| A comparison of the utilization of initially-applied labelled ammonium and nitrate nitrogen by wheat grown in a pot experiment | Botha, A.
D.P. | 1991 |
KeywordsAmmonium, 15N, nitrate, pot experiment, utilization, wheat AbstractThe utilization of initially-applied 15N-labelled ammonium and nitrate nitrogen by wheat plants grown in soil was investigated in a pot experiment under controlled growth chamber conditions. The application rate was approximately 140 kg N ha−1) and the treatments consisted of {NH4}NO3, NH4{NO3}, {NH4NO3}, {NH4}2- SO4, K{NO3} and nil nitrogen. The ions in brackets ({ }) indicate those enriched with 15N to c. 5 atom %. On average, according to the isotope technique, 67.24±2.48% of the nitrogenous fertilizer was utilized by wheat. Significantly more nitrate N was recovered in the plants than ammonium N. Furthermore, when fertilized, less soil nitrogen is utilized by the plants compared with the controls, and the application of nitrate suppressed the uptake of soil N more than when ammonium N was applied. The results confirmed that, on average, the conventional method of determining fertilizer recovery by difference yielded lower values (47.49±8.93%) than those obtained with the tracer technique. AuthorsBotha, A.
D.P. and Pretorius, D. C. Year Published1991 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1991.10634588 This article contributed by:
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| A comparison of three methods of soil water content determination | Little, K. M. | 1998 |
KeywordsDelta-T ThetaProbe type ML1, gravimetric soil water content measurement, Standard D.2 Speedy Moisture Tester, volumetric soil water content measurement. AbstractIn forestry the need to manage plantations on a sustainable site-specific basis requires the understanding and management of any growth limiting factors. Soil water regime is a factor considered to be of prime importance with respect to explaining differences in tree growth. In research studies measurement of soil water content is carried out on a regular basis and due to theft and vandalism, soil water sensing equipment cannot usually be left on site. Other rapid methods to determine soil water content therefore have to be found. The ThetaProbe and Speedy Moisture Testèr were compared as alternative measures of soil water content determination in the top 10 cm of the soil to the more traditional gravimetric method. These methods were tested in KwaZulu-Natal on two contrasting soils in terms of clay content, organic carbon content and soil water content. Regression analysis performed to compare the two different methods with the gravimetric method as a reference, indicated that they were similar on a soil specific basis at the P < 0,001 level of significance. With calibration, they were found to be equally suitable for the purpose of taking the measurements. Results and problems encountered are discussed for each method. AuthorsLittle, K. M., Metelerkamp, B. and Smith, C. W. Year Published1998 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1998.10635121 This article contributed by:
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| A comparison of two methods of inducing water stress in wheat (Triticum aestivum L.) | Strauss, J. A. | 1998 |
Keywordswater stress, Triticum aestivum L., polyethylene, glycol, withholding of water AbstractThe aim of this study was to compare the withholding of water and the use of polyethylene glycol (PEG) as methods of inducing water stress in spring wheat cultivars (Triticum aestivum L.) grown in the Western Cape. Water stress was induced in two cultivars that had previously shown differences in drought tolerance. Proline accumulation in plants and the reduction of 2,3,5-triphenyltetrazoliumchloride (TTC) were used as indicators of water stress in the test plants. Proline accumulation proved to be a more sensitive indicator of water stress compared to TTC, showing significant increases with both the withholding of water and PEG as methods to induce water stress. Although both methods of stress induction proved to be effective, the withholding of water may be more appropriate due to the possibility of root injuries with PEG. Good control of climatic conditions and measurements of plant water potential will, however, be essential if the withholding of water is used to induce stress. AuthorsStrauss, J. A. and Agenbag, G. A. Year Published1998 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1998.10635129 This article contributed by:
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| A complex dormancy mechanism in seeds of the weed Rubus cuneifolius | van Staden, J. | 1984 |
KeywordsRubus cuneifolius, germination, dormancy, scarification, stratification AbstractBoth the endocarp and embryo contribute to the dormancy of Rubus cuneifolius seed. Whereas scarification was found to break the dormancy imposed by the endocarp, embryo dormancy could only be overcome by a combination of treatments. These treatments consisted of a one-month stratification period followed by incubation at an alternating temperature ot 10–20 °C in the presence of light. S. Afr. J. Plant Soil 1984, 1: 48–50 Authorsvan Staden, J. and Campbell, Peta L. Year Published1984 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1984.10634108 This article contributed by:
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| A critical soil sulphur level for maize (Zea mays L.) grown in a glasshouse | Grobler, L. | 1999 |
KeywordsMaize, production rate, sulphur and sulphur fertilisation. AbstractSulphur is an essential nutrient for the production of the amino acids cysteine and methionine, which are important for protein syntheses. Previous studies showed that sulphur deficiencies are becoming common because of the tendency to use more concentrated and liquid fertilisers. The objective of this study was determining the threshold concentration values for sulphur in different soils, above which no yield increase can be expected with increased sulphur fertilisation. Four soils, low in sulphur, were selected and treated with five sulphur levels. After four to five weeks the first deficiency symptoms appeared at the lowest sulphur levels. The plants were harvested after ten weeks. It was found that sulphur had a definite effect on yields and 10 mg kg-1 in soil can be used as a threshold value. AuthorsGrobler, L., Bloem, A. A. and Claassens, A. S. Year Published1999 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1999.10635012 This article contributed by:
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| A diallel study of yield differences among six well-adapted semi-dwarf spring wheats | Marais, G. F. | 1988 |
KeywordsGeneral combining ability, specific combining ability, Triticum aestivum AbstractA diallel study of the variability for yield that remained after an effort to exclude some of the factors known to contribute strongly to yield variation in the Winter Rainfall Region, was done. Overdominance resulted in strong heterosis effects which persisted in the F2. Little or no additive variation was expressed across the five environments sampled, while highly significant specific combining ability effects were evident. AuthorsMarais, G. F. and Botma, P. S. Year Published1988 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1988.10634261 This article contributed by:
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| A drought assessment model for Karoo rangeland | Venter, J. C. | 2002 |
KeywordsRange management, range production, risk assessment AbstractThe KAROO drought assessment model simplifies veld growth responses to rainfall variability by simulation of the growth and dieback of a hypothetical plant species. Soil water content is treated as a simple weighting factor which determines the plant's growth rate as a weighted average of two basic growth rates, viz. those under well- watered and dry soil conditions. Multiple growth stages of variable extent are postulated on the basis of evolutionary forcing by Karoo rainfall patterns. The model was fitted to growth data of a Karoo dwarf shrub species, assuming three growth stages which are initiated when the annual growth equals 0 (on day 1), 3 and 50% of that of an equivalent, well-watered plant. The averaging of basic growth rates needs further investigation in order to better simulate compensatory growth after drought. AuthorsVenter, J. C. Year Published2002 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2002.10634445 This article contributed by:
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| A family of stochastic models for droughts | Zucchini, W. | 1991 |
KeywordsDrought, rainfall, simulation, stochastic model AbstractThere is no single quantitative definition of a drought; what constitutes a drought depends both on water needs and on storage capabilities. In this paper a family of models is proposed which is sufficiently flexible to cover a range of different situations; the user may select some of the parameters to suit his particular application. The input to the model is a sequence of rainfall values which in turn may be generated by a stochastic model, thus enabling the simulation of a long sequence of rainfall data which allow the user to study the distribution of droughts of any given duration or severity. Several of illustrative examples are given. AuthorsZucchini, W., Adamson, P. T. and McNeill, L. Year Published1991 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1991.10634835 This article contributed by:
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| A field evaluation of the differential tolerance to soil acidity of forty-eight South African maize cultivars | Mendes, Ana
Paula | 1985 |
KeywordsAl tolerance, genotype × lime interactions, soil acidity, Zea mays L. AbstractA field experiment was conducted on a Normandien clay loam (Plinthic Paleudult) to compare the acid tolerance of 48 commercially grown maize (Zea mays L.) cultivars. Cultivars were compared in terms of grain yield, plant height and leaf Al content at four levels of lime (0; 2,5; 10 and 15 t ha−1). Statistically significant cultivar × lime interactions were noted in the case of all three criteria. In the absence of lime relative yields ranged from over 90% to less than 10%, relative plant height varied from approximately 80% to 50%, and relative leaf Al content from less than 150% to over 300%. With a few notable exceptions, probably caused by environment × cultivar interaction, cultivar rankings obtained with the different performance criteria were generally very similar. After statistical separation of the cultivars into classes, either ‘tolerant’, ‘intermediate’ or ‘intolerant’ in their reaction to acidity, 23 of the cultivars were identically classed using either yield, height or Al content in the absence of lime as performance criterion. On average, ‘tolerant’ cultivars were 33% taller than ‘intolerant’ cultivars in the absence of lime, produced more than double the yield, and had a 60% lower leaf Al content. Significantly, several of the least acid tolerant cultivars were among the best performers in the absence of acidity. It is considered encouraging that such large cultivar differences in acid tolerance were observed. Not only is it apparent that wide genetic diversity already exists among local maize cultivars with regard to acid tolerance, but the magnitude of the differences is such that the practical consequences are inescapable. S. Afr. J. Plant Soil 1985, 2: 215–220 AuthorsMendes, Ana
Paula, Farina, M.
P.W., Channon, P. and Smith, Marie Year Published1985 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1985.10634173 This article contributed by:
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| A field method to determine three dimensional infiltrability of vineyard soils | Myburgh, P. A. | 2002 |
KeywordsDrip irrigation, infiltrability, three dimensional, vine bank, vineyard AbstractA method is described to measure water intake from a small, shallow pond in which a 5 mm constant water head is maintained. Since water is supplied to the soil at near atmospheric pressure, infiltrability rather than infiltration rate is determined. Furthermore, water intake occurs in three dimensions, which simulates water intake under drippers. Therefore, the water intake process can be regarded as three dimensional (3-D) infiltrability. The small pond also simulates a condition often encountered in practice. Hence, 3-D infiltrability, expressed as litres per hour, will give an indication of dripper discharge rates that will cause water infiltration problems. Three-D infiltrability, measured in four vineyards showed that this parameter could vary significantly between vine banks and inter row spaces. The method was capable of measuring 3-D infiltrabilities that varied from 0.4 Mr1 to 14.0 1. h−1. Unlike more conventional infiltration methods, this method allows measurement of water intake on vine banks where water is supplied in most irrigated vineyards. The method also has a further advantage that the surface is completely undisturbed during an infiltration run. It can also be used to determine whether a surface crust is responsible for poor water uptake under drippers or not. This can be useful in making decisions with respect to soil amelioration or irrigation management practices to improve water infiltrability. AuthorsMyburgh, P. A., Howell, C. L. and Brink, D. Year Published2002 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2002.10634460 This article contributed by:
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