of tension. A unique critical ‘rewet’ mass was
                                                  calculated for each individual column using the PVC
                                                  column tare, dry/filled mass, and —300 kPa water-
                                                  retention value specific to its amendment formulation. All
                                                  columns were weighed weekly. When a column mass
Figure 2. Formulated root zones shown in the fell below its unique critical mass, it was re-saturated
incubators. During the experimental period,       with dilute nutrient solution (from the bottom) overnight,
each housed three vertically-stacked trays        and the column/event/date recorded. Average re-
                                                  irrigation frequency was every 46, 98, and 283 days for
 the 1.78, 2.19, and 2.45 kPa atmospheric vapor pressure incubations, respectively.

At 138, 274, or 436-days following experiment initiation, three replications of each root zone formula
maintained at each hydration/dehydration frequency were removed from the incubators and dried in a
forced-air oven (80 C) to constant mass. After cooling in a desiccator, the root zones were separated by
depth and stored in air-tight polyethylene bags for analysis (Doerr et al., 2002). Traditional soil
physicochemical analysis (pH, EC, LOI, bulk density, and CEC) of amended root zone sub-samples is
currently underway. Moreover, molarity of ethanol droplet (MED) and intrinsic sorptivity methods (Leeds-
Harrison and Youngs, 1997) are currently being implemented to characterize soil water repellency (SWR)
in both the ‘as-formulated’ root zones as well as sand sub-samples eluted of particulate SOM. Ideally,
multivariate and/or principle components analysis will elucidate the specific influence of time, organic
substrate, hydration/dehydration cycle frequency, and/or amendment rate on SWR development in these
amended sand-based root zones. Likewise, wide-scale extrapolation of these confined and very limited
experimental results to construction or renovation of intensively utilized/maintained turfgrass systems is
discouraged prior to validation by field experiments. Results will be presented during the conference.

ASTM Intl. 1998. Standard test methods for: saturated hydraulic conductivity, water retention, porosity,
     particle density, and bulk density of putting green and sports turf root zones. ASTM F1815-97.
Doerr, S.H., L.W. Dekker, C.J. Ritsema, R.A. Shakesby, and R. Bryant. 2002. Water repellency of soils:
     the influence of ambient relative humidity. SSSAJ 66:401-405.
Hallett, P.D., K. Ritz, and R.E. Wheatley. 2001. Microbially derived water repellency in golf course soil.
     Intl. Turf. Soc. Res. J. 9:518-524.
Leeds-Harrison, P.B., and E.G. Youngs. 1997. Estimating the hydraulic conductivity of aggregates
     conditioned by different tillage treatments from sorption measurements. Soil Till. Res. 41:141-147.
Schlossberg, M.J., A.S. McNitt, and M.A. Fidanza. 2005. Development of water repellency in sand-based
     root zones. Intl. Turf. Soc. Res. J. 10:1123-1130.

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