Defoliation Frequency of defoliation has a major effect on dry matter yield of herbage, herbage quality and sward botanical composition and density. A typical frequency for rotational grazing is every 3 weeks or slightly longer. A typical regrowth period before a silage cut is 6 weeks. The more N is applied, the more frequently should the sward be defoliated. Timing of defoliation can influence botanical composition, by penalizing species which are growing strongly at the time of defoliation.
Timing can affect the extent of stem development.
Yield potential is higher when stems are developing, but the nutritive value of mature stems is low. Severity of defoliation affects herbage production and sward vigour. Disadvantages of a low height of defoliation are that only a small photosynthetic surface is left to support regrowth, the intake of grazing animals is restricted and cut crops dry a little less well and are more likely to be contaminated with soil. Selectivity of defoliation by grazing animals affects the quality and quantity of herbage ingested and the botanical composition of the sward. Sheep and cattle given a free choice between perennial ryegrass and white clover tend to select a mixed diet with perhaps two thirds clover.