摘要:

Criteria based on shrink-swell potential,viz.linear shrinkage and COLErod, were used to distinguish between melanic and vertic soil horizons of the Mooiplaas region in central Kruger National Park. For linear shrinkage the proposed boundary value separating melanic and vertic horizons lies at 14%, with ranges from 6 to 14% and 14 to 22%, respectively. Because a significant relationship existed between linear shrinkage and COLErod, the latter could be regarded as a reliable guide for measuring the expansiveness of soils. In addition, this method is fast, requires no expensive laboratory equipment, can be done with relative ease in the field, and furnishes reproducible results. Melanic horizons had COLErod values of 7–13% and vertic horizons 13–20%.S. Afr. J. Plant Soil1985, 2: 171–174

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634164

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Op 'n sandgrond met 9% klei in die B21-horison het ammoniumsulfaat hoër koringopbrengste gelewer as kalksteenammoniumnitraat en ureum. 'n Sandleemgrond met 20% klei in die B21-horison, het geen verskille tussen stikstofbronne getoon nie. Logingstudies in grondkolomme het aangetoon dat feitlik geen ammoniumstikstof uit laasgenoemde grond geloog word nie. Nitraatloging is aansienlik en baie hoër uit die sandgrond as uit die grond met meer klei. Omsetting van ammonium na nitraat is betreklik stadig in hierdie gronde, want 'n betekenisvolle vorming van nitraat het eers met die derde loging aan die lig gekom. Logingsverliese van stikstof was gevolglik baie kleiner in die geval van ammoniumsulfaat as vir ammoniumnitraat.S. Afr. Tydskr. Plant Grond1985, 2: 175–178

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634165

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

The susceptibility of soils to the deleterious effects of sodicity was assessed for samples which varied with respect to physical, mineralogical and other properties. For this purpose soil samples were collected from different locations in South Africa. The effect of electrolyte concentration and sodium adsorption ratio (SAR) on hydraulic conductivity (HC) was determined with permeameters, while the combined effects of raindrop impact energy and low electrolyte concentration of rain on infiltration rate (IR) were assessed using a rainfall simulator. Soils proved to be either stable or susceptible to the effects of sodicity as indicated by modulus of rupture, air-water permeability ratio, HC and IR measurements. Sesquioxides and organic matter promoted stability. Final IR was always less than HC due to crust formation even at low exchangeable sodium percentage (ESP) levels as a result of the dispersive effects of both mechanical impact (physical disruption) of rain drops and low electrolyte concentration (chemical dispersion). When the chemical effect was reduced (ESP>1 or higher electrolyte concentration as a result of surface gypsum application), final IR was higher.S. Afr. J. Plant Soil1985, 2: 179–186

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634166

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Differentiation of reproductive buds of the Starking apple (Malus domestica) was studied by scanning electron microscopy. Differentiation of reproductive structures was initiated during the first week of January when the shoot apex flattened. In terminal flower primordia, sepal primordia were evident in the second week of January, petal and stamen primordia from the end of January to mid-February and carpel primordia in mid-February. Floral organs developed slowly from March to August and pollen sacs were only formed in the anthers at the end of this period. Development accelerated during September and ovules formed three weeks before full bloom. The carpels rapidly increased in length and fused with the receptacle at their dorsal ends. The inner and outer integuments of the ovule developed and the filaments of anthers lengthened rapidly during the last three weeks before full bloom.S. Afr. J. Plant Soil1985, 2: 187–190

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634167

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

The effect of the crop of the previous season on cell size of the cortical region of flower primordia, flowers and fruit size in Starking Delicious apples was investigated. Cell number was monitored from the onset of differentiation of the sepal primordia of terminal flowers until maturity. A heavy crop during the previous season resulted in a decrease in cell number of the cortical tissue at the base of the developing flowers and fruit, and in reduced fruit size. The reduction in cell number was already evident eight weeks after the onset of differentiation of the sepal primordia. Although a decrease in the cell numbers of fruit was accompanied by large cells, these larger cells did not compensate for the reduction in cell numbers as determined by fruit size. The effect of crop size on fruit size persisted during the following two seasons notwithstanding thinning practices aimed at normalizing cropping levels. Lower cell numbers were evident when fruit of similar sizes were compared.S. Afr. J. Plant Soil1985, 2: 191–196

