Information

Level 4 Data summaries and links to related documents and reports

Key findings

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. Mean annual runoff and soil loss from 1952 – 1973 (Adamson, 1974)

Treatment

Slope length

m

Slope

%

LS1

Runoff 

mm

Soil loss t/ha

EMC 1

gm/L

Normalised2 Soil loss

t/ha

Normalised3 EMC

gm/L

Soil conservation measures

360

12.5

6.3

167.2

0.389

0.233

0.062

0.0369

Untreated

360

10.6

4.8

624.8

36.331

5.815

7.567

1.211

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

 

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