Irrigation effects on growth, stress, visual quality and evapotranspiration of ornamental grasses.

摘要

Deficit irrigation research has proven extremely effective for reducing the amount of irrigation applied to various types of landscape plants including trees, shrubs, and herbaceous ornamental plants. This research has yet to delve into one of the most common classes of drought tolerant plants, ornamental grasses. Deficit irrigation treatments were based on evapotranspiration of a short reference crop (Kentucky bluegrass evapotranspirtation, ETo). In 2012 three ornamental grass species were planted, and an on-site atmometer was used to estimate ETo. The three species used for trialing were Panicum virgatum 'Rotstrahlbusch' (Rotstrahlbusch Switchgrass), Schizachyrium scoparium 'Blaze' (Blaze Little Bluestem), and Calamgrostis brachytricha (Korean Feather Reed Grass). Treatments were applied and data was collected in 2014 and 2015 on two separate studies. The first study was in-ground and consisted of four treatments based on ETo (0%, 25%, 50%, and 100%). The second study was a mini-lysimeter and consisted of three treatments based on ETo (25%, 50%, and 100%). Only Schizachyrium scoparium 'Blaze' (Blaze Little Bluestem) was used in the lysimeter study. Data collected in both studies included plant water potential, biomass accumulation, green up date, flowering date, height, width, circumference, floral impact, landscape impact, overall habit, self-seeding, and color. The in-ground component also measured infrared canopy temperature and soil water content, while the lysimeter study included daily weight measurements which were then transferred to evapotranspiration readings. Plants in the 0% treatment were smaller and not considered visually suitable for landscape use. All three species in the 25% treatment performed equivalent to the 50% and 100% treatments in all categories. The only exception was plants in the 25% mini-lysimeter study were more stressed than the 50% or 100% treatments during periods of drought. These plants were all considered visually suitable for landscape use based on visual ratings. This suggests that as long as ornamental grasses are kept on a strict weekly regiment of 25% ETo, and are never exposed to periods of drought, they will be physiologically as well as aesthetically usable in the landscape trade. A weekly amount of 0.25 inches of irrigation on weeks without precipitation was determined to be a usable number for those installing and maintaining ornamental grasses.