| A rapid demonstration of the self-thinning rule using radish | Smith, F.R. | 2011 |
KeywordsIntraspecific competition, plant density, plant mass, power rule, Raphanus sativa AbstractThe self-thinning rule describes the relationship between individual mass and density in crowded evenly-aged plant populations in which the slope of the relationship is always greater than -1. This study investigated whether the rule could be demonstrated in six weeks using radish (Raphanus sativa L.) grown in trays (0.033 m2) in a greenhouse. Seeds of a radish cultivar were sown in a 4:2:1 mixture of sand, potting soil and compost and watered twice daily to field capacity. One week later, seedlings in each tray were thinned out to one of 19 densities ranging from 4 to 64 individuals. Thereafter, the radishes were left to grow for a further five weeks under the same watering regime and then harvested. The log-log regression of average fresh mass against density produced a slope of −0.76 which deviates significantly from the expected −4/3 power rule. This result indicates that initial plant densities need to be higher if the self-thinning rule is to be demonstrated successfully. AuthorsSmith, F.R. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640024 This article contributed by:
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| A review of advances in hydropedology for application in South Africa | Huyssteen, C.W.
van | 2008 |
Keywordshydrology, morphology, redox, soil hydrology, temporal stability AbstractAbstract Hydropedology is internationally a new and fast-growing science. It is therefore pertinent to take heed of developments in this regard to guide current and future research in South Africa. This paper aims to discuss the initiation and advances in the interdisciplinary science of hydropedology. Hydropedology has been defined to interlink pedology, soil physics, and hydrology to bridge scales and to transform soil survey data into soil hydraulic information. As such hydropedology could contribute to the understanding of various environmental and ecological issues. In this regard pedotransfer functions relate simple soil characteristics (e.g. morphological features) to more complex parameters (e.g. soil hydraulic properties) that are relatively difficult to measure. The hydrology of soil types (HOST), published in the United Kingdom to aid hydrological studies and analyses, is a good working example of a pedotransfer function. HOST is based on three conceptual models of water flow processes in the soil: soil on a permeable substrate with a deep aquifer (>2 m); soil on permeable substrate with a shallow water table (<2 m); and soil with an impermeable or semi permeable layer within 1 m of the surface. The three conceptual models are further subdivided into 11 models, which can be subdivided into 29 HOST classes. A useful tool for the summation of long-term soil water content data is the temporal stability of spatially measured soil water contents which is defined as the time invariant average of spatially measured soil water contents and offers a valuable method to study the relationship between soil and water. It has been used to reduce the number of measurements needed in catchment characterization and is therefore also a valuable tool in site selection. Understanding redox reactions in soil and the influence thereof on the development of redoxi-morphic colour patterns, are vital in discerning the relationship between soil water regime and soil morphology. Redoximorphic colour patterns are manifested as redox depletions and/or redox accumulations. The former is evident as grey matrices, cutans, mottles, or pore linings, while the latter is evident as Fe masses, pore linings, nodules, or concretions. AuthorsHuyssteen, C.W.
van Year Published2008 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2008.10639924 This article contributed by:
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| A review of research achievements on maize stem borer, Busseola fusca (Fuller) and Diplodia ear rot caused by Stenocarpella maydis (Berk. Sutton) | Flett, B.C. | 2010 |
KeywordsBusseola fusca, Stenocarpella maydis, Zea mays AbstractResearch that focused on maize production on the central Highveld of South Africa was traditionally, since the early twentieth century, dealt with by the Department of Agriculture at Potchefstroom. During the 1970s the Highveld Region at Potchefstroom assigned a group of researchers with an interest in maize to a unit termed the Summer Grain Centre that in 1992 became part of the Agricultural Research Council’s Grain Crops Institute. Members of this group in particular gave research attention to various aspects of crop protection in maize, including the soil insect complex, the maize stem borer complex, maize streak disease, the ear rot complex and various leaf diseases. This paper deals with research progress on the African stem borer, Busseola fusca, and ear rot caused by Stenocarpella maydis. The emphasis is on research with a practical application rather than that of an academic nature. AuthorsFlett, B.C. and Rensburg, J.B.J.
van Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639972 This article contributed by:
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| A review of the post harvest handling of fruits in South Africa over the past twenty five years | Dodd, M. | 2010 |
KeywordsCold chain, export, packaging, subtropical fruit, tropical fruit AbstractDuring the past 25 years there has been a tremendous amount of positive change in the post harvest handling of fruits in South Africa, primarily due to the adoption of many new technologies developed in response to changes in the industry. Important factors that impacted on the fruit industry during this time were a variable profitability due to large changes in the exchange rate of the Rand compared to other trading currencies and freeing up the market which has aided in the growth of the industry. This review provides an overview of the scientists and developments in the citrus, avocado, mango, litchi, pome fruit, table grape, stone fruit including plums, nectarine, peach and apricot industries. The fruit industry is vitally important to South Africa as a foreign currency earner and a large provider of stable employment. AuthorsDodd, M., Cronje, P., Taylor, M., Huysamer, M., Kruger, F., Lotz, E. and Merwe, K.
van der Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639974 This article contributed by:
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| A revised perspective on principles of soil classification in South Africa | Turner, David P | 2013 |
Keywordsdiagnostic horizons, horizon definitions, soil classification, soil depth AbstractLimited significance has been given to the formal recognition of certain subsoil materials in the South African Soil Classification System. Three principles in the current classification system are discussed using variants of soil profiles associated with the Avalon soil form. The retention of the arbitrary depth criterion is questioned in favour of the recognition of an enlarged ‘sphere of pedological interest’ extending formal classification to deeper soil materials. This implies that a greater number of soil classes will be required but these additional classes may be accommodated by recognising an additional soil group class in the classification system. It is proposed that the definitions of diagnostic horizons be rewritten to focus on the central concept of the horizon properties, dispensing with limitations on the nature of overlying or underlying horizons. An open class structure to the classification system is advocated. AuthorsTurner, David P Year Published2013 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2013.804602 This article contributed by:
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| A settling tower for quantitative deposition of urediniospores of Uromyces viciae-fabae | Negussie, T. | 2005 |
KeywordsInoculation technique, Lens culinaris, lentil rust AbstractAn inoculation technique resulting in uniform spore deposition for obtaining reproducible and accurate data on host responses is required for quantitative studies of resistance expression. The feasibility of obtaining uniform spore deposition on Lens culinaris, a plant with compound leaves, was investigated using a settling tower. Uniformity of spore deposition on adhesive coated glass slides was assessed by dispersing 1,2,4 and 8 mg spores of Uromyces viciae-fabae, the causal agent of lentil rust, into the tower. When an 8 mg spore quantity was discharged the number of spores deposited per square centimetre did not vary significantly (P > 0.05) between the different locations of the glass slides on the target area. A linear, relation was found between mass of spores discharged into the tower and spores deposited. Counts for 1, 2, 4 and 8 mg were, respectively, 82, 244, 384 and 972 spores per square centimetre. Uniformity of spore deposition increased as the amount discharged increased, and the coefficient of variation was inversely related to the spore quantity dispersed. When plants of lentil cultivar EL-142 were exposed to spores in the settling tower, differences in numbers of lesions per square centimetre leaf area were non-significant (P > 0.05) within and between inoculation runs. Following dispersal of 8 mg urediniospores for a 3 min settling period, a mean of 140 uredinia (standard deviation = 7) occurred per square centimetre leaf area. AuthorsNegussie, T. and Pretorius, Z. A. Year Published2005 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2005.10634696 This article contributed by:
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| A simple method for supplementing long-term weather records in a maize-modelling exercise | Clemence, B.
S.E. | 1991 |
KeywordsCrop models, missing data, weather records AbstractMissing weather data is a very real problem when using daily-incrementing crop growth simulation models. This is especially true in the case of daily air temperature and solar radiation data. The aim of this study was to compare two simple methods of supplementing the input weather record, and to determine whether the estimates could be used with confidence in the case of the CERES-Maize model. Wet and dry day monthly means of daily maximum and minimum temperature and sunshine duration were calculated for four long-term weather stations in Natal. Ordinary monthly means of these elements were also computed. The two sets of means, which were calculated from the most recent 5 years of the weather record, were appended program-matically to daily rainfall data for the preceding 10 years of the weather record, in each case replacing totally the observed daily temperature and sunshine duration values. The weather files thus created were then used as inputs to the CERES-Maize plant-growth model. Yield, flowering date and maturity date estimates so gained were compared with similar estimates over the same period using real temperature and sunshine data. Yield estimates based on supplemented data compared excellently with those using the full weather record, with mean percentage differences for the four sites ranging from 1.23% to 9.34%. Yield estimates based on wet and dry day means for the weather record were slightly better than those derived using ordinary monthly means. This was also true in the case of the flowering and maturity date estimates. AuthorsClemence, B.
S.E. Year Published1991 PublicationSouth African Journal of Plant and Soil Locations- Cedara, KwaZulu-Natal, South Africa (-29.5339, 30.2733)
- Dundee, South Africa (-28.1725, 30.2314)
- Kokstad, KwaZulu-Natal, South Africa (-30.5539, 29.4268)
- tabamhlope, South Africa (-29.1178, 29.6444)
DOI10.1080/02571862.1991.10634575 This article contributed by:
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| A simple, accurate method of estimating maximum total evaporation from a wheat crop during the daylight period | van Zyl, W. H. | 1988 |
KeywordsAerodynamic considerations, evaporation formulae, evaporimeters, energy balance considerations AbstractThe use of empirical relationships for the calculation of the energy and aerodynamic components of the Penman-Monteith equation were tested against measured data. Accurate estimates of maximum total evaporation, Em, from a wheat crop were obtained. The empirical equation utilizes measured or estimated total radiation flux density, St, in the energy component, plus evaporation from a screen Piché atmometer to account for aerodynamic influences. The agreement of estimated Em versus lysimetrically measured Em was good. The high index of agreement of 0,98 and a low mean absolute difference of 0,51 mm over the daylight period were obtained with St measured. When St was estimated, using an appropriate formula, these statistics were 0,98 and 0,57 mm, respectively. Authorsvan Zyl, W. H., de Jager, J. M. and Maree, C. J. Year Published1988 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1988.10634266 This article contributed by:
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| A single point sorption test for the routine determination of the phosphorus requirement of low to moderate P-fixing soils | Smith, Marie F. | 2003 |
KeywordsLangmuir, Temkin isotherms, phosphorus adsorption, P-fixation, phosphorus requirement AbstractThe phosphorus requirement (P0.11) of low to moderate P-fixing soils from the South African tobacco industry and KwaZulu-Natal was interpolated from multiple point P sorption isotherms. The relationship between P0.11 and a single point sorption measurement, consisting of the P concentration left in solution after equilibrating for 24 h additional rates of either 70 or 100 mg P kg−1 soil, over the soils of the tobacco industry was investigated using non-linear regression analysis. The results showed that a high degree of correlation existed between both variables, suggesting that P0.11 could simply and accurately be predicted from a single P sorption measurement instead of a multiple point sorption isotherm. Confirmation of the predictive value of the functions best fitting the data from the soils of the tobacco industry was validated using data of the soils from KwaZulu-Natal. The results showed that values of P0.11 predicted for the soils of KwaZulu-Natal, using the single point P sorption test in conjunction with the regression functions developed for the soils of the tobacco industry, were highly significantly correlated to the P0.11 values interpolated from multiple point P sorption isotherms. The implication of these findings for the routine determination of the phosphorus requirement of soils by soil testing laboratories and P fertiliser recommendations is discussed. AuthorsSmith, Marie F. and Henry, P. C. Year Published2003 PublicationSouth African Journal of Plant and Soil Locations- Rustenburg, North West, South Africa (-25.6597, 27.2432)
- Groblersdal, Limpopo, South Africa (-25.1619, 29.3981)
- Brits, North West, South Africa (-25.6333, 27.7819)
- Groblersdal, Limpopo, South Africa (-25.1619, 29.3981)
- Pretoria, Gauteng, South Africa (-25.7313, 28.2184)
- Irene, Centurion, Gauteng, South Africa (-25.8812, 28.2263)
DOI10.1080/02571862.2003.10634922 This article contributed by:
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| A slope sequence of Podzols in the southern Cape, South Africa 1. Physical and micromorphological properties | Hawker, L. C. | 1992 |
KeywordsFluctuating water table, leaching, lithological discontinuity, micromorphology, multiple ironpans AbstractIn South Africa the characteristics of Podzols, with or without placic horizons, and the complex processes involved in their formation, are generally still poorly understood. To investigate both these aspects thoroughly, these soils were studied in the landscape context, described and sampled in detail and the soil properties characterized. This introductory article describes the study area, comprising a representative slope sequence of three soil profiles, together with their micromorphological and physical properties. It was found that no litho- logical discontinuity is responsible for Bhs (spodic) horizon development in any of the three profiles described. However, some of the placic and ironpan development observed was at lithological boundaries, where major differences in chemical and mineralogical properties are to be expected. The podzolized horizons have developed in relatively finely textured, intensely weathered material of suspected aeolian or colluvial origin. The fineness of the parent material possibly accounts for the absence of E-horizon development above the spodic horizon. There was evidence of clay illuviation and accumulation of sesquioxides in all profiles, masked by the accumulation of amorphous inorganic and organic complexes. AuthorsHawker, L. C., van Rooyen, T. H. and Fitzpatrick, R. W. Year Published1992 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1992.10634610 This article contributed by:
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