Michael Knee, Daniel K. Struve, Michael H. Bridgewater, and Joseph W. Phillips, Department of Horticulture and Crop Science, The Ohio State University.
Seeds of Gleditsia triacanthos (honeylocust), Gymnocladus dioicus (Kentucky coffee tree), and Cercis canadensis (redbud) were obtained from local (Columbus) trees. Seeds of Robinia pseudoacacia (black locust) were purchased from Sheffield Seeds (Locke, New York).
Individual seeds were germinated in April 2000 in 10 cm square pots containing Metromix 360 (Scotts Sierra Horticultural Products Co., Marysville, Ohio). Seedlings were grown in the greenhouse until October when they were potted up in the same medium in 25 cm dia. containers and coated internally with Spinout (Griffin Corp., Valdosta, Georgia). The containers were over-wintered in a bed of shredded woody prunings provided by the Ohio State grounds staff.
In early June 2001 the containers were rearranged so that half remained in mulch and half were placed on a limestone gravel bed. The gravel and mulch areas were arranged in six blocks. Each container was irrigated with a spray emitter (Spot-Spitter, Roberts Irrigation, San Marcos, California) that delivered 2 L of water twice a day. For one irrigation cycle each week, the water was replaced by liquid fertilizer (Peters Professional 20:20:20, Scotts Sierra Horticultural Products Co., Marysville, Ohio) at 200 mg L-1 N.
On June 18, July 30, and October 3, six trees of each species in mulch and on gravel were disconnected from the irrigation system. The surface of the medium of three trees in each group was covered with aluminum foil in an attempt to minimize evaporation from the container. Each pot and tree was weighed between 9 and 10 a.m. for three consecutive days to measure water loss. If a tree and pot fell below 4 kg, it was watered and weighed again.
After three days, the length of the main stem was measured, and the leaf area was measured using a Licor 3600 meter (Licor, Lincoln, Nebraska). Roots were washed free of medium, and root and shoot (stem and leaf) dry weights were obtained after drying at 60°C for 7 days.
The temperature of the medium in the containers was measured on three days in August using an Aquaterr soil moisture meter (Geneq, Inc., Montreal, Canada).
Meteorological data were collected during the experiment with an ET 106 weather station (Campbell Scientific, Logan, Utah). Six remaining trees of each species from gravel and mulch were held over the winter in a mulch bed and planted at random in the Ohio State University Chadwick Arboretum in early April 2002. Their heights were measured at planting and again at the beginning of October.
Data were subjected to analysis of variance or regression analysis using SAS 8e (SAS Institute, Cary, North Carolina). The significance of treatment effects is shown in Table 1.
| Table 1. Significance of Effects of Species, Location in Mulch or on Gravel and Their Interaction (S*L) for Data Presented in Other Tables and Figures. | ||||
| Data | Presented | Probability of Null Effect | ||
| Species | Location | S*L | ||
| Tree height | Figure 1 | 0.0001 | 0.891 | 0.104 |
| Root dry weight | Figure 2 | 0.0001 | 0.039 | 0.545 |
| Shoot dry weight | Figure 3 | 0.0001 | 0.187 | 0.033 |
| Leaf area | Figure 4 | 0.0001 | 0.458 | 0.978 |
| Tree height | Table 2 | 0.0001 | 0.866 | 0.200 |