Am. Ridley et al., WATER-USE AND DRAINAGE UNDER PHALARIS, COCKSFOOT, AND ANNUAL RYEGRASSPASTURES, Australian Journal of Agricultural Research, 48(7), 1997, pp. 1011-1023
The water balance equation was used to calculate plant water use and d
rainage below a depth of 1.1 m for phalaris, cocksfoot; and annual rye
grass pastures and bare fallow at Rutherglen in north-eastern Victoria
. Rainfall from 1990 to 1993 averaged 693 mm/year. Soil water use was
greater under perennials over the summer-autumn period and the soil pr
ofile was approximately 50 mm drier at the beginning of each drainage
season. Following autumn rains, soil water profiles under all treatmen
ts converged, usually reaching similar water contents within 4-6 weeks
. Over 4 years, soil under phalaris became 33 mm drier, and cocksfoot
24 mm drier (P < 0.001), than under annual ryegrass or bare fallow. Ph
alaris had higher actual evapotranspiration (P < 0.05; average, 642 mm
/year) than cocksfoot (619 mm/year) and annual ryegrass (606 mm/year),
the latter two not differing significantly. Drainage occurred during
winter and early spring, ranging from 2 to 12 mm in 1991 (515 mm rainf
all) to >100 mm/year in 1990 and 1992 (671 mm and 901 mm rainfall, res
pectively). The variation between years was greater than the differenc
es between pastures in any one year. Averaged over the 4 years, draina
ge losses below ! lm decreased in the order bare fallow > annual ryegr
ass > cocksfoot > phalaris, although differences between the 3 pasture
types were not statistically significant. Drainage under phalaris and
cocksfoot may have been overestimated relative to annual ryegrass and
fallow because of subsurface flow, at the top of the B horizon, betwe
en the wetter and drier plots. The drainage under phalaris may also ha
ve been overestimated because this pasture extracted water below the d
epth of soil water measurement. Allowing for these effects, the estima
ted drainage under phalaris may have been 49-56 mm/year compared with
80-87 mm/year under annual ryegrass, an overall reduction of more than
one-third. Although perennial pasture grasses are unlikely to stop al
l recharge to groundwater in high rainfall areas (>600 mm/year) of sou
th-eastern Australia, they offer a practical way to combine profitable
agriculture with reduced land degradation.