agricultural production guidelines
m
Veld in KwaZulu-Natal
Co-ordinated Extension KwaZulu-Natal Veld 9.3 1999
RESTING OF VELD
J M B Smith
KwaZulu-Natal Department of Agriculture
Rests Based on
Animal Requirements
Rests Based on Plant
Requirements
INTRODUCTION
Frequent, intense grazing reduces grass vigour and yield. In order to maintain the vigour of the veld, it is necessary to rest the vegetation at certain critical growth stages. The frequency and duration of these rests will depend on the nature and condition of the veld. Rests should provide adequate opportunity for seeding, seedling establishment, restoration of carbohydrate reserves and root growth. Rests may be divided into those which are of short-term benefit to the animal, and those specifically designed to improve the condition of the veld.
RESTS BASED ON ANIMAL REQUIREMENTS
Rests to accumulate sufficient forage
The daily intake of the animal is related to the quantity, quality and height of the sward. After each defoliation, the period of absence should be sufficient to optimise these conditions. Short periods of absence would ensure a high quality of herbage on offer, but would reduce bulk and the height of the sward. Periods of absence will, however, vary in length, depending on the rate of growth and rate of decline in quality of the herbage, if optimum conditions for intake are to be provided at different times during the season.In sourveld areas, where herbage becomes unpalatable relatively early, the period of absence should be fairly short. Although of benefit to the animal, such periods of absence would be of little value to the veld. In the mixed veld and sweetveld areas, where palatability declines at a relatively slower rate, the period of absence can be of sufficient duration to enable plants to develop adequate leaf area to manufacture carbohydrates to ensure continued vigour. The period of absence in the sourveld, the mixedveld, and the sweetveld should be approximately 30 days, 45 days and 60 days, respectively.
Rests to provide out-of-season fodder
Rests may be applied to allow for the accumulation of material for conservation as hay or foggage. The conserved material is used during winter, or as a drought reserve. These rest periods in a planned grazing system could be of benefit to both the plant and the animal. However, caution is needed in the sourveld areas, where over-resting can lead to the degeneration of basal cover, and an undesirable change in species composition.
RESTS BASED ON PLANT REQUIREMENTS
Relatively longer periods of rest are designed to benefit the plant community, with the emphasis on improving the species composition, density and vigour of the sward. Four types of rest may be distinguished in this regard.
This rest is designed to permit the plant to produce leaf material from food reserves in the storage organs, and, through photosynthesis, to replace these carbohydrate reserves. This rest is of particular importance to veld that was severely grazed during the autumn of the previous season. Such grazing would have interfered with the translocation of food reserves into the roots of the plants.Spring rest
Summer rest
The aim of this rest is to promote seed production by species which form seed at this time, as well as to restore reserves. This applies in particular to important species such as redgrass (Themeda triandra), speargrass (Heteropogon contortus) and tridentgrass (Tristachya leucothrix). This rest can also, however, serve a useful secondary purpose in sweetveld areas, where rested veld can be used for winter grazing. During summer, when conditions are optimal for photosynthesis, the large leaf area which accumulates during a rest, allows for the production of adequate quantities of carbohydrates. This energy will, however, be used mainly by the plant for growth rather than for storage in the roots.Autumn rest
This rest is designed to allow photosynthesis to proceed uninterrupted when the plant growth rate has slowed down. This excess energy is then used for root growth, and for the replenishment of reserves which are used for growth at the onset of the following season. Sufficient green leaf area must be present during the autumn rest for the production of carbohydrates. Summer rests which are followed by autumn rests are, therefore, particularly effective in promoting plant vigour. Autumn rests are very necessary where veld has been overgrazed in summer, grazed in winter, or for veld that will be grazed first the following spring.Full-season rest
This rest allows for the physiological functions of the plant to proceed unhindered for the full growing season. It is very applicable in sourveld and mixed veld, as partial rests result in selective grazing due to the sour grasses becoming mature and unacceptable to stock. Therefore the rest is continued through to the end of the season, and the residual material is removed by mowing or burning before the start of the next season. In sweetveld, a full-season rest is particularly beneficial for degraded veld, as it promotes vigour and seed production. It is also used for the accumulation of forage for winter grazing, or to provide a hot burn to control bush encroachment.In the sourveld areas, where perennial grasses are dominant, seeding rests generally are ineffective, as the desirable species germinate poorly and the seedlings are very delicate. Here the aim should be to encourage tiller development in the favoured species by resting in late summer and autumn to allow the accumulation of carbohydrate reserves to proceed. The residual material is then removed (by burning or mowing) to stimulate the development of daughter tillers. The veld should then be rested through the early spring to enable the new tillers to develop and establish themselves.
In the sweetveld, where annuals form part of the sward, rests should be designed to promote seeding and the development of seedlings. Once seeds have been scattered, animals should be introduced to assist in burying the seed. The grazing will also open the grass canopy to allow light into the sward for seedling establishment. In spring, the veld should again be rested to permit the seedlings to become established.
Resting must be planned and applied to meet the requirements of the veld, otherwise it may result in a waste of forage that potentially could be used by animals. Veld which is in good condition may require only the period of absence in a rotational grazing system in order to maintain vigour. This applies, in particular, to mixed and sweetveld, where the periods of absence are relatively long. However, in the sourveld, where the period of absence is relatively short, approximately 25% of the veld should receive a full-season rest each year.
LITERATURE CONSULTED
TAINTON, N.M. 1971. An analysis of the objectives of resting grassveld. Proceeding of the Grassland Society of southern Africa 6 : 50 ) 54.
TAINTON, N.M. 1981. Veld and pasture management in South Africa. Pietermaritzburg : Shuter & Shooter.