| Biomass production, weed suppression, nitrogen and phosphorus uptake in white oat (Avena sativa L.) and grazing vetch (Vicia dasycarpa L.) cover crop bicultures under an irrigated no-till system | Chiduza, C | 2012 |
KeywordsConservation agriculture, cover crop mixtures, no-till farming, soil cover, weed species count AbstractCultivation of a multipurpose cover crop is of interest to Eastern Cape farmers experiencing soil infertility and weed pressures. The objective of the study was to investigate effects of oat–vetch bicultures on biomass production, weed suppression, and nitrogen (N) and phosphorus (P) uptake. The study was conducted between 2009 and 2010. Treatments included 90% oat + 10% vetch, 70% oat + 30% vetch, 50% oat + 50% vetch, 100% vetch, 100% oat and a weedy fallow as control. Bicultured cover crops had significantly (p < 0.05) higher biomass compared to sole vetch in both seasons but reduced biomass compared to sole oat only in 2010. Weed suppression increased with an increase in biomass. Weedy fallow had the least weed suppression (p < 0.05) at all sampling times, whereas sole oat provided the best early weed control compared to the rest of treatments. Nitrogen uptake by sole vetch was comparable to 50% oat + 50% vetch and 70% oat + 30% vetch. Phosphorus uptake differed only in the 2010 season and 90% oat + 10% vetch, 70% oat + 30% vetch and sole vetch had the best uptake. Weedy fallow had the least N and P uptake during the two seasons. Bicultures can be used for improved biomass, weed suppression, and N and P uptake with potential of alleviating soil degradation effects in the Eastern Cape province. AuthorsChiduza, C, Muchaonyerwa, P and Muzangwa, L Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.741719 This article contributed by:
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| Family selection gains for quality traits among South African sugarcane breeding populations | Zhou, MM | 2012 |
Keywordsbroad-sense heritability, covariance parameters, selection gains, sugarcane AbstractIn sugarcane breeding, family selection has been shown to produce larger gains than individual plant selection. During family selection, whole families of seedlings are selected or rejected based on data derived from replicated family plots. The objective of this study was to determine predicted family selection gains and evaluate their implications for variety improvement in terms of quality traits among sugarcane breeding populations of the South African Sugarcane Research Institute's regional breeding programmes. The data was collected from seven breeding populations and analysed using the Statistical Analysis System (SAS). All the quality traits showed highly significant family effects variance components. There were consistent increases in heritability and gains to selection with advancing population series indicating benefits from indirect recurrent selection. Brix % cane, because it costs less to measure, could be used to evaluate within family variability. The B, C, U and F populations produced larger and more consistent selection gains than K, T and S. Recurrent selection could be used to enhance breeding for quality traits. AuthorsZhou, MM and Lichakane, ML Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.743606 This article contributed by:
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| Yield and quality response of rose geranium (Pelargonium graveolens L.) to sulphur and phosphorus application | Sedibe, MM | 2012 |
Keywordsoil quality, phosphorus, rose geranium, sulphur AbstractSulphur and phosphorus are essential plant macronutrients. Sulphur is involved in the formation of chlorophyll, activation of enzymes and is part of coenzyme A. Phosphorus forms part of the structure of nucleic acids and phospholipids. Two separate studies were conducted to determine the effects of sulphur and phosphorus levels in nutrient solutions on yield and quality of hydroponically grown rose geranium as well as setting standards of sulphur and phosphorus amounts to be used in the production process. The effect of four levels of sulphur (0.36, 1.90, 3.44 and 4.98 mmol l−1) was investigated in the first study and in the second study four levels of phosphorus (0.1, 0.8, 1.5 and 2.2 mmol l−1) were also investigated. All treatments were assigned in a completely randomised block design with five replicates. The results of the first study showed a significant effect of sulphur on the number of branches, plant height and foliar fresh mass. Foliar fresh mass and oil yield peaked at the 3.44 mmol l−1 concentration. The second study showed that plant height and the number of branches was not affected significantly by phosphorus, but foliar mineral phosphorus, magnesium and potassium were affected. Oil yield of rose geranium increased linearly with increased phosphorus concentrations. Both the guaia-69-diene content and the citronellol:geraniol ratio were greater at the highest phosphorus level, which indicated that oil quality can be enhanced by using relatively high phosphorus concentrations in nutrient solutions. AuthorsSedibe, MM and Allemann, J Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.744108 This article contributed by:
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| Control measures for the encroacher shrub Seriphium plumosum | Snyman, HA | 2012 |
Keywordsbankrupt bush, Molopo, Seriphium plumosum (Stoebe vulgaris), shrub encroachment, slangbos, vaalbos AbstractSeriphium plumosum encroachment in South Africa has converted extensive areas of grassland into less productive shrubland–grassland, but its control is not being seriously addressed at present. Therefore, the short-term response of S. plumosum to different applications of nitrogen (N), phosphate (P), lime, sodium chloride (NaCl) and a soil-applied suspension herbicide, Molopo (active ingredient tebuthiuron), was examined. The lime and P-fertiliser treatments lead to no deaths of S. plumosum for any of the concentrations. The smaller the shrubs, the more sensitive they were to both N and NaCl applications. The minimum N-fertiliser applications of 30, 60, 120, 1 000 and 2 000 kg ha−1 were responsible for 100% death of shrubs with heights of 200, 300, 400, 500 and 600 mm, respectively. Sodium chloride application of only 100 kg ha−1 lead to 100% death of shrubs smaller than 400 mm high. Although high applications of NaCl led to total death of shrubs 600 mm high, the enormous problem of saline/sodic soil accompanying it must not be disregarded. Molopo successfully killed all shrubs up to a height of 600 mm. As the plant reaches maturity, the root:shoot ratio increases significantly. It was proved that S. plumosum encroachment is not linked to overgrazing. These results confirm the vulnerability of S. plumosum in semiarid areas, following changes in soil characteristics, which can be used in the control of this invasive plant. A combination of methods is recommended for S. plumosum control. AuthorsSnyman, HA Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.745905 This article contributed by:
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| Influence of mono- and biculture cover cropping systems on soil polysaccharides and aggregate stability in a sandy loam Oakleaf soil in Eastern Cape, South Africa | Mupambwa, HA | 2012 |
Keywordsaggregate fraction size, mean weight diameter, oat, soil polysaccharides, vetch AbstractMono- and biculture cropping systems are thought to affect aggregate stability by influencing soil polysaccharides but the exact relationship is uncertain. The objective of this study was to determine the effects of cover cropping systems on polysaccharides and aggregate stability in an Oakleaf soil. Two experiments involving a cereal, two legumes and a weedy control, either in mono- or biculture, were done. The crops were oat (Avena sativa L.), vetch (Vicia dasycarpa L.) and lupin (Lupinus angustifolius L.). All cover crops in both cropping systems increased soil polysaccharides. Cover crops in both systems improved aggregation either by increasing macroaggregates and/or lowering the percentage of the 0.25–0.106 mm aggregate fraction size. The mean weight diameter increased under the mono- but not biculture system. The hot-water extractable polysaccharides fraction was actively involved in aggregation in the Oakleaf soil. The correlation between hot-water extractable polysaccharides and the mean weight diameter was negative (r= −0.55) for the monoculture system and positive (r= 0.71) for the biculture system. Microaggregates coalesced even when such increase in size did not trigger a significant increase in the mean weight diameter. Secondly, microaggregates also seemed to serve as building blocks for macroaggregates. AuthorsMupambwa, HA and Wakindiki, IIC Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.748220 This article contributed by:
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| Estimation of frost occurrence and duration of frost for a short-grass surface | Savage, MJ | 2012 |
Keywordsdielectric constant, grass-surface temperature, ice AbstractThe estimation of frost duration (FD) was investigated using dielectric, infrared surface temperature and grass temperature subhourly measurements. Near real-time FD data and information displays and alerts were also made available via a web-based system. FD was estimated using a dielectric leaf wetness sensor (LWS) method, for which the sensor voltage was between 274 and 284 mV with a voltage rate of change less than 10 mV h−1 for a 4 min period, and two temperature methods for which infrared thermometer (IRT) and grass temperatures were compared with 0 °C. FD estimation using the LWS method ensured that most of the transitional dry-to-wet and wet-to-dry events were not included in the FD count. Generally, the IRT method yielded the largest estimate of FD, grass temperature method lower and LWS method lowest. Micrometeorological measurements showed consistent air temperature gradients of 2.25 °C m−1 for cloudless nocturnal frosted conditions with few air temperature measurements at 1 m and none above indicating frost occurrence. At the very least, automatic weather station systems should contain a grass thermometer or preferably an IRT for determination of FD with near real-time data and graphics displayed, including timeous alerts of frost occurrence and FD, using the Internet. AuthorsSavage, MJ Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.748938 This article contributed by:
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| Estimation of leaf wetness duration for a short-grass surface | Savage, MJ | 2012 |
Keywordsdielectric leaf wetness sensor, grass-surface temperature, nocturnal grass temperature AbstractThe measurement of leaf wetness duration (LWD) was investigated using subhourly dielectric, infrared surface temperature, dewpoint temperature, grass temperature and relative humidity (RH) measurements. Near real-time LWD data and information displays and alerts were made available timeously via a web-based system. LWD was estimated above a short-grass surface using five methods: dielectric leaf wetness sensors (LWS); a constant RH for which wetness events were registered for RH greater than 87%; RH between 70–87% if RH increased by more than 3% in 30 min; and two dewpoint depression-based methods for which surface-measured temperature, using an infrared thermometer (IRT), and grass temperature were compared with the dewpoint at either 0.1 or 2 m. The RH methods generally overestimated LWD compared to the other methods. There was reasonable agreement between IRT- and grass-temperature methods if rain days were excluded but these methods showed poor agreement with LWS measurements of LWD. Microclimatic and radiative conditions, during nocturnal condensing events, are reported. Automatic weather station data would have more value if grass temperature was included for determination of LWD by comparison of grass temperature with a measured dewpoint, with timeous alerts and web-based display of near real-time LWD data and graphics. AuthorsSavage, MJ Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.750017 This article contributed by:
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| Evaluating the Streif index against commercial subjective predictions to determine the harvest date of apples in South Africa | Lötze, Elmi | 2012 |
Keywordsmaturity, prediction, starch breakdown AbstractFor the local deciduous fruit industry, which mainly exports fruit, determination of the optimum physiological harvest maturity for apples to ensure high fruit quality after long-term storage is still an important goal. This is performed by a subjective determination based on a weekly rate of change of all or some of the ripening parameters such as fruit firmness. In Europe, the Streif index (SI) has been implemented to reduce this subjectivity. The aim of this project was to evaluate this index under local conditions. Historical physiological data for Golden Delicious and Starking apples (Malus domestica Borkh.) from various orchards in the Ceres area were analysed. Significant correlations were obtained between the SI and subjective predictions of the release date for harvesting, after adapting the local starch breakdown values. However, during seasons when the starch conversion rates were very low during the early season, the SI alone may not be sufficient to indicate the release date for harvesting. A multilinear regression equation was also fitted to the maturity data. Likewise the accuracy of this model was influenced by season and variation between individual sites. Both methods can be applied commercially to support the otherwise subjective determination of the harvest dates. AuthorsLötze, Elmi and Bergh, Oloff Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.691558 This article contributed by:
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| Carbon and nitrogen mineralisation and inactivation of the Cry1Ab protein in Bt maize (MON810) residues during composting | Muchaonyerwa, P | 2012 |
Keywordschemical composition, compost, Cry1Ab protein, decomposition, lignin AbstractAbstract A study was carried out to determine the effects of composting Bt maize residues on carbon (C) and nitrogen (N) contents and activity of the Cry1Ab protein in the compost. Residues (leaf plus stem) of mature Bt maize (DKC 7815B) and its near-isoline (CRN 3505) were composted using 1 m3 wooden boxes. Temperature, C and N transformations, and activity of the Cry1Ab protein were monitored throughout the composting period. Residues of the hybrids used in this study composted similarly as shown by the temperature profiles, pH, C and N dynamics. The C:N ratios decreased from 33 and 23 for the Bt maize and near-isoline, respectively, to 15. Composting reduced the activity of the Bt protein in the residues, with a half-life of 3.3 d, to 22%, 7% and 3% of the initial level (90.5 ng g–1) in 7, 14 and 35 d, respectively, and approached undetectable levels after 63 d. The findings of this study suggest that Bt maize composts in the same way as conventional maize. The composting rapidly reduced the much higher C:N ratio of Bt maize and in the process eliminated the active Bt proteins in the residues, thus rendering them much safer for soil application. AuthorsMuchaonyerwa, P, Daudu, CK and Mnkeni, PNS Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.700076 This article contributed by:
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| Phylogenetic studies of selected isolates of Potato virus Y (PVY) infecting vegetable crops in KwaZulu-Natal, Republic of South Africa | Ibaba, JD | 2012 |
Keywordspepper, potato, tomato AbstractPhylogenetic relationships of Potato virus Y (PVY) isolates infecting vegetable crops in KwaZulu-Natal, Republic of South Africa, were investigated. A 1 067 bp amplicon covering part of the coat protein gene and the 3′ non-translated region (NTR) of three PVYO isolates infecting tomato (Solanum lycopersicum L.), one PVYO isolate infecting pepper (Capsicum annuum L.) and one PVYN Wilga isolate infecting potato (Solanum tuberosum L.) were amplified, cloned and sequenced. The 5′ NTR, P1, HC-Pro and part of the P3 regions (2 559 bp) of a PVYN isolate infecting potato were amplified, cloned and sequenced. Sequence data were compared with sequences of PVY isolates from different geographical locations and subjected to phylogenetic analyses. The PVYN isolate clustered with the European sublineage N and has five unique amino acid residues. The PVYN Wilga isolate branched with the American PVYO isolate in the O lineage. All PVYO isolates infecting tomato and pepper were grouped in a new sublineage within the O lineage. AuthorsIbaba, JD and Gubba, A Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.700738 This article contributed by:
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