Pj. Dolling et al., ACIDIFICATION RATES IN THE CENTRAL WHEAT-BELT OF WESTERN-AUSTRALIA .2. ON A DEEP YELLOW SAND, Australian journal of experimental agriculture, 34(8), 1994, pp. 1165-1172
The rate and mechanisms of acidification were determined on a sandy du
plex soil (depth of sand 30-45 cm) under a cereal-annual pasture rotat
ion in Western Australia. We also evaluated the effect of rotation (in
tensity of cropping) on relative acidification of a sandy duplex soil.
Rate of acidification was based on a linear regression analysis betwe
en soil pH and years since clearing. Sites were sampled to a depth of
50 cm in 10-cm increments and measurements included soil pH, pH buffer
ing capacity, and bulk density. The effect of different rotations on t
he acidification rate was determined by soil sampling a rotation exper
iment which had been established for 25 years. Sampling and measuremen
ts were similar to the regression analysis. From regression, the rate
of acidification for the profile was 0.15 kmol H+/ha.year, requiring 7
.7 kg CaCO3 to neutralise. Most of the acidification could be accounte
d for by removal of alkaline products. Acidification was occurring to
a depth of 30 cm, the acidification rate decreasing with depth. In the
surface 20 cm the pH decline was 0.005-0.006 units/year. In the rotat
ion experiment, the rate of acidification relative to continuous wheat
without fertiliser nitrogen (N) ranged from 0.35 kmol H+/ha.year (17.
5 kg CaCO3) for continuous wheat with fertiliser N to 0.92 kmol H+/ha.
year (45.8 kg CaCO3) for continuous pasture. Between these rates was 1
year pasture-1 year cereal (0.41 kmol H+/ha.year, 20.5 kg CaCO3) and
2 years pasture-1 year cereal (0.82 kmol H+/ha.year, 41.2 kg CaCO3). A
cidification was occurring to 60 cm depth in all rotations, mostly due
to nitrate leaching, removal of alkaline products, and build-up of or
ganic matter.