Ref ID : 292
786. Du Plessis, M.C.F. Grondagteruitgang/Land degradation. Symposium on
agriculture and pollution.Anonymous Anonymous Pretoria: 1985. The non-
agricultural activities of man compete with agriculture for land. The demands
on land made by increasing urban, industrial, mining, recreation and other
developments, and the attendant infrastructure - largely the result of a fast-
growing population - leave an ever-shrinking area for producing food and fibre.
Higher yields per unit will be required in future. Land use selection will need
to be based strictly on information provided by impact studies which predict the
effects that various uses will have on agriculture. A long-term master plan for
land use in the RSA is needed. The physical (e.g. soil erosion, compaction),
chemical (e.g. soil acidification, salinization) and biological (e.g.
undesirable invader plants, eelworm infestations) degradation of soil are caused
by incorrect management practices, which usually are a reflection of defective
farm management expertise. Purposeful, dynamic extension, properly supported by
research, and an intensified application of the law, will undoubtedly help to
reduce and prevent soil degradation. Aug .
Reprint : Not in File,
Keywords : SOIL EROSION; LAND DEGRADATION; DESERTIFICATION ASSESSMENT;
POLLUTION; POPULATION; LAND USE; EROSION; SALINIZATION
Ref ID : 444
787. Du Plessis, M.C.F. Grondagteruitgang/Land degradation. SA Tydsrif vir
Natuurwetenskap en Tegnologie 5(3):126-138, 1986.
Reprint : In File,
Keywords : SOIL EROSION; LAND DEGRADATION
Ref ID : 293
788. Du Plessis, M.C.F. and Mostert, J.W.C. Afloop en grondverliese by die
Landbounavorsingsinstituut Glen. Southern African Journal of Agricultural
Science 8:1051-1060, 1965.
Reprint : In File,
Keywords : SOIL EROSION; SEDIMENTATION; FREE STATE; RUNOFF; EROSION
Abstract : An experiment is described where water and soil loss are measured
over a period of 14 to 18 years. The experimental ground is 9 X 100 feet with a
5% slope. Natural veld subjected to different forms of treatment, a plot
cultivated with grazing, and different types of ground works and fertilising
were used. The top soil consisted of a red, sandy loam. Results showd that the
greatest amount of water and soil loss occurred on bare soil, while the least
loss and erosion occurred where the veld was protected. The ground which was
reasonably grazed and had been burned showed only loss which overlapped with
that from barren ground. Natural grazing ground which had been used for grazing
but which had not been burned had much less water and top soil loss. The
highest incidence of soil loss occurred from barren ground, followed by that
cultivated with unfertilised maize. The least soil loss was seen to occur with
natural veld and cultivated grazing. Where the veld was protected, soil loss
occurred least.
Ref ID : 1361
789. Du Plessis, S.J. The vital importance to South,Africa of food production by
the white agricultural sector.Anonymous Anonymous Pretoria:Ministry of
Agriculture. :1-29, 1973.
Reprint : In File,
Keywords : POPULATION
Notes : The information presented in this address is intended to show that the
contribution of the white agricultural sector in SA has, with some singular
exceptions, thus far succeeded remarkably well in the onerous task of producing
food in adequate quantities and at reasonable prices for the rapidly increasing
population of this country, even while many other countries of the world are
experiencing serious setbacks in production. The value of such contribution can
hardly be overestimated and should strengthen the close relationship we know to
exist between the urban and rural sections of the population in this country.
Ref ID : 1145
790. Du Plessis, W. In situ conservation in Namibia: the role of national parks
and nature reserves. Dinteria (23):132-141, 1992.
Reprint : In File,
Keywords : CONSERVATION; NAMIBIA; EROSION
Notes : This paper gives an overview of the conservation areas present in
Namibia. Each unit will be discussed in terms of its position, size, main plant
communities, its representativeness in protecting the main vegetation type in
which it is situated, some unique features, specific problems and areas in and
around these reserves that need more urgent attention to prevent genetic
erosion.
Ref ID : 1256
791. Du Preez, C.C. Proceedings 9th National Congress. In: Soil Science Society
of Southern Africa,Anonymous Durban:Department of Agriculture and Fisheries,
1981,p. 50-55.
Reprint : In File,
Keywords : SOUTHERN AFRICA; IRRIGATION; FLOODS
Abstract : The effect of certain tillage treatments and irrigation methods on
soil compaction at Vaalharts was investigated. Four crops were used, viz.
maize, cotton, groundnuts and wheat. The soil is the Annandale series of the
Clovelly form. For each crop a series of four tillage treatments and two
methods of irrigation, i.e. sprinkler and flood, were investigated. To
determine compaction under different treatments, soil strength was determined
with a constant rate penetrometer. Readings were taken at the upper, middle and
lower ends of the beds to determine variation in soil strength over the length.
To determine seasonal variation in soil strength, three readings were taken
during the season. Duplicate penetrometer readings were taken at 20 mm
intervals down the profile to a depth of 460 mm. A mean value was calculated
for each 100 mm. On different tillage treatments zones of lower soil strength
were identified. There was no significant difference between the effects of
flood and sprinkler irrigation on soil compaction. Soil strength did not vary
over the length of beds irrigated by flooding. In the beginning of the growing
season tilled soil had a very low soil strength. Flood and sprinkler irrigation
compacted the soil in such a way that soil strengths increased noticeably during
the season. It was shown that the soil could be compacted to its natural
maximum degree by only two irrigations. The natural maximum compactness of
these sandy soils is sufficiently high for the root development of certain crops
to be restricted. Apart from compaction due to natural causes, that due to
agricultural machinery has the greatest effect. The main offender is the
tractor wheel running in an open furrow. Compaction can best be avoided by a
primary deep tillage combined with minimum secondary tillage. To curb the
compacting effect of tractor wheels, tractor traffic must be controlled.
Ref ID : 1813
792. Du Preez, C.C. and Snyman, H.A. Organic matter content of a soil in a semi-
arid climate with three long-standing veld conditions. African Journal of Range
and Forage Science 10(2):108-110, 1993.
Reprint : In File,
Keywords : CLIMATE; VELD CONDITION; SOIL EROSION; EROSION
Abstract : The effect of maintaining veld in three conditions viz. poor,
moderate and good, for 15 years, on the organic carbon (C) and total nitrogen
(N) content (as measures of organic matter content) of a fine sandy loam soil
was investigated. Composite soil samples were collected and analysed to a depth
of 300 mm at 50-mm depth intervals from plots with the imposed veld conditions.
The organic C and total N content of the soil under the three veld conditions
differed significantly (<0.05). Both variables declined as the veld condition
degraded. Total N differed less than the organic C. The largest differences
were measured in the 0 - 50 mm layer and the smallest in the 250 - 300 mm layer.
Losses of soil organic matter can be attributed to reduced phytomass production,
increased soil erosion and change in soil climate. It is suggested that the
loss of soil organic matter from degraded veld may inhibit veld recovery.
Ref ID : 579
793. du Toit, P.C.V. Veld management to minimize the impact of drought in Natal,
Cedara:Department of Agriculture and Water Supply, 1986.
Reprint : Not in File,
Keywords : DROUGHT; VELD MANAGEMENT; GRAZING EFFECTS
Ref ID : 949
794. du Toit, P.C.V. Stocking rate vs defoliation of karoo bushes. Karoo Agric
5(1):17-21, 1993.
Reprint : In File,
Keywords : CARRYING CAPACITY; GRAZING EFFECTS; STOCKING RATE
Notes : The purpose of this paper is, firstly to test the hypothesis that sheep
select material thinner than 2 mm. This hypothesis was rejected. Secondly, the
paper attempted to determine to what degree this hypothesis can be used as an
indicator of optimum stocking rates. It was found that measurements of grazed
stems of less palatable karoo shrubs can be used to calculate optimum stocking
rates and to monitor applied stocking rates. It is the intention that the work
reported on in this article be expanded to farms where measurements of the
grazed-stem diameters of the dominant species can be supported by known past
animal production stocking rates. The database created this way, can then be
used to monitor applied stocking rates.
Ref ID : 1766
795. du Toit, P.C.V. The grazing index method of range condition assessment.
African Journal Range Forest Science 12(2):61-67, 1995.
Reprint : In File,
Keywords : MONITORING; METHODOLOGIES; KAROO DESERTIFICATION; GRAZING EFFECTS;
CARRYING CAPACITY; PRODUCTION POTENTIAL; VEGETATION CHANGE
Abstract : Owing to the difficulty of examining succession theory in the Karoo,
it is suggested the ecological index method (EIM), be replaced by the grazing
index method (GIM), through the introduction of grazing index values (GIV) for
Karoo plant species. The GIM may provide more acceptable range condition scores
and more realistic estimates of the current grazing capacity. Using GIVs,
arrived at by scoring the agronomic attributes of the plant species
(productivity, forage value, perenniality), the estimated current grazing
capacities are found to be closely similar to the grazing capacity norms
established for the different agro-ecological areas in the Karoo. The manner in
which the range condition survey is conducted and the application of the grazing
index method, ensures the computation of a figure representative of the
agronomic potential of the area to support livestock. The cover figure and the
range condition score determined for a sample site, can be employed in
monitoring the trend in changes in the vegetation, brought about by climatic and
biotic variables. Grazing capacity norms are closely related to median annual
precipitation (r2 = 0.98). The GIM is more closely related to grazing
capacities than the EIM (r2 = 0.96 and 0.68 respectively).
Ref ID : 1285
796. du Toit, P.C.V. Estimating grazing-index values for Karoo plants.Anonymous
Anonymous Pretoria:Department of Agriculture. :1-15, 1995. 0 621 16106 3.
Reprint : In File,
Keywords : METHODOLOGIES; VELD CONDITION
Notes : At present, the Ecological Index Method (EIM), described by Vorster is
used to calculate grazing capacities in the Karoo. The Karoo plant species are
allocated index values on a group basis, giving rise to a disjunct 10, 7, 4, 1
ecological index value series (EIV). The group classification is based on the
ecological importance of the grass species, whilst the index values accorded the
karoo-bush species are based on relative palatibility ratings. These index
values are used when the veld condition scores are computed. The veld-condution
score is an index of the state of health of that portion of veld, alluding to
its ability to sustain animal production. Previous research revealed that the
index values currently used to calculate the veld condition score, may lead to
either over- or under-estimation of the current grazing capacity. The
construction of a single series of index values based on different variables for
different plant groups is inappropriate. However, the greatest disadvantage
lies in the fact that the series makes it impossible to distinguish between
closely related species which have different grazing values. In order to
correct these apparent shortcomings, the index values of the common species in
the Karoo were subjectively adjusted by means of a species-by-species
comparison. The objectives of this paper are: (1) to illustrate the methods
employed; (2) to debate the merits of the methodology used and (3) to supply a
list of index values for various species.
Ref ID : 1373
797. du Toit, P.C.V. Research note Grazing-index method procedures of vegetation
surveys. African Journal of Range & Forage Science 14(3):107-110, 1997.
Reprint : In File,
Keywords : VELD CONDITION; KAROO DESERTIFICATION
Abstract : In the past, veld condition in the Karoo was assessed using the
ecological index method. This recently changed to the grazing index method on
account of the differently estimated grazing index values being used. The
principles governing the method of survey remain the same. The method employs
canopy-spread-cover strikes to record the species composition of different
sites. By appropriate management of these line-point data, different sites can
be compared with one another by employing the Z-index of agreement (similarity).
Ref ID : 1374
798. du Toit, P.C.V. Description of a method for assessing veld condition in the
Karoo. African Journal of Range & Forage Science 14(3):90-93, 1997.
Reprint : In File,
Keywords : VELD CONDITION; KAROO DESERTIFICATION; CARRYING CAPACITY; BOTANICAL
SURVEY; METHODOLOGIES
Abstract : In the past, veld condition in the Karoo was assessed according to
the ecological index method. This has recently been replaced by the grazing-
index method. The principles governing the method of botanical survey remain
the same, but this methodology has not been described in detail. The objective
of this paper is to address this shortcoming. The method is based on canopy-
spread-cover strikes, and these strikes are assumed to represent mass as well as
number of the species. Through the application of the individually estimated
grazing-index values of the different species, the index of veld condition is
computed from either line-point or clipped-quadrat data. With appropriate data
management, both the line-point and the clipped-quadrat data yield acceptable
indices of veld condition, from which values, current grazing capacities, can be
estimated for assessed sites.
Ref ID : 1182
799. du Toit, P.C.V. Die weidingsindekswaarde-tegniek van weikapasiteitberaming:
(3) Tegniekevaluasie. Grootfontein Agric 1(1):28-31, 1998.
Reprint : In File,
Abstract : See the English abstract under ID no: 1183.
Ref ID : 1754
800. du Toit, P.C.V. Effects of grazing and resting treatments on animal
performance and vegetation condition in the False Upper Karoo at the
Grootfontein Agricultural Development Institute, Eastern Cape. South African
Journal of Science 94:507-512, 1998.
Reprint : In File,
Keywords : EASTERN CAPE; VELD MANAGEMENT; RAINFALL; DROUGHT; VELD CONDITION;
GRAZING EFFECTS; RESTORATION; PLANT-ANIMAL INTERACTIONS; CLIMATE CHANGE;
BOTANICAL SURVEY; BUSH ENCROACHMENT
Abstract : The 'Camp Number 6' veld grazing trial was started in 1934 to examine
the best management options for Karooveld. The experiment has served mainly to
demonstrate the effects of various seasonal grazing treatments on the
vegetation. In addition to annual botanical surveys, animals were weighed on a
regular basis. Since this practice was begun, valuable data, which strengthen
generally recommended veld management principles, have been gathered. The year-
rotation (rotational rest) and the three-paddock system generally outperform the
continuous grazing treatments on apronveld. Definite advantages accrue to a
rotational grazing management system by incorporating a year of rest, as the
accumulated forage is carried over for consumption during the following year,
while the vegetation still produces more material to be utilised. Mixing of
different 'veld types' in one paddock and the variable animal production
realised in these treatments underline a basic tenet of the grazing management
philosophy, namely, the separation of veld into homogeneous units in order to
ensure their optimal, individual grazing management. Favourable rainfall
following periods of drought leads to a great increase in annual species, mainly
of Aristida congesta and Aristida adscensionis, which then cover the bare areas
where the veld has degraded. This improves the cover, but due to the low
grazing index values of these species, they have relatively little influence on
improving the veld condition scores, and consequently the grazing capacity of
the land.
Ref ID : 1180
801. du Toit, P.C.V. Die weidingsindekswaarde-tegniek van weikapasiteitberaming:
(1) Tegniekontwikkeling. Grootfontein Agric 1(1):21-23, 1998.
Reprint : In File,
Abstract :
See the abstract in the English translation under Du Toit et al. ref ID no: 1183
.
Ref ID : 1181
802. du Toit, P.C.V. Die weidingsindekswaarde-tegniek van weikapasiteitberaming:
(2) Indekswaardes van sommige plante. Grootfontein Agric 1(1):24-27, 1998.
Reprint : In File,
Abstract : See the English abstract under ID no: 1183.
Ref ID : 1183
803. du Toit, P.C.V. and Botha, W.V. Grazing index method procedures.
Grootfontein Agric 1(1):32-34, 1998.
Reprint : In File,
Keywords : VELD CONDITION
Abstract : In the past, veld condition in the Karoo was assessed by using the
ecological index method. This recently changed to the grazing index method, on
account of the differently estimated grazing index values being used. The
principles governing the method of survey remain the same. Through the
application of the individually estimated grazing index values of the species,
the index of veld condition is computed from the line-point data. Appropriate
management of the line-point data yields acceptable indices of veld condition,
from which current grazing capacities can be estimated for assessed sites.
Ref ID : 1734
804. du Toit, P.F. Acacia karroo intrusion: The effect of burning and sparing.
Proceedings of the Grassland Society of southern Africa 7:23-27, 1972.
Reprint : In File,
Keywords : BUSH ENCROACHMENT; EASTERN CAPE; DROUGHT; FIRE; SAVANNA; GRAZING
EFFECTS; ALIEN PLANTS; MONITORING
Abstract : An investigation was conducted in the Eastern Cape sweetveld to
determine the effect of frequency of burning, extended sparing and controlled
grazing on the establishment of seedlings of A. karroo. After eradication of a
mature A. karroo stand, seedling establishment in the area concerned was
recorded annually in permanent transects on paddocks neither grazed nor burnt,
burnt annually, burnt biennially and burnt triennially. Grazing and resting
treatments were superimposed on the burning treatment. After seven years of
reinvestation of A. karroo was determined on all paddocks and population height
was sampled for evidence of layering. None of the treatments proved effective
in preventing seedling establishment and there was no difference between
treatments, seedling establishment being directly correlated to the original
thorn tree density. Despite severe drought conditions there was a continuous
establishment of seedlings, and at the termination of the trial no layering was
evident in the community. Fire, while not preventing establishment, did retard
seedling development.
Ref ID : 2242
805. du Toit, P.F. Verslag werkgroep: riglyne vir bosbenutting en biologiese
beheer van bos of die voorkoming van bosverdigting. Proceedings of a workshop on
bush encroachment and bush thickening held in Pretoria. Pienaar, A.J.Anonymous
Pretoria:Department of Agriculture and Fisheries. :N1-N4, 1980.
Reprint : Not in File,
Keywords : BUSH ENCROACHMENT
Ref ID : 1829
806. du Toit, P.F. and Aucamp, A.J. Effect of continuous grazing in the Dohne
Sourveld on species composition and basal cover. Journal of the Grasslands
Society of Southern Africa 2(4):41-45, 1985.
Reprint : In File,
Keywords : GRASSLAND
Abstract : In the grazing trial conducted at the Dohne Agricultural Research
Station, natural grassland was grazed continuously for 36 years with cattle. In
a second investigation conducted on similar grassland, paddocks were grazed or
rested, in all combinations of the four seasons of the year, over a ten year
period. Changes in botanical composition and cover of the sward were monitored
at regular intervals. The results of these investigations indicate that under a
regime of non-selective grazing the composition of Dohne Sourveld is remarkably
stable. After 36 years of continuous grazing the species composition of the
sward was largely maintained. Floristically Dohne Sourveld is dominated by a
small number of grass species of which Andropogon appendiculatus, Elionurus
muticus, Heteropogon contortus, Sporobolus africanus, Themeda triandra and
Tristachya leucothrix are the most important. These species react differently
to under-utilization or increasingly severe defoliation, enabling them to be
classified into decreaser or increaser categories. Severe defoliation resulted
in a marked decrease in basal cover but only small changes in relative species
composition. As the intensity of defoliation increases, decrease in grass cover
is associated with an increase of forbs, such as Senecio retrorsus.
Ref ID : 1021
807. du Toit, P.F., Aucamp, A.J., and Bruwer, J.J. The national grazing strategy
of the Republic of South Africa: Objectives, achievements and future challenges.
Journal of the Grassland Society of southern Africa 8(4):126-130, 1991.
Reprint : In File,
Keywords : GOVERNMENT INITIATIVES; VELD MANAGEMENT; VELD CONDITION; SUSTAINABLE
AGRICULTURE; POLICY; CONSERVATION
Abstract : Over the past few years various measures have been applied to address
the problem of the retrogression of southern African rangelands. However, it
has become apparent that many of these measures were ad hoc and not part of a
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