摘要:

SummaryWhen the 1/3 and 15 atm. percentages were used as the upper and lower limits of available‐water, respectively, the values for the available‐water capacities (AWC's) of the soils studied were smaller than those obtained by using the direct sampling technique for the upper limit, and the permanent wilting percentage (determined on soil cores) for the lower limit of available‐water; the differences varied from 9 to 76 per cent with a mean of almost 40 per cent for the eleven soils studied. The importance of techniques for the determinations of the AWC of soils is discussed. The moisture characteristic of a soil could be considerably influenced by the structure of the soil sample on which the determination was made, and it is concluded that the moisture characteristic should be determined on undisturbed soil

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1965.tb01416.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SummaryLandscape information relevant to site description is discussed. It includes surface form (in plan and profile), micro‐relief, aspect, height above sea level, and relative relief of the site in the local setting. Techniques for description of surface form are described which require the recognition and mapping of breaks and changes of slope bounding morphological units of the landscape. These units consist of ‘flats’ and ‘slopes’ that make up the facets of the landscape and may possess characteristic angles. The regional setting of the site is described by morphological map, values for drainage density and stream frequency, location with respect to drainage lines of a particular order, and the directional pattern of facets. Methods for the record of surface profiles by observation and measurement of small‐scale morphological units are described. A slope classification appropriate to British conditions is

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1965.tb01417.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SummaryThe plateaux of Northern Rhodesia have a characteristic pattern of soils which, with variations, covers many thousands of square miles. A representative sequence of soils ranging downslope from red, through yellowish brown to grey is described. The soils are composed of material in an advanced stage of weathering and are shown to be developed more or lessin situfrom biotite gneiss. Redeposition of material once eroded is relatively unimportant. The colour sequence in this instance is attributed to the proportion of free iron oxides in the soil.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1965.tb01418.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SummaryBacteria made up an average of 90 per cent of the microbial populations of twenty‐four soil samples, mainly of the A0H horizon, from four peat‐podzol transitions.Bacillusspp., which averaged 67 per cent of these bacteria, were usually the predominant group. Gram‐negative non‐spore‐forming organisms (15 per cent),Streptomyces(8 per cent), and Gram‐positive cocci (5 per cent) occurred irregularly andArthrobacterandNocardiastrains rarely. A large proportion of the strains utilized glucose and malate, and a smaller proportion starch, citrate, and protein. A few strains liquefied pectin but none decomposed cellulose or xylan. In eight populations examined, 80 per cent of the bacteria required yeast extract for growth. Fungi usually formed only a small proportion of the populations. All the species, exceptPenicillium nigricansandTrichoderma viride, were isolated from only one transition. Yeasts occurred irregularly, usually in small numbers. Whilst no microbial group responded to the addition of glucose, nitrate, and phosphate to two soil samples, bacterial numbers increased after the addition of peptone and ye

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1965.tb01419.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SummaryA description is given of the distribution and characteristics of a vesicular laterite associated with the Early Cainozoic erosion surface in coastal Natal, together with the chemical and mineralogical characteristics of the soil formed by its decomposition. The relationship between cyclic erosion surfaces, the laterite, pre‐weathering, and the dominance of parent material in soil formation in coastal Natal clearly indicate the dependence of the processes of soil formation on the geomorphic history of this regio

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1965.tb01420.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SummaryRates of oxygen uptake and activities of enzymes hydrolysing sucrose and starch were determined in soils under pastures of grasses and clovers at bimonthly intervals at eight sites in New Zealand with different climates. Differences between sampling periods were significant in most soils. Values of oxygen uptake and enzyme activities were not generally significantly correlated between themselves nor with the moisture contents of the soils nor their prior rainfall history. It has not been possible to suggest an optimal sampling period for different soils. The oxygen uptakes of all soils increased two‐ to threefold in the presence of glucose. Mean annual values of oxygen uptake of the eight soils were significantly correlated with their contents of organic carbon, reducing sugars produced on incubation in buffer, and rates of hydrolysis of starch, but not of sucrose. Climatic factors and the composition of the pastures probably influence the activities of carbohydrase enzymes in soil. The ratios of the activities of enzymes hydrolysing sucrose to those hydrolysing starch were greatest in the driest soils under predominantly grass pastures at sites with the lowest mean annual temperature

