Bw. Murphy et Tc. Flewin, RILL EROSION ON A STRUCTURALLY DEGRADED SANDY LOAM SURFACE SOIL, Australian Journal of Soil Research, 31(4), 1993, pp. 419-436
This study reports on the degree of rill erosion from a 0.65 ha site w
ith a hardsetting red duplex soil having a structurally degraded surfa
ce soil. Rill erosion was measured after a series of relatively low in
tensity rainfall events (all <1 yr return period) that resulted in abo
ve average rainfall over a period of 78 days. The rill erosion was est
imated by measuring the volume of rills in the field. The soil charact
eristics indicated that the soil was a structurally degraded soil with
low aggregate stability (2-5% of total soil), very low organic matter
levels (0.91% for 0-50 mm) and relatively high bulk density (1.56 g/c
m3). The low aggregate stability resulted in the rapid breakdown of so
il aggregates and settling of the soil under rainfall causing surface
crusting and low infiltration rates (4.08 mm/h) as well as decreasing
depressional storage. This resulted in high runoff and rill erosion, t
he total volume and mass of soil loss being equivalent to 48.3 m3/ha a
nd 78.0 t/ha respectively. This high level of soil loss was considered
to result from the combination of the poor structural condition of th
e soil, the tilled or loosened soil condition at the onset of the rain
fall events, the duration and number of the low intensity rainfall eve
nts and the low evaporation rates between rainfall events. The results
suggest that to reduce soil loss to acceptable levels under the condi
tions of the study, it is necessary to adopt management practices that
increase surface cover, maintain infiltration rates, reduce tillage a
nd increase soil aggregate stability in combination with erosion contr
ol earthworks. The study also looked at the prediction of soil loss us
ing the USLE equation, and confirmed that the equation should not be u
sed to predict erosion for individual events or erosion resulting from
concentrated flow, rather it should be used to estimate expected long
-term soil loss for a particular soil under a given set of management
practices.