Growth and physiology of deciduous shade trees and conifers in response to cyclic irrigation regimes

Nursery water management is becoming increasingly important as input costs rise and water use regulations increase. Irrigation regimes consisting of varying combinations of irrigation rates and cycle frequencies were tested to investigate their effect on the growth and physiology of PIP-grown conifers and deciduous shade trees. The project consisted of two studies: 1) examining the effects of cyclic irrigation and reduced irrigation rates on seven taxa of deciduous shade trees, and 2) examining the effects of cyclic irrigation and reduced irrigation rates on four conifer species. Growth and physiological responses were measured throughout two growing seasons and were more responsive to irrigation rate than cycle frequency. In the first study, we found that 50% reductions in daily irrigation rates produced conifers of similar size to those produced with the typical irrigation rate. However, the same reduction in the irrigation rate of PIP-grown deciduous shade trees decreased stem radial growth of most species tested. Applying water in multiple cycles did not affect tree growth in either study. Of the various methods of calculating WUE, carbon isotope discrimination was the most sensitive to irrigation regimes.