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Grazing for pasture management - annual pasture zone

P.T. Doyle, M. Grimm and A.N. Thompson

Department of Agriculture, Albany WA 6330


Pasture growth rates vary considerably with seasons. Varying management practice is the best, and perhaps the only way, of coping with seasonal variability. Season and management can have more influence on pasture production than do introductions of new species or cultivars of pasture plants. The value of fertilisers depends on the efficiency of pasture utilisation, within the limits set by seasons. The ultimate objective in growing pasture is to produce a specified animal product, while sustaining those pastures.

Traditional set stocking practices rely on assuming mean plant growth rates over many seasons, yet between season variation gives rise to considerable variation in animal product, pasture production and composition. Stocking rate trials have often applied the same treatments to plots, year in year out, without taking into account seasonal effects. Ideally we should be matching demand and grazing pressure (i.e. animal feed consumption rate) to plant growth rate.

Rather than describe grazing management as a "system", such as a set stocking system, it may be worthwhile defining the criteria for tactics that can be used in response to observed events or conditions as the season progresses. Definition of the tactics must include their effects on objectives for animal production, and pasture growth.

Early in the growing season when the main risk factor is overgrazing, the main alternatives are; deferment of grazing until a critical plant mass is reached, nitrogen applications to grass/ broadleaf dominant swards, pest control, and strip (ration) grazing. The choice of tactics depends on what happened in the previous spring, summer, and autumn. Late in the season the main risk factor is undergrazing and the main alternatives are; intensive grazing, strip grazing, pasture manipulation (physical or chemical topping), fodder conservation and pest control. In the annual pasture zone cropping is an important part of the rotation. Cropping may result in productivity penalties on the pasture in the following year due to reduced plant density, loss of grasses, and less legume seed set under the crop. Tactics are needed to deal with these effects.

We conclude that grazing management needs to be flexible to cope with seasonal variability, in order to produce a specified animal product (live-weight, fertility, fibre characteristics). Research objectives should be to;

Define critical values of feed on offer for optimising objectives for animal production, pasture growth rate, utilisation of dry matter, and acceptable seed production for pasture persistence. The critical values to achieve different pasture growth potentials need to be defined.

Criteria need to be developed for pasture assessment and animal measurements that allow choice of the best grazing tactics. These skills must be something that farmers can learn and use.

`Decision trees' are needed that enable best-case/worst-case projections to be made for a season, and that can be updated with actual measurements on a monthly basis through the season. The purpose is to plan for best-bet grazing tactics, since many stock factors cannot be changed at short notice. Current computer models of pasture growth are not robust enough in their predictions for annual production, but may be useful for short period projections with input from regular animal and pasture monitoring.

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