摘要:

The causes, adverse effects and control of soil compaction, with special reference to Southern African conditions, are reviewed. The main causes for soil compaction are the well-rounded and -sorted fine sand fraction of the aeolian sandy soils combined with compression by soil tillage equipment. Layers with high penetration resistance decrease rooting depth and density which lead to a reduction in plant nutrient uptake, water uptake and water-use efficiency. A system of deep tillage combined with controlled wheel traffic to predetermined lanes is recommended as a measure of control.S. Air. J. Plant Soil1985, 2:109–114

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634148

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Twelve dry bean cultivare were grown for seven days on filter paper soaked with nutrient solution containing a range of up to 10 mmol Al dm−3. Differential response to Al toxicity, measured as taproot elongation, occurred at Al concentrations of≧2 mmol dm−3. Fifteen cultivare (including four cultivare classified in terms of Al tolerance by the nutrient-solution method) were grown in pots containing an acid (64% acid saturation of CEC), P-deficient clay loam subsoil (Plinthic Paleudult), differentially treated with Ca(OH)2and CaHPO4. 2H2O. After 35 days the plants were classified in terms of tolerance to acid, low P soil conditions, on the basis of relative topgrowth yields. Three of four cultivare screened by both methods were classified identically: lapar-Rai-54 and W126 as tolerant, and BAT331 as sensitive.S.Afr. J. Plant Soil1985, 2: 115–119

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634149

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Die koue- en daglengtereaksies van koringkultivars in groeikaste is ondersoek as aanduiding van die produksiegebiede waar die betrokke kultivars sal aanpas. Die resultate toon dat die 24 koringkultivars wat ondersoek is, uiteenlopende koue- en daglengtereaksies vertoon. Klassifikasie van die kultivars op grond van hierdie inligting het goed ooreengestem met die nasionale kultivar-aanbevelings wat grootliks op die opbrengsprestasie In kultivarveldproewe gebaseer is.S.-Afr. Tydskr. Plant Grond1985, 2: 120–122

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634150

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

The seasonal abundance ofBusseola fuscamoths at five localities in the maize production area of South Africa was monitored by means of Robinson light traps. Geographical variation in the flightpattern was shown to exist betweenlocalities from east to west. Both the time and magnitude of the three seasonal moth flights seem to be governed by climatic factors. It is pointed out that the severity and the time of occurrence of larval infestations in different localities are largely predetermined by the time of planting.S.Afr. J. Plant Soil1985, 2: 123–126

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634151

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Sterk eenjarige winterlote van 'n tien-jaar-oue Merton-793-moederplantasie is opgedeel in steggies van 30 cm lengte. Die basale steggie is gesny vanaf die punt van aanhegting, met die tweede en derde steggie in opeenvolgende posisies nader aan die lootpunt. Die posisie van steggies op die loot het geen verskil in bewortelings- persentasie voor bot tot gevolg gehad nie. Verskille in persentasie oorlewing tussen steggies vanaf verskillende lootposisies is egter verkry nadat steggies toegelaat was om te bot en te groei. Hierdie verskille het verband gehou met die werklike hoeveelhede koolhidrate wat die steggies bevat het.S.-Afr. Tydskr. Plant Grond1985, 2: 127–129

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634152

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

The major wheat-producing areas in the Winter Rainfall Region are geographically divided into the Rûens and Swartland. The question whether the Rûens and Swartland should be regarded as non-similar areas, each meriting its own wheat-breeding programme, is considered. Correlations between cultivar means obtained in the two regions, interaction variance components, the nature of patterns regarding yield at different flowering dates and the similarity in choice of cultivars by farmers in the two areas, all sėem to point to a high degree of similarity. It is concluded that it may not be worth while to conduct separate breeding programmes.S. Afr. J. Plant Soil1985, 2: 130–134

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634153

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

An evaluationofthe present system of testing of advanced wheat lines was made in terms of expected genetic gain from selection. Indications are that this system can function quite effectively if properly managed. The feasibility of substituting high potential test sites for low potential test sites in order to facilitate yield testing was also investigated. It was concluded that it may be more appropriate to select test sites on the basis of production intensities, predominant soil types and annual rainfalls. One such solution was derived and is proposed for implementation in the Winter Rainfall Region.S. Afr. J, Plant Soil1984, 2: 135−140

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634154

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

In 'n waterkultuureksperiment met koring is die invloed van verskillende P-toedienings (0,02 tot 5,0 me H2PO4dm−3) en van verskillende NH4:NO3-verhoudings (0:15 tot 12:3) met 'n Hoagland-voedingsoplossing (no. 2) as kontrole bestudeer. Normale groei is reeds by 'n laer P-voorsiening (0,2 me dm−3) as die kontrole (1,0 me dm−3) verkry. Die hoogste P-voor-sieningsvlakke het opbrengs verlaag by die laagste NH4: NO3-verhoudings. Beter opbrengs is verkry met intermediäre NH4:NO3-verhoudings, waarvoor hoër P-voorsiening noodsaaklik was. By hoëP-voorsiening het chlorose-simptome tussen die blaarnerwe voorgekom wat vererger het met hoër NH4:NO3-verhoudings. Plantontledings dui daarop dat behalwe by die hoogste NH4: NO3-verhouding, die chlorose-simptome toegeneem het met hoër P-status in die bogroei. Die teenoorge- stelde tendens het ten opsigte van die P-status in wortels voorgekom. By hoëP-voorsiening is dit moontlik dat NO3die vervoer van P vanuit die wortels na die bogroei verminder en gevolglik die simptome wat met hoëP-status in die bogroei geassosieer word, verminder. Die N-status van die bogroei het verhoog van die laagste na die hoër P-voorsiening. Hierdie verhoging was meer wanneer slegs NO3voorsien is, as wanneer NH4en NO3voorsien is. Hieruit is afgelei dat P-voorsiening minder kritiek is vir N-opname as beide NH4en NO3voorsien word.S.-Afr. Tydskr. Plant Grond1985, 2: 141−145

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634155

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Recovery of growth following atrazine and cyanazine toxicity and the effect on subsequent grain yield of sorghum were studied in nutrient solutions in two separate experiments. In Experiment I, concentrations of atrazine and cyanazine were decreased at weekly intervals based on halflife values of 60 and 15 days respectively. Cyanazine was initially more toxic to sorghum than atrazine. By the termination of the experiment cyanazine-treated plants had recovered better and outyielded atrazine-treated plants. Although significant yield reduction resulted in all treatments, the degree of initial toxicity was not necessarily reflected in grain yield. In Experiment II, sorghum was exposed to atrazine for periods of 1, 2, 4, 8, 12 and 16 weeks before returning to atrazine-free solutions. Grain yields were reduced significantly in all treatments except where sorghum was exposed to atrazine for one week only. Recovery was a function of the degree and persistence of toxicity. Grain yield reduction was associated with the commencement of recovery after the differentiation of the growing point to the reproductive phase.S.Afr. J. Plant Soil1985, 2: 146–150

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634156

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor

摘要:

Veldkapasiteit (VK) isin situbepaal op verskeie gronde in Wes- Kaapland. Grondtekstuur het gewissel van sand tot sandklei. Veldkapasiteit is op vyf dieptes bepaal en het gevarieer van 4,9% tot 27,2% op massabasis. Matrikspotensiaal by VK het gewissel van−9,1 tot−1,4 kPa. In totaal is 105 bepalings op 23 persele uitgevoer. Faktorontledings het 11 grondfisiese eienskappe in vier faktore gegroepeer ten opsigte van hul verwantskappe metin situ-VK.Hierdie faktore het aangetoon dat klei-inhoud, growwesand, matriksdigtheid (pb), versadigde hidrouliese geleivermoëen tydsverloop vanaf versadiging tot VK, die beste voorspellers van VK sal wees. Meervoudige re- gressies het bewys dat 'n voorspellingsvergelyking met vier ver- anderlikes, te wete klei, growwesand, pb enKs, 78% van die variasie in VK verklaar. Die regressiekoëffisiënte vir growwesand, Pb enKswas negatief, en klei positief, ten opsigte van VK (R= 0,88). Daar was 'n uitstekende reglynige verband tussen VK en waterinhoude wat by 10, 33 of 1500 kPa in die laboratorium bepaal is op versteurde monsters of onversteurde grondkerne (R= 0,89** - 0,97**). Deurdat waterretensie by hierdie drukke tussen 79% en 94% van die variasie inin situ-VK-waardes verklaar, kan hierdie maklike en vinnige laborato- riumbepalings as akkurate voorspellers van VK gebruik word.S.-Afr. Tydskr. Plant Grond1985, 2: 151−156

ISSN:0257-1862    

DOI:10.1080/02571862.1985.10634157

出版商:Taylor&Francis Group    

年代:1985

数据来源: Taylor