Water conservation potential of modified turf grass irrigation in urban parks of Phoenix, Arizona

Large amounts of water are consumed by urban parks in arid regions such that efficient irrigation practices are needed. In Phoenix, Arizona, extensive 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 an ecohydrological 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 building confidence in the model through comparisons to data, we created long-term scenarios to explore differences between flood and sprinkler irrigation practices and analyse the effect of changes in irrigation scheduling. 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% could be achieved, in particular with small changes in watering depths. 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.