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634168

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

A six-year flood irrigation trial with lucerne (Medicago sativacv. Karoo) was conducted on a sandy loam soil in the south-western part of the Cape Province at Oudtshoorn. Two cropping practices, whereby one or two forage cuttings are followed by a seeding period, were investigated. The treatments comprised the application of 90, 135 and 180 mm (50–100% PAW) of water, as well as the same amounts, but in two equal parts, during a production period. Seasonalévapotranspiration (ET) varied from 382 to 668 mm, depending on the amount of irrigation per application. The halving of applications and doubling of irrigation frequency, did not increase ET above that of the full applications. Mean seasonal crop factors (ET/Ep) ranged from 0,40 to 0,70 for different levels of irrigation with a peak of 0,99 during the first forage period for a 180 mm application. Forage yields per unit area increased with an increase in irrigation level. The halving of applications also led to an increase in yield. Larger forage yields were obtained during the second than during the first production period. Growth rate of lucerne was enhanced remarkably at high irrigation levels, or when half-quantity irrigations at double the frequency were applied. Water use efficiency was highest for those treatments comprising of the smallest applications and the highest irrigation frequency. Seed yield was higher when less water was applied. Seed production was also increased when irrigation was applied in two parts.S. Afr. J. Plant Soil1985, 2: 197–202

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634169

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Germination and coleoptile growth of nine seed lots of maize (representing seven cultivars) were studied at 25°C (constant), 13°C (constant) and also at 7°C (7 days) followed by 25°C. Relative germination response to sub-optimal temperatures reflected relative differences in germination rate at 25°C. Exposure to 7°C before incubation at 25°C had a marked stimulatory effect on germination of cold- resistant cultivars at the higher temperature. Low temperature appeared to have a differential effect on germination rate and coleoptile growth. Differences in the magnitude of respiration rate did not relate to differences in low temperature susceptibility but kernels of cold-resistant cultivars failed to exhibit a typical respiratory lag phase.S. Afr. J. Plant Soil1985, 2: 203–206

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634170

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Four planting dates (early October to mid-January) were used to obtain a range of environmental conditions for growing three sunflower cultivars. The effect of planting date on phenological development was small compared to that of genotype though the hybrid S0404 responded significantly to photoperiod. Large differences in seed yield occurred between planting dates and this was found to be related to moisture stress during flowering. Fatty acid composition of the seed oil was related to temperature during the seed filling stage and moisture stress during flowering.S. Afr. J. Plant Soil1985, 2: 207–210

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634171

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Influence of fertilization on the oil concentration and oil quality of sunflower seed. Fertilizer trials (N,P,K and lime) were conducted over two seasons at three localities. Results indicate that 150 kg N ha−1fertilizer decreased the oil concentration of the seed by approximately 2% and the linoleic acid concentration of the oil by approximately 3%, whereas the protein concentration and the oleic acid concentration increased with increasing levels of nitrogen. Phosphorus and potassium fertilization had no effect on these characteristics. Nitrogen fertilization could therefore be used to alter the oil: protein ratio of the seed as well as the linoleic acid:oleic acid ratio of the oil.S. Afr. J. Plant Soil1985, 2: 211–214

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634172

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

A field experiment was conducted on a Normandien clay loam (Plinthic Paleudult) to compare the acid tolerance of 48 commercially grown maize (Zea maysL.) cultivars. Cultivars were compared in terms of grain yield, plant height and leaf Al content at four levels of lime (0; 2,5; 10 and 15 t ha−1). Statistically significant cultivar×lime interactions were noted in the case of all three criteria. In the absence of lime relative yields ranged from over 90% to less than 10%, relative plant height varied from approximately 80% to 50%, and relative leaf Al content from less than 150% to over 300%. With a few notable exceptions, probably caused by environment×cultivar interaction, cultivar rankings obtained with the different performance criteria were generally very similar. After statistical separation of the cultivars into classes, either‘tolerant’,‘intermediate’or‘intolerant’in their reaction to acidity, 23 of the cultivars were identically classed using either yield, height or Al content in the absence of lime as performance criterion. On average,‘tolerant’cultivars were 33% taller than‘intolerant’cultivars in the absence of lime, produced more than double the yield, and had a 60% lower leaf Al content. Significantly, several of the least acid tolerant cultivars were among the best performers in the absence of acidity. It is considered encouraging that such large cultivar differences in acid tolerance were observed. Not only is it apparent that wide genetic diversity already exists among local maize cultivars with regard to acid tolerance, but the magnitude of the differences is such that the practical consequences are inescapable.S. Afr. J. Plant Soil1985, 2: 215–220

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634173

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor