摘要:

SummarySamples of tilled soil were impregnated with paraffin wax and were sectioned by sawing. The distribution of angles of incidence between voids and aggregates on the sections were investigated using random lines in three orientations. The angular distributions were found to be isotropic. Incidence angles near to normal were found to be more probable than in idealized beds of spherical aggregates.Distributions of aggregates and voids were examined along horizontal lines on the soil sections using an approach developed in communications theory. Soil structures in the size range from I to 5 mm were defined exactly by sets of sixteen transition probabilities. Differences were observed in the tilths produced by a mouldboard plough, a tine cultivator, and a rotary cultivator. The soil structures were different at different depths and changed with time after tillage.Transition probabilities measured in this way can be used in stochastic processes to simulate large tilths in a computer. The techniques described here could be adapted to the study of the distribution of soil structural features at any scale.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1976.tb01996.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe oxygen uptake and respiratory quotient (RQ) of field cores from three soils of different texture classes were studied using electrolytic respirometers. Critical values of air‐filled pore space (f), above whichRQwas always near unity, that is, corresponding to the transition from anaerobic to aerobic respiration, were defined for each soil. These critical values agreed with minimum values off required for plant growth as reported in the literature, suggesting thatRQcan be used as an index of adequate soil aeration.Oxygen uptake by the three soils reached a maximum atfvalues slightly above the critical values, corresponding to the highest moisture content at which oxygen diffusion was non‐limit

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1976.tb01997.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryA very fine sandy loam soil was severely puddled in the laboratory and subjected to varying numbers of freeze/thaw‐wet/dry cycles in an attempt to restore its original level of structural stability. After only three cycles the stability of the treated soil reached its maximum value, which was slightly greater than that of untreated soil collected from the field. A higher level of soil organic matter was accompanied by an increase in structural stability as determined by the dispersion ratio technique and a technique involving partial dispersion in Calgo

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1976.tb01998.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe drop‐cone method, in which a 30° cone of mass 80 g is allowed to sink into a soil sample at a selection of moisture contents, was used to determine the moisture content/cone penetration curve in the region of the plastic limit for eighteen soils.The moisture content corresponding to the minimum of the curve is shown to be always numerically less than, but to correlate closely with, the plastic limit. It is suggested that the plastic limit be redefined as the moisture content corresponding to the minimum of the moisture content/cone penetration curve, with the advantages that the test is more closely related to soil behaviour, less subjective, at least as reproducible as the Casagrande test and may be carried out simultaneously with the liquid limit te

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1976.tb01999.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryIsotherms for the sorption of inorganic phosphate (P) by three contrasting soils during 40 h showed a dependence on solution: soil ratio. Above a final solution P concentration of 0.5 μg ml−1, more P was sorbed at a solution: soil ratio of 5:1 than at 40:1 for a given level of P in solution. With time up to 146 h, the effect of solution: soil ratio on P sorption was kinetically controlled.Equilibrium solution P concentrations, estimated by extrapolation of the linear relationships between solution P concentration and the reciprocal of time to I/t= o (i.e.t=∞)appeared to be coincident for each solution:soil ratio at high and the low levels of added P. Consequently, sorption isotherms at equilibrium would be coincident, irrespective of the solution soil ratio used.The kinetic control of solution: soil ratio on P sorption is interpreted in terms of the number of P sorbing sites and initial solution P concentration on the rate of P sorption by s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1976.tb02000.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe effects of the salts were studied using I per cent suspensions of gibbsite at pH 5.5 and 26°C. At 480μM phosphate and I mM calcium, the kinetic pattern was an initial rapid adsorption reaction, which approached equilibrium in 24 h, revealing a slower reaction. Adsorption isotherms determined at 24 h, with a range of final phosphate concentrations from 0.1 to 1000 μ in solution, were not affected by 20 mM sodium or potassium chloride or 10 mM magnesium chloride. Increasing calcium chloride from o to 20 TIM increased the adsorption of phosphate over the range from 1 to 100 μM final phosphate concentration. At lower (0.1 μM) and higher (1000 μM) phosphate, the effect of calcium was smaller.These results help to explain several effects of the various cations on the adsorption of phosphate by clays and soils, when effects of neutral salts on pH are also consi

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1976.tb02001.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe effects of the nitrate salts of zinc, cadmium, and strontium on the adsorption of phosphate by gibbsite have been measured at pH 5.5 and 25° C. At solution phosphate concentrations greater than 10 μM strontium and cadmium increased phosphate adsorption whilst zinc had no effect. At lower phosphate concentrations zinc and cadmium increased adsorption of phosphate in a different manner from strontium, sodium, potassium, magnesium, or calcium. Zinc and cadmium at 1 mM concentration inhibited phosphate adsorption, perhaps because they are specifically adsorbed as indicated by pH‐shift data.A postulated surface complex consists of two adjacent adsorbed phosphate ions and a central divalent cation of appropriate size, charge, and possible co‐ordinating prope

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1976.tb02002.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryUltrasonic dispersion of acid‐pretreated soils in aqueous acetylacetone at pH 8, and at a solvent: soil ratio of about 45: I, extracted from 61 to 97 per cent of the organic sulphur from five Scottish soils. Narrowing the ratio to about 9:1 reduced the proportion extracted but was more convenient for the subsequent isolation of the organic components. Gel permeation chromatography of the extracts yielded materials containing from 14 to 60 per cent of the soil organic sulphur. Most of the soils gave four distinct fractions which contained from 21 to 38 per cent carbon, 0.2 to 2.1 per cent nitrogen, and 0.1 to 0.8 per cent sulphur. There was no consistent similarity between corresponding fractions of the various soils. Considerable amounts of iron and aluminium were extracted, presumably incorporated in organic complexes. Since they were obtained under very mild conditions, the fractions should provide useful starting materials for qualitative investigations on the nature of soil organic sulphu

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1976.tb02003.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryTwo methods have been used for the identification and determination of uronic acids in soils and soil fractions. The uronic acids were released by hydrolysis with sulphuric acid. After partial purification by ion‐exchange chromatography they were separated either by further ion‐exchange or by gas‐liquid chromatography of derivatives. The latter method is preferable for determination of the specific activities of uronic acids in soil tracer work. Both galacturonic and glucuronic acids were detected in the four Scottish soils examined, the galacturonic acid being present in slightly greater amounts in each soil. Mannuronic acid was not detected. The total amount of uronic acids found ranged from about 4 mg to 6 mg/g

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1976.tb02004.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryElectron paramagnetic resonance (e.p.r.) spectroscopy has been used to show that humic acids, which were isolated from a range of soils and from which most of the iron was removed by boiling with hydrochloric acid, contain copper in the form of porphyrin complexes. The amounts of porphyrin‐bound copper in the acid‐boiled humic acids were estimated to be ≤ 20 mg/kg (equivalent to 0.05‐0.9 mg/kg in the soils). The acid‐boiled humic acids from cultivated mineral soils showed no great capacity for further uptake of copper as copper porphyrin when treated with CuSO4, most of this additional copper being held by groups not involving N‐donor groups. In contrast, copper treatment of the acid‐boiled humic acid from a raised bog peat produced a large increase in copper‐porphyrin signal strength, indicating that in the peat there are considerable amounts of porphyrin by which added copper could be complexed. It is suggested that porphyrin groups may be involved in the fixation of copper by organic

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1976.tb02005.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY