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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. Source

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. Source

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. Source

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 Source

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. Source

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