agricultural production guidelines
m
Veld in KwaZulu-Natal
Co-ordinated Extension KwaZulu-Natal Veld 6.3 1999
INTERPRETATION OF VELD CONDITION DATA
M B Hardy
Western Cape Department of Agriculture
Stocking Rate
Rotational Grazing
Rotational Resting
Veld Burning
INTRODUCTION
Veld condition data will assist the farmer to assess the potential of the veld for livestock production, as well as to formulate veld management practices. Recommendations regarding stocking rates, grazing systems (such as rotational grazing and rotational resting) and veld burning may be derived from a knowledge of veld condition. The concept of veld condition, and the assessment of veld condition are covered in Production Guidelines 6.1 and 6.2, respectively, in this series.
The stocking rate set by the farmer should be guided by the estimated current grazing capacity. Current grazing capacity (CGC) is calculated according to various formulae, the most common of which is:
CGC = PGC x X
where PGC represents the potential grazing capacity of the benchmark, and X represents a numerical rating for the site. The PGC’s of veld in KwaZulu-Natal has been estimated for each Bioresource Group, and are presented in Table 1. The values presented in Table 1 were derived for veld in benchmark condition (refer to the species lists for benchmark sites in Production Guidelines 4.2 to 4.10 in this series). Most farms will not achieve this potential even if species composition and basal cover are equal to the benchmark, because factors such as steep topography and erodible soils will tend to reduce the capacity of the veld to carry animals. Furthermore, in most cases, the species composition and basal cover of veld are poorer than the benchmark. The current grazing capacity of veld is therefore generally somewhat lower than the figures presented for the benchmark in Table 1.
An adjustment is made for these site factors, and takes the form of value of the ‘numerical rating’ (X) provided in the above equation. This numerical rating is derived in the following manner.
Table 1. Potential grazing capacities of benchmark sites in the Bioresource Groups of KwaZulu-Natal (data adapted from Tainton, Edwards & Mentis, 1980).
Bioresource Group
Max.
(AU/ha)Min.
(ha/AU)1 & 2
3, 4 & 17
5, 6 & 7
8 & 9
11,12 & 15
13,14 & 16
18
19 & 20
21, 22 & 23
Coast Forest and Palm Veld
Coast Hinterland Ngongoniveld & Thornveld
Midlands Mistbelt & Northern
Highland Sourveld
Moist Tall Grassveld
Dry Tall Grassveld
Mixed Thornveld
Zululand Thornveld
Lowveld and Valley Bushveld & Sandy Bushveld
0.5 - 0.6
0.6 - 0.7
0.6 - 0.7
0.6 - 0.7
0.6 - 0.7
0.4 - 0.5
0.5
0.4 - 0.5
0.3
1.8 - 2.0
1.5 - 1.8
1.5 - 1.7
1.5 - 1.7
1.5 - 1.8
2.1 - 2.7
2.1
1.9 - 2.3
3.5
- Composition factor (CF). The species composition of the site is scored by undertaking a botanical survey and veld condition assessment (refer to Production Guideline 6.2 in this series). The score represents the composition factor in the equation below. It has been scaled to provide a maximum value of 0.33, a value which applies to veld that is in excellent condition (i.e. equivalent to the condition of the benchmark site). As the composition declines, so the value for the composition factor is decreased.
- Topographic factor (TF). Site topography is taken into account by applying the following values to the sample site, as appropriate:
TF = 0.33 if slope is 0 to 5%, provided that it is not a drainage channel;
TF = 0.26 if slope is 5 to 15%;
TF = 0.13 if seasonally wet;
TF = 0.00 if slope is >15%, or if it is a drainage channel, or if it is severely eroded.
- Soil erodibility factor (SEF). Soil erodibility is taken into consideration as follows:
SEF = 0.0417F - 0.0417
where F is the soil erodibility rating derived from Table 2. These ratings are then incorporated into the following equation:
X = CF + TF + SEF
and the current grazing capacity (CGC) of the site is then calculated as:
CGC = PGC x X
An alternative method for calculating current grazing capacity is presented in Production Guideline 2.5 of this series.
