Krj. Smettem et al., Obtaining soil hydraulic properties for water balance and leaching models from survey data. 1. Water retention, AUST J AGR, 50(2), 1999, pp. 283-289
A physico-empirical 2-parameter power law model of the draining water reten
tion curve (WRC) based solely on clay content is described and further deve
loped using 6 datasets obtained from Australian and New Zealand soils. The
slope of the WRC, or pore-size distribution index, is well described by the
model but the bubbling pressure, or inflection point is poorly described.
Without a good estimation of the bubbling pressure it is not possible to sc
ale the physico-empirical model to the WRC. To achieve the scaling, a singl
e measured point on the WRC in the unsaturated range is required. The resul
ting estimated water contents may be satisfactory for application within br
oad-scale leaching risk models and for generalised extrapolation of results
from detailed experimental sites but caution is still required for quantit
ative applications of nitrate leaching models at a particular site.
It is concluded that soil surveys could usefully include a single WRC measu
rement in the field at each sampling location to improve their utility for
water and chemical transport modelling.