Information

Impacts of soil conditions on hydrology and water quality on a brown clay in south west Queensland - Wallumbilla (1983-2000).

Level 1 - General description

Purpose

The study was designed to quantify hydrology, water quality and erosion, and production impacts of alternative stubble management strategies (burning, disc incorporation, sweep tillage and zero tillage -chemical weed control).

A range of surface conditions were created with different tillage and crop practices to explore functional relationships between soil surface conditions, runoff, erosion and soil water storage.

Further, a rainfall simulator was used to examine the influence of different management options on infiltration of rainfall and runoff.

Methods (brief)

Soil water, runoff, suspended sediment and crop production were monitored on four contour bay catchments (4-6 ha) (1% slope) over a 17 year period (1983-2000) to examine the influence of soil surface conditions. The site was chosen to represent a wide range of clay soils with high water holding capacity, where fallowing to store water for crop production is an essential risk management tool.

The soil at the site is described as a brigalow/belah clay. The soil was dry with some cracks present. The site had light standing stubble (1000 kg/ha) and had not been cultivated.

A rainfall simulator was applied to the following four plots:

A) No-till/high cover similar to B but with some extra stubble to recreate conditions which might have occurred with higher wheat yields (cover 90%)

B) No-till/cracked was not cultivated, some cracks were present standing stubble (cover 60%)

C) No-till/low cover similar to B except stubble was mostly removed to simulate grazing (cover 10%)

D) Scarified was ‘cultivated’ with a shovel to create conditions similar to those left behind a scarifier. The soil surface was furrowed (cover 30%)

Key findings

Accumulation of soil water in fallows was inefficient, with fallow efficiencies ranging from –7 to 40% due to high evaporation and runoff losses. Runoff amount was determined by soil water content, which was strongly influenced by antecedent rainfall, water use, and evaporation patterns. Surface cover and roughness had subtle influences on runoff, and a greater effect on suspended sediment concentration. Runoff and suspended sediment losses were considerably lower under pasture than cropping.

Table 1: Summary of Average Annual Runoff and Soil Erosion for Wallumbilla ROSL study. Howleaky simulation results presented for trial period and long term annual average.

Description of Management system

Observed

(1983-1995)*

Predicted

(1983-1995)

Predicted

(1900-1995)

Cover

(%)

Runoff

(mm)

Sediment loss

(t/ha)

Runoff

(mm)

Sediment

loss

(t/ha)

Runoff

(mm)

Sediment

loss

(t/ha)

Chisel tillage (1983-1995)

 

10-50

53

3.1

54

6.7

65

6.7

Scarify tillage

 

 

 

 

53

6

64

5.5

Minimum tillage(1983-1995)

 

20-60

47

2.5

50

4.4

63

2.6

Pasture (A condition) (1990-1995)*

 

50-95

9.4

0.2

13

0.5

31

0.6

Cultivating soil which has cracks decreases infiltration and increases runoff (Figure 1). Removal of stubble increases runoff, a similar effect to cultivating this soil when cracked.

Full details in Freebairn DM, Wockner GH, Hamilton NA, Rowland P (2009). Impacts of soil conditions on hydrology and water quality from a brown clay in the north-eastern cereal zone of Australia. Australian Journal of Soil Research. 47: 389-402

Location

The site at Fairlands, Wallumbilla, Lat is 149°06E and Long is 26°28S

Related studies

Greenmount – A study of soil erosion on a Vertosol of the Eastern Darling Downs, QLD

Greenwood - A study of soil erosion on a Vertosol of the Eastern Darling Downs, QLD

 

Level 2, level 3, level 4 and level 5