摘要:

SUMMARYEleven horizons of acidic soils developed from Lower Palaeozoic sedimentary rocks in mid Wales contained varying amounts of poorly ordered minerals. In nine of these over 70% of the phosphate adsorption capacity was attributed to poorly ordered minerals. Iron oxide with substituted Al, and a separate Al oxide, together accounted for the phosphate adsorption of the poorly ordered fraction. Aluminium‐substitution had no major effect on the adsorption capacity of Fe oxide, but since Al occurred in both active minerals it masked the effect of Fe on phosphate adsorption in simple correlations. The relative contribution of the two mineral forms to phosphate adsorption varied widely between soils. Aluminium as a substituent in Fe oxide and in ‘free’ oxide form was responsible for the soils’ reactivity towards NaF, but no distinction could be made between these poorly ordered forms. For certain horizons both poorly ordered Al and Si were correlated with OH−release, but Al oxides were more important than

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02127.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYA sigmoidal, non‐hysteretic two‐part retentivity function having only two constants in addition to porosity was developed for use in soil‐water flow simulation models. Values of the constants, shapes of the retentivity curves, and soil textural properties were related by fitting the retentivity function to retentivity data generated using regression equations. Two sets of regression equations, which relate water content at specific matric potentials to soil texture and bulk density, were used, one for British soils and one for South African soils. Hydrologically inhomogenous soils may be modelled by varying the values of the retentivity constants through the profile to reflect changing soil prope

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02128.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYSamples of air or water were extracted daily from porous pots buried within the rooting zone of trees planted on a deep peat soil. For most pots, the O2concentration in the fluid increased with the number of samples taken each day, presumably because air was drawn into the pot from shallower depths. Sampling frequency should therefore be chosen as a compromise between the needs to increase precision and to minimize introduced bias.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02129.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYSamples from 70 horizons from UK soils were tested for structural stability, and a comparison was made between the results from the following six tests: (i) Emerson, (ii) Janse&Koenigs, (iii) Thorburn, (iv) Childs (soil moisture characteristic), (v) Williams&Cooke slump test, and (vi) wet sieving. Both correlations and systematic differences were observed between the tests, suggesting that different aspects of stability were emphasized by different test procedures. The tests leading to classes (i), (ii) and (iii) were found to be more subjective than those leading to indices. It is suggested that (v) may be applicable to less stable soils, and (vi) to more stable soils. Childs’ test was time consuming and subject to some erratic results; two new indices of stability are proposed to increase the reliability of this tes

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02130.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYRecommendations are made regarding the analysis and presentation of cone resistance data. Methods for eliminating extreme readings due to stones are compared and the effects of stones on variability and treatment comparisons are discussed. Results showed very high variability between positions, even at 100 mm separation. Measurements separated by more than 1 m were independent of each other except where trends in other soil properties influenced cone resistance. The assessment of compaction under wheels is described for cone resistance measurements made under the rut centre‐line. Parameters are derived from measurements made on two‐dimensional, vertical grids to quantify the depth, extent and intensity of compaction and loosening. The usefulness of penetrometers in tillage and traffic studies is discus

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02131.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYComparison of neutron probe count rate ratios measured at 10 cm depth, with bulk soil water contents measured 3–5m away from the access tubes, confirmed that in swelling/ shrinking clay soils, recharge may be over estimated. This is due to the drying soil shrinking form the access tube, creating an air gap and radial cracks which allow preferential re‐writing of the soil near the access tube. Installation of access tubes into dry soil was only a short‐term answer.Comparison of results obtained for bulk soil and for small colds shows that calibrating the neutron probe using small diameter cores may be lead to serious under estimates of changes in water content in shrinking clay

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02132.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY