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A method used in Australia for estimating stocking rates

R.A. PERRY * and D.G. WILCOX **

(*) R.A. Perry, Chief, Division of Land Resources Management, CSIRO LRM, Private Bag, Wembley WA 6014 Australia.

(**) D. Wilcox, Senior Adviser, Rangeland Mgt. Section, Jarrah Rd., South Perth, Western Australia 6151.


Reference


SUMMARY

A rapid, approximate method of estimating stock carrying capacities of rangelands is described. The known carrying capacity of a selected common land type is used as a standard. The carrying capacity of other land types is estimated by multiplying the standard by a series of ratings for rainfall, slope, soil, ground vegetation, browse and range condition. Separate estimates are made for good years and drought years.

The concept of fixed carrying capacities for various types of land is undesirable for many reasons. However, there are occasions when estimated stocking rates are required by decision makers, e.g. to assess alternative strategies for management or development.

The general features of a method developed in Australia (by the New South Wales Soil Conservation Service) could be adapted for use in Africa. The method is simple and uses practical experience rather than research results. Estimates can be upgraded easily if new information becomes available.

The method has been used in the Alice Springs district of Central Australia, where mean annual rainfall is 150 mm in the south and 350 mm in the north, mainly falling in summer. The rangelands have been mapped into broad land types.

The most widespread of these types (mulga land) was chosen as a standard. Mulga land has a flat topography with red clay loam soils about 1 metre deep. The ground vegetation is mainly annual grasses and fortes with some perennial grass. Browse shrubs (mulga) from 3 to 5 m high occur at about 300 shrubs/ha.

From practical experience areas of mulga land in good condition with a mean annual rainfall of 250 mm have a stocking rate of about 3 cattle/km² in years of average or better rainfall, and 1 cattle/km² in drought years. This figure of 3 cattle/km² was used as the standard, and the estimated stocking rates of all other land were determined relatively by applying a series of factors. Two estimates were made: 1) for average and better years and

2) for drought years.

The factors used were:

Mean rainfall
Slope (mainly for water runoff or runon)
Soil (depth and stoniness)
Ground vegetation
Browse vegetation
Range condition

For the mulga land described above in good condition under a mean annual rainfall of 250 mm, all these factors were given a value of 1. A value of each factor for other types was estimated from the best information available.

For example, the values of the factors for another type of land with different characteristics could be:

Characteristics

Ratings

Good years

Drought

Mean annual rainfall - 300 mm

1.2

1.2

Slope - gentle, some runoff

0.8

0.8

Soil - sandy, 60 cm depth

0.8

0.8

Ground vegetation - annuals

0.9

0.9

Browse - good cover of desirable species

0.9

1.3

Range condition - medium

0.5

0.5

Product

0.31

0.25

The product of the ratings for good years is:

1.2 × 0.8 × 0.8 × 0.9 × 0.9 × 0.5 = 0.31

The estimated stocking rates for this range type are then calculated by multiplying the stocking rates of the standard by the product, for example, in the above case:

Good years 3 X 0.31 = 0.9 cattle/km²
Drought years 1 X 0.25 = 0.25 cattle/km²

Only lands within 8 km of water are considered; any land beyond 8 km from water is given zero stocking rates.

The method is approximate, but has the advantage of being quick and using only simple practical information.

Reference

CONDON (R.W.), NEWMAN (J.L.) and CUNNINGHAM (G.J.), 1969. Soil Erosion and Pasture Degradation in Central Australia. Part III; The Assessment of Grazing Capacity; Journal Soil Conservation Service of New South Wales. Vol. 25: pp. 225-295.


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