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Productivity and properties of red and grey gradational soil types in the Victorian wimmera

W.K. Gardner, R. Flood, J. Carter, T. Young, S. Drum, and M. Jasper

Wimmera Research Station, Private Bag 260, Horsham VIC 3401

The main soils cropped in the Victorian Wimmera are gradational clays, and it has long been recognised by farmers that there are considerable differences in crop performance on different types.


Wheat was sown during 1990 at two sites (site 1 "black" soil, Northcote Ug 5.24, site 2 "red" soil, Northcote Ug 5.34) approximately 20 km apart in the western Wimmera region of Victoria using identical management. Root growth was assessed using the core break method at maturity (1). Soil moisture was measured gravimetrically at flowering and maturity. Soil cores (5 cm) were taken to 140 cm and separated into 20 cm increments and analysed for a range of chemical and physical properties.

Results and discussion

Yields at site 1 averaged 3.65 Oa, whereas at site 2 yields were only 1.42 Roots had on average penetrated to 115 cm at site 1 but only 88 cm at site 2 and soil moisture decreased between anthesis andinaturity to a depth of 120 cm at site 1 but only to 80 cm at site 2. Standard chemical and physical tests revealed only minor differences between the two soils, but marked differences were apparent when the electrical conductivity of saturated extracts (EC.) were measured (Fig. 1).

Figure 1. Electrical conductivity of saturated extracts of two soils from the western Wimmera. Yield of wheat is reported to be reduced when EC exceeds 6.0 dS/m (2) and although the values are higher for the red soil, they do not explain the yield differences observed.A hypothesis has been developed that the subsoil structure of the red soil has deteriorated due to infiltration of rain water and dispersion of the unstable clay, resulting in a massive plasticine- like zone which prevents root growth of annual crops and pastures.


Ellis, F.B. and Barnes, B.T. 1980. Plant and Soil 55, 283-295.2.

Maas, E.V. and Hoffman, G.J. 1977. J. Irrig. Drainage Div., ASCE 103 (IR2), 115-34.

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