Productivity and water use of grazed subsurface drip irrigated perennial pasture in Australia
2015
Dairy farmers in the southern Murray–Darling (M–DB) of Australia are considering subsurface drip irrigation (SDI) for pasture production in response to reduced water supply. Use of SDI in pasture production is a significant departure from previous SDI knowledge because in pasture irrigation (1) uniform moisture, nutrients and pasture growth is sought across the full paddock width, (2) the pasture is grazed by dairy cattle, and (3) is grown on duplex soils with distinctive hydraulic behaviour. A field experiment was conducted on two dairy farms with contrasting subsoil hydraulic characteristics to investigate the impact of SDI design (tape spacing) and operation (irrigation frequency) on pasture productivity and hydrology under grazed conditions. Treatments comprising of tape spacing (0.6, 1.0 and 1.4 m) and irrigation frequency (D or 4D) were imposed. SDI successfully supported contiguous perennial pasture under grazing during a period of drought. The impact of SDI design and operation on pasture accumulation and its spatial variability differed strongly between sites, reflecting soil hydraulic characteristics. Pasture composition and irrigation efficiency were insensitive to SDI design and operation at both sites. Water balance analysis indicated that deep percolation was the main pathway for water loss in SDI pasture production, though the dominance of this over surface runoff will be influenced by soil hydraulic properties. SDI can support grazed pasture production on the duplex soils of the southern M–DB; however, its performance may be insufficient to offset the high economic cost of SDI technology.
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