摘要:

SUMMARYA simple, sensitive method developed for the analysis of geostandards was used to measure the accumulation of Cd in soils from superphosphate applied annually to grass‐land and arable soils for many years. Rates of application were equivalent to 33 kg P and 5 g Cd ha−1yr−1for 95 yr in three experiments in England and to 37 kg P and 20 g Cd ha−1yr−1for 30 yr in one experiment in New Zealand. Very little Cd accumulated in the surface horizons (0–22.5cm) of either of the arable soils from England; about one‐quarter of the applied Cd was detected in the sub‐soil (22.5–45.0 cm) of one experiment (Broadbalk) but none in the second (Barnfield). About one‐half of the applied Cd was retained in the 0–22.5 cm horizon of grassland soils from both England and New Zealand. The light (<2.2 gcm−3) organic‐rich fraction of Park Grass soil from Éngland contained about three times as much Cd as the heavier, mineral‐rich fraction. This suggests that when Cd is incorporated into organic matter its mobility is decreased and soil pH then has smaller effects on its mobility. Uptake of Cd by grass‐clover pasture in New Zealand averaged only 0.4 g Cd ha−

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00011.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThis paper describes the microaggregate structure of residual clay soils of the red earth order in East and Central Africa, examined by low‐power microscopy, and the effects of gradual moistening and sudden wetting of the soil. Results showed a markedly angular microstructure termed fragmental, resulting from simple cleavages in the soil mass, a microgranular structure involving minute spherical bodies, either discrete or in small compound aggregates, and two types of intermediate structure. The several types of microaggregate and associated profile characteristics are described in detail, and are compared with those studied more recently in West Africa. The microgranular soils also contain larger pellet bodies originating as residual cores of rotted rock. Present evidence for the distribution of these soils is outlined and possible factors in their occurrence are reviewed, including age of land surface and termite activit

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00012.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYTwo field experiments in which straw has been removed or incorporated for 17 yr (loamy sand) and 10 yr (sandy clay loam) were sampled to examine the effect of straw on the C and N contents in whole soil samples, macro‐aggregate fractions and primary particle‐size separates. The particle size composition of the aggregate fractions was determined. Aggregates were isolated by dry sieving.Straw incorporation increased the number of 1–20 mm aggregates in the loamy sand but no effect was noted in the sandy clay loam. Straw had no effect on the particle size composition of the various aggregate fractions. After correction for loose sand that accumulated in the aggregate fractions during dry sieving, macro‐aggregates appeared to be enriched in clay and silt compared with whole soil samples. Because of the possible detachment of sand particles from the exterior surface of aggregates during sieving operations, it was inferred that the particle size composition of macro‐aggregates is similar to that of the bulk soil.The organic matter contents of the aggregate fractions were closely correlated with their clay + silt contents. Differences in the organic matter content of clay isolated from whole soil samples and aggregate fractions were generally small. This was also true for the silt‐size separates. In both soils, straw incorporation increased the organic matter content of nearly all clay and silt separates; for silt this was generally twice that observed for clay.The amounts of soil C, derived from straw, left in the loamy sand and sandy clay loam at the time of sampling were 4.4 and 4.5 t ha−1, corresponding to 12 and 21% of the straw C added. The C/N ratios of the straw‐derived soil organic matter were 11 and 12 for the loamy sand and sandy clay loa

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00013.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYIn the United Kingdom silty soils have been classified as unsuitable for direct drilling since these soils may produce seed‐beds that are inadequate for satisfactory crop emergence. This judgement was based on problems encountered in the first 2–3 yr of direct drilling as well as on an appreciation of soil physical properties. Longer‐term experimentation (10 yr) has indicated that, subsequent to that initial period, soil conditions after zero‐tillage are not a major limitation to growth of autumn‐sown cereals. This eventual parity between simplified and conventional tillage can be attributed largely to improvement in the surface of direct‐drilled land. In the tenth experimental year this layer comprised more strongly developed aggregates, of greater stability, than those from the annually ploughed soil. Porosity and soil strength measurements did not indicate that root growth would be severely restricted below this depth. When this soil was wet in winter it was weak and relatively unstable and so it would most likely be unsuitable for sequential direct drilling of spring‐sown crops.At the same site soil that had been continuously under grass throughout the same 10 yr period developed better structure than that in the arable area, in part because of a greater earthworm population and an increased organic matter accumulation. In any subsequent change to arable usage this improved structure would best be conserved by avoiding soil inversion and using direct drilling or some other simplified method o

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00014.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYDrop‐cone penetration was measured bothin situand on minimally disturbed cores at a selection of soil matric potentials for four soils. The drop‐cone penetration/water content relation was linearin situand, if results for very low water contents were excluded, for the cores. The slope of the line for the field data was much greater than for the core data and this raises doubts about the value of other thanin situmeasurements of soil strength for predicting field behaviour. Vane shear strength is negatively correlated within situdrop‐cone penetration. The drop‐cone test is a useful strength test for small volumes of soil, but care must be taken in selecting the mass of the cone as this affects the volume of soil which will influence the test

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00015.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYA penetrometer has been designed for field use to simulate the stresses exerted on the ground by the hoof of a walking cow, and to measure the resulting deformation of the soil. The extent of deformation produced by the penetrometer in two intact topsoils under pasture was found to be small and independent of water content, whilst significant correlations between soil strength and water content were obtained using a cone penetrometer and a hand‐held shear vane. The results imply that the deep hoofprints associated with poached pasture are not produced immediately upon treading wet soil, but only after a progressive loss of soil strength due to repeated treading. Thus the rate of loss, which is deduced to be a measure of the susceptibility of pasture to poaching, cannot be estimated directly from a single measure of soil strengt

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00016.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY