摘要:

Field experiments were conducted on two soil types over a period of five years (1986–1990) to investigate the effects of tied ridges and planting systems on the grain yield response of maize to applications of crop residue and residual N and P fertilizers. Grain yields were increased by the use of tied ridges. Further increases in grain yields resulted from residual N and P and crop residue applied separately or together. Under all fertilization practices, planting in the furrow of tied ridges resulted in higher grain yields than planting on top of tied ridges. The effect of the tied ridges in increasing grain yields was generally better in the drier periods and the more so when the ends of the ridges were tied. In wetter seasons the open end tied ridges gave higher yields than the closed end tied ridges. The effect of tied ridges on grain yield response of maize to application of crop residue and residual N and P fertilizers was influenced by rainfall and by soil type.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635130

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The present investigation was initiated because of the limited success achieved in the past at attempts to revegetate chrysotile tailings with their associated inherent environmental risk factors. The current set of experiments and surveys, as with several previous studies, were conducted at Msauli chrysotile mine, Mpumalanga Province, South Africa. All soil and leaf samples were collected, and the total percentage canopy cover, species frequency, percentage cover per species, percentage alive biomass, and phenology per species quantified. This was done in nine randomly selected 1m2areas, on both the upper (steeper) and lower (less steep) slopes of previously revegetated slopes, with comparable samples from areas within the native vegetation serving as controis. Nine composite (consisting on average of three 500g samples) replicate soil samples per slope gradient, as well as leaf samples (ca. 5g of dried above ground leaf material) representative of the species composition, were sampled in the same plots where the plant surveys were conducted. The same procedure was followed, both in areas where the tailings were removed, or not prior to reyegetation, in areas that can qualitatively be described as: well revegetated, poorly revegetated and areas with no plant cover, on both a north and south facing slopes, respectively. Although having been independently assayed, the soil and leaf analysis data per slope gradient were pooled as no statistically significant differences could be detected. Three data sets of the same number of composite replicate samples (comparable native vegetation served as control) and descriptive vegetation data were also collected on the top level surface of two chrysotile tailings dumps that had prior to revegetation been covered with 300mm and 500mm of topsoil, respectively. As with the above, the soil and leaf analysis data were once again pooled because of the absence of any statistically significant differences. The die-back phenomenon observed at Msauli can probably primarily be ascribed to an inadequate supply of Ca, of which the low Ca concentration per se is both responsible for the imbalances in terms of N metabolism (N02- accumulation) and limited root development. Also, the low Ca concentrations encouraged the uptake of Fe to potentially toxic levels, as was reflected by the high foliar Fe concentrations of the plants on the revegetated areas. The potentially toxic B concentrations in both the soil and plants sampled on the revegetated areas necessitates an increase in the Ca concentrations, which will also limit the stress response of anthocyan production. In this regard it is interesting to note that the incorrect use of CaSO4to lower the high pH values assoduted with chrisotile tailings probably suppressed the uptake of K, a situation worsened by the high Mg concentrations. The plant symptomatic response of general chlorosis, as well as the rapid development of brown necrotic lesions along the leaf margins, are probably the consequence of MgCl absorption. The generally low micronutrient and heavy metal concentrations typifying the revegetated areas can probably be ascribed to the low solubility of their hydroxides at the alkaline pH values of these areas. Since no statistically significant differences either in terms of nutritional status or vegetative variables monitored could be observed in the areas where top soil layers of different thickness were used, this would not seem to be one of the primary factors determining revegetation success. Because of the poor correlation found to exist in terms of species composition between the native vegetation and that typifying the revegetated areas it would seem futile to use any other seed in revegetation attempts than that already adapted to the serpentine site specific conditions.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635131

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The Transvaal teak (Pterocarpus angolensis)is being over utilised in its natural habitat, although it is a protected tree in South Africa, Swaziland and Namibia. The phloem sap of this species has several traditional, medicinal uses and the wood is used primarily for furniture and fuelwood. The aim of this study was firstly, to determine which seed pre-treatments would ensure optimal germination and secondly, to evaluate the potential antimicrobial activity of the phloem sap. The initial germination trial was conducted by using unsterilised seeds in the dark, which resulted in low germination rates (7.78%) and high percentages of fungal infections (45.56%), primarilyAspergillus nigerand aFusariumsp. In the second experiment the seeds were sterilised with a mixture of 60 g Thiram and 70 g Captan and germinated in an alternating light/dark environment. In both experiments the seeds were subjected to either a hormonal, heat or control pre-treatment and were allowed to germinate at three different temperature regimes. Different sap concentrations were tested for antimicrobial activity against both gram positive (Staphylococcus aureus) and gram negative (Escherichia coli; Pseudomonas aeruginosa)procaryotes as well as two eucaryotes (Candida albicans; Aspergillus niger), with negative results. The phloem sap was analysed by means of GC-MS and a few compounds, which have been identified, are reported.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635132

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Accurate identification of breeding material is very important for the plant breeder. In South Africa, high molecular weight glutenin subunits (HMW-GS) have so far been used for wheat cultivar identification. This method can often not distinguish between cultivars, and other techniques need to be investigated. The aim of this study was to compare HMW-GS, low molecular weight glutenin subunits (LMW-GS) and random amplified polymorphic DNA (RAPDs) for wheat cultivar identification. Five commercial wheat cultivars were analysed using the above three methods. The HMW-GS failed to distinguish between the five cultivars. LMW-GS could clearly distinguish between the cultivars, but banding pattern interpretation was more complicated than for HMW-GS. RAPDs could distinguish between the five cultivars with three different primers, but were expensive and would need an increased number of primers with an increase in cultivars. We concluded that HMW-GS should be used for initial cultivar identification, as it is simple and reliable. Where they fail to distinguish between cultivars, the LMW-GS should be used for final identification.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635133

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The study was undertaken to estimate surface cast production by microchaetid earthworms and to compare the physical and chemical properties of the casts with the surrounding non-cast soil. An average of 104 (range 64–132) and 192 (range 182–222) t ha−1of surface casts were produced at Alice and Dimbaza sites in central Eastern Cape during the period September 1995 to August 1996. The casts had an average height of 6.8 cm and diameter of 5.6 cm and had higher silt and clay (66.2 vs 62.9%) but lower sand (33.8 vs 37.1 %) sized partides than the non-cast surface soil. The casts also had a higher proportion of water stable aggregates > 0.5 mm (76.7 vs 67.2%), mean weight diameter, bulk density (1.55 vs 1.37 Mg m−3) and retained more water than the non-cast soil. Earthworm casts had significantly higher available Bray 1-P, exchangeable K, Ca, Mg and Na than the non-cast soil. Levels of organic C and pH were also elevated in earthworm casting compared to surrounding soil. The large amounts of casts that are deposited on the surface can play an important role in modifying the hydraulic properties at the soil surface and help minimise runoff and erosion. Because of the high concentration of nutrients in casts compared to non-cast soil, potential may exist for using the casts to supply plants with nutrients.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635134

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Herbicide resistance raises the possibility that the agricultural industry and crop producers might loose a valuable chemical tool that is essential for the control of weeds in wheat (Triticum aestivumL.) production. The recognition of herbicide resistance occurred relatively recently (1960), despite the widespread use of selective herbicides worldwide. Resistant biotypes ofAverta fatuaL. to diclofop-methyl (±)2-[4-(2,4dichlorophenoxy)phenoxy]propanoic acid were confirmed in the western Cape. Recently, farmers and chemical companies reported resistance ofLoliumspp. to several selective herbicides in small grains in the western Cape. The main objective of the present study was to assess resistance ofLoliumspp. against ACC-ase inhibitors used in wheat production. Seed ofLoliumspp. which were suspected to be resistant was sown in pots in a glasshouse at a temperature regime of 15°C/20°C (night/day). During the 2–4-leaf stage, the plants were sprayed with four herbicides viz. diclofop-methyl, clodinafop-propargyl (2-propynyl (R)2-[4-(5-chloro-3-fluoro-2-pyridinyloxy)-phenoxy-pro pionate], tralkoxydim (2-(1 [ethoxyimo)propyl]-3-ktydroxy-5-(2,4,6-trimethylphenyl)cyclohex-2-enome) and imazamox, 2[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-(methoxymethyl)-3pyridinecar bolic acid at double the registered rates. Four weeks after herbicide application, percentage control was measured by comparing fresh plant mass. This study confirmed resistance ofLoliumspp. to ACC-ase inhibitor graminicides registered for use in wheat in the western Cape.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635135

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Combining ability of R-lines with respect to malt quality and stem borer resistance was evaluated in two trials. Crosses between three R-lines and eight R-lines were made for malt quality and three R-lines and seven R-lines for stem borer resistance evaluation. The R-line RTx432 showed superior combining ability for both characteristics, indicating its potential value to the local sorghum industry.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635136

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor