摘要:

SummaryThe scanning electron microscope has been used to compare the microstructure of an old grassland soil with that of an arable soil of the same soil series. The micrographs give more direct evidence than previously available of the presence of an adherent, presumably organic, matrix binding the clay and other particles of the old grassland soil. Fungal hyphae were also observed. Neither of these features was present to the same extent in the old arable soil.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1974.tb01110.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SummaryIn a field experiment to determine the direct and indirect effect on soil structure, of sub‐surface piped drainage as compared with natural surface drainage only, in ploughed and unploughed soil, a factorial systematic design with four replicated blocks was used. Structural changes were monitored during 8 months of natural rain and finally irrigation, by measuring surface heights and soil strength (penetration resistance) in relation to moisture content and matric suction, at plough sole depth (27 cm). A compaction test using a tractor with differentially loaded wheels, was applied at various times after irrigation, measuring the resulting wheel sinkage and wet density of the soil.The effects of the drainage treatments were found to be temporary, except a ‘crusting’ effect during the drying of the unploughed surface drained soil. The ploughed soil with sub‐surface drainage showed greater frost heave than the undrained soil. The soil strength at 7.5‐22.5 cm. depth was linearly related to the matric suction within the range of –3 to 20 cm‐water. The compaction data for the unploughed soil suggested relationships between matric suction, sinkage, and wet density, but complicated interactions prevented any general conclusion. In the ploughed soil, compaction data established the beneficial effects of subsurface drainage in reducing damage from tractor traffic, decreasing wheel sinkage and reducing compaction both below and 16 cm from the track edge. A rise in matric suction of 10 cm‐water, in the range 2‐24 cm‐water was, on the average, as effective in reducing rutting as a wheel load reduction of 670 kg (0.54 kg/cm2reduction of tyre inflation pressure). It was concluded that for clay soils having a temporary excess moisture, draining the water table to below 50‐60 cm depth should be recommended as a precautionary measure to minim

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1974.tb01111.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SummaryRemoulded soils compress more rapidly than undisturbed soils at the same initial density and water content. Soils with larger particles compress more rapidly than those with smaller particles. Soils compress more slowly when they are more densely packed. Soils expand more slowly than they compress between the same two pressures.Implications of these results are that soils which are not tilled would be less susceptible to compaction, and that tractors and other vehicles would cause less compaction when travelling at higher speeds.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1974.tb01112.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SummaryA model is described for predicting the movement of soluble unadsorbed anions (such as nitrate or chloride) in fallow freely drained soil under field conditions. The model includes routines for estimating both the downward leaching of salts (after excess rainfall or irrigation) and the capillary movement of anions to the soil surface (after evaporation). The profile is divided into layers each of which is characterized by a maximum and minimum water content (the field capacity and evaporation limit respectively). Daily amounts of rainfall and evaporation are applied to the surface and the redistribution of water and salts is calculated (on a layer‐to‐layer basis) from the initial water and salt contents of each layer by adding or subtracting water to or from the moisture content until the stated maximum or minimum value is reached. Salt transfer is calculated from the amount af water movement on a proportional basis. The predictions of the model have been tested using field data for the redistribution of nitrate and chloride in a sandy loam soil. Good agreement was obtained for chloride, but the results for nitrate showed some deviations probably due to the effects of denitrificat

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1974.tb01113.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SummaryOver 300 samples of London Clay from twenty‐one widely scattered sample locations in the London and Hampshire Basins were to be examined in detail by X‐ray diffraction techniques. The quantitative method of Schultz (1964) was chosen as being most suited for the analysis of the samples. Series of tests designed to investigate the reproducibility characteristics of the method were conducted. These showed that the sampling, sample preparation, and interpretation procedures used all introduced cumulative reproducibility errors of roughly equal magnitude which completely overshadowed errors introduced by machine‐response variation. It was also established that minerals whose contents were below 10 percent of whole sample failed to be consistently quantitatively estimated.The accuracy of this method of analysis depended heavily on Schultz's quoted ‘intensity factors’ which were involved in the calculation of individual mineral contents. The authenticity of these factors with regard to the London Clay suite of minerals was checked by comparing accurately determined mineral percentages of six standard London Clay samples with the results obtained by use of the Schultz procedure and factors. The method was found to be basically sound although the intensity factors for quartz, total clay minerals, carbonates, and illite had all to be slightly adjusted. The accurate quartz percentages were established by three different X‐ray diffraction techniques and the carbonate percentage checks were accomplished by specially designed wet chemical methods. The total clay mineral and illite contents checks were carried out by back‐calculation of the Al2O3, and K2O percentages as determined from full wet chemical analysis. Using the adjusted factors, quartz percentages are estimated accurate to ±6 percent, total clay minerals to ±7 percent, carbonate percentages to ±1.5 percent, and illite contents to ±4 percent

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1974.tb01114.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SummaryThe humic acids of four soils from Denmark have been extracted by EDTA. The humic acids were separated from EDTA by precipitation with Ba2+. The ash content was lowered by treatment with HF and HC1. The ash content in the four humic acids was less than 0.6 per cent. Chemical analysis of the humic acids supply some evidence for the suggestion that EDTA extracted organic matter is a more definite fraction than humic acid extracted by NaOH.It was shown that an alkaline humate solution stored in sterile, sealed ampoules under N2does not change its initial pH, indicating that the protolytic equilibrium is established instantly. It is therefore proposed that the titration of humic acid should be carried out as quickly as a normal acid‐base titratio

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1974.tb01115.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SummaryPhosphate sorption capacity estimated by Piper's (1942) ‘anion exchange capacity’ and Bache and Williams's (1971) phosphate sorption index were correlated with soil pH, clay, organic matter, ‘free iron oxides’ and ‘extractable aluminium’ (McLean et al., 1958) for topsoil and subsoil samples from twenty tropical and twenty British acidic soil profiles. These two groups of soils did not differ significantly in phosphate sorption. Extractable aluminium and free iron oxide were well correlated with phosphate sorption, free iron oxide being superior to aluminium in freely drained British soils but not in poorly drained ones. Organic matter content correlated well with phosphate sorption for the poorly drained British soils, and for the tropical soils when sorption capacitywas measured using a high phosphate co

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1974.tb01116.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1974.tb01117.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SummaryA study was made of the concentrations of ethylene and oxygen in the soil atmosphere under field conditions at three contrasting sites. The duration of the experiments ranged from 6 weeks to 9 months. A clear relationship between high moisture content and both the production of ethylene and the depression of oxygen levels was found in a sandy loam, although there was great variability between replicate sampling points. Concentrations of oxygen in a heavy clay soil remained below 10 per cent (v/v) throughout the winter and spring, followed by a gradual rise to near‐atmospheric levels. Concentrations of ethylene were not correlated with those of oxygen, except in the winter, but rose logarithmically with soil temperature during the spring, increasing by twenty times over the range 4‐1 I °C. There was no significant difference between plots which had been subjected to different drainage treatments, and again there was great variability from point to point. In a more permeable clay soil, however, the levels of oxygen were higher, and were related to the proximity to drains and the height of the water table, but not to the levels of ethylene. The concentration of ethylene showed a similar logarithmic increase with temperature to that observed in the heavy clay, and exceeded I ppm throughout the period May‐July.The factors which have the greatest influence on the concentrations of ethylene in the soil were considered to be temperature, depression of oxygen concentration, the availability of substrates for microbial activity and the effect of soil moisture content on the air‐filled porosity of the soil. Concentrations of ethylene greatly in excess of those which, under some circumstances, inhibit root growth, are likely to be of widespread occurrence in heavy soils during the spring and early summer and in light soils when unusu

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1974.tb01118.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SummaryStudies were made of the seasonal changes in the occurrence of nitrous oxide in the atmosphere of two clay soils. During the winter of 1971‐2 the nitrous oxide concentrations at both sites were in the range 20‐50 ppm. Levels increased with rising soil temperatures in spring, the mean values reaching 50‐170 ppm in May; some individual samples contained 1500‐6500 ppm. The level of nitrous oxide was inversely related to the oxygen content of the soil atmosphere and was also correlated with the nitrate and nitrite concentration of the soil water, but could not be correlated with either the proximity of field drains, soil moisture content or r

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1974.tb01119.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY