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11/4/2018 » 11/6/2018
2018 Annual Conference

2016 Impacts of Effluent Water Irrigation on Soil Properties and Health of Deciduous and Evergreen T
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Impacts of Effluent Water Irrigation on Soil Properties and Health of Deciduous and Evergreen Trees on Golf Courses

Submitted by Dr. Yaling Qian, Professor Department of Horticulture and Landscape Architecture, Colorado State University
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Background and Objectives: During the past 10+ years, we have conducted studies to evaluate long-term effluent water irrigation on soil and turfgrass. Results indicate a substantial impact of effluent water on soil properties, including increased soil sodium exchangeable percentage ESP, increased soil Na, B, and P content with reduced K and Mg content. The accumulation of salts (especially Na) has potential to harm the growth of landscape plants. In the past several years we further studied the effects of effluent water irrigation on soil structural and chemical behaviors to the entire root zone or even beyond the root zones. We found that, after 10 years irrigation with effluent water, soil pH and soil sodium exchangeable percentage increased, and the degree of increases were greater at deeper soil depths that at the surface depths. Aerification and calcium addition helped to displace sodium and reduce ESP at the surface 6-8 inches, although soil ESP increased significantly at 15-40 inches below the soil surface. The greater degrees of increases in ESP and pH in deeper soil depths indicated it is possible to manage turfgrass root zone, but it is difficult to manage soil sodium and pH at deeper soil depths, which would in turn impact deeper rooted plants such as trees.
During the study we observed difference degrees of decline in the landscape plants. The degree of decline appears to relate to tree species, water quality, irrigation methods, and drainage effectiveness. Information is needed to determine the relative tolerance of trees to effluent water irrigation and the changes of leaf tissue mineral contents under effluent water irrigation.

The Objectives:
1). To determine soil property changes after 11 years irrigation with effluent water
2). To determine the impacts of effluent water irrigation on the health of deciduous and evergreen trees on golf courses
3). To determine leaf mineral composition of different deciduous and evergreen trees after 10 years of irrigation with effluent water compared to fresh water irrigated trees

For objective 1, we collected soil samples from three golf courses prior to, 5 years, and 11 years after effluent water irrigation on these sites. Most of the field work has been done. However, we need more time to analyze the data and the graduate student needs time to write up his thesis.

Objectives 2 & 3 are the main tasks for 2016

To address objectives 2 and 3, we will re-visit these landscapes sites. During onsite visits, performance of landscape plants will be recorded with a digital camera, and the extent of foliar damage, shoot dieback, and crown density will be rated and recorded. At the same time, we will survey each golf course to determine what trees and how many trees have been removed due to decline or death.

Concurrent with plant health evaluations, plant tissues will be sampled. Plant samples will be collected on golf courses in Denver area that started to use recycled water for irrigation in 2004. Landscape plants to be evaluated will include conifers and deciduous trees. The most common deciduous trees to be evaluated include: American Elm, Green Ash, Cottonwood, Oak, Coffee Tree, Honey Locust, Ohio Buckeye, Hawthorn, Crabapple, Silver Maple, and Rose. Conifers to be evaluated include: Scotch pine, Austrian Pine, Pinion Pine, Ponderosa Pine, and Colorado Spruce. These trees will be tagged for future reference.

Leaves of different trees and shrubs will be tested for sodium, chloride, boron, potassium, and other metal ions by inductively-coupled plasma atomic emission spectrophotometry (ICP-AES). Chloride content will be analyzed by the C1 – selective electrode. These parameters will be compared to the benchmark data collected from fresh water irrigated trees in the same areas. The relative tolerance of different landscape plants to recycle water will be assessed.

As such we can determine relative tolerance of different conifers and deciduous trees to recycle water and to select plants that better adapt to irrigation with recycled water. We will also conduct statistical analysis to determine if any particular ion is the major cause of decline in individual conifer and deciduous tree species.
This project will help us to understand the responses of urban landscape plants to recycled water irrigation. Proper selection of landscape plants is critical to the long-term success of water reuse in urban landscapes.


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