Professor and Center Director Arizona State University
Large amounts of water are consumed by urban parks such that efficient irrigation practices are needed. In Phoenix, Arizona, turf grass areas are supported using flood or sprinkler irrigation that also require fertilizers. Residential green waste compost has the potential to serve an alternative fertilizer if its higher costs can be offset through water conservation. In this study, we conducted a monitoring and modelling effort for a compost experiment in two urban parks with either flood or sprinkler irrigation. Soil moisture, evapotranspiration, and turf greenness data along with a soil water balance model were used to determine if compost treated plots were different from control plots in each park. After comparisons to data, we created long-term scenarios to explore differences between flood and sprinkler irrigation practices and analyze the effect of changes in irrigation scheduling. We found that irrigation water inputs largely decouple the urban dynamics from precipitation forcing. Multiple lines of evidence indicated that green waste compost applications did not appreciably change soil moisture or vegetation conditions in either urban park. Major differences, however, were noted between the two irrigation practices in terms of the seasonality of the soil water balance, plant water stress and the sensitivity to interannual fluctuations in precipitation. Model scenarios showed that significant irrigation reductions from 15% to 30% can be achieved with small changes in watering depths. Conditions in urban parks also resulted in extraordinary rates of evapotranspiration which can exceed the available net radiation when heat was advected from the surrounding built environment. Evaporation from sprinklers at night was identified the major mechanism for evaporative losses during these oasis conditions. As a result, irrigation management in urban parks can meet water conservation targets that potentially offset green waste compost costs while also benefitting the soil water balance through reductions in water losses.
