摘要:

Water in the soil is held by capillary and adsorption forces. These forces are mainly a function of clay content and mineralogy. To neglect the influence of clay mineralogy when estimating the water-holding properties of soil, implies that only a part of these forces is considered. It is convenient to use some easily measurable soil property to quantify the effect of clay mineralogy, In this study cation exchange capacity (CEC) was used for this purpose. For 320 soil samples of the Highveld Region, water content at a matrix potential of - 33 kPa,−1 500 kPa and the percentage water retained between−33 kPa and - 1500 kPa (ΔW), were compared with different parameters. The water retentivity of disturbed soils can be predicted more accurately if variations in CEC are taken into account. Highly significant multiple correlation coefficients of 0, 97, 0, 96 and 0, 91 respectively, were calculated for the relationships of CEC (me/100 g soil) and clay content with water content at−33 kPa and - 1 500 kPa and withΔW.S. Afr. J. Plant Soil1984, 1: 33–38

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634106

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Tree- and root-growth parameters correlated well with a number of soil properties Useful relationships were established between unconfined penetrometer resistance, air capacity (at FWC), tree growth and root development.Tree and root growth were also restricted in the soil where the long-term air-filled porosity was almost continuously less than 15%.S. Afr. J. Plant Soil1984, 1: 39–47

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634107

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Both the endocarp and embryo contribute to the dormancy ofRubus cuneifoliusseed. Whereas scarification was found to break the dormancy imposed by the endocarp, embryo dormancy could only be overcome by a combination of treatments. These treatments consisted of a one-month stratification period followed by incubation at an alternating temperature ot 10–20°C in the presence of light.S. Afr. J. Plant Soil1984, 1: 48–50

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634108

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Five soybean cultivars (Hill, Geduld, Forrest, Welkom and Oribi), previously selected for Al tolerance or sensitivity by a rapid seedling evaluation method, were grown in acid soil treated with varying rates of lime and P. After 35 days the plants were harvested and measurements of leaf area, shoot, root and nodule dry mass as well as elemental analysis were carried out. Lime had a significant effect on growth whilst P had relatively little effect. Classification for tolerance to soil acidity appeared to depend on the criterion used in the classification. Agreement with the‘rag doll’-classification was obtained when comparing the cultivars, with respect to their relative shoot and leaf area yields, at the unlimed and first liming level. In the absence of lime the highest shoot yield occurred at the Intermediate level of P. Forrest appeared to perform consistently poorly in unlimed soils and could be classified as highly sensitive to acid soil infertility. However, it would be speculative lo classify the other cultivars into tolerant sensitive or intermediate groups. There was a strong indication that yield depressions in Forrest may not be attributed entirely to Al toxicity and that the relative balance of P, Fe and Cu may be involved Significant decreases in plant Al, Zn, Fe, Mn and Mg were observed with Increasing lime levels.S. Afr. J. Plant Soil1984, 1: 51–56

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634109

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Isotopically exchangeable Al was determined in soils and clay minerals by equilibration with28Al. Best results were obtained with a weak extractant and an equilibration time of eight min. The calculated amount of isotopically exchangeable Al was independent of the amount of carrier-Al added with the28Al. In some soils isotopically exchangeable Al did not appear to be related to the amount of Al which could be extracted by various electrolyte solutions. This technique provides an improved means of studying the exchange reactions of Al in acid soils and clay minerals.S. Afr. J. Plant Soil1984, 1: 57–60

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634110

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Fifty hillslope profiles with associated soils in the Roodepoort area, Transvaal, were examined to determine the relationships between soil depth and hillslope characteristics. A meso-scale approach was adopted which implied the relationship between three soil depth phases and the hillslope units on a scale of 1:10 000. Although anomalies occur, it was found with the aid of statistical techniques, that a definite trend exists between soil depth and slope gradient. For the less than 8% slope class, soil depth variations could be ascribed to differences in parent rock and position in the landscape, whereas for slopes steeper than 8% slope, gradient apparently becomes the dominant determinant of the shallow soil depth. Because the soil depth-hillslope relationships were sufficiently well established by this study, it enabled the construction of three models to represent the varied conditions of the Roodepoort area.S. Afr. J. Plant Soil1984, 1: 61–66

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634111

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Available research findings concerning (he activity of atrazine in the plant and soil are presented in a brief review. The role of the environment is emphasized. This review is supplemented by recent research results of the University of Pretoria concerning evaluation of soil characteristics as a norm for the prediction of atrazine activity in turf soils, the comparison of a few maize hybrids with respect to their resistance towards atrazine and the influence of moisture and temperature on atrazine activity in light-textured soils. Guidelines for future research and for the use of atrazine are given.S. Afr. J. Plant Soil1984, 1: 67–72

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634112

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor