Dohne Agricultural Development Institute

Stutterheim, South Africa

Dohne Agricultural Development Institute

Stutterheim, South Africa
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Jordaan M.,Dohne Agricultural Development Institute | Coetzer G.M.,University of the Free State | Allemann J.,University of the Free State
South African Journal of Plant and Soil | Year: 2017

Out-of-season onion production is used to produce onions for the early market (April to September) when onion prices peak. No information with regard to this production method is available for the Eastern Cape. Field experiments were therefore conducted in Adelaide, Cradock and Middelburg (situated in the Fish River catchment, Eastern Cape, South Africa) to determine its viability in this area. The short-day onion cultivar ‘Z516’ was established with sets (bulbs 10–12 mm diameter) and seed on five planting dates (late January, mid February, late February, mid March and late March) in a randomised block with four replications. Marketable and unmarketable yields were recorded and percentage marketable yield of total yield calculated. Results indicated that seed is not suitable for out-of-season onion production. Sets produced the highest marketable yields and marketable yield percentage when planted in Adelaide in late February (39.68 t ha−1 [93%]), mid-March (62.60 t ha−1 [92%]) and late March (50.40 t ha−1 [89%]) and matured from April to September when onion prices peak. Cradock is marginal and Middelburg is unsuitable for out-of-season onion production because of low winter temperatures, especially from May to September. © 2017 Southern African Plant & Soil Sciences Committee.


Ntwana B.,Stellenbosch University | Ntwana B.,Dohne Agricultural Development Institute | Agenbag G.A.,Stellenbosch University | Langenhoven P.,ASNAPP
South African Journal of Plant and Soil | Year: 2011

The study was conducted at eleven sites in the Cederberg Mountains, about 200 km north of Cape Town, during March 2006, to gain some information on soil characteristics of natural habitats of Buchu (Agathosma betulina) and determine possible variations in Buchu oil quality at different sites. Plant samples were collected and plant height was recorded at each site. Soil samples were taken as close as possible to the sampled plants, while the direction of the slope was also recorded. The soil analyses indicated that soils of the Cederberg Mountains are mostly very sandy with low levels of nutrients. The pH of the soil was found to vary between pHKCl 3.7and 5.3. Plant height varied with age and between sites and the analyses of the leaves indicated low levels of most of the inorganic elements. Essential oil from the sites showed slight variations, but generally low pulegone levels, high levels of diosphenol and the absence of measurable amounts of cis-trans acetylthio-p-menthan-3-one isomers indicated that all the material originated from pure A. betulina genetic material. High levels of diosphenol also indicated that the material was from diosphenol chemotype.


Nyangiwe N.,Dohne Agricultural Development Institute | Nyangiwe N.,Stellenbosch University | Harrison A.,University of Pretoria | Horak I.G.,University of Pretoria | Horak I.G.,University of the Free State
Experimental and Applied Acarology | Year: 2013

The objective of the study was to establish to what extent the native tick species Rhipicephalus decoloratus has been displaced by the invasive introduced tick, Rhipicephalus microplus at two communally grazed areas in the Eastern Cape Province, South Africa. To this end ticks were collected monthly from five cattle over a period of 2 years and from 10 drag-samples of the vegetation over a period of 1 year at each locality. Whereas 10 years previously only R. decoloratus and no R. microplus had been recorded in the vicinity of the two sites, R. microplus now comprised the bulk of collections at both. Furthermore, significantly more R. microplus were collected from cattle at both localities during the 2nd year of the survey than during the 1st. In addition to 83 instances of intraspecific coupling, there were 17 instances of R. microplus males coupled with R. decoloratus females. Collections made from cattle and goats on two farms close to the study sites revealed that R. microplus was present on both host species and that it significantly outnumbered R. decoloratus on one of the farms. Rhipicephalus decoloratus and R. microplus larvae as well as larvae exhibiting characteristics of both species were collected from the vegetation. © 2013 Springer Science+Business Media Dordrecht.


Mzini L.L.,Dohne Agricultural Development Institute | Winter K.,University of Cape Town
South African Journal of Plant and Soil | Year: 2015

The internal qualities of edible vegetable crops have not been widely researched in South Africa. The aim of this study was to determine possible accumulation of nutrients and heavy metals within these crops after being irrigated with greywater (generated from bathing and dishwashing activities), potable water (from a tap stand) and diluted greywater (1:1 ratio). Trials were conducted at the Umtata Dam Research Station, in a completely randomised design testing combinations of cabbage and onion, Swiss chard (here referred to as spinach) and beetroot, and carrot and lettuce across four sequential planting seasons. Greywater for gravity-fed drip irrigation was collected at a central point from a nearby small informal settlement. Chemical and nutritional content analysis on edible portions of vegetables was carried out. Crude protein (CP) was significantly elevated by 20% (4.5 mg kg-1) and 25% (57 mg kg-1) on cabbage (during the first season) and lettuce, respectively, when irrigated with diluted greywater compared with the control, whereas the CP of onion (during first season) and carrot was significantly higher by 40% (2.4 mg kg-1) and 31% (36.4 mg kg-1), respectively, due to greywater irrigation compared with potable water. Significant increases in nutritional elements, such as iron (Fe) and zinc (Zn), were observed on cabbage (in both seasons), onion (first season) and spinach when irrigated with diluted greywater, whereas in lettuce the Fe content was significantly elevated by greywater irrigation. There were no significant differences in cadmium (Cd) in spinach and lettuce due to greywater irrigation. The study concluded that the insignificant content of heavy metals observed posed no obvious human health risk from consumption of vegetables irrigated with greywater. © 2015 © Southern African Plant & Soil Sciences Committee.


Mzini L.L.,Dohne Agricultural Development Institute | Winter K.,University of Cape Town
South African Journal of Plant and Soil | Year: 2015

Research on the use of greywater for irrigation has focused attention largely on greywater quality and biomass of the crop, but not on the quality of edible vegetable crops, whereas aesthetical appeal of the vegetables determines the acceptance in fresh produce markets. Thus a field experiment was established at the Umtata Dam Research Station where combinations of cabbage and onion, spinach and beetroot, and carrot and lettuce were planted to coincide with four different planting seasons. Crops were irrigated with greywater generated from household activities such as bathing and dishwashing, diluted greywater (1:1 with potable water), and potable water from a tap stand. The yield and aesthetical appeal were measured. There were significantly higher yields and aesthetical appeal of cabbage from using diluted greywater. Onion yields were significantly higher when irrigated with greywater. Similarly, spinach had significantly higher yields but many leaves were infested with leaf-spot disease, which significantly lowered its marketability from greywater treatment. Beetroot yield was reduced by 47% (4.7 t ha-1) when irrigated with greywater compared to the control and external quality was not affected by any of the three water treatments. Carrot also did not show any significant difference in yield, but carrots that were irrigated with potable water were significantly more appealing. Lettuce irrigated with diluted greywater was significantly more appealing than other treatments. Crops that were irrigated with greywater resulted in higher yields, but compromised the quality of the crop to meet fresh produce market requirements. © 2015 © Southern African Plant & Soil Sciences Committee.


Mzini L.L.,Dohne Agricultural Development Institute | Winter K.,University of Cape Town
Water SA | Year: 2015

In the search for alternative and reliable water sources to irrigate vegetables for backyard gardens, an experimental field was set up in the vicinity of the Umtata Dam, north-west of the town of Umtata, to test grey-water quality and its effects on soil nutrient content following 4 successive growing seasons. Samples of grey-water that were generated from informal housing adjacent to the Umtata Dam were collected from kitchen and bath tubs/washing basins. These samples were analysed before being used for irrigating vegetable crops. Te results showed that grey-water quality was ‘fit for purpose’ for irrigating edible vegetable plants. Although the average Na+ (16 mg/ℓ) and Cl- (15 mg/ℓ) ions were significantly higher (p = 0.05) for grey-water than other treatments, both were below the limit of 100 mg/ℓ set in the South African Water Quality Guidelines. Te concentrations of nutrients and heavy metals found in the grey-water samples were significantly lower compared to the World Health Organization guidelines for the safe use of grey-water and within the target water quality range (TWQR) prescribed by South African guidelines for irrigation water. However, the study strongly recommends that grey-water be diluted in order to lower the salt content and to improve the irrigation water quality. Results from an analysis of soil samples showed no significant differences in pH as a result of applying grey-water throughout the soil profile of up to 90 cm depth. Na content of the soil irrigated with grey-water was not significantly different than that of plots where diluted grey-water and potable water were used. Therefore, the grey-water used in this study does not appear to cause an accumulation of salts and heavy metals in soil, in the short term. © 2015,South African Water Research Commission. All rights reserved.


Mtumtum N.,Dohne Agricultural Development Institute | Mtumtum N.,University of KwaZulu - Natal | Modi A.T.,Dohne Agricultural Development Institute
Indian Journal of Horticulture | Year: 2014

A field study of wild watermelon (Citrullus lanatus) establishment and yield using seed to compare the effects of different population densities (3,000, 6,000, 9,000 and 12,000 plants ha-1) and mulching rates (0, 2.5 and 5 t ha-1) with grass mulch on soil water, temperature, vine length, number of branches and leaves per plant, fruit number per plant and per hectare, total yield, fresh and dry fruit mass was conducted. The fruit per hectare and total yields increased as the plant population increased resulting in high yields in the range from 6,000- 12,000 plants per hectare. Yield was more influenced by plant population than by mulching. Mulching did not affect growth and yield of wild watermelon but it affected soil temperature and soil moisture. More water was conserved, while soil temperature was reduced upon increased mulching. This was shown by 31 and 12.6% increase in volumetric water content when the amount of mulch was increased by 2.5 and 5 t/ ha, respectively. However, this was associated with only 1°C change in temperature, which may be significant for critical stages of plant growth. © 2015, Horticulture Society of India. All rights reserved.


O'Connor T.G.,SAEON | O'Connor T.G.,Dohne Agricultural Development Institute | de Ridder C.H.,Dohne Agricultural Development Institute | Hobson F.O.,Dohne Agricultural Development Institute
African Journal of Range and Forage Science | Year: 2010

Seed ecology may play a role in the widespread increase of Acacia karroo in savanna and grassland. Accordingly, fecundity, predation, mortality by fire, dispersal by livestock, and seed longevity were studied. Seed production per tree (P of pod production, pods per tree) was positively related to tree height, negatively related to tree density, and was greater for sites receiving run-on. Predispersal predation by bruchids, cerambycids, and wasps depleted seed production by 18%. The ant Messor capensis effectively eliminated surface seed except during the early dry season following seed shed. Rodent predation of seed was minimal. Fires >100 °C killed most exposed seed but a thin layer of soil increased survival and maintained germinability. A greater proportion of ingested seeds passed through cattle (57%) and sheep (50%) than through goats (15%). 50% of seeds were recovered within 48 h. During passage, soft seeds were digested, some hard seeds were softened, but most were egested as hard seeds; germinability was not increased. Cattle were confirmed as dispersal agents. Using experimental seed banks, it was shown that buried or surface-exposed seeds did not persist for longer than a year, but 24% of surface-shaded seeds persisted for two years. Most seeds germinated but most buried seeds died before emergence. Seed persistence in deep shade should facilitate invasion into grassland. Seed banks of A. karroo did not exceed 18 seeds m -2 because of the above-described effects. Seed availability (fecundity, dispersal by cattle, seed longevity) is concluded to contribute to the invasiveness of A. karroo, but use of fire may offer partial control of seed availability. © NISC (Pty) Ltd.


PubMed | Dohne Agricultural Development Institute
Type: Journal Article | Journal: Experimental & applied acarology | Year: 2013

The objective of the study was to establish to what extent the native tick species Rhipicephalus decoloratus has been displaced by the invasive introduced tick, Rhipicephalus microplus at two communally grazed areas in the Eastern Cape Province, South Africa. To this end ticks were collected monthly from five cattle over a period of 2 years and from 10 drag-samples of the vegetation over a period of 1 year at each locality. Whereas 10 years previously only R. decoloratus and no R. microplus had been recorded in the vicinity of the two sites, R. microplus now comprised the bulk of collections at both. Furthermore, significantly more R. microplus were collected from cattle at both localities during the 2nd year of the survey than during the 1st. In addition to 83 instances of intraspecific coupling, there were 17 instances of R. microplus males coupled with R. decoloratus females. Collections made from cattle and goats on two farms close to the study sites revealed that R. microplus was present on both host species and that it significantly outnumbered R. decoloratus on one of the farms. Rhipicephalus decoloratus and R. microplus larvae as well as larvae exhibiting characteristics of both species were collected from the vegetation.


PubMed | Dohne Agricultural Development Institute
Type: Journal Article | Journal: Tropical animal health and production | Year: 2015

Milk production parameters of purebred Jersey (J) cows and FleckviehJersey (FJ) cows in a pasture-based feeding system were compared using standard milk recording procedures. Milk, fat and protein production was adjusted to 305 days per lactation and corrected for age at calving. Effects of breed, parity, month and year were estimated for milk, fat and protein yield as well as fat and protein percentage, using the general linear model procedure. Fixed effects identified as affecting milk production parameters significantly were breed, parity and year. FJ cows produced significantly more milk than J cows (6141102 and 539895 kg milk, respectively). Similarly, fat and protein yields were significantly higher in FJ (2724 and 2013 kg, respectively) than in Jersey cows (2463 and 1942 kg, respectively). Fat and protein percentages only differed slightly in absolute terms being 4.610.04% fat in the Jersey compared to 4.470.04% fat in the FJ. Protein levels for J and FJ cows were 3.620.03 and 3.510.03%, respectively. Despite a lower fat percentage, FJ crossbred cows may be more productive than purebred Jersey cows which may be due to heterotic effects.

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