摘要:

Aangesien stralingsintensiteit met plek en tyd varieer, is die invloed daarvan op groei en ontwikkeling van mielies in 'n veldproef ondersoek. Drie stralingsintensiteite (100%, 75% en 42% van voile sonlig) en drie plantpopulasies (1.2, 2.7 en 5.5 plante m−2) is gebruik. 'n Stralingsintensiteit van 75% sonlig het dieselfde graanopbrengs as voile sonlig gelewer. By die 42% behandeling het graanopbrengsdrasties verlaag. Oesin- deks is nie deur die verskillende behandelings bei'nvloed nie. By lae stralingsintensiteite en hoëplantpopulasies het groter blaaroppervlakte verhoudings en BOI-waardes voorgekom wat waarskynlik tot die groter fotosintetiese doeltreffendheid bygedra het.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634622

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Honeybee foraging activity in commercial sunflower fields was studied at Settlers, 100 km north of Pretoria. Foraging activity, which was studied by means of the conventional strip count method, commenced after sunrise and reached a peak of 38 foragers per 100 capitula at 10:00. A moderate decline followed between 11:00 and 15:00 (mean number of 32 foragers per 100 capitula), whereafter another peak of 40 foragers per 100 capitula was reached two hours before sunset. Examination of returning foragers revealed that pollen foraging predominated until 09:00 and nectar foraging prevailed thereafter. Cross-pollination efficiency of honeybee foragers was good as more than 50% of foragers landed on the outer ring of florets and then moved to the inner ring where fresh pollen is available, before flying to the next head. Movement between heads was indiscriminate, which enhanced pollen movement.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634623

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Twee glashuisproewe en een veldproef is uitgevoer om die gevoeligheid van koringcultivars vir die wilde-haweronkruiddoder tralkoksidim, die breëblaaronkruiddoder bromoksinil en 'n mengsel van die twee te bepaal. Waar tralkoksidim teen dubbel die hoogste aanbevole dosisse met die benatter Addit(R)in die glas- huis op 16 koringcultivars en twee -lyne toegedien is, het die 16 cultivars en die twee lyne fitotoksisiteit teenoor tralkoksidim getoon. In 'n tweede glashuisproef waar tralkoksidim met Addit(R)in 'n tenkmengsel met bromoksinil teen dubbel die hoogste aanbevole dosis op 36 koringcultivars en vier -lyne toegedien is, het 26 van die cultivars fitotoksisiteit getoon. Drie cultivars wat in die glashuisproewe gevoelig was vir tralkoksidim en tralkoksidim plus bromoksinil tenkmengsel, en wat geregistreer is vir beide hierdie middels, is in 'n derde proef in die veld geplant en gespuit met tralkoksidim en bromoksinil en 'n mengsel daarvan teen aanbevole en dubbeldosisse. Die geregistreerde benatter vir tralkoksidim (Addit(R)) is in die veldproef teen enkel en dubbeldosisse ingesluit. Graanopbrengs van die cultivars het getoon dat die tralkoksidim teen dubbeldosis in 'n mengsel met bromoksinil fitotoksies op slegs SST 102 was.Nomenklatuur: Tralkoksidim (2-[1-(etoksie-imino) propiel]-3-hydroksie-5-(2,4,6-trimetielfeniel) sikloheks-2- enoon), difensokwat (1,2-dimetiel-3,5-difeniel-1H-pyrazolium), bromoksinil (3,5-dibromo-4-hidroksiebensoëni-triele).

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634624

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

The influence ofBusseola fuscaincidence and damage onFusarium moniliformeandStenocarpella maydisear rots was studied in the field using artificial infestation withB. fusca, mechanical damage and pathogen inoculation.B. fuscainfestation increased the incidence ofF. moniliformeinfected maize ears irrespective of artificial or naturalF. moniliformeinfection. Mechanical damage plusF. moniliformeinoculum also resulted in a high incidence ofF. moniliforme-infected ears suggesting that physical damage to the ear will increaseF. moniliforme-infected ears. Fungus-infected rotten kernel percentages ofB. fusca-damaged treatments did not differ significantly from the control. The insignificant correlation (r=−0.206;P= 0.695) betweenF. moniliforme-infected ears and per cent rotten kernels indicates that in the case of the former, when used as a disease criterion, damage was localized and did not result in significant grain quality reductions. NeitherB. fuscanor physical damage significantly affected the incidence ofS. maydis-infected ears or rotten kernels. Therefore, under the conditions of this study, the control ofB. fuscawill not result in significant grain quality improvement.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634625

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

The AMMI model, which incorporates both additive and multiplicative components into an integrated, powerful, least squares analysis, is used for the analysis of cultivar trials at different localities. These trials are a major experimental component in crop production and plant breeding research. Multilocation trials have as objectives the assessment of the success of yield predictions, the grouping of sites for evaluation and the interpretation of genotype-environment interactions. The data used originated from the National Lucerne Evaluation Program and the lucerne cultivars were representative of dormancy groups 4–9, i.e. semi-, intermediate-, non- and highly non-dormant. Expected trends in results from the yield trials were not obvious using the additive main effects model (ANOVA), while the application of the AMMI model resulted in rankings of cultivars in different environments which could readily be explained by the breeding history and dormancy of the cultivars.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634626

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effect of the level of water deficit on the yield of grain and total above-ground biomass of maize planted at greatly differing densities was investigated in a strictly controlled field experiment, repeated for four seasons. Differences in water supply were obtained by the seasonal variation in rainfall and by supplementing the rainfall with irrigation in some of the treatments. In each season the highest level of water represented conditions of adequate soil water supply. An abundant supply of inorganic nutrients enabled the study to be confined to an investigation of the interaction between level of soil water supply and planting density on the yields of maize. At adequate levels of soil water supply yields of grain and total above-ground biomass increased over the whole range of planting densities. The highest density employed (111 111 plants ha−1) gave rise to a LAI in excess of 8. Reduction in the supply of soil water caused a reduction in the critical planting density for maximum biomass production, but did not affect the asymptotic nature of the relationship between biomass yield and planting density. The relationship between the grain yield and planting density was influenced by a deficient level of soil water in two ways: firstly, by changing the nature of the yield response from nearly asymptotic to distinctly parabolic, and secondly, by reducing optimum density to lower levels as water stress became more severe.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634627

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

In South Africa, there is an extreme paucity of information relating maize (Zea maysL.) yields to soil and plant K levels and most K fertilizer recommendations are highly subjective. Controversy also surrounds the practice of relating K fertilizer recommendations to estimates of yield potential. The work reported here was conducted to address these shortcomings. The yield and plant compositional response of maize to a range of soil K levels was studied for eight seasons on a Metz clay soil (clayey, kaolinitic, thermic Plinthustalf). Relative yields were related to exchangeable soil K and the leaf parameters: K content, (Ca + Mg)/K and K DRIS index. Although grain yield maxima varied from 5.85 to 10.80 Mg ha−1, 91% of the relative yield variability was explainable in terms of exchangeable soil K. Leaf-based indices were also closely related to relative yield, but were sensitive to variations in topsoil moisture status prior to sampling and were not considered diagnostically superior to the K soil test. It is concluded that the optimum K level in this soil isc.0.32 cmol L−1, that there is no justification for relating K requirement to estimates of yield potential and that leaf diagnostic criteria should be interpreted with circumspection.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634628

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Glasshouse and field studies were conducted to examine the effect of high phosphorus (P) application on the tolerance of the maize cultivar SSM2041 to atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-tria- zine]. Two glasshouse experiments were conducted. In one, seedlings were exposed to five P concentrations and in the second, low (3:12) and high (12:3) NH4+:NO3-N ratios were combined with 310 and 403 mg P L−1, respectively. In the field study, fertilizer [3:2:1 (25%) + Zn] was band-placed in the field in a Hutton soil (15% clay) at levels of 150, 200, 300, 405 and 600 kg ha−1. Atrazine was applied at levels of 0.5 and 15 mg L−1in the glasshouse experiments, while rates of 0, 2.5, 5.0, 7.5, 10, 12.5 and 15 kg ai ha−1were used in the field. It was found that the tolerance of maize seedlings to atrazine was not influenced by fertilizer levels in the field. Under glasshouse conditions, high P levels alone did not significantly affect the tolerance of maize seedlings to atrazine. Growth was significantly impeded where 310 and 403 mg P L−1were used in combination with the 12:3 NH4+:NO3-N ratio. Atrazine, and the combination of high NH4+:N03-N ratio with 403 mg P L−1, lowered apparent CO2fixation significantly. Differences in P concentrations in the shoots of plants grown under controlled conditions could not satisfactorily explain the differential rates of CO2fixation. The tolerance of maize seedlings to atrazine was not influenced by high P application in the root zone or relatively high P concentrations in the shoots.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634629

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Six herbicide treatments are registered in South Africa for the control ofLantana camaraL. (lantana). Three of the treatments were selected for a costing analysis of the initial control of lantana, based on their suitability for specific situations in which lantana commonly occurs as a weed. For the investigation, a work study was performed to separate the cost of preparative operations (slashing) and herbicide application. The volume of the registered concentration of herbicide that was applied was recorded to permit costing of the chemical. Approximately 27 man days ha−1were required to slash medium to dense stands of lantana and 3.5 man days ha−1for sparse infestations. For chemical treatment of the stumps, imazapyr (Chopper®) in water was cheaper than picloram/triclopyr (Tordon Super®) in diesel owing to the respective costs of the carriers. The application of glyphosate (Roundup®)to lantana coppice was also more expensive than imazapyr application to the stumps. The efficacy of all three herbicides was high. As reinfestation of cleared areas usually occurs, follow-up treatment of lantana is essential. The cost of two seasons of follow-up treatment using glyphosate as a foliar spray was also recorded. The importance of follow-up measures for both budgeting purposes and the effective control of lantana, is emphasized.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634630

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

'n Bewegende gemiddelde daaglikse minimum en maksimum lugtemperatuur is vir 23 weerstasies bereken wat in die katoenproduserende gebiede van Suid-Afrika aanwesig is. Hierdie data is gebruik om daagliks kumulatiewe daggrade (ΣDG) oor die periode 3 September tot einde van Mei aan elke lokaliteit te bereken en met 'n regressievergelyking te beskryf. Verskille tussen die lokaliteite is statisties ondersoek. Die hoeveel- heid daggrade wat vanaf die intreedatum van 13°C gedurende die lente tot die uittreedatum daarvan in die herfs akkumuleer, is aan elke lokaliteit bepaal. Die waarde is beskou as die bruikbare daggrade (DGb) om 'n opbrengspotensiaal vir katoen daar te stel, en deels volwasse te maak. Siegs 1600 tot 1900 DGb is in Sen- traal-Transvaal, in Wes-Transvaal-Vryburggebied en Griekwaland-wes aanwesig om 'n opbrengspotensiaal daar te stel. Hierteenoor is 2400 tot 3000 DGb in die Laeveld en die Limpopovallei bruikbaar om 'n opbrengs te vorm.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634631

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor