Soil Chemistry and Associated pH Changes in Victorian Pastures

Year of study:

1993

Lead organisation & collaborators:

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:

To determine how the chemistry of pasture soils had changed since the development of pastures and how changes in soil pH were related to changes in C and N cycles.

 

Hypotheses:

Pasture-based agricultural ecosystems affect soil chemistry.

Changes in soil chemical properties were assessed by assuming that the soils found in the reference areas are the result of natural processes while the soils found in the pasture areas are the result of natural processes plus agricultural effects.

Basis of trial:

An earlier paper presented the results of a survey looking at the impacts of pastures on pH. This analysis seeks to identify specific site factors that contribute to soil acidification.

Location Details

Management practices tested: Pasture-based agricultural ecosystems

Trial Site 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

Summary of key findings of trial:

Changes in total soil P and electrical conductivity were not associated with changes in pH.

Changes in soil organic C or total soil N, representing the C and N cycles, were not associated with soil pH changes in permanent dryland pastures. (It could not be concluded that these cycles do not contribute to acidification and alkalinization of pasture soil.)

The consequences of soil acidification have been an undesirable increase in extractable A1 and Mn, and loss of exchangeable cations, especially exchangeable Mg.

Trial Design:

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:

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.

Treatment results:

Variation in soil C with time and management influence:

Soil organic C was not found to have changed in mixed, perennial or unimproved pastures in general

Variations in soil pH with time and management influence:

Changes in soil pH were not associated with changed in total soil P, total soil N, or soil organic C.

Other measures of treatment response:

The amount of total P in improved pastures (annual, mixed and perennial) was found to have significantly increased compared with the reference area.

Increases in total N were found in mixed and perennial pastures.

 

 Reportage

How results have been reported:

Journal article

How a copy of any relevant reports can be obtained:

Crawford D. M., Baker T.G., Maheswaran J. (1995) Changes in Soil Chemistry Associated with Changes in Soil pH in Victorian Pastures, Australia Journal of Soil Research, 33, 491-504

http://www.publish.csiro.au/?paper=SR9950491

Level of review of results:

Peer reviewed

Next steps

The causes of soil pH changes would be better determined by investigations of these cycles at selected sites.

The application of Ca in superphosphate may be important to the loss of exchangeable Mg and may result in nutritional deficiencies in plants or animals.

Analysis of soil below the 20 cm depth is needed to assess cation reserves within reach of plant roots.