Changes in soil water content under annual, perennial, and shrub-based pastures in an intermittently dry, summer-rainfall environment

Soil water content (SWC) was monitored in an intermittently dry environment in 2003-08, for the following pasture types: perennial ryegrass (Lolium perenne cv. Skippy), lucerne (Medicago sativa cv. Venus), phalaris (Phalaris aquatica cv. Atlas PG), a lucerne/phalaris mixture, digit grass (Digitaria eriantha ssp. eriantha cv. Premier), and old man saltbush (Atriplex nummalaria). Perennial ryegrass and phalaris pastures persisted until late winter-early spring 2005 and, after that time, were maintained as degraded annual grass pastures and bare fallows, respectively. For all pasture types, mean SWC was generally higher for the 0-0.9 m soil depth than the 0.9-2.1m(63 v. 51 mm of water per 0.2 m soil layer). At a soil depth of 0-0.9 m, few significant differences in SWC occurred among pasture types. However, significant differences among pasture types were recorded in SWC at depths of 0.9-2.1 m for these perennial-based pastures with low herbaceous plant densities. At this depth the SWC of lucerne/phalaris was lower (P<0.05) than that of perennial ryegrass and phalaris pasture types in March 2005 (Day 500), and that of the degraded annual grass pasture in August 2006 (Day 1000) and December 2007 (Day 1500). Overall, maximum extractable water was highest (P<0.05) for digit grass and old man saltbush pasture types (similar to 180 mm) and lowest for the bare fallow (99 mm). Estimates of root depth were highest (2.0 m) for the lucerne/phalaris pasture type.