Lk. Heng et al., Seasonal differences in the soil water balance under perennial and annual pastures on an acid Sodosol in southeastern Australia, EUR J SO SC, 52(2), 2001, pp. 227-236
Replacement of native deep-rooted grasses by shallow-rooted ones has result
ed in greater losses of water and nitrogen by drainage. To counter this eff
ect we have tested the hypothesis that liming, and the conversion of annual
grass pastures to perennial grass pastures, could improve the sustainabili
ty of grazing systems in the high rainfall zone (> 600 mm per annum) in sou
theastern Australia, through better use of water and nitrogen. A field expe
riment consisting of sixteen 0.135ha (30m x 45m) grazed paddocks representi
ng four pasture combinations (annual pasture (mainly Lolium rigidum) withou
t lime (AP-); annual pasture with lime (AP+); perennial pasture (mainly Pha
laris aquatica) without lime (PP-), and perennial pasture with lime (PP+))
was carried out from 1994 to 1997 on an acid Sodosol (Aquic Hapludalf) in s
outhern New South Wales, Australia. Measurements were made of surface runof
f, subsurface flow (on top of the B horizon) and soil water content. The re
sults showed that perennial grass pastures, especially PP+, extracted appro
ximately 40 mm more soil water each year than the annual grass pastures. As
a result, surface runoff, subsurface flow and deep drainage were at least
40 mm less from the perennial pastures. These measurements were further sup
ported by a simulation of soil water deficit and deep drainage for AP- and
PP+ paddocks, using 10 years' past meteorological records. Overall, the res
ults suggested that well-grown, phalaris-based pastures could reduce rechar
ge to groundwater and make pastoral systems more sustainable in the high ra
infall zone.