Arboriculture & Urban Forestry 35(5): September 2009 ‘Siouxland’ were established in the tubes,grown for 3.5 months (March through July 2006) in a greenhouse in Ithaca, NY, U.S., and kept at a constant 24°C (80°F) under 15 hours HID lighting and daily manual irrigation (Haffner 2008). For nine days, July 6–July 14, 2006, predawn single leaf tissue samples were col- lected and held in moist sealed bags to transport to the pressure bomb location in a lighted laboratory location. The first pre-dawn observation occurred at 9 hours after final irrigation to column runoff to establish drainage prior to any transpiration demand effect. Pre-dawn plant water potential and volumetric moisture percentage scatter plots were developed to define plant available moisture in the compacted stone-soil matrices, and compare the impact of the differing aggregate source materials. From linear regression on negative natural log transformed data, moisture content at 1500 kPa was derived. Otherwise, the data collection protocol between Florida and New York were held in common. Using the same stockpiles of CU and CS blends, field plots were installed and compacted as 64 m2 (689 ft2 ) square blocks to a depth of 60 cm (24 in) in three 20 cm (8 in) lifts and compacted to 1.98 Mg m-3 (124 lb ft-3 ), verified by sand-cone density tests (Table 1). Infiltration potential was measured three times at ran- dom locations in each treatment block using a Cornell Sprinkle Infiltrometer (Ogden et al. 1997) reporting an average of seven readings taken every two minutes during a testing run. Infiltration capacity was measured for discussions on storm water control use when planted with a turf wearing surface (Haffner 2008). RESULTS Initial Studies, 1996–1997 The difference between observed saturated moisture content and three-hour free-drain moisture losses were consistent with sample density differences, decreasing from 9% to less than 1% of total porosity, as density increased from 1.87 to 1.99 Mg m-3 (116.7 to 124.2 lb ft-3 ) (Table 2). The data set was limited to low tension observations due to the repeated breakage of the ceramic pressure plates. Attempts to develop traditional moisture desorp- tion curves were halted. The measured hydraulic conductivity in constant head flow on the two samples (test samples a,b) were 0.02–0.03 cm s-1 (0.08–0.12 inch s-1 ), in the order of magnitude of a clean, well-graded silty sand and gravel (Atkins 1997). Planted Study, Florida 2002 An estimate of plant available moisture percentage from initial drainage to study end was 7.8% with loamy sand, versus 11.3% in sandy loam systems. The negative natural log transformed slope coefficients were different (P < 0.001) between treatments (16.9% for loamy sand versus 14.8% for sandy loam), demonstrating that the soil texture in two otherwise same systems impacted moisture release behavior (Figure 1), as well as initial porosity in system density resulting from equivalent compaction effort (Table 3). The difference between soil texture treatments within this study were manifest in the first predawn observation (Table 2) at 13.4% volumetric moisture in loamy sandy systems, versus 16.3% in san- dy loam systems (significantly different at α = 0.05, P < 0.001). The difference in density between treatments suggested an impact of the soil texture on stone matrix formation, given the weight ratios and compaction effort were otherwise equivalent. Free drainage time prior to the first data collection in the Florida study 275 Figure 1. Predawn stem section water potential data transformed into a negative natural log and plotted for linear regression slope analysis for treatment comparison and assignment of high matric tension (assigned at 1200 kPa or -7.09 to determine plant avail- able moisture endpoint). Regression line endpoints correspond with minimum and maximum value observations on the x axis for each treatment. was 10.5 hours, versus 3 hours of the 1996 data; and the sample depth was 28.6 cm, versus 15.2 cm (11.3 in and 6 in, respectively, meaning direct comparisons between studies were not feasible). System densities were lower than expected for paved ap- plications (90% assumed target density, rather than at 95% minimum) due to the nursery container lowering compac- tion efficacy. The lower densities and associated increased po- rosity were presumed to have some influence on volumetric plant available moisture, compared to a more compact system. Planted Study, CU CS Structural Soils 2006 There was a comparable matrix porosity (Table 4) between ag- gregates and matrix formation, if the Stalite was treated as a light solid aggregate forming the lattice (apparent Specific Gravity 1.44 provided by the supplier) in phase diagram calcu- lation. Stone matrix formation as soil fines introduced were as- sumed to have been similar for mixture ratio development (Table 4). While compaction almost eliminated macro-porosity in the soil-only samples (2.2% of total voids), it was demonstrated to have been conserved in the stone-soil systems (Table 4). Plant available moisture v/v percentage of the CS was an es- timated 9.8%, while the CU was 7%. Aggregate type influenced the slope of the negative natural log transformed moisture tension regression relationship from 17.3% in the CS, to 25.4% for CU (P < 0.001) (Figure 2). Again treatment differences were observed to be a function of the initial pre-dawn observation endpoint of 15.8% in the CS, versus 11.6% in the CU (P < 0.001). The ag- gregate source significantly influenced moisture release behavior, and the Stalite aggregate increased water storage at low matric ten- sion. Plant available moisture was lower in the Cornell study com- pared to the Florida study, in large part due to a higher compacted density allowed by the rigid tubes designed for planted compac- tion studies. Infiltration rate observations in both field plots were in excess of 1 cm s-1 (0.4 in s-1 ), at the maximum flow capacity of the Cornell sprinkle infiltrometer, thus the reported values are the maximum flow reading of the tool. The rate was consistent with the order of infiltration magnitude of clean uniform sand. ©2009 International Society of Arboriculture
September 2009
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