Estimated reading time: 6 minutes
In Part 1 of this short series, I discussed the characteristics of different grass species. This article takes a closer look at the interaction between the grazing animal and the different grass plants available for grazing.
Every farm and every camp contains different grasses that can be classified as palatable, semi-palatable and unpalatable. In addition, the grazing pattern animals will follow will be different for each.
Grazing patterns of animals
Animals are able to ‘sense’ the differences between different grass species and different plant communities. When they enter a well-rested camp where all the grasses (palatable and unpalatable) are grown out (Figure 1), they will start selecting the more palatable species and the more palatable areas in the camp first.
The palatable species will be grazed during the first few days and later on, as the leaves of the palatable ones become fewer, the animals will gradually start grazing the more semi-palatable species. This grazing pattern is illustrated in Figure 2.
If animals remain in the camp for a longer period, they will start grazing the unpalatable species too (Figure 3), which can result in overgrazing.
As stated earlier, if the animals remain in the camp for too long, they will overgraze the veld, which will damage the palatable species as they will be grazed too short. Less harm will be done if the animals are taken out before they start grazing the unpalatable species (Figure 2). This is called the take-half-leave-half approach.
Take-half-leave-half approach
The theory behind the take-half-leave-half approach is that palatable grasses are selected before and on a bigger scale than semi-palatable and unpalatable grasses. Figure 4 illustrates to what level the different grasses should be grazed. Only half of the semi-palatable and two-thirds of the palatable grasses should be removed, and the unpalatable ones should not be grazed. The palatable grasses should not be grazed down to ground level (at least 10cm of the tuft should be left).
If animals remain in the camp for too long, overgrazing of the palatable and semi-palatable grasses can cause permanent damage to the veld. Figure 5 gives an indication of the difference between ungrazed veld (a), the take-half-leave-half concept (b), overgrazing (c) and severe overgrazing (d).
Effect of overgrazing on grass
The leaves of the grass plant act as ‘food factories’. They produce sugar and starch, which are the energy sources used for the growth of the grass tuft. When plants are grazed moderately, enough sugar and starch can be produced to feed the entire grass tuft. The excess energy will then be stored in the roots and in the base of the tufts, mainly during late summer and autumn. This stored energy is essential for overwintering (when no energy is produced) and for regrowth during the start of the following growing season.
When an area is overstocked with grazing animals, it will lead to overgrazing of the grass plants. If animals defoliate the same tuft repeatedly the leaves will be grazed too frequently and too short, and sugar and starch (energy) production will decline. In such a situation the energy reserves that were stored in the roots during the previous autumn will be utilised. The roots might then die off because of energy depletion. If overgrazing continues, the entire grass plant will die. That is the main reason why some parts of South African veld are in such a poor condition.
Figure 6 illustrates what happened to the roots of plants under different grazing intensities.
The plant on the left-hand side of the figure was defoliated (grazed) every three weeks, to a height of 14cm, and the results showed that a strong root system was left. On the right-hand side the plant was also defoliated every three weeks, but to a height of 2cm. It is clear that this plant was overutilised, resulting in a decline of the root system. In future this plant will therefore experience poor growth. The root system in the middle is that of a plant grazed to a height of 8cm, which was less harmful to the root system.
Veld rest
Veld rest is a crucial management principle. The consequences of overgrazing or overutilisation, as explained earlier, have emphasised the need for regular periods of rest to maintain the vigour of grass tufts.
It is also beneficial to the animal, as they can graze young, nutritious plant material in the form of regrowth after a short rest. However, this can only apply if the stocking rate is realistic, in which case the palatable grasses are not grazed too severely. Proper veld rest is possible by applying the take-half-leave-half approach, in which case a good grazing camp system is important. – Prof Chris Dannhauser, Stockfarm
For enquiries, contact Prof Chris Dannhauser on 082 873 4736 or email chriswei@vodamail.co.za.
