Thirteen species of shade trees including four oak and three maple species were planted from bare root whips in Spring 2001 at the Michigan State Univ. horticulture station near Benton Harbor, Mich. Forty trees of each species were planted and placed under a randomized complete block design consisting of four fertigation treatments in a 2 × 2 factorial (with and without irrigation; with and without nitrogen fertilization). Fertilized trees received 168 kg per hectare of ammonium nitrate annually via the drip system. We measured tree height, stem diameter, and stem volume index (D2 H) at the end of each growing season. We also measured photosynthetic gas exchange with a portable photosynthesis system. After three growing seasons irrigation increased stem volume and height growth. Fertilization has not increased stem volume and height growth, yet there is an interaction between irrigation and fertilization meaning that among irrigated trees fertilizer produced significantly more growth. Species effect on growth was significant (P < 0.001); honey locust trees have grown the most with an average height increase of 1.28 meters in 2003. `Crimson King' Norway maple and goldenchain trees grew the least averaging less than.305 meters of height growth per year. There is no interaction between species and fertigation responses meaning that all species had similar responses to the treatments. From light response curves obtained with a portable photosynthesis system Amax (maximum rate of CO2 assimilation) varied significantly by species and treatment, but showed no interaction between species and treatment effects. Implications for the nursery industry along with further photosynthetic responses will be discussed.
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