摘要:

SUMMARYCoefficients of gas diffusion (hydrogen through air) were measured on packings of Portland stone chips over a range of water contents. The chips were obtained by crushing blocks of Portland stone on which similar gas diffusion measurements had been previously made. The packings had a tri‐modal pore‐size distribution: pores between the stone chips; pores within the chips but between ooliths; pores within the chips and within ooliths. As the water content of the packings was progressively decreased, the diffusion coefficient for the packings increased in three steps corresponding to successive drainage of the three pore modes. The previous results for the blocks were used to give good theoretical prediction of the three steps obtained by measurement. These results support earlier speculation that a similar stepwise increase in diffusion coefficient in soils might have been caused by micro‐pedal structure within soil c

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00352.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYThe principles of colour perception are outlined and applied to the problems of soil colour measurement using ‘Munsell Soil Color Charts’. As care is needed in using these charts to make an accurate assessment of soil colour, recommendations for the correct methods for soil colour measurement are outlined. The three soil colour characteristics of Munsell Hue, Value and Chroma are commonly used in multivariate analyses as orthogonal, equi‐dimensional, linear variables that describe perceived colour space. Such an approach may be inappropriate because the angular separation of Hue and an approximately 2.5:1 scaling relationship between Value and Chroma should be accounted for in any model of perceived colour space. An appropriate and simple polar transformation of Munsell colour data is compared with some other coordinate systems for representing colour space, including the CIELAB system. This polar transformation is recommended for processing colour data in multivariate ana

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00353.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYThe effect of liming the A and B horizons of a number of acid soils on the subsequent adsorption of phosphate by soils retained moist or allowed to dry was investigated. Air‐drying increased the phosphate adsorption capacity but the reason was not clear.When A horizons were maintained moist, incubation with lime for six weeks increased phosphate adsorption by four samples and had no effect on another. When A horizons were air‐dried, the effect was considerably reduced or reversed. For B horizons, which had considerably greater phosphate adsorption capacities than A horizons, liming decreased phosphate adsorption irrespective of whether the soils remained moist or were dried. The relative decrease in adsorption was, however, greater when the soils were dried.In a more detailed study using one acid soil it was shown that incubation of the soil with lime for six weeks had no effect on phosphate adsorption by moist A and B horizons but after 36 weeks incubation liming decreased adsorption by the moist samples. If soils were dried then liming decreased phosphate adsorption after six or 36 weeks incubation. Such relative effects of liming on phosphate adsorption were confounded by the fact that air‐drying greatly increased the phosphate adsorption capacity of the unlimed soil. The drying effect was at least partially reversible following rewetting of the soil.Results were interpreted in terms of the lime‐induced increase in soil pH causing (i) the surface charge conferred on soil oxide surfaces to become more negative (thus decreasing phosphate adsorption) and (ii) the precipitation of exchangeable Al as hydroxy‐Al polymers resulting in the formation of new, highly active, adsorbing surfaces (thus increasing phosphate adsorption). Phosphate adsorption by moist limed soils can, therefore, be increased, decreased or unaffected depending on the relative magnitudes of these two processes. It is suggested that after liming, and/or air‐drying, crystallization of amorphous materials progressively decreases their surface area and adsorbing capacity. Thus, liming tends to decrease phosphate adsorption when the soil

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00354.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYAdsorption and desorption of phosphate by lepidocrocite and hematite, the latter obtained by thermal decomposition of the former, were studied and related to changes in mesoporosity of the solid surface. Differences between the oxides in the accessibility of their surfaces to phosphate seems to control the fractional amounts of ‘rapidly’ and ‘slowly’ adsorbed phosphate. Results of isotopic exchange of the phosphate adsorbed at high surface coverage can also be explained in terms of the mesoporosity of the s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00355.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYTransport and deposition of suspended particles occur during many soil processes. The mechanisms of removal of particles from suspension during saturated flow are described, and a simple equation of depth filtration is used to test experimental data. A method for labelling dilute clay suspensions with14C‐paraquat is developed. Particles are removed from flowing suspension even when they are dispersed. The depth filtration equation holds only under these conditions, though the mechanisms of removal of particles from suspension by the soil are unclear. A surprisingly large reduction in flow rate accompanies passage of dilute clay suspensions through soil column

