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Understanding productivity decline in subterranean clover-based pastures in south-western Australia

Timothy Scanlon1, Len Wade1, Megan Ryan1

1 School of Plant Biology M084, The University of Western Australia, Crawley WA 6009.
Corresponding Author:


Subterranean clover-based pastures are believed to have declined in productivity and persistence over the past thirty years in the southern areas of Australia. This pasture decline has significantly affected the carrying capacity of sheep in areas of the south-west of Western Australia, and thus, animal production for wool and meat has also declined. The basis of this pasture decline is not yet clear. Field and farmer surveys were used as basis for identifying patterns in pasture composition and performance, and their associations with climatic, edaphic, abiotic, biotic and managerial factors. The overall objective was to identify targeted environments with related constraints, examine their characteristics using a multivariate approach, and consider strategies that may be suitable for their alleviation. From a field survey of 96 sites in the south west of Western Australia, pasture compositional data were compared with environmental and nutritional factors to measure impacts on pasture productivity. By understanding pasture composition and related pasture growth, the aim of this PhD thesis is to understand the basis of pasture decline, and the strategies that may be suitable for its alleviation in targeted situations. Pattern of pasture composition are presented.


For at least 20 years, there has been a view that legume-based pastures are declining in productivity, a phenomenon termed “Pasture Decline” (Carter et al 1982). Previous surveys in New South Wales concluded that pasture decline manifested as an increase in weeds and a decrease in pasture legumes as well as fewer grasses and perennials, and that this change in botanical composition resulted in less vigorous pastures (Reeve et al, 2000). In Western Australia, the Department of Agriculture has researched pasture decline and identified contributing factors to be: variable seasonal conditions, increased cropping, increased diseases and insects and inappropriate or lax management such as low grazing intensity (Gillespie, 1983). However, data on pasture decline are limited and are often subjective. A review by Wolfe and Dear (2001) highlighted the lack of evidence on the decline in both legume and total pasture productivity, and suggested that analytical surveys to determine relationships between management and pasture composition would be valuable. A field sampling survey was undertaken in the south-west of Western Australia during the 2004 growing season to collect data that could quantify and identify factors of pasture decline.


Sixteen farms were identified for sampling based on property management factors revealed by a farmer survey conducted June-August 2004. The field samples were taken in a nested design, with two paddocks per farm, three sites per paddock and whole plant samples from each site. The 53 variables measured at each site were statistically processed using the programs R and Genstat to produce a regression tree and nodal grouping characteristics.


The regression tree analysis (Figure 1) split the sites into seven significant groups, indicated by the labels 1 to 7. Each group had differing legume pasture compositions, with compositions differing from site to site, with differences within paddocks of individual farms. Two groups had a high proportion of grass (1 & 2) at the expense of legume. A single group had a high proportion of bare ground (3) with low levels of legume of 6.9%. Two groups had high levels of broad-leaved weeds (4 & 5) which lowered proportions of legume and grasses. The groups 6 & 7 had high proportions of legume, with 7 having the highest proportion of legume at 60.4%. Composition and soil factors, calcium and zinc nutrition, were responsible for the resulting groupings of sites.

Figure 1: Regression tree of legume pasture composition and groups with corresponding levels of percentage legume, grass, broadleaf, and bare ground and the associated soil calcium and zinc nutrition. + very low, * low, ** medium, ***high, **** very high.


Optimal pasture composition is related to pasture legume content, with higher levels occurring in pastures with optimum nutrition and management. By understanding how an individual site’s composition relates to growth through nutritional and management factors, alleviation of pasture decline in targeted situations may be possible. This is currently being investigated. This paper demonstrates that significant site groupings exist with differing compositions. Relationships in pasture growth and improved management strategies are being explored.


Carter ED Wolfe EC Francis CM 1982. Problems of maintaining pastures in the cereal-livestock areas of southern Australia. Proceedings of the 2nd Australian Agronomy Conference Wagga, 68-82.

Gillespie DJ 1983. Pasture deterioration- causes and cures. Western Australian Journal of Agriculture, 3-8.

Reeve IJ Kaine G Lees JW Barclay E 2000. Producer perceptions of pasture decline and grazing management. Australian Journal of Experimental Agriculture 40, 331-341.

Wolfe EC Dear BS 2001. The population dynamics of pastures with particular reference to southern Australia. In Competition and Succession in Pastures (ed. P. G. Tow, Lazenby, A.). CABI Publishing, New York.

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