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1965.tb01421.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SummaryActivities of enzymes hydrolysing sucrose and starch were lowered significantly in all air‐dried soils, except some naturally arid soils, stored at room temperature by more than 20 per cent and 50 per cent respectively, compared with values for fresh soils. These reductions in activities resulted mainly from the initial drying which also appreciably reduced the numbers of viable bacteria. Activities of enzymes hydrolysing sucrose generally decreased on storage at −20° C but changes were slight over long periods. Inactivation of enzymes hydrolysing starch was greater and tended to increase with length of storage. Inactivation was due partly to the effects of freezing and thawing and was greater in dry than in moist samples of soils. Activities were changed least by storage at 4° C and a significant decrease from fresh values was found occasionally in only two of the thirteen soils. Starch‐hydrolysing activity was significantly increased in two very moist soils stored for 41 weeks, probably due to germination of a few seeds. Although different soils can differ in their storage behaviour, storage in a refrigerator is most suitable and air‐drying least suitable for subsequent assays of thes

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1965.tb01422.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SummaryIn the “terra firme” of the Amazon basin near Manaus, podzol soils occur carrying heath forest. The parent materials are geologically young sandy sediments deposited in valleys. There are no indications that man's activity is one of the pedogenetic factors of the podzol development. Podzols have gradational contact with flanking brown soils developed on loamy Tertiary sediments carrying tropical rain forest. In the ‘terra firme’, that means outside the actual flood plains of the River Amazon and its tributaries, there are sand areas in which soil investigations following the catena principle have been carried out by the author. In the Manaus area the most important pedogenetic factors of the podzol development are lithology and topography. The podzols seem to have developed from parent soils which are characterized by bleaching and eluviation of organic and inorganic substances. The very small Bhlayers of podzols which are not correlated with the some metres thick Aehorizons are due to lateral percolation of rain water. On the Tertiary ‘serie of the Barreiras’ brown loams are found carrying high tropical rain forest. On podzols and more differentiated brown soils heath forest is found. Generally, tropical podzols are associated with black‐water rivers. Because the field work was restricted to the Manauús area, the modus of podzol development described in this paper is valuable for that region only. Further studies are necessary to explain the sources of ‘black water’ of other parts o

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1965.tb01423.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SummaryA new method for determiningI4C in soil is described.Ryegrass roots and tops uniformly labelled with14C were allowed to decompose for 4 years in soil under field conditions. About one‐third of the labelled (ryegrass) C was left in the soil after 6 months but thereafter decomposition was much slower, about one fifth of the labelled C remaining after 4 years. Throughout the period, labelled C was less resistant to decomposition than unlabelled C, i.e. the C present in the soil before the labelled ryegrass was added. Even in the fourth year after addition of the ryegrass, the percentage of labelled C in the soil decomposing per year was four times that of unlabelled C.Initially, ryegrass tops decomposed more quickly than roots but after I year the differences disappeared and the same amount of residual C remained from each. For periods of I year and over, the percentage of labelled C retained in a soil with 2.4 per cent organic C was the same as in a soil containing 1 per cent organic C. The percentage C retained was the same when either 0.3 per cent ryegrass tops or 0.6 per cent ryegrass tops were added to the soil. Similar amounts of labelled plant C were retained in soils incubated for 1 year in two contrasting seasons (1959 and 1962

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1965.tb01424.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SummaryIn the various types of loess soils, represented in the form of a catena, migration and alterations of 2: 1 layer‐minerals are the essential cause of a differentiating influence on the phenomena of K‐fixation. The K‐fixation is much greater in river alluvial than in loess soils. The high values of fixation are due to the large contents of clay consisting mainly of expanded 2:1 layer minerals. The river alluvial soils in the delta generally fix much more K than those in the region of the headwaters. By means of pot experiments the alterations of exchangeable‐ and fixed‐K have been examined in their dependence on the varying degree of soil exhaustion by cropping. Although an alluvial soil with K fertilizer showed a large amount of exchangeable‐K, fixed‐K partly diffused into the exchangeable form, and hence precise distinction between exchangeable‐ and fixed‐K was not possible. In contrast, the quantity of exchangeable‐K in the B horizon of a grey‐brown podzolic soil had to be exhausted to the level of the unfertilized soil before fixed‐K was released. In this case the difference in binding strength between exchangeable and fixed‐K could be clearly shown. The release of non‐exchangeable‐K from unfertilized soils was accompanied by a corresponding increase of fixation. Thus, when fertilizer is omitted, charges are set free in the 2:1 layer mineral which will fix an

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1965.tb01425.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY