摘要:

The plant species compositional response of veld at Ukulinga to application, over 30 years, of nitrogen, phosphate and lime is reported. Two types of nitrogen fertilizer were applied at four levels with and without phosphate, lime and lime + phosphate. Each treatment was replicated three times. Data on veld composition were obtained using a Levy bridge and observing 100 points per plot. The response of the veld to fertilization was examined using detrended correspondence analysis, providing simultaneously a samples and species ordination. The amount, but not the form, of nitrogen fertilizer strongly affected veld composition. Phosphate and lime had a lesser effect on veld compositon, but the presence of phosphate enhanced the effect of nitrogen on some grasses.S. Afr. J. Plant Soil1986, 3: 1–10

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634177

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Chemical analysis of plant fractions of maize cultivars TX 24 and HL 1 grown in liquid culture containing Al showed that the action of Al was directed at the uptake of Ca and Mg and the transport of P and K. Highly significant cultivar differences in the pattern of Al uptake, notably at low solution Al concentrations were identified. P transport between roots and shoots diminished with increased root Al concentrations. An Al-induced decline in root metabolism was found to occur in intact roots (20 h) and cultivar differences in the ability to maintain root respiration in the presence of Al coincided with cultivar differences in P transport. In the absence of Al, both cultivars responded to low Mg levels by taking up correspondingly more Ca and K without significantly affecting yield. It is therefore suggested that a major requirement for these ions involves charge neutralization. Furthermore, since the root Mg concentrations recorded in these experiments were comparable to those found in plants showing a high degree of Al injury, it was also concluded that these Mg levels were adequate to meet specific functional requirements for this element in the plant. A hypothesis was developed which involved interference by Al in root metabolism which depressed active ion movement and thereby lowered the cation retention capacity of the root. This concept accorded with the linear relationships observed between leaf P and root concentrations of Ca and Mg found in Al-stressed plants.S. Afr. J. Plant Soil1986, 3: 11–17

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634178

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

The effect of herbicides which scorched the lower leaves of maize was compared in three seasons. The first season was relatively dry whilst the other two were wetter seasons. A mixture of cyanazine + atrazine + paraquat + a wetting agent was applied as a directed spray at the base of maize plants at weekly intervals from four till eight weeksafterplanting. These treatments were compared with weedfree, unsprayed maize. Plant heights ranged from 0,1–1,0 m at spraying. Many of the younger maize plants were severely scorched and some were killed by the earliest treatment (4 weeks) and grain production was lower but only significantly reduced in one season out of three. Maize which was sprayed at later stages lost some lower leaves but this did not affect grain production or did not consistently affect other maize attributes.S. Afr. J. Plant Soil1986, 3: 18–20

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634179

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

As the natural pattern of development and rubber synthesis in guayule (Parthenium argentatum) is cyclic any treatments to improve growth and rubber production should be synchronized with the normal sequence of events pertaining to growth and metabolism. Starting with 25-week-old seedlings an attempt has been made to acquire information about rubber deposition, growth and defoliation. Observations were made in the field as well as at the light and electron microscope level. Rubber is deposited mainly in the bark during winter. The highest deposits were found in the secondary stem tissue.S. Afr. J. Plant Soil1986, 3: 21–26

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634180

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Thirty-three maize (ZeamaysL.) inbreds were screened for tolerance to atrazine (2-chloro-4-ethylamino-6- isopropylamino-1,3,5-triazine) in a glasshouse using a sand culture technique. Tolerance ranged from 95,7–51,0% of the control. The continuous pattern of tolerance exhibited by the inbreds indicated polygenic inheritance. Six inbreds categorized as either highly tolerant or less tolerant were hybridized in all possible combinations. The six inbreds and Fl crosses were evaluated for tolerance to atrazine (6 p.p.m. v/v) under controlled conditions. Leaf mass data strongly suggested additive gene effects. Broad-sense heritability (0,66) indicated the potential for increasing hybrid tolerance to atrazine by breeding. The nature of gene action could not be established when veinal chlorosis was used as a measure of atrazine toxicity.S. Afr. J. Plant Soil1986, 3: 27–30

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634181

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Ammonia volatilization from five soils, ranging in clay content from 7,6 to 49,9%, were determined after pH values of the soils were adjusted to 8,0. Ammonium sulphate, limestone ammonium nitrate, urea, monoammonium phosphate and diammonium phosphate were applied on the soil surface at levels equivalent to 0,15, 30, 60,120 and 240 kg N ha−1. After a contact period of three days ammonia losses were determined. Ammonia was lost from all soils under all treatments, losses increasing with increasing levels of application. Loss of ammonia from the various fertilizers was ranked as follows: LAN

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634182

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Fifty hillslope profiles with associated soils were examined in the Roodepoort area, Transvaal, to determine the relationships between soil and site characteristics, as well as the applicability of the toposequence concept. A mesoscale approach was adopted, which implied a relationship between soil form on the one hand, and hillslope unit and site curvature on the other, at a scale of 1:10 000. Whereas significant statistical relationships were established between certain soil forms and site characteristics, a rather low predictability of soil pattern according to drainage- toposequences was found. The latter could be due to the land form configuration, to underlying bedrock with its peculiar weathering front, to the occurrence and form of the water table, or to the chosen scale of study. Nevertheless, it was concluded that studies of this nature can contribute to an understanding of how the soil-landscape system functions.S. Afr. J. Plant Soil1986, 3: 35–40

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634183

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Die konvensionele metode vir die bepaling van hitte-eenhede is vergelyk met 'n nuwe benadering. Data uit sewe kultivarproewe insluitende daaglikse maksimum en minimum temperature is gebruik om die hitte-eenhedevereistes van drie kultivars te bepaal. Twee vergelykings is gebruik, een verteenwoordig die konvensionele hitte-eenhedebenadering en die ander een die nuwe benadering. Onafhanklike data van 16 kultivarproewe, wat oor drie jaar uitgevoer is, is gebruik om die voorspellingswaarde van die verskillende vergelykings vir die somerreënsaaigebiede van Suid-Afrika te toets. Akkumulasies van relatiewe hitte-eenhedeY, wat volgens die vergelykingY=−0,014X2+ 1,08X- 6,9 waarX= (2Tx+Tn)/3,Tx= daaglikse maksimum temperatuur enTn= daaglikse minimum temperatuur, bereken is, het die beste voorspellings gegee van die aantal dae van plant tot 50% blom. Kriteria wat gebruik is om voorspellingswaarde te beoordeel is: goeie ooreenstemming tussen gemiddeldes van die werklike en berekende aantal dae tussen plant en blom, klein afwykings van berekende waardes vanaf hul gemiddeldes en temperatuuronafhanklikheid van die afwykings. Beoordeel volgens hierdie norme is die nuwe benadering meer betroubaar as die ou benadering en behoort dus gebruik te word om die ontwikkeling van sonneblom te voorspel vir die somerreënsaaigebiede van Suid-Afrika.S.-Afr. Tydskr. Plant Grond1986, 3: 41–44

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634184

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

The regression coefficients of a modifiedÅngström formula, initially postulated as being constant under all climatic conditions, have with widespread use been shown to vary not only spatially but also due to variable sunshine duration conditions. Daily sunshine duration and solar radiation data sets were analysed in order to assess the variations of the coefficients a and fa in the formulaK/Ko= a +bn/Nunder differing conditions of relative sunshine duration in South Africa. The results show that whereas coefficient a tends toward being linearly related to sunshine duration, coefficientbexhibits a hyperbolic type relationship. The statistical relationships between both coefficients and sunshine duration are, however, weak. The study also shows that the equations suggested by Rietveld for deriving the coefficients a andbare not valid under South African conditions.S. Afr. J. Plant Soil1986, 3: 45–48

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634185

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

The effect of Alar (succinic acid 2,2-dimethylhydrazide) and pruning on cassava (Manihot esculentaCrantz) was studied under subtropical conditions in Natal. Alar application in early summer had little effect on shoot growth and did not increase yield. Pruning at the start of the second growing season stimulated shoot growth and led to a low tuber growth rate. Alar reduced shoot growth but did not lead to an increase in tuber yield.

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634186

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor