Growth and Physiology of Living Christmas Trees Under Cyclic Irrigation

Water use regulations and the cost of applying water are increasing as the availability of potable water is decreasing. Irrigating cyclically, or applying daily water allotments in multiple irrigation events, instead of the traditional once daily application method may lead to increased crop growth and decreased water use. The objective of this study was to quantify the effects of varying irrigation regimes on the growth and physiology of common Christmas tree species in pot-in-pot production. Four species of conifers (Abies fraseri, Picea pungens, Picea glauca var.  densata, Pinus strobus), grown in 3- and 7-gallon containers, were randomly assigned to irrigation regimes with varying combinations of amounts (low, medium, high) and cycle frequencies (once or 4 times daily). Daily amounts for 3-gallon containers were based on 75%, 150%, or 225% PET, and amounts for 7-gallon containers were based on 75% or 150% PET. Water was applied using pressure compensating drip emitters or spray stakes. Mid-day gas exchange and monthly tree caliper and height were measured during the 2008 growing season. Diurnal gas exchange and water potential of 7-gallon A. fraseri were measured on two dates during the growing season, and substrate media temperature and moisture of 7-gallon containers were monitored throughout the season. Preliminary data indicate a strong species effect on growth response to irrigation regimes. P. strobus and P. pungens grown in 3 gallon containers and receiving 4x daily irrigation applications had greater assimilation and  caliper growth than trees of the same species irrigated once daily, while assimilation and caliper growth of A. fraseri and P. glauca was unaffected by cyclic applications.  Mid-day stomatal conductance of A. fraseri, P. pungens, and P. strobus grown in 7-gallon containers increased with cyclic irrigation indicating that multiple applications alleviated mid-day water stress. Differences in growth and physiological responses to treatments could be due to inherent differences in species morphology, tree size, and growth rate.