Bibliography: Land Degradation in South Africa project

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.

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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.

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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.

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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.

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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.

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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.

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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