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Talore D.G.,University of Pretoria | Tesfamariam E.H.,University of Pretoria | Hassen A.,University of Pretoria | du Toit J.C.O.,Grootfontein Agricultural Development Institute | And 2 more authors.
Plant and Soil | Year: 2015

Background and aims: The Karoo biomes of South Africa are major feed resources for livestock farming, yet soil nutrient depletion and degradation is a major problem. The objective of this study was to assess impacts of long-term (>75 years) grazing during spring (SPG), summer (SUG), winter (WG) and exclosure (non-grazed control) treatments on soil nutrients, penetration resistance and infiltration tests. Methods: A soil sampling campaign was carried out to collect soil to a depth of 60 cm to analyse bulk density, soil physical and chemical parameters as well as soil compaction and infiltration. Results: Generally, grazing treatments reduced soil organic C (SOC) stocks and C:N ratios, and modified soil properties. There was higher SOC stock (0.128 Mg ha−1 yr−1) in the exclosure than in the SPG (0.096 Mg ha−1 yr−1), SUG (0.099 Mg ha−1 yr−1) and WG (0.105 Mg ha−1 yr−1). The C:N ratios exhibited similar pattern to that of C. From the grazing treatments, the WG demonstrated 7 to 10 % additional SOC stock over the SPG and SUG, respectively. Conclusions: Short period animal exclusion could be an option to be considered to improve plant nutrients in sandy soils of South Africa. However, this may require a policy environment which supports stock exclusion from such areas vulnerable to land degradation, nutrient and C losses by grazing-induced vegetation and landscape changes. © 2015 Springer International Publishing Switzerland


PubMed | Grootfontein Agricultural Development Institute, Yale University, Brown University, University of California at Davis and Colorado State University
Type: | Journal: Proceedings of the National Academy of Sciences of the United States of America | Year: 2017

Plant functional traits are viewed as key to predicting important ecosystem and community properties across resource gradients within and among biogeographic regions. Vegetation dynamics and ecosystem processes, such as aboveground net primary productivity (ANPP), are increasingly being modeled as a function of the quantitative traits of species, which are used as proxies for photosynthetic rates and nutrient and water-use efficiency. These approaches rely on an assumption that a certain trait value consistently confers a specific function or response under given environmental conditions. Here, we provide a critical test of this idea and evaluate whether the functional traits that drive the well-known relationship between precipitation and ANPP differ between systems with distinct biogeographic histories and species assemblages. Specifically, we compared grasslands spanning a broad precipitation gradient (200-1,000 mm/y) in North America and South Africa that differ in the relative representation and abundance of grass phylogenetic lineages. We found no significant difference between the regions in the positive relationship between annual precipitation and ANPP, yet the trait values underlying this relationship differed dramatically. Our results challenge the trait-based approach to predicting ecosystem function by demonstrating that different combinations of functional traits can act to maximize ANPP in a given environmental setting. Further, we show the importance of incorporating biogeographic and phylogenetic history in predicting community and ecosystem properties using traits.


du Toit J.C.O.,Grootfontein Agricultural Development Institute | van den Berg L.,Grootfontein Agricultural Development Institute | O'Connor T.G.,South African Environmental Observation Network
African Journal of Range and Forage Science | Year: 2015

Fire is rare in semi-arid eastern Karoo dwarf shrublands, South Africa, and responses to fire are largely unknown. Recent increased grassiness, and hence fuel loads, at Grootfontein in the Eastern Cape allowed an accidental fire (24.3 ha) to carry, and afforded the opportunity to examine compositional and structural effects of fire on a grassy dwarf shrubland. Sampling seven months after the fire, 108 species (102 perennial) were encountered, of which 74 were resprouters, six were fire sensitive (non-sprouters), and the remainder (rare, non-perennial or herbaceous) had an unknown response. The dominant pre-fire shrub, Eriocephalus ericoides, was extirpated by the fire, as was the unpalatable and sometimes invasive Ruschia intricata. All grass species resprouted, and grass became the dominant life-form after the fire, indicating a possible conferred competitive advantage. Resprouting shrubs grew to only a small fraction of their pre-burn size. The unpalatable, aromatic shrub Stachys rugosa was the dominant post-burn shrub. Extirpated species will need to regenerate from seeds, but no seedlings were found in the gaps where shrubs had stood. The widespread ability to resprout confers resilience on this vegetation, but fire does induce changes in structure, in the dominance of life forms, and it decreases canopy cover. © 2015, Copyright © NISC (Pty) Ltd.


du Toit J.C.O.,Grootfontein Agricultural Development Institute
African Journal of Range and Forage Science | Year: 2014

Themeda triandra Forssk. is a common perennial grass in southern African grasslands that tolerates low nutrient soils. Establishment of the species into degraded or transformed areas is difficult, but there have been some advances with clonal propagation using tillers. To generate propagules (tillers), tiller production of plants must be maximised. This research focused on the growth response of T. triandra to fertilisation with nitrogen (N), phosphorus (P), and potassium (K) each at three levels in a fully factorial pot experiment. Fertilisation increased growth. The number of tillers and aerial shoot mass were controlled by an N × P interaction, and total mass and root mass were controlled by N and by P, with N having a larger effect. Mass per tiller was not related to treatment. Shoot:root ratio and root mass per tiller were controlled by N. Potassium had no effect on any response. For maximum tiller production of T. triandra, plants should be fertilised with high levels of N and P. © 2014, Copyright © NISC (Pty) Ltd.


Garritsen C.,University of Pretoria | Van Marle-Koster E.,University of Pretoria | Snyman M.A.,Grootfontein Agricultural Development Institute | Visser C.,University of Pretoria
Small Ruminant Research | Year: 2015

Pedigree integrity plays a crucial role in the achievement of genetic progress in livestock selection programmes. DNA marker-based parentage testing has become a useful tool for amending inaccuracies in on-farm pedigree records. In the current study, the extent of inaccurate and incomplete pedigree records was quantified in 381 South African Angora goats using a 12 microsatellite markers. Eight half-sib families with a total of 317 Angora kids, 40 kids with unknown sires and an additional 16 putative sires were included in the study. 14.3% of the on-farm pedigrees were amended, including incorrect (according to the DNA verification) or incomplete records. Estimated breeding values (EBV) for fleece traits (fibre diameter and fleece weight) as well as body weights (birth weight and weaning weight) were calculated for 21 sires using ASREML, firstly for the breeder's recorded pedigree and secondly for the DNA-verified pedigree. An overall greater effect was observed in body weight traits than in fleece weight traits with regard to sire EBVs and the ranking thereof. The significant change realised in sire ranking after DNA marker-based pedigree verification emphasises the importance of pedigree integrity in maximising selection accuracy for the production of the highest quality mohair clip in the South African Angora goat industry. © 2015 Elsevier B.V.


Toit J.D.,University of KwaZulu - Natal | Toit J.D.,Grootfontein Agricultural Development Institute
African Journal of Range and Forage Science | Year: 2010

Productivity and mortality of grass plants following drought may be controlled by interactions between defoliation and severity of the drought. Prudent grassland management might mitigate deleterious changes in species composition in multispecies grasslands. This study, conducted in a horticultural tunnel, explored the interactions of drought duration, and the period of uninterrupted postdrought growth before defoliation, on phytomass, tiller production and mortality of Aristida junciformis, Eragrostis curvula, Hyparrhenia hirta and Themeda triandra. Pretreatment tiller production was highest for Aristida and Eragrostis, followed by Hyparrhenia and then Themeda. Mortality was positively related to tuft size and drought duration. Tiller mortality was controlled by a species × drought interaction and the covariate tuft-size. All species lost tillers following a 28-day drought, with the highest loss in Eragrostis and lowest in Themeda. Phytomass production was positively related to recovery, and inversely related to drought duration. Species-specific differences in production were apparent only in the no-drought treatment, where Hyparrhenia produced more phytomass than Themeda and Eragrostis. Aristida had the lowest phytomass production and showed little plasticity across drought treatments. Results indicated that postdrought rest is important for phytomass production, and that species may exhibit a tradeoff between productivity and survival. © NISC (Pty) Ltd.


du Toit J.C.O.,Grootfontein Agricultural Development Institute | O'Connor T.G.,SAEON
Transactions of the Royal Society of South Africa | Year: 2016

Minimum temperatures and frost are ecologically and agriculturally important parameters as they can cause mortality in plants and livestock, shape the position of biome boundaries, influence the lifecycles of pests and diseases, and influence the availability and quality of livestock feed. This study examines minimum temperature data from 1916 to 2014 for a site on the Nama-Karoo/Grassland biome ecotone. Temperatures of at least −6 °C occur almost every year, while temperatures of below −10 °C occurred in 15 of the years on record. Temperature data did not exhibit a random pattern, but rather showed the period from 1935 to 1960 to be particularly cold in terms of absolute minimum temperatures, the probability of occurrence of frost and the duration of the dormant (frost) season. The results provide a platform for interpretation for ecological and agricultural processes that have been recorded in several long-term trials at Grootfontein. The patterns of variation in the data indicate that short (c. 50-year) temperature datasets may give misleading indications in trends in temperature, and for an empirically-based interpretation of climate change, long-term datasets of approximately a hundred years are needed. © 2016 Royal Society of South Africa


du Toit J.C.O.,Grootfontein Agricultural Development Institute | Sekwadi K.,Grootfontein Agricultural Development Institute
African Journal of Range and Forage Science | Year: 2012

The non-selective, soil-applied herbicide tebuthiuron (1-(5-tert-butyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea) is registered for the control of the indigenous encroacher shrub Seriphium plumosum (Asteraceae) in South Africa. The use of tebuthiuron on a farm in the Cymbopogon-Themeda veld type in the Zastron district of the Free State has led to the formation of bare patches in the grass layer. This study investigated patterns of emergence and survival of monocotyledonous oats (Avena sativa) and dicotyledonous cabbage (Brassica oleracea) in soils collected from bare patches resulting from the application of tebuthiuron between two and eight years earlier. Untreated soils provided a control. Both oats and cabbage emergence was high and not related to herbicide application. After about two weeks, plants growing in tebuthiuron-treated soil began to die, and after 60 d only four of the 299 emerged seedlings were alive, but showed signs of mortal phytotoxicity. Mortality in the control was low. It was concluded that tebuthiuron residues in the bare patches may preclude recolonisation by seed for at least eight years following application. © 2012 Copyright NISC Pty Ltd.


du Toit J.C.O.,Grootfontein Agricultural Development Institute | O'Connor T.G.,South African Environmental Observation Network | Van den Berg L.,Grootfontein Agricultural Development Institute
South African Journal of Botany | Year: 2015

The Nama-Karoo is a semi-arid inland biome in South Africa dominated by dwarf shrubs with grasses, shrubs, geophytes and herbs at varying levels of abundance. The position of the Nama-Karoo/grassland boundary is determined in part by rainfall amount, and in recent years there has been an increase in grassiness, correlated with good rains. This has allowed wildfires, an unusual occurrence, to burn at several sites in the central and eastern regions of the biome. The general effect of fire has been to convert dwarf shrublands to grassland with the extirpation of several nonsprouters species. A collection of photographs describes this effect. It is anticipated that these nonsprouters will recolonise by seed over time, but could be eliminated if fire frequency is high enough to eliminate their seedbank. It is predicted that if grassy conditions persist in the Nama-Karoo, then fire will be an important factor that shapes the Nama-Karoo/grassland boundary. © 2015.


du Toit J.C.O.,Grootfontein Agricultural Development Institute | O'Connor T.G.,South African Environmental Observation Network
Water SA | Year: 2014

Rainfall is a key driver of ecosystem processes, especially vegetation dynamics, in semi-arid regions. Rainfall amount, including droughts and extended wet periods, seasonality, and, possibly, concentration, influence vegetation composition in the eastern Karoo. A monthly rainfall record of 123 years from Grootfontein was analysed to search for evidence of cyclicity in rainfall amount, seasonality, and concentration. Rainfall was substantially higher during the late 1800s and after 1990 than it was during the rest of the 20thcentury. Extended sequential below-average runs of years characterised the drought periods of the early 20thcentury and the 1960s. There was strong evidence of an approximately 20-year rainfall cycle, except for spring rain. Additionally, annual and seasonal rainfall showed evidence of a longer cycle, between 44 and 77 years, which may be related to the southern oscillation index. The additive effects of the two cycles described annual and seasonal rainfall with R2values typically > 0.5. Rainfall seasonality was also related to the longer-term cycle, while rainfall concentration showed some evidence of having entered a new, more concentrated state since 1988. The analysis reveals that rainfall at Grootfontein is not a random process, but rather appears driven by cyclical processes. Rainfall at the site is predicted to decline over the next approximately 20 years, and the high levels of variation and complex causal factors will make it difficult to discriminate between natural variation and possible effects of climate change on rainfall.

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