INFLUENCE OF AMENDMENT, IRRIGATION FREQUENCY, AND MATURITY/AGE ON SOIL WATER REPELLENCY DEVELOPMENT IN SAND-BASED ROOT ZONES Maxim J. Schlossberg Pennsylvania State University, 116 ASI Bldg., University Park, PA, 16802 USA email: email@example.com David R. Moody Pennsylvania State University, 116 ASI Bldg., University Park, PA, 16802 USA email: firstname.lastname@example.org Andrew S. McNitt Pennsylvania State University, 116 ASI Bldg., University Park, PA, 16802 USA email: email@example.com Michael A. Fidanza Pennsylvania State University, Berks Campus, Reading, PA, 19610 USA email: firstname.lastname@example.org 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 () NS aggregates, and ultimately, severe soil water repellency 85 Non-compacted (SWR) in the uppermost layer of sand-based root zones. 83 Compacted NS Considering the increasingly frequent practice of sand- 81 based root zone amendment; improved accuracy in 79 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 3 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 o 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 o 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. References 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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