摘要:

Soil respiration is a major contributor to the carbon flux in apple orchards, but very little data exist for citrus. Daytime soil respiration, grass respiration, and grass photosynthesis were recorded in a ‘Nules’ clementine (Citrus reticulataBlanco) orchard on ‘Carrizo’ citrange or ‘X639’ rootstock in Stellenbosch, Republic of South Africa, under typically variable spring weather conditions such as cool to hot, and clear to cloudy days. The amount of CO2contributed by the citrus roots and the Oakleaf soil type to the carbon fluxes in the orchard, was evaluated. Soil respiration rate in the citrus rows varied between 0.1 and 0.4 g CO2m−2h−1and increased with temperature, with a Q10of about 1.4. After rainfall or irrigation, soil respiration was higher, especially at elevated temperatures. The rootstocks ‘Carrizo’ and ‘X639’ were characterised by slightly different rates of soil respiration. The difference was more pronounced after irrigation, and soil respiration of ‘X639’ exceeded that of ‘Carrizo’ by 0.03 to 0.04 g CO2m−2h−1. Grass respiration between the rows ranged from 0.7 to 1.4 g CO2m−2h−1and grass net photosynthesis exceeded 1.0 g CO2m−2h−1, indicating that the grass strips between the tree rows act as a sink for CO2during the light period. It was concluded that soil respiration represents a major source of CO2in a citrus orchard.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635124

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The potentially acidifying impact of air pollution coupled with agriculture and forestry has stimulated interest in the spatial assessment of soil quality deterioration in the highveld and eastern escarpment region of South Africa. Current information on soils is available as 1:250 000-scale land type maps depicting areas of relatively uniform soil pattern for which there is a quantitative inventory of soil series distribution. The objective of this study was to convert this information into a regional map showing the sensitivity of soils to acidification. Topsoils from 143 modal profiles, representing 57 soil series of the binomial classification system, were analysed for acid neutralizing capacity (ANC) using a simple method of pH measurement in acetate buffer solution. The relationship between ANC and relevant textural and chemical properties was then employed to classify, directly or by pedogenic inference, all the 504 series in the binomial system into 4 sensitivity categories. Arclnfo geographic information system (GIS) software was them employed to depict land types, classified in terms of their content of acid-sensitive soils, in a way which allows the most sensitive areas of the highveld to be identified as a basis for facilitating research and land use planning activities. The system for classifying soils in terms of acid sensitivity can be applied to any area in South Africa for which land type maps are available.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635125

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A number of staining procedures were evaluated after sodium dodecyl sulphate (SDS) Polyacrylamide gel (PAGE) electrophoretic runs of different wheat cultivars of the Western Cape. The staining method developed by Neuhoff, Arold, Taube and Ehrhardt, (1988) intensified a specific high molecular weight (HMW)-Glu-1 band in comparison with the other HMW-Glu-1 bands of a cultivar. This HMW-Glu-1 band is a genetic marker for good breadbaking quality. The protein content of this band, which showed a variation in its mobility and with a mass between 113.5 kDa and 103.5 kDa, was calculated by using laser densitometric scannings. This protein content can be expressed as a percentage of the total protein content of the SDS-soluble wheat protein of the specific cultivar and can be used to classify cultivars in different groups which correspond to their bread baking quality. This is, therefore, a fast, reliable and easy way to determine or predict breadbaking quality.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635126

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Fire is an important tool for the management of grazed savanna grasslands in the Eastern Cape, South Africa. The aim of this study was to quantify the influence of veld burning frequency on soil properties especially organic matter, pH, exchangeable Ca, Mg, K, Na and extractable P. Soil samples were collected from different depths in plots of a 17-year old experiment where burning frequencies were: no burning (B0), annual (B1), triennial (B3) and sexennial (B6). A land under continuous grazing and not burned (G) and strips between the plots (R) were also sampled for comparison. Burning significantly (p < 0.05) increased the pH and concentration of exchangeable Ca, Mg, Na and K but reduced the organic C and extractable P of the soil. The soil properties differed significantly between surface (0–10 cm) and lower (10–40 cm) layers: Ca, Mg, Na and pH increased with depth while K, organic C and extractable P decreased down the profile. Soil organic C was in the order B0>G>B3>B6>B1>R. The trend in the distribution of extractable phosphorus in the soil profiles mirrored that of organic C suggesting that most of the P was organic in nature. It is concluded that fire can make a significant contribution to the distribution of nutrients in a veld soil by rapidly mineralising the above ground biomass into ash. However, concern about the sustainability of a fire-managed system is raised in view of the high losses of carbon, nitrogen and sulphur from the biomass during burning. Considering the importance of organic matter in maintaining soil fertility and productivity, the use of other methods of nutrient cycling and redistribution should be encouraged.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635127

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Maize root rot is common in South Africa and various factors may influence disease severity.Phomaspp.,Trichodermaspp.,Fusariumspp.,Macrophomina phaseolina(Tassi) Goid. andExserohilum pedicellatum(Henry) Leonard and Suggs are the primary fungi isolated from infected roots. Since soil micro flora are affected by prevailing soil conditions, tillage practices may affect the incidence of soilborne fungi. Field trials, to determine the effect of tillage practices on disease severity, were carried out at Bloekomspruit and Mmabatho during the 1992/93, 1993/94 and 1994/95 seasons. Tillage practices applied were no-till, rip, mouldboard, disc and chisel plough treatments. Fungi were isolated from discoloured and apparently clean root tissue, quantified and identified. Significant interactions between isolation frequencies, effect of seasons and tillage practices were recorded forFusarium equiseti(Corda) Sacc.,Fusarium moniliformeSheldon,Exserohilum pedicellatumandPhomaspp. at Bloekomspruit andMacrophomina phaseolinaandPhomaspp. at Mmabatho. The effects of tillage practices on root discolouration and yield were inconsistent during these seasons at both localities. These inconsistent results may be due to the long period required to modify the soil profile by various tillage practices.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635128

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The 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 aestivumL.) 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.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635129

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor