International Journal of Irrigation and Water Management

International Journal of Irrigation and Water Management ISSN 2756-3804 Vol. 7 (10), pp. 001-013, October, 2020. © International Scholars Journals

Full Length Research Paper

Mixed landscape water demand and drainage in a subtropical-monsoonal climate varies with irrigation frequency and season

Hongyan Sun¹, Michael D. Dukes², Roger Kjelgren¹ and Richard Beeson Jr.^1,3

¹Beijing Key Lab of Greening Plants Breeding, Beijing Institute of Landscape Architecture; Mid-Florida Research & Education Center, University of Florida.

²Center for Landscape Conservation and Ecology, University of Florida.

³Mid-Florida Research & Education Center, University of Florida.

Accepted 30 September, 2020

Abstract

We used drainage lysimeters to study water balance and plant growth of mixed (woody plant-turf) landscapes irrigated at three rates of root zone water depletion based on local reference evapotranspiration (ET_O) in a subtropical-monsoonal climate: slow/dry (60%), intermediate (75%) and fast/wet(90%) of ET_O. Planting design for each lysimeter was identical: a Magnolia virginiana tree imbedded in St. Augustine grass (Stenotaphrum secundatum) turfgrass bordered by two Viburnum odoratissimum shrubs grown as a hedge. Landscape monthly actual evapotranspiration (ET_A) was calculated as the difference between inputs (irrigation and precipitation) and output (drainage). Magnolia (height, projected canopy area, and trunk diameter) and viburnum (height and canopy volume) growth was measured every three weeks. Total drainage over three years from the 0.6 depletion (driest) treatment was 20 and 45 cm for the dry and wet season, respectively, half that of the 0.9 depletion (wettest) treatment. The dry treatment had the lowest ET_A both seasons, and average dry season Plant Factors (PF=ET_A÷ETo) was about 15% lower than the wet season (0.76 versus 0.98). Plant growth was largely unaffected by irrigation-depletion treatments. For subtropical climates, dry season irrigation scheduling based on a mixed landscape PF of 0.75 is reasonable to maximize growth following transplanting. Once established, dry season irrigation schedules can be based on a 0.6 PF value to maintain performance while minimizing drainage. Irrigation of mixed landscapes during the monsoonal wet season is only needed during exceptional dry periods.

Keywords: Drainage lysimeter, monthly ET_A, Plant Factor, plant growth, Viburnum odoratissimum, Magnolia grandiflora, Stenotaphrum secundatum.