Balancing substrate depth and irrigation inputs influence the aesthetic quality ofPaspalum vaginatumwhen grown on adaptive extensive green roof systems

Abstract

Turfgrass use on extensive green roofs could offer a sustainable solution for increasing urban greening within the existing built space in contemporary cities. The aim of the study was to determine Paspalum vaginatum 'Platinum TER' drought tolerance when grown under extensive green roof conditions and two irrigation regimes. Treatments included: (i) six extensive green roof substrates formulated from mixing locally available materials; (ii) two substrate depths (7.5 or 15 cm) and (iii) two irrigation regimes (60% ETc or 100% ETc). Turfgrass drought tolerance was measured, using digital image analysis, as the number of days until a treatment reached 50% green turf cover (GTC). In both study years (2011 and 2012), for each one of the six substrate types, higher GTC values were reached when deeper profiles (15 cm) were combined with the higher irrigation regime (100% ETc), while the worst drought tolerance turfgrass response was obtained when the swallow substrate (7.5 cm) was combined with the deficit irrigation regime of 60% ETc. It was found that increasing substrate depth resulted in delay of drought stress symptoms expression, while irrigation regime affected the velocity of GTC reduction over time with lower irrigation regime resulting in faster GTC decline compared to higher irrigation regime. It was also concluded that the imposed drought stress to the turfgrass by the reduced irrigation could be compensated by increasing substrate depth. Thus, in buildings with adequate load bearing capacity, it is preferable to select a substrate depth of 15 cm since it will result in 40% reduction on irrigation inputs compared to substrate depth of 7.5 cm.