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00356.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYTwo Oxisols from the B2 horizon at similar locations 2 km apart on the Brazilian coastal plain with a udic, isohyperthermic regime were practically identical in chemical composition but differed markedly in colour; one was a dark reddish brown, the other a pale ochre. Mossbauer spectra at 295 K, 80 K and 4.2 K indicated a clear difference in iron oxide mineralogy. Iron was present as aluminous hematite and goethite, with Al substitutions of approximately 20% in the two phases. However, the relative proportion of iron present in hematite and goethite was 45:55 in the first sample and 12:88 in the second. Possible reasons for these differences are discussed.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00357.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYDuplicate, bulked surface soil samples, from sites 10m apart, were collected at 97 locations 1000 m apart on a regular grid measuring 8x11 km. Data were obtained for Ag, Ba, Be, Cd, Co, Cr, Cu, Li, Mn, Ni, Pb, V and Zn. One field sample was a good predictor of its nearby duplicate for Co, Cu, Ni and Pb, satisfactory for Ba, Be, Cr, Mn and Zn, but poorer for Cr, Li and V. Maps of the variation in precision of the field samples did not reveal any association between abandoned mine sites and high variability. The median coefficient of variation for trace elements in the field duplicates was between 8 and 19.5%.The duplicated field data were averaged to yield a mean soil metal concentration at each sample location. Concentrations of Ba, Be, Cr, Li, Sr and V were comparable with other published values for similar soils in Missouri. Concentrations of Co, Cu, Mn, Ni, Pb and Zn were higher which was explained by pollution from mining activities. A graphical technique was used to calculate background levels for metals in the second group. Samples of forest litter were collected at 12 locations: Ag, Ba, Cd, Mn, Sr and Zn concentrations were higher in the litter whereas Li and V concentrations were higher in the subjacent mineral soil. Computer isoline maps of the distribution of elements revealed an association between areas of high soil Cu, Co, Ni, Pb and Zn and abandoned mines or mineralized rocks.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00358.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYThe paper surveys the changes in pH, organic matter type and degree of podzolization of poorly buffered, freely drained, siliceous soils in Britain caused by the predominant plant species and semi‐natural vegetation types. Changes in vegetation with succession, especially with varying grazing and burning regimes, and also with stand regeneration, are outlined, and their implications for soil change noted. Many cyclic changes in species a bundance seem to occur naturally which cause an alternation of contrasting trends in soil acidity and podzolization, thus tending to maintain a long term equilibriu

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00359.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYMeasurements were made in southern Nigeria of soil organic C, N, S and P after forest clearance and cultivation of the site over a period of 22 months. Sampling depth, initially 0–10 cm, was adjusted as soil bulk density increased. Assuming a first order decay equation, the resulting mineralization constants for C, N, P and S were 0.179, 0.193, 0.136 and 0.262, giving half lives of 3.5, 3.3, 4.7 and 2.3 years. The amounts of N and P mineralized in the surface soil layer were equal to or exceeded the uptake of N and P by one crop of soybeans and three crops of maize. The observations are discussed in relation to a model that might be used for the more effective use of nutrients after a forest fallow.Also reported is the spatial variability of the soil C, N, S, organic P and total P at the time of forest clearance. Total and organic P had a high long‐range variability which is related to the clay content. C, N and S had high short‐range variability which is attributed to the veget

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00360.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYResults are presented from a three year lysimeter investigation, employing single (15NH4NO3) and double (15NH415NO3) labelled ammonium nitrate to study the uptake of soil and fertilizer nitrogen by cut ryegrass at 250, 500 and 900 kg N ha−1a−1. Average annual recoveries of nitrogen were equivalent to 99,76 and 50% of the nitrogen added at 250, 500 and 900 kg N ha−1, respectively.At 250 kg N ha−1the difference between the overall nitrogen recovery and the fertilizer recovery was almost entirely attributable to pool substitution resulting from mineralization/immobilization turnover (MIT). At 900 kg N ha−1both the low overall recovery of nitrogen and the low fertilizer recovery reflected the large excess of available nitrogen over crop requirements. No evidence of ‘priming’ was obtained.Analysis of the results from single and double labelled lysimeters using simultaneous equations indicated that at 250 kg N ha−1,∼70% of the nitrogen in the crop was derived from the ammonium pool. At 500 kg N ha−1this dropped to 64%, while at 900 kg N ha−1the figure was 59%. There was a suggestion that at the lower application rates, preferential uptake of ammonium was occurring but that as N supply exceeded crop requirements, nitrate was the major N source.Despite the preferential exploitation of the ammonium pool, at 250 and 500 kg N ha−1pool substitution resulting from MIT resulted in lower recoveries of fertilizer ammonium compared

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00361.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY