摘要:

The efficiency of agricultural research in the RSA and the reporting of results need to be improved. Clarifying the accepted procedure for research and identifying common weaknesses in the resultant publications could contribute towards achieving this goal. All research originates with a question and is therefore, in essence, the acquiring of new knowledge. The following steps need to be taken: (1) Present a clear definition of the question to be answered. This should be stated in such a way that it defines rigorously the objective of the research. (2) Study all relevant observed facts from previous research work. (3) Formulate an hypothesis based on the observed facts. This is achieved by inductive reasoning. (4) Collect reliable data by observation, review or experiment to test the hypothesis. (5) Interpret the results to verify or reject the hypothesis. This is the process of deductive reasoning. If the hypothesis is verified it becomes the answer to the question, if rejected a new hypothesis is needed and the process repeated. Common pitfalls are a failure to define the objective clearly and inadequate study of previous research work, failure to formulate a clear hypothesis, inadequate data and poor interpretation of results. Common weaknesses in publications are lack of conciseness, haphazard literature citations, weak logic, unnecessary tables and diagrams and unsupported generalizations. It would be advantageous if more attention was given in the training of agricultural research scientists to the correct procedure for carrying out research work.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635072

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Preharvest sprouting significantly reduces the quality of the South African wheat crop. This study classified the preharvest sprouting resistance of 17 South African winter wheat cultivars sampled over a range of typical winter wheat growth environments. Sampling was performed under field conditions and sprouting responses were evaluated under controlled conditions. Variation in sprouting response between cultivars was predominantly genetically determined and varied from 1.7 to 7.4 on a scale from 1 (no visual sprouting) to 8 (fully sprouted). Canonical variate analysis and AMMI analysis, as well as the use of hierarchical clustering of cultivars over environments using the AMMI estimates, identified four distinct groups ranging from resistant to susceptible. The AMMI model was used as it combines the additive main effects of the analysis of variance with the interaction effects of principal components analysis. In general, Betta, and certain cultivars derived from Betta, showed good to moderate resistance to preharvest sprouting, while the hybrids Caritha and Carol, as well as the purelines Tugela and Tugela-DN, tended to be highly susceptible to sprouting.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635073

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Min is bekend oor die effek van boerderypraktyke soos bewerking, bemesting en bekalking op die fosforfraksies in gronde van die somerreënvalgebied (25°-30°S; 24°–30°O) in Suid-Afrika. Die doelstellings van die studie was om die effek van gewasverbouing op die totale (Pt), anorganiese (Pa) en organiese (Po) fosforfraksies van hierdie gronde te kwantifiseer en om vas te stel hoe die Pa- en Po-fraksies, wat ten opsigte van planttoeganklik- heid verskil, deur gewasverbouing beïnvloed word. Siegs die effekte van gewasverbouing op Pt, Paen Poword hier gerapporteer. Bewerkte en nabygeleë onversteurde bogronde (0–200 mm) is by 50 lokaliteite, wat verspreid in die ondersoekgebied voorkom, versamel. 'n Opeenvolgende ekstraheringsprosedure is gebruik om die Pa(NaHCO3-Pa, NaOH-Pa, HCI-Paen residuele-Pa) en Po(NaHCO3-Po, NaOH-Poen residuele-Po) in die monsters te fraksioneer vir kolorimetriese bepaling. Daarna is Pt, Paen Podeur sommering van die relevante fraksies bereken. Die Ptvan die bewerkte gronde was in 76% van die gevalle groter as die van nabygeleë onversteurde gronde. Dit is omdat die toename in Paweens bemesting groter was as die afname in Poweens mineralisasie. Gevolglik is die bydrae van Patot Ptgroter as die van Potot Ptin die bewerkte gronde, wat nie die geval in die onversteurde gronde was nie. Die korrelasies van organiese C, totale N en totale S met Poin die bewerkte gronde is oorwegend lare as in die onversteurde gronde. In beide die onversteurde en die bewerkte gronde het Pt, Paen Pogoed onderling gekorreleer. Klimaatsparameters en grondeienskappe het 'n kleiner persentasie van die variasie in die drie fosforfraksies verklaar.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635074

