A MODEL FOR ESTIMATING LAWN GRASS WATER REQUIREMENT, CONSIDERING DEFICIT IRRIGATION, SHADING AND APPLICATION EFFICIENCY

A comprehensive approach was undertaken to study the factors involved in urban irrigation water use and to identify the potentials for saving water. Four different areas of urban irrigation were studied. Irrigation management, water application efficiency, the relation of ET to quality of lawn grass, and the effect of shading on ET requirements of lawn grass.; Weekly irrigation water use by homeowners was measured. These measurements were compared to weekly estimated ET needs of lawn grass. It was found that water application by homeowners did not correspond to the weekly ET requirements.; Irrigation water application uniformity tests were conducted. Two groups, homeowners with hand-move sprinklers and homeowners with solid-set (underground) sprinkler systems, participated in the study. Catch cans were used to measure the applied water all over the irrigated areas. Water application followed as closely as possible the actual practice by homeowners. It was found that distribution uniformities (and, therefore, application efficiencies) varied significantly and were relatively low.; An experiment was conducted to find the relationship between grass quality and different levels of moisture availability. Twenty small plots were established. Irrigation water representing different percentages of ET were applied to each of five treatments. Color slides were taken of the experimental plots for evaluation of grass quality. A linear relationship was found between percent of potential ET applied and percent of potential quality obtained.; A solar radiation measurement system of pyranometers was set up to evaluate the incident solar radiation in the shadow of a building as well as under direct sunshine. The pyranometers were calibrated to read incident solar radiation. A diffuse fraction was defined to indicate the part of solar radiation that is effective under conditions of shading. Solar radiation data from Salt Lake City for clear and cloudy days were studied. A linear relationship between percent of potential ET requirement and percent of solar radiation available to lawn grass was developed. The relation was used to calculate the ET reduction under shading conditions.; From the results of the experiments, an empirical model for determining irrigation water needs of urban landscape vegetation was developed.