Zoysia matrella cover rate and drought tolerance in adaptive extensive green roof systems

Abstract

Turfgrass use in adaptive extensive green roof systems could provide a sustainable solution for increasing urban greening in semi-arid regions. The aim of the study was as follows: (i) to investigate the effects of four different substrate formulations from locally available materials (S15:Pum60:P20:Z5, S15:Pum60:C20:Z5, S30:Pum40:P20:Z10, and S30:Pum40:C20:Z10, where S, sandy loam soil; Pum, pumice; P, peat; C, compost; and Z, zeolite in volumetric proportions as indicated by their subscripts), and two substrate depths (7.5cm and 15cm) on the lateral growth of Manilagrass (Zoysia matrella L. [Merr.] ‘Zeon’); (ii) to evaluate the capacity of locally produced compost to be substituted for peat as an organic substrate amendment in an effort to reduce its horticultural use; (iii) to determine the effect of increasing soil participation in substrate formulations on growth and drought resistance of Manilagrass; (iv) to evaluate the effects of the four substrate types and two substrate depths on Manilagrass drought resistance. The measurements included: (a) determination of substrate characteristics, such as particle size distribution, saturated and dry bulk density, total porosity, water potential curves, in situ substrate moisture, pH and electrical conductivity and (b) determination of turfgrass quality and physiological status that included green turf cover (GTC), normalized difference vegetation index (NDVI), and leaf stomatal resistance (LSR). It was found that during establishment, when adequate irrigation of turfgrass was applied, the deeper profiles (15cm) combined with compost-amended substrates (S15:Pum60:C20:Z5 and S30:Pum40:C20:Z10) provided higher GTC values while the shallow profiles (7.5cm) with peat-amended substrates (S15:Pum60:P20:Z5 and S30:Pum40:P20:Z10) provided the lowest GTC. The opposite phenomenon was observed during water-deficit periods, since the peat-amended substrate S15:Pum60:P20:Z5 combined with the deeper profile (15cm) resulted in the least drought stress imposition to Manilagrass while providing the highest GTC and NDVI and the lowest LSR values. By contrast, the compost-amended substrates S15:Pum60:C20:Z5 and S30:Pum40:C20:Z10 increased the drought stress imposition to Manilagrass when combined with shallow profiles (7.5cm). Substrate depth was the most influential factor, since Manilagrass drought stress was alleviated as substrate depth increased from 7.5cm to 15cm.