RESEARCH RESEARCH
Do amendments reduce
water use?
UWA researchers Pieter Poot and Gausul Azam report on the second year of their Horticulture Innovation Australia funded project on amending sandy soils to retain irrigation water and reduce turfgrass water use.
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any Australian cities are predicted to face water shortages due to increased temperatures, declines in rainfall and an increased demand for water as a result of the expansion of our cities. Western Australia’s capital city, Perth, might experience a water deficit as early as 2020. More than 10 per cent of Perth’s annual water use is associated with irrigating community parks, gardens and sports fields. In addition, a substantial fraction of household water is used for watering home gardens including turfgrass. Water restrictions have been introduced to both scheme water and bore water in response to increasing water demands and declining rainfall. Thus, turfgrass managers and home owners are facing the ongoing challenge of maintaining turfgrass with less water. As there is increasing evidence that public and private green spaces are important for maintaining physical as well as mental health, developing approaches for maintaining turfgrass under limited irrigation is essential. Maintaining turfgrass under limited water supply is challenging, especially in sandy soils (such as on Western Australia’s coastal plain) which have a relatively low water retention capacity and a tendency to become water-repellent. Turfgrass on sandy soils is often dependent on frequent irrigation during the summer (e.g., every 2-3 days). Amending sandy soils with materials containing smaller particle size (e.g. clays) or which have a porous structure (e.g. zeolite) that stores water internally, has been shown to increase the water holding capacity of these soils. These materials are also likely to slow the movement of
AMENDMENTS USED Below is a list of the amendment treatments included in the experiment. Values in parentheses represent the percentage at which amendments have been incorporated in the top 10cm of the soil (weight fresh product/weight soil). l Bentonite (5%) l Compost (10%) l Kaolinite (Ca and silt amended; 10%) l Ready Grit™ (10%) l Spongelite (5%) l Zeolite (5%) l Bentonite (5%) + Compost (10%) l Kaolinite (10%) + Compost (10%) l Ready Grit™ (10%) + Compost (10%) l Spongelite (5%) + Compost (10%) l Zeolite (5%) + Compost (10%) l Control (no amendments added) 58
AUSTRALIAN TURFGRASS MANAGEMENT 18.3
irrigation water beyond the rootzone, increasing soil water available for turfgrass and hence decreasing the demand for irrigation. The aims of the current project were to obtain independent evidence of the efficacy of a range of soil amendments in decreasing the irrigation requirements of turfgrass and to identify the mechanisms responsible for the variation in efficacy.
EXPERIMENTAL APPROACH The research has been conducted at the University of Western Australia’s (UWA) Turf Research Facility at Shenton Park which has a sandy soil typical for the Perth metropolitan area. Six amendment types (i.e.: five inorganic and one organic, see inset), as well as the corresponding inorganic/organic blends, were rotary hoed into the top 10cm of the experimental plots (2.5m x 3.5m). Combined with untreated control plots, these 11 amendment treated plots were organised in blocks of 12 plots, with eight blocks all together in the experiment. Soft-leaf buffalo (‘Palmetto’) was laid in late October 2013 and given three months to establish before commencement of two irrigation treatments; l A low irrigation treatment administered twice a week (43 per cent evapotranspiration (ET) replacement; four blocks); and l A high irrigation treatment administered three times a week (65 per cent ET replacement; 4 blocks). Results of the first irrigation season were outlined in the May-June 2015 edition of Australian Turfgrass Management Journal. Results indicated that plots with clay-type amendments (i.e. bentonite and kaolinite) and those including compost had higher top soil water contents, but that despite this, all plots developed severe browning in the low irrigation treatment.