摘要:

Die invloed van verskillende nitraat: ammoniumverhoudings by sub- en supra-optimale stikstofkonsentrasies op die opname en benutting van stikstof is ondersoek. Effektiewe stikstofbenutting is in terme van saadopbrengs per eenheid opgeneemde stikstof gemeet. Die beste nitraat: ammoniumverhouding was 3:1 by 100 mg N l−1. Hierdie verhouding het 'n hoogs betekenisvolle hoër benutting van opgeneemde stikstof bo 'n 1:0- of 1:1-verhouding by 100 mg N l−1gehad. Nitraat: ammoniumverhoudings van 3:1 en 1:1 by 400 mg N l−1was erg nadelig ten opsigte van saadproduksie en die effektiewe benutting van stikstof. 'n Hoër ammonium-N-konsentrasie by dieselfde stikstofkonsentrasie in die voedingsoplossing het die stikstofinhoud (%N) in die plantdele betekenisvol verhoog. Hierdie verhoging het egter nie gepaard gegaan met 'n verhoogde stikstofopname nie.S.-Afr. Tydskr. Plant Grond.1986, 3: 57–60

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634189

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

The effect of photoperiod and temperature on the pre-flowering phase length of 11 soybean cultivars was studied. Heat units (10 to 30°C) and night hours (sunset to sunrise) were used as measures of temperature and photoperiod respectively. Highly significant negative correlations were found between pre-flower phase length and heat units, especially in the early cultivars. Indications of an interaction between photoperiod and temperature were observed. Partial correlation analyses indicated that in respect of days to flowering, the medium and late cultivars were equally responsive to photoperiod and temperature. The early cultivars were more responsive to temperature. Photothermal units gave a measure of the interactive effects of photoperiod and temperature on the length of the pre-flower phase. Highly significant correlations between days to flower and photothermal units were found.S. Air. J. Plant Soil1986, 3: 61–65

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634190

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

A range of concentrations of a number of herbicides was tested in field trials, for the control ofChromolaena odorata(L.) R.M. King and H. Robinson. The results obtained show that triclopyr, 2,4,5-T and tebuthiuron were consistently the most effective, regardless of application time or site. A dose-related response was evident in the treatments, the higher the concentration the greater the percentage mortality ofC. odorata.Application during late summer (March) resulted in greater mortality than early summer (December) application. Tebuthiuron and in one case, imazapyr, caused mortality of plantation trees. Based on these studies, triclopyr was adjudged to be the most suitable herbicide for the control ofC. odorataoccurring in a number of situations.S. Afr. J. Plant Soil1986, 3: 66–70

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634191

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Sucrose, glucose and fructose were the major free sugars in the leaves, stems and inflorescences ofT. triandra, while small quantities of rhamnose, xylose, galactose, mannose, ribose, cellobiose, sedoheptulose and erythrose were also present. Several polysaccharides and components with lower molecular weights, possibly dextrins and oligosaccharides, were extracted by water at room temperature (20°C) and boiling point (96°C). These carbohydrates were biosynthesized from a number of different monosaccharides. No fructans were found, confirmingT. triandra'sclassification among the panicoid grasses which mainly store reserve carbohydrates in the form of sucrose and starch.S. Afr. J. Plant Soil1986, 3: 71–75

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634192

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634193

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

The relative severity of drought in natural grassland during three growing seasons was analyzed for three South African weather stations. Computer simulation of grassland water use, based upon weather records, was used to quantify drought and to compare the conditions which prevailed during 1981/82, 1982/83 and 1983/84 to expected conditions at Glen, Bethlehem and Potchefstroom. Probabilities for expected conditions were estimated from frequency distribution analysis of simulations from historical weather records. All three sites suffered at least one year of extreme drought, in which grassland water use was lower than that expected during the driest year in ten.

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634194

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

A rapid and simple method for the extraction and quantification of the herbicide atrazine, the atrazine hydroxylating agent in maize plants DIMBOA, and the hydroxylated product hydroxy-atrazine, is described. These substances were quantified by means of HPLC techniques, employing a RP-18 column and a mobile phase of methanol:water (40:60), buffered at pH 7,4. This method was developed to determine the efficiency of the atrazine hydroxylation detoxifying mechanism in maize plants cultivated under different environmental stress conditions.

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634195

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

The effect of different pre-treatments on the dormancy of the hard-coated seeds ofAcacia longifoliaAndr. Willd. was determined. A final germination figure of 100% could be obtained with hotwatertreatments, acid scarification and manual scarification. However, if germination rate was taken into consideration, acid scarification proved superior to all other treatments.

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634196

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

The effect of temperature and light intensity on the dehiscence of anthers ofMangifera indicaL. cv. Haden andon the in vitro germination, stainability and viability ofmango pollen grains was studied. Pollen of two mango cultivars grown in South Africa was compared, viz. Haden, a shy bearer, and Sensation, a prolific cultivar. Temperature had a marked effect on the tempo of anther dehiscence, irrespective of the light intensity. A 30% sucrose solution yielded the highest mean percentage germination and pollen tube length in both cultivars. The percentage aborted pollen was 31,3% in Haden and 24,5% in Sensation. Pollen from anthers at the moment of dehiscence showed the highest percentage viability of 56,1% in Haden and 81,1% in Sensation.

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634197

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

In 'n langtermyn bemestingsproef met koring onder besproeiing het groot verskille in grondvrugbaarheid oor jare ontwikkel, wat ook in groot verskille in graanopbrengs weerspieëf word. Opbrengs en opbrengskomponente was kleiner op persele wat geen P-bemesting ontvang as op persele wat geen K ontvang. N het 'n minder beperkende rol gespeel as gevolg van die gebruik van sojabone as wisselbougewas. Die opbrengskomponente wat die grootste bydrae tot verhoogde graanopbrengs gelewer het, was getal are per eenheidsoppervlakte, gevolg deur die getal blompakkies per aar, terwyl korrelgrootte minder deur die wisselende vrugbaarheidsvlakke beïnvloed is. Getal korrels per blompakkie het nie verskil nie. 'n Toename in een komponent het nie tot 'n kompenserende afname in enige van die ander komponente gelei nie. Aanduidings is gevind dat grondvrugbaarheid die opbrengskomponente indirek beïnvloed het, via die invloed daarvan op blaaroppervlakteduurte.

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634198

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor