Information

Runoff and soil loss studies – Wagga Research Station

Level 1 General description

Purpose: 

Adamson (1974): To determine the long term effects of soil conservation structures and improved land use management on runoff and soil loss.

Adamson (1978): The purpose of this study was to determine the relationship between rainfall erosivity and soil loss.

Hamilton (1970): To provide information on the magnitude of production loss of wheat that could be expected as a result of sheet erosion.

Methods (brief)

Adamson (1974) monitored two catchment areas of similar size for rainfall, runoff and soil loss. One catchment was treated with soil conservation structures and sown to improve pasture whilst the other catchment remained as a naturalised pasture with a high proportion of native grasses.

Adamson (1978) measured runoff and soil loss from plots 41.5 metres long on an 8% slope under varied crop rotations.

Hamilton (1970) implemented a study across five Research Stations within the NSW wheat belt to measure depressions in wheat yield and quality. The study comprised of three treatments, implemented on 2 blocks within each site:

  1. Control – no soil removed
  2. Three inches of surface soil removed
  3. Six inches of surface soil removed

Three replicates of each treatment were randomized on each of the two blocks. The first block had a wheat-fallow-wheat rotation and the second, a fallow-wheat-fallow rotation.

Key findings (brief)

Adamson (1974)

  • Overall reductions in runoff and soil loss occurred. The overall reduction in runoff is 74 per cent while sediment losses have been reduced by 99 per cent.
  •  Much of the reduction in runoff is attributed to the contour furrows which restrict overland flow and increase depression storage.
  • Effects are greatest in years with below average to average rainfall. When above average rainfall is recorded, annual yields of runoff increase but soil losses do not increase proportionately.
  • During storms, the greatest reduction in runoff occurs for the earliest part of the storm. With increasing depths of precipitation the effect of runoff reduction is less. Eventually rate of runoff may exceed that from the untreated catchment.
  • Base flows commence at higher discharges and have lower recession values than do base flows from the untreated catchment.

Adamson (1978)

  • The highest monthly soil loss occurred in April, a period of high rainfall erosivity. This coincided with the late fallow-early crop phase when soil tilth was very fine, surface conditions were smooth and vegetative cover was minimal.
  • The second highest average monthly soil loss occurred during February, which has the highest rainfall erosivity.
  • Rough fallows provide soil protection.
  • Small soil losses occurred in October which has similar rainfall erosivity to February. The crop is well developed at this stage and therefore provides further soil protection.

Hamilton (1970)

  • The removal of top-soil depressed wheat yields and brought about a decline in wheat quality. When 3 inches of soil was removed wheat yields dropped by 20 to 50% and protein percentage of the grain by 5 to 20%.

 

Table 1. Catchment conditions, mean annual runoff (mm) and sediment loss (t/ha) and derived sediment concentrations for two pasture catchments near Wagga from 1952 – 1973 (Adamson, 1974)

Treatment

Slope length

m

Slope

%

LS

Runoff 

mm

Sediment loss t/ha

EMC 1

gm/L

Normalised2 Soil loss

t/ha

Normalised3 EMC

gm/L

Soil conservation measures

360

12.5

6.3

7.6

0.018

0.233

0.062

0.8158

Untreated

360

10.6

4.8

28.4

1.65

5.815

0.344

5.810

1 Soil loss divided by runoff, primary sediment source, no allowance for deposition.

2 USLE factor used to correct normalised data to an LS =1

3 EMC normalised to an LS =1

Location

Wagga Wagga Soil Conservation Service Research Station 35oS, 147oE

Related studies

Hamilton (1970) documented similar studies at Cowra, Wellington, Gunnedah and Inverell  Soil Conservation Research Stations.

 

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