Table 2. Soil erodibility and F-ratings on a gradient from deep or clayey soils to shallow or sandy soils, and associated SEF values.
|
Soil type |
Erodibility rating |
F-rating |
SEF |
|
Deep, permeable, leached, organic and clayey ... ranging to ... Shallow, impermeable, not leached, sandy and with little humus |
Very low Low Moderate High Very high |
>6.0 5.0-5.9 4.0-4.9 2.5-3.9 <2.5 |
0.33 0.26 0.20 0.11 0.00 |
Rotational grazing is the successive occupation of different camps by a group of animals during the year so that not all the veld is grazed simultaneously. Two forms of rotational grazing are discussed in Production Guideline 9.2 in this series, viz. controlled selective grazing (CSG), or high production grazing (HPG); and non-selective grazing (NSG), or high utilization grazing (HUG). The use of these different forms of rotational grazing depends on the condition of the veld and specifically the dominance of the different categories of grass species (i.e. decreaser and increaser species). Besides applying the correct form of rotational grazing, appropriate adjustments must also be made to the stocking rate.
This represents veld in ideal condition for livestock production. The application of a CSG system will ensure a high production of good-quality forage, good animal performance and the maintenance of the veld in good condition. However, a periodic severe defoliation is required to maintain the veld in a Decreaser stage. In sourveld and mixed veld areas, fire is the most effective means of applying a severe defoliation, and would normally be used once every four years. In sweetveld areas, a severe defoliation in the form of NSG should be implemented once every three or so years (Trollope, 1986).Decreaser dominated veld
Increaser I dominated veld
This refers to veld which has been understocked or
selectively grazed. In order to promote a dominance of the more desirable
Decreaser species, it is necessary to apply NSG. This should be combined with
veld burning, or the provision of nitrogen/protein licks, so as to minimise
any negative effect that NSG may have on animal performance.
Increaser II dominated veld
Veld that has been overstocked results in the
removal of Decreaser and Increaser I species from the system, and their
replacement by pioneer Increaser II species. The application of CSG will
favour the less abundant Decreaser species and encourage these species to
dominate the sward. Such grazing management will also ensure good animal
performance.
Patchy Increaser I and II dominated veld
This veld develops in situations where there are a
few large camps in the grazing system, and either continuous grazing, or a
very extensive form of rotational grazing, is applied. Both result in
selective grazing, which encourages Increaser I species in non-selected areas,
and Increaser II species in repeatedly-selected patches. Species of both these
Increaser categories predominate in patches due to the uneven utilisation of
the Decreaser species in the sward. Both are generally less productive and
less palatable than Decreaser species.
Veld condition can be improved in patchy Increaser I and II dominated veld by subdividing the large camps to form a multi-camp system, and applying a combination of NSG and CSG. NSG can be combined with either veld burning or the provision of nitrogen/protein licks to improve animal performance, and to achieve uniform grazing, as described earlier. This treatment should be applied for a maximum period of no more than two growing seasons, after which CSG should be applied to encourage the Decreaser species. The NSG treatment will have the effect of severely defoliating the Increaser species, at least some of which are less tolerant of grazing than the Decreaser species, while the vigour of the Decreaser species will be improved during the period that CSG is applied.
Rotational resting is the successive withdrawal of camps from grazing on a rotational basis for specific purposes. The principle reasons for resting veld are for seeding, the restoration of vigour, or to provide a fodder reserve for periods of scarcity. Where bush encroachment is a problem, rests may be applied to build up a fuel load to permit the application of a hot fire.
These rests are not normally required in sourveld and some mixed veld areas. In sweetveld, a seeding rest is applied when the Decreaser species have declined in abundance in the grass sward. Such a rest is therefore appropriate when either Increaser I or Increaser II species predominate, but, in practice, is more important in veld that has been overstocked and where there is a serious lack of Decreaser grass species, and the basal cover of the sward is very low. Generally, the most widely applicable rest period for veld in this condition is from January to January, because it maximizes the production of seed by redgrass (Themeda triandra), the most important and widely-distributed Decreaser species in the veld.Seeding rests
Vigour rests
Resting the veld to restore plant vigour is
necessary in sourveld, mixed veld and sweetveld, and under all veld
conditions. Such rests are aimed principally at the Decreaser species. In the
sweetveld areas, this necessitates resting the veld for a full year so that
the grass plants can grow to maturity, at which stage they are still valuable
forage for livestock. In the mixed veld and sourveld areas, a shorter rest,
comprising the late summer and autumn period (January to April), is adequate
for this purpose, and reduces the extent to which the grass becomes mature and
unacceptable to livestock. A full season's rest should also be applied in
mixed veld and sourveld where such rests are required, particularly where
sheep form an important part of the grazing system.
Reserve fodder rests
A fodder reserve rest is necessary under all veld
conditions, but enjoys priority when the veld is in excellent condition and
seed production is not important. It is intended to provide a fodder reserve
for that time of the year when there is the greatest likelihood of a fodder
deficiency. In most veld types, this occurs during late winter to early spring
(August to September). In the sweetveld areas, the most appropriate rest
period for this purpose is from July to July, while in the mixed veld and
sourveld areas, it is from January to July. When applying these rests it is
important to use NSG beforehand so as to ensure that only relatively new,
nutritious forage is available to the animals at the end of the rest period.
Veld condition data can be used to indicate whether or not veld burning has been used effectively in the past, and whether or not it now has a role to play. Burning should be used, in combination with NSG, when the veld is dominated by Increaser I species. Such treatment is designed to promote the vigour and growth of Decreaser species which require regular defoliation. Burning may also be necessary in Increaser II dominated swards (e.g. when they have been allowed to grow out), since, if left undefoliated, they will actively shade out the more heavily-grazed Decreaser species.
GENERAL
Besides providing insight into which veld management strategy is the most appropriate for the farm, veld condition assessment has several other potential advantages.
- C The farmer gains an intimate knowledge of the farm.
- C Different areas of the farm may be divided into management units based on a knowledge of the species composition, topography, soil erodibility, and, particularly in the drier regions (e.g. savanna), plant density or basal cover. Areas prone to bush encroachment may be identified, and management designed to reduce these processes could be implemented. Areas sensitive to grazing can be identified and separated from those areas more tolerant of grazing.
- C Veld condition assessment provides a powerful tool for monitoring the effects of grazing and fire management on the veld. Firstly, when purchasing a farm, veld condition should be evaluated to determine whether the potential of the veld for animal production will provide an acceptable return on capital invested. If the farm has been severely overgrazed for many years it may require several years of lenient utilization and regular fires to improve its forage production potential. For the first few years, therefore, the new owner may have to accept a relatively low level of animal production from the veld. Secondly, a farmer who designs a management system to improve or maintain the species composition of the veld could evaluate the results of such management by conducting regular veld condition assessments (e.g. every 4 years). The Weighted Key Species approach, discussed in Production Guideline 6.2 in this series, may be used for monitoring purposes.
The use of veld condition assessment, together with an understanding of the principles of good veld management, will assist the farmer in maintaining a stable fodder supply (and therefore sustained animal production), whilst conserving the vegetation and preventing excessive soil erosion.
LITERATURE CITED
TAINTON, N.M.; EDWARDS, P.J. & MENTIS, M.T. 1978. A revised method for assessing veld condition. Proceedings of the Grassland Society of southern Africa 15:37 - 42.
TROLLOPE, W.S.W. 1986. Land use surveys: assessment of veld condition in Ciskei. Republic of Ciskei National Soil Conservation Strategy 1.