Water use and drainage of subtropical, mixed landscapes varies with turf coverage and season

Abstract

We conducted a three-year drainage lysimeter study of mixed (woody plant-turf) landscape water demand relative to reference evapotranspiration, drainage, and plant growth in humid, subtropical central Florida. The aim was to develop information to guide more efficient water planning, landscape design, and irrigation management in a seasonally dry monsoon climate using three representative landscape species – southern magnolia (Magnolia virginiana), sweet viburnum (Viburnum odoratissimum), and St. Augustinegrass (Stenotaphrum secundatum) – at turf coverage of 90, 75, and 60% of the total landscape area. Water inputs (daily rainfall, irrigation) and drainage were recorded with a datalogger to calculate monthly actual evapotranspiration (ETA) for each lysimeter using a water balance approach. Growth was measured non-destructively (magnolia height, canopy and trunk diameter, viburnum dry mater, canopy cross section, and volume) every three weeks, while turf clippings were collected during the spring to late fall growing season. Woody plants imbedded in turf with ostensibly deeper root systems underlying turfgrass roots were more efficient at scavenging water, minimizing drainage, and leaching risk. Reducing turfgrass coverage to 60% diminished drainage by 70 cm in the wet season and 50 cm in the dry season compared to 90% turfgrass cover, and increased rainfall utilization rate to 0.81 compared to 0.40 for 90% turf across both seasons. Mixed turf-woody plant landscape ETA differed minimally across turf coverage treatments during the dry season, with approximately 70% of reference ETA versus 90% during the wet season, likely due to less surface evaporation. To conserve water and reduce drainage during the monsoonal dry season, mixed turf-woody plant landscape irrigation can be scheduled based on water demand at 70% of local evapotranspiration (0.7 Plant Factor). These results give water suppliers and landscape architects tools to design urban landscapes and develop regulations to efficiently promote and track mixed landscape irrigation water consumption in a monsoonal climate with a pronounced dry season. Further, water managers can reduce drainage and risk of groundwater pollution by encouraging design of landscapes with woody plants imbedded in turfgrass to scavenge water moving below the turfgrass root zone.