Soil pH Changes under Victorian Pastures

Year of study:

1993

Lead organisation & collaborators (if any):

Department of Agriculture, Department of Conservation and Natural Resources

Contact:

D. M. Crawford

Best available science assessment:

Overall Score: 34

Overall rating: Very high

Objectives

Conceptual model

Study design

Soil analysis

Production & financial

Method reporting

Data analysis

Results reporting

Publication

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Project details

Objectives:

Investigate soil pH changes under long term pastures of various types.

Hypotheses:

The hypothesis is that pasture based management systems affect soil pH. It was assumed the soil pH of undisturbed and ungrazed reference areas is the result of natural processes, while the soil pH of adjacent pastures is the sum of natural processes and anthropogenic effects.

Basis of trial:

To report on changes in surface soil pH in Victorian pastures over a broad range of grazing systems and soils.

Location details:

107 pasture sites across Victoria were assessed. Around a dozen of the sites are located in the Gippsland region.

Sites were selected had a reference (undisturbed) area immediately adjacent to the pasture area, (and the reference area contained little or no volunteer clover) and annual rainfall was greater than 450 mm.

(The sites were also selected base on the following management history criteria. Sites were also classified using simple site characteristics (annual, mixed. Perennial or unimproved pastures))

Pre-trial management:

Sites were selected based on the following management history criteria:

  • Not subjected to physical disturbance other than that necessary for sowing
  • Pasture area had carried pasture for at least 75% of the time since development for agricultural use
  • Current pasture had been established for at least 15 years
  • Not been limed;

Relatively little if any grazing had occurred on the reference area.

Trial Management:

Historical management continued

Management practices tested:

Pasture-based agricultural ecosystems

 

Summary of key findings of the trial:

Acidification was most evident in sites with moderately and slightly acid reference soils. There was no evidence of further acidification in sites with strongly acid reference soils, (pH increased under improved perennial pasture)

Possible causes of acidification or alkalinisation were not clearly evident from the association of site factors with pH changes.

It was evident that site factors were confounded.

Methodology

Trial Design Layout

Measurement areas were established at each site (reference area and cropping area). Sites were generally sampled in autumn or spring. At each site, 20 cores (2.5 cm diam.) were removed from each of the pasture and reference areas, respectively. Sampled areas were approximately 0.01 ha and were within 100 m apart and sampled so as to exclude edge effects.

Soil Sampling Method:

The 01 horizon was discarded from each core before sectioning into four depths (0-5, 5-10, 10-15 and 15-20 cm).

Corresponding depths from 10 cores were bulked within each area. 16 composite samples represented each site. The samples were dried (40┬░C, 4 days) and ground to pass a 2 mm sieve. Soil pH in a suspension (1 :5) of soil and 0.01 M CaCl2 (pH,) or soil and water (pH,) was measured after 1 h shaking, using a glass pH electrode with a KCl reference glass probe.

 

Variation in soil pH with time and management influence:

On average, sites that had annual and mixed pastures showed acidification in the 0-10 cm depth but showed no change in the 10-20 cm depth.

The average for sites with unimproved pastures showed no significant change in soil pH.

The average for sites with perennial pastures showed alkalinization had occurred throughout the 0-20 cm depth.

However, pH, annual rainfall and pasture type appear to be confounded

The number of years since a site was cleared was not related to pH

Reportage

How have results been reported?

Journal article

How a copy of any relevant reports can be obtained:

Crawford D.M., Baker T.G., Maheswaran J. (1994): Soil pH Changes Under Victorian Pastures, Australian Journal of Soil Research, 32, 105-15

http://www.publish.csiro.au/?paper=SR9940105

Level of review of results:

Peer reviewed

Next steps

It is recommended that an understanding of acidification or alkalinisation will only be gained by fundamental studies of C and N cycles of the agricultural ecosystem at individual sites.