THE USE OF CUTTING TREATMENTS DESIGNED TO SIMULATE DEFOLIATION BY SHEEP

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Abstract
A series of cutting treatments was designed to simulate the defoliation process under sheep grazing, in order to obtain more accurate measures of the production processes in the sward than can be obtained in the presence of the grazing animal. Two rotational grazing managements were simulated, together with three continuous grazing managements involving the maintenance of a roughly constant LAI within a sward, as described earlier (10). Harvested yield was measured, and the dry weight of material which died without heing harvested was estimated. From these, gross aerial growth, i.e., the amount of new living material produced in the sward, was calculated. The maximum harvested yield was obtained by rotational defoliation to 3 cm every 4 weeks, hut this was derived from the minimum gross aerial growth. Maximum gross aerial growth occurred under the simulated continuous grazing treatments at the higher levels of LAI. This difference was due largely to the death and subsequent decay of leaves. Up to 50% of the material which grew was lost in this way. The need to distinguish between growth and harvested yield when evaluating grazing managements was stressed.