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Daar is voorheen vasgestel dat gewasverbouing die anorganiese (Pa) en organiese (Po) fosforinhoud van gronde vanaf die somerreënvalgebied (25°-30° S; 24°-30° O) in Suid-Afrika beïnvloed het. Dus kan die Pa- en Po-fraksies, wat in planttoeganklikheid varieer, ook moontlik beïnvloed word. Die gevolg hiervan is dat die potensiaal van 'n grond om P te voorsien ook kan verander. Die doel met hierdie Studie was dus om die effek van gewasverbouing op die Pa- en Po-fraksies, wat in planttoeganklikheid verskil, te kwantifiseer. Bewerkte en nabygeleë onversteurde bogronde (0–200 mm) is by 50 lokaliteite, wat verspreid in die ondersoekgebied voorkom, ver-samel. 'n Opeenvolgende ekstraheringsprosedure is gebruik om die Pa(NaHCO3-Pa, NaOH-Pa, HCI-Paen residuele-Pa) en Po(NaHCO3-Po, NaOH-Poen residuele-Po) in die monsters te fraksioneer vir kolorimetriese bepaling. Die bydrae van die Pa-fraksies tot Pahet in die onversteurde gronde soos volg toegeneem: NaHCO3- Pa< HCI-Pa< NaOH-Pa< residuele-Pa. Toegediende P, wat nie deur die gewasse gebruik is nie, het in dieselfde volgorde in die Pa-fraksies geakkumuleer as wat die planttoeganklikheid daarvan afneem: NaHCO3-Pa> NaOH- Pa > HCI-Pa> residuele-Pa. In die onversteurde gronde neem die bydrae van die Po-fraksies tot Posoos volg af: NaOH-Po> residuele-Po> NaHCO3-Po. Die maklik mineraliseerbare NaHCO3-Pohet in 62% van die gevalle weens gewasverbouing gedaal. Gewasverbouing het in 36% gevalle 'n afname en in 34% gevalle 'n toename van NaOH-Potot gevolg gehad. Residuele-Po, wat gewoonlik die meeste weerstand teen mineralisasie bied, het in 54% van gevalle as gevolg van gewasverbouing gedaal. Dit wil voorkom asof die toediening van P die mineralisasie van NaOH-Potot 'n mate teengewerk het. Die onderlinge korrelasies tussen die Pa-fraksies en ook tussen die Po-fraksies is van 'n relatief lae orde. Klimaatsparameters en grondeienskappe verklaar min van die variasie in beide die Pa- en Po-fraksies.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635075

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Three different anther culture methods for the South African tobacco cultivars C11 × WOSB and CDL 28 were tested. The yield of haploid plantlets produced using a solidified or double-layer medium was significantly higher than with the use of a liquid culture medium. The former two media showed no significant differences. Important considerations which must be taken into account when deciding on the optimum culture method for anther cultures are also discussed.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635076

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

'n Potproef is onder temperatuur-gekontroleerde toestande in 'n glashuis onderneem met 'n fynsandgrond wat aanvanklik vry van rhizobium bakterieë was.Glycine max(L.) Merrill (kultivar Prima) is met 'n mengsel van twee bekende rasse vanBradyrhizobium japonicumgei'nokuleer. Die invloed van vier peile (0, 10, 20 en 40 kg N ha−1) gemerkte15NH4-N wat gedurende vier groeistadia (V1, R2, R4 en R5) toegedien is op die opbrengs en N- samestelling van sojaboonsaad is ondersoek. Die aantal peule, sade en biomassa van die plantdele is bepaal. Stikstoffraksies wat in die bogrondse plantdele en saad uit die grond en kunsmis benut en simbioties gebind is, is met die isotooptegniek bepaal. Die aantal peule, sade, blaar- en saadmassa, totale N en proteïenproduksie is met N-bemesting in die V1-groeistadium, verhoog. Stikstof wat in die R2-groeistadium toegedien is het min effek op saad-opbrengs en proteïengehalte. Toediening van N gedurende die R4-groeistadium, wanneer atmos- feriese N aktief gebind word, het saadopbrengs, biologiese N-binding, grond-N-opname en proteïenproduksie onderdruk. Die saadmassa en proteïenproduksie is met N-toedienings in die R5-groeistadium ook verhoog. Hoër N-peile, toegedien in die V1- en R5-groeistadia, het blaar-, saad- en totale bogrondmassa laat toeneem. Ongeag die N-peil, het latere toedienings die misstofgebruikseffektiwiteit in die saad verbeter.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635077

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Saline soils pose a great problem to reclamation of mined areas in arid regions. Experiments were carried out in order to determine the tolerance of six Namaqualand pioneer species to varying levels of salinity. Both perennial and ephemeral species were used and results of all species showed that increased salinity induced a significant decrease in biomass production. With increased salinity, biomass allocation towards the leaves increased, while that towards the stems decreased in both perennial and ephemeral species, but biomass allocation towards the other plant organs varied. Of the six species tested, the perennials seemed to be better suited for rehabilitation purposes under saline soil conditions.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635078

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Grey leaf spot (Cercospora zeae-maydisTehon and E.Y. Daniels) is a relatively new disease of maize in South Africa and is capable of reducing grain yields by 20–60% in KwaZulu-Natal. Fungicides are widely used for control, but must be applied at the correct stage of disease development. Repeated applications may be necessary for effective control to be achieved. There is a paucity of information on the economic justification of these control measures. The aim of this study was to estimate the economic benefits of single and multiple sprays applied to maize at different stages of disease development. The economic analysis was based on the average operating costs of 18 dryland maize farms in the Winterton and Karkloof areas, where fungicides have been used to control the disease. These costs were used in the analysis of data generated from trials at Cedara to determine the most effective times and frequency of fungicide application for the control of grey leaf spot. Triple-spray treatments under both high and low disease levels provided better control of disease (higher-yield gains over non- sprayed treatment) but did not always give highest added profit ha−1. Least risk-averse farmers would probably select the triple-spray programme under high levels of disease, since it provided highest added profit ha−1. The double-spray programme, with lower added profit ha−1under high levels of disease may, however, be preferred by more risk-averse individuals. Under low levels of disease, the single-spray treatment, giving higher added profit ha−1, may be more attractive to least risk-averse farmers.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635079

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor