摘要:

A Presidential Address provides an opportunity for an account of the state of the subject and a reading of the signposts which seem to point to future progress. The broad philosophical aspects of soil science were discussed by E. M. Crowther (1953) a quarter of a century ago in ‘The Sceptical Soil Chemist’, a paper which is worth reading again. This year our Vice‐President, D. J. Greenland (1978) discussed ‘The Responsibilities of Soil Science’. I shall concentrate on discussing some ways in which soil scientists may contribute further to agricultural de

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00978.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryIn a study of the moisture regimes of some of the most commonly occurring soils of the Central Lowlands of Scotland, three field techniques are compared. Soil tensiometers were used to measure matric suction and results are presented for a brown forest soil, a gteyed brown forest soil and a surface water gley soil. Borehole water levels are given for the surface water gley soils (and gleyed brown forest soil) for the two years under study. A close relationship between matric suction and borehole levels was established but this was not maintained once a soil moisture deficit occurred. Piezometer data was recorded and is shown to give little useful information due to the low hydraulic conductivity of the subsoils.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00979.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryThe moisture regimes of two fen soils and two chalk soils in Lincolnshire were investigated using a neutron probe moisture meter. Soil moisture deficits were calculated and compared with those predicted using meteorological data. Measured deficits were in fairly close agreement to those predicted by two separate models, the main variation seeming to depend upon the dryness of the year, the crop and the soil type.Measured deficits were also compared with laboratory estimates of available water and it was found that the chalk soils dried to higher suctions than was at first expected.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00980.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryThe concentration of oxygen at three depths (15, 30 and 60 cm) has been measured in a direct‐drilled or ploughed clay soil of low hydraulic conductivity (Evesnam series) which was cropped with winter wheat in three consecutive growing seasons (1972/73 to 1974/75). The mean oxygen concentrations between January and March varied with the seasonal rainfall; in the relatively dry winter of 1972/73they were 20 per cent (v/v) at 15 cm and 12 per cent (v/v) at 60 cm, but in the wetter winters of 1973/74 and 1974/75 they were less than 11 and 6 per cent (v/v) at 15 and 60 cms respectively. Direct drilling resulted in higher oxygen concentrations at 15 cm than ploughing in both wetter winters, the mean concentration being 10.2 and 7.2 per cent (v/v) in direct‐drilled and ploughed plots respectively. Frequency distributions of values obtained at individual sampling points showed that when the mean oxygen concentration of the soil at 15 cm decreased to its annual minimum (in January‐March), a significantly higher proportion of the sampling points under direct drilling continued to show concentrations of oxygen greater than 10 per cent (v/v).The results are interpreted as indicating that the higher oxygen concentrations found in this soil after direct drilling are due to the development of a system of continuous large pores and channels which would otherwise be destroyed by annual plou

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00981.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryA radioisotope dilution technique was used to measure the surface concentrations of Ca and P on hydroxyapatite equilibrated at pH values ranging from 5.19 to 8.81. The concentrations were rarely equal to those calculated for a stoichiometric surface. In general the molar surface Ca/P increased from a value less than the stoichiometric figure of 1.67 at low pH values to a value greater than 1.67 at high pH values. The solution Ca/P showed the opposite trend with pH.The deviations of the surface concentrations of Ca and P from stoichiometric values were attributed to adsorption and desorption of the elements at the solid surface. The extent of these reactions was influenced by both surface charge and the solution concentration of Ca and P. The relevance of the pH dependence of the surface composition of hydroxyapatite to the interpretation of solubility studies on the solid is discussed.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00982.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryAfter incubation with soil, phosphate was desorbed in dilute calcium chloride solutions. After short periods of incubation, the amount of phosphate desorbed increased rapidly at first but then net re‐adsorption occurred. After long periods of incubation, desorption was slower and there was no net re‐adsorption with prolonged desorption.Desorption was described in terms of two limiting values: the amount of phosphate (K) which would be desorbed as the concentration of phosphate approached zero, and the solution concentration of phosphate (Co) at which no desorption occurred. Both values decreased as the period of incubation increased. The value ofKincreased during the desorption phase, but the value of Codecreased. The decrease in Coduring desorption was most marked after short periods of incubation and was important in describing the trend for re‐adsorption of phos

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00983.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryPhosphate was added to soil, incubated at a range of periods and of temperatures, and the rate of desorption was measured at several solution: soil ratios at 25°C. One sample was incubated at a high temperature for several days and the rate of desorption was measured at 5, 15, 25 and 38 °C. A regression approach was used to describe the results which were interpreted in terms of a model in which phosphate was present (a) in solution, (b) adsorbed in equilibrium with the solution, and (c) firmly held.When neither adsorption nor desorption occurred, the phosphate concentration in solution increased with temperature. This was interpreted as an effect of temperature on the position of the equilibrium between solution phosphate and adsorbed phosphate. The direction of the effect indicates that adsorption was exothermic. When either adsorption or desorption occurred the rate increased with temperature and to a similar extent. For both reactions, the change in heat content was small. Thus, while temperature affected the rate of interchange between adsorbed and firmly‐held forms it should not affect the position of the equilibrium between these fo

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00984.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryThe adsorption of Zn by soils which are different in their major cation‐exchange materials was measured at equilibrium Zn concentrations up to 10−2M in 10−2to 10−3M CaCl2. The results are interpreted on KZnCa[Zn]soilplots, where KZnCais the selectivity coefficient defined by the equationAll natural samples except those containing halloysite exhibited no or very small specific Zn adsorption. All Ca‐saturated samples exhibited specific Zn adsorption dependent on cation‐exchange materials. The cation‐exchange sites with high selectivities for Zn (KZnCa>10) constitute more than 40 per cent of the total exchange sites in soils containing allophane, imogolite, and halloysite, whereas those with moderate to low selectivities for Zn (KZaCa<10) predominate in montmorillonitic, vermiculitic, and humic soils. Differences in the contribution of the respective cation‐exchange materials to specific Zn adsorption are discussed relating to differences in the origin of their

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00985.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryPotassium‐calcium exchange equilibria in, and the kinetics of K release from, soil from the Nil and PK treatments of the Saxmundham Experiment, Rotation 1, and the Ga, Ca + K and K saturated panicle size fractions of the soils were investigated.The free energy and enthalpy ot exchange showed K preference in all the solids. Selectivity for K decreased with increasing particle size and pre‐treatment with K salts. A comparison of the ‘differential enthalpy of exchange: per cent K saturation’ relationship for the whole soil with those of the particle size fractions suggests that soil dispersion during particle size separation also decreased K selectivity significantly. When related to the mineralogical composition of the soil, the differential enthalpy data suggest that maximum K. selectivity is associated with a vermiculite/smectite component of inter‐stratified minerals in the soil.Isotopic exchange using4sCa on the decalcified solids showed a measurable rate of exchange for the Ca forms of the<0.2 and 0.2–2 /μm fractions. This is attributed to traces of blocking materials (CaCO3or hydroxy‐aluminium polymers), which are removed or rendered porous during treatment with dilute KCl solution, so that isotopic exchange with Ca is then much more rapid.The kinetics of K extraction with a Ca saturated resin, interpreted on the basis of a three‐compartment model, suggest that sorbed K and K released by ‘fast’ and slow processes, representing sites of low and high K selectivity, were associated with minera‐logically distinct phases in the various p

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00986.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryMixtures of the dipolar organic solvents formic acid (FA) and dimethyl sulphoxide (DMSO) were used to extract organic matter from soils. At 100 °C optimum extraction from a calcareous clay loam was with 80/20 v/v FA/DMSO, corresponding to a maximum in dielectric constant.Extraction of seven soils with boiling FA/H, O (107 °C) and FA/DMSO (112 °C) indicated that similar amounts of C and N are generally dissolved by the two solvent mixtures. However, FA/DMSO was about twice as efficient as FA/H2O for the ver‐miculite‐rich, calcareous, organic clay loam, removing 66 per cent of its C and 54 per cent of its N.Zr(IV) hydroxide in acidic aqueous acetone was a better flocculant than Ti(IV) for the dissolved organic matter. Model compound studies, together with hydrolytic and NMR studies, indicated that Zr precipitates carbohydrate‐like but not aromatic organic components. The quantity of Zr sorbed to the organic matter corresponds closely with its C.E.C. determined by Ba r

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00987.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY