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SUMMARY The composition of organic matter was studied in clay (< 2 μm), fine silt (2-6.3 μm), medium silt (6.3-20 μm), coarse silt (20-63 μm) and sand (63-2000 μm) fractions of the Ap-horizon of a clay loam (Orthic Humic Gleysol) from Bainsville (Ottawa, Canada) by organic C and total N analyses and pyrolysis-field ionization mass spectrometry (Py-FIMS). The C and N contents were largest in fine silt and medium silt and smaller in coarse silt and sand. Differences in the contents of organic matter and absorbed water were significantly (r= 0.945***) reflected by the amounts of volatilized matter during Py-FIMS. The Py-FI therniograms and mass spectra showed clear differences in thermal stability and molecular composition of organic matter between the organo-mineral size-fractions. Abundances of carbohydrates, phenols and lignin monomers, alkylaromatics and N-containing compounds decreased, whereas abundances of lignin dimers and lipids increased with increasing equivalent diameters. An exception was the sand fraction which was dominated by the characteristic features of plant residues. The six compound classes, calculated using signals of biomarkers, accounted for 35% to 60% of the recorded total ion intensity. The thermal evolution of the selected compound classes, which are important constituents of soil organic matter (SOM), indicated the stability of humic and organo-mineral bonds in particle-size fractions, Moreover, the influence of mineral matrix on organic matter composition was shown by significant correlations between relative abundances of carbohydrates, N-containing compounds, lipids, lignin dimers, and proportions of phyllosilicates.

SUMMARY The one-dimensional (1-D) image analysis system described in the companion to this paper (Part I) was used to analyse horizontal sections of pore space (≥ 180 μm) in four forest soil profiles with impeded drainage. Parameters were interpreted with respect to structure in the images. Mean solid intercept length is inversely proportional to extent of pore space. It was longer for blocky structures than massive structures, which had extensive, fine pore space. It decreased with decreasing ped size, increasing development and increasing intrapedal porosity. The solid intercept length distribution separated the effects of intrapedal porosity. For blocky structures, the pore intercept length distribution indicated the sizes and quantities of fissures and intrapedal pores. All profiles had an horizon with blocky structure with lower porosity owing to greater distance between interpedal pore space and low extent of intrapedal pore space. The deeper, more massive horizons had extensive, fine pore space separating fine aggregates.

SUMMARY A sequential alkali extraction procedure followed by ultrafiltration and quantitative 31P nuclear magnetic resonance (NMR) spectroscopy was used to examine organic phosphorus in a Brown Chernozem, and an adjacent Gleysol developed under native prairie vegetation, and a Grey Luvisol formed under aspen forest in Saskatchewan, Canada. Differences in the nature of organic P in the native soils were related to moisture status and vegetation. In the grassland soils, a greater proportion of orthophosphate diester P was found in the bottom-slope Gleysol. This difference was partly attributed to less favourable conditions for mineralization in the bottom slope soil compared with the mid-slope Brown Chernozem. Teichoic acid P occurred only in the native Grey Luvisol (NMR δ p.p.m. 0.36-0.95) under boreal forest and not under native grassland. At all three sites, soils under long-term cultivation were also examined and while orthophosphate monoester P (83.4-94.6% total Po), orthophosphate diester P (3.9–8.7% total Po) and teichoic acid P (12.7% total Po in forested Grey Luvisol) were detected in native soils, only orthophosphate monoester P was found in the corresponding soils that had been cultivated for 70–80 years. These findings suggest that orthophosphate diester P and teichoic acid P are more readily mineralized in the soil environment than orthophosphate monoester P forms.

SUMMARY The morphology is described of eight surface-water gley soils developed in til in Wales and central and northern England. Physical and chemical analyses as well as micromorphological observations are used to investigate processes affecting the genesis of the soils. The characteristic property of surface-water gley soils, namely slowly permeable subsurface horizons, causes a degree of periodie waterlogging within the profile. Effects of gleying and shrink/swell processes are described. Three main aspects of weathering are shown to be operating: decalcification in two of the three calcareous profiles, the breakdown of coarse into finer particles and the alteration of the clay fraction, chiefly the formation of mixed-layer minerals from mica. Argillic B horizons are present in some soils. In profiles developed in calcareous till the degree of decalcification relates strongly to the amounts of recognizable clay concentrations as seen in thin section. Of the other five profiles three clearly have argillic B horizons. Problems associated with the identification of argillic B horizons in surface-water gley soils in till are discussed.

SUMMARY Nine different gley profiles from England and Bangladesh were studied; out of these, four English soils contained variable amounts of lepidocrocite. The amounts of lepidocrocite present in various layers of these soils decreased with increasing concentrations of Si(OH)4 in the soil solution. The amount of lepidocrocite formed was negatively correlated (r= -0.78) with the atomic ratios of Si/Fe in the citrate/dithionite extracts. Lepidocrocite was absent from the other five profiles, including three surface water gley soils from Bangladesh. These soils contained relatively large concentrations of Si(OH)4 in soil solution, ranging between 0.7 mm and 1.0 mm. The atomic ratio of Sid/Fed in the citrate/dithionite extracts was higher in these soils. Enborne soil contained maximum amount of citrate/dithionite extracted silicon (2.30 mg g−1) with no X-ray crystalline iron oxides in the profile.

SUMMARY Concentrations of oxygen and carbon dioxide were measured in an upland peaty gley soil during two growing seasons and a deep peat during one season. Measurements were compared with the soil water regimes on both soils. Comparison was also made between planted areas of Sitka spruce and Lodgepole pine, and areas of the native vegetation (Molinia grassland on the peaty gley, and Calluna heath on the deep peat). In 13 m tall pure stands of the pine and spruce on the peaty gley soil about 28% of the rainfall was intercepted by the canopy and evaporated without reaching the soil, and the watertable was deeper and matric potentials were lower than under grass. When the matric potential fell below −5 kPa in the upper soil layers, high oxygen concentrations prevailed. In undisturbed peat, waterlogged conditions produced an anaerobic regime virtually to the surface, but a 1 m deep drainage ditch lowered the watertable and created an aerobic regime within the top 0.3 m of peat. The presence of tree crops on drained plots increased the depth of drying during the summer months, and aerobic conditions reached 0.4 m depth under Sitka spruce and 0.5m under Lodgepole pine. On the peaty gley also, Lodgepole pine dried and aerated the soil to a greater depth than Sitka spruce during the summer, but no difference in water regime was evident in the winter.

SUMMARY Lepidocrocite and goethite are pedogenetic crystalline Fe oxyhydroxides in the soils of mid-Wales. Lepidocrocite is more abundant and widespread, occurring in brown earths (Denbigh series) as well as morphological gleys. It is commonly dominant in horizons intermediate in depth. Goethite occurs in subsoils and was found to be dominant in the subsoil of surface water gleys (Cegin series). Apart from the Cegin series, a large proportion of the total free Fe occurs in non-crystalline forms. This amounted to 50–80% of the free Fe in organic and eluvial horizons of podzols. Despite lower proportions of non-crystalline Fe in Bs horizons, amounts were similar to those in eluvial horizons. Data on the distribution of crystalline and non-crystalline free Fe together with correlations observed between Fe and C extracted by pyrophosphate suggest that transformation and translocation of Fe in the podzols examined are governed by its association with organic fractions.

SUMMARY P-Zn interactions can affect fertilizer use and produce Zn deficiencies with certain crops. Phosphorus-Zn sorption-desorption reactions were studied in topsoil and subsoil samples from three Quebec soils. Soils were equilibrated with P solutions, then with Zn solutions, and finally with solutions containing no P or Zn. The first equilibration evaluated P sorption (Ps), the second evaluated Zn sorption (Zns) after P sorption (Ps), and the third evaluated Zn desorption (ZnD) as related to added P. Subsequently, Zn fractions were extracted sequentially with KNO3 (Znkno3), NaOH (ZnNaOH) solutions and concentrated HN03+ H202(ZnHNO,). One mmole sorbed P resulted in increases of 0.5 to 1.0 meq (mean = 0.72) increases in cation exchange capacity (CEC). Increased Zns with added P was equivalent to 4 to 5% of the increase in CEC induced by Ps in the Uplands (sand) and St. Bernard (loam) soils, and 0.4 to 0.9% in the Dalhousie (clay) soils, while one meq increase in CEC resulted in 1.5-3.5% decrease in ZnD. There existed positive correlations between Ps and extractable soil Fe materials. Phosphate sorption enhanced associations between Zns, ZnD or Zn fractions and soil organic or crystalline Fe contents, confirming that P addition increased specific sorption of Zn on Fe components. Other mechanisms including precipitation, P-induced negative charge and ‘bridge’ effects are also discussed.

SUMMARY The systematic nature of the 34S natural abundance variations (δ34S) in a prairie and boreal forest ecosystem enabled construction of hypotheses regarding the origin and cycling of S in the two soil-plant systems. By considering the 34S abundance variations in relation to soil S transformations, a better understanding of S isotope fractionation in soils was also achieved. The δ34S values suggest that atmospheric S becomes increasingly more important as a S input as pedogenesis proceeds in these soils. The origin and movement of sulphate salt in a saline seep was evaluated using δ34S values, demonstrating the usefulness of the δ34S technique in soil salinity studies. The 34S-enrichments and depletions found in soil organic S fractions were consistent with postulated differences in lability, mobility, and turnover rate. Wheat plants growing on the saline, sulphate-saturated prairie soil were found to be enriched in 34S relative to surrounding S sources, providing indirect evidence for release of 34S-depleted H2S by the plants as a S-stress relief mechanism.

SUMMARY The gley podzols of the west coast of South Island, New Zealand, typically exhibit permanent waterlogging extending from the surface to depths of 1–3 m. Their formation is explained by a continuation of processes which give rise to Peaty Podzols with thin iron pan (Ironpan Stagnopodzols; Placaquods). Iron pans initially formed within the upper B horizon are breached by acidic reducing waters and reform at a succession of lower levels down to 3 m or more below the surface.

Summary A small scarp foot valley cut in blocky Coombe rock contained three layers of calcareous material which had been washed into it, the middle one of which was soil material. Mineralogical analyses showed that there was a lithological discontinuity immediately beneath the soil material but not above it. It seemed possible that there had been a complete inversion of soil horizons by successive erosion phases upslope and deposition in the valley bottom. Micromorphological analyses showed that the particular arrangement of soil fabric in three profiles due to decalcification, gleying, and the reorganization of clay plasma varied logically according to slope position and inferred water regimes. The soil, although thin, had been developed in place. Charcoal flakes from the soil gave a radiocarbon date of 3910±220 years BP. The material that buried the soil is a combination of slopewash and ploughwash initiated by man's clearance and cultivation of the land begun in the late Neolithic or early Bronze Age.

Summary The water and oxygen status of four upland soils under Sitka spruce plantations was studied for 2 years. In a brown earth, waterlogging only occurred ephemerally in the subsoil and oxgen concentrations were generally high. In contrast, waterlogged and near-anaerobic conditions persisted for much of the year in stagnogley and stagnohumic gley soils. In a peaty stagnopodzol moist conditions occurred above and below the thin ironpan, but while high oxygen concentrations generally persisted in the subsoil, low concentrations were common in the soil above. In the brown earth, healthy roots of Sitka spruce were present at a depth of 85 cm, but in the gley soils rooting was mainly limited to 25 cm and many roots were dead. In the peaty stagnopodzol, roots penetrated the ironpan and grew in the subsoil to 75 cm depth.

SUMMARY Soil water regime, oxygen status and rooting pattern under Sitka spruce were characterized in five soil types: a waterlogged peaty gley, a peaty gley, a flushed peaty gley, a surface water gley and a brown forest soil during 1982. The waterlogged peaty gley had a high water-table which only dropped below 30 cm depth for 46 d during the summer. Below the water-table the profile was anoxic and rooting was restricted to a depth of 12cm. The peaty gley experienced seasonal waterlogging with a winter water-table around 15cm depth. Roots that grew further down the profile during the summer as the topsoil dried to –100 kPa matric potential were later killed when the water-table rose. The top 30 cm of the flushed peaty gley remained oxygenated even below the water-table. Roots survived below the winter water-table. The top 30 cm of the surface water gley and brown forest soil were freely draining and remained aerated throughout the year. The platinum electrode polarographic method demonstrated that there was a sharp transition to anoxic conditions just above the water-table at the first two sites.

SUMMARY Gaseous N loss, through denitrification and NH3−volatilization, was monitored throughout the growing season after spring application of 15N labelled urea fertilizer to peaty gley soils supporting N-deficient Sitka spruce. From the 15N data, it was calculated that only about 0.28% of applied N was lost through NH3-volatilization, almost all within the first few days after fertilizer application. Approximately 0.05% of applied N was calculated to be lost through denitrification. Denitrification decreased slowly over a 4-month period after fertilizer application. Rates of NH3-volatilization correlated with available NH4+ in the litter layer, while for the early part of the study when N-losses were highest, denitrification rates correlated with available NO3− in the litter layer. Observations of gaseous N-loss are also discussed in relation to data from lysimetry, changes in soil pH, and the soil moisture regime.

SUMMARY Detailed observations of gley features in soils derived from grey Upper Greensand rocks have been compared with their moisture regimes as determined by water-levels in dipwells. There was good correlation between the incidence of grey ped face and matrix colours of low chroma, prominent ochreous mottling within the matrix and duration of waterlogging. Careful examination of soil macromorphology can be used, despite inherent greyness, to assess the drainage status and Wetness Class of these soils. Physical and micromorphological analyses suggest that the wetness of some Upper Greensand soils is due to the combination of low vertical permeability in the underlying rock, and moderate horizontal permeability in the overlying horizons. Such circumstances allow perched water-tables to form in wet weather, sustained by lateral flow when rainfall has ceased.

Summary Image analysis was used to measure and characterise the voids in two sets of soil samples; (i) a surface water gley soil of the Deighton series and (ii) soils from a compaction experiment. The results show that the Deighton soil contains two impervious horizons separated by a much more porous horizon. In all the horizons most of the pore space is due to pores >180μm diam. In the case of the soils from the compaction experiment compaction was shown to change the shape, orientation and size distribution of the pores considerably. The range of measurements demonstrates that image analysis is applicable to several areas of soil research.

SUMMARY Eleven horizons of acidic soils in mid-Wales developed from Lower Palaeozoic sedimentary rocks were examined. Selective extraction of Al and Si provided evidence against the occurrence of significant quantities of poorly ordered Al-silicates. Fe0 was weakly correlated with Al0, but very closely correlated with Al0 minus Al extracted by cold 5% Na2CO3, implying that poorly ordered Al occurs in part as a substituent in Fe oxide and in part in a form unassociated with Fe oxide. Support for this was obtained by analysis of oxide fractions concentrated from aqueous suspensions by sequential ultracentrifugation and through the examination of synthetic Al-substituted Fe oxides. Fe oxide containing Al substituted at an almost constant level was the dominant constituent of the poorly ordered fraction in four of the five Bs horizons examined. The occurrence of Al in this form is an important mechanism by which Al is retained in aerobic but highly acidic Bs horizons.

SUMMARY The morphological, physical, chemical and mineralogical properties of eight prominent classes of soil developed in the coast aeolianites and sands of Natal are presented. These data and information on soil geography lead to the conclusion that: (i) losses of silica and bases and relative accumulation of iron (the ferrallitic process) have given rise to red and yellow kaolinitic materials; (ii) clay eluviation has given rise to coarse textured topsoils and to B2t horizons; and (iii) the hydromorphic process has caused grey colours in many sandy topsoils, plinthite development at some E/B horizon interfaces and gleying of some B2 horizons. In the soils on the older aeolianites, there is no evidence of either podzolization or the coarser textured topsoil being a younger geological deposit. The development of yellow soils in younger aeolianites may indicate a cooler climate than existed when red materials developed from the older aeolianites.

Summary Results of a two-stage random sample survey were used to give information about the usefulness of some soil morphological properties for distinguishing between the four taxonomic units, all gley or gleyed soils. A multivariate logistic method of discriminant analysis was used. The classifications by soil surveyors and by the statistical analysis were mainly in good agreement, but many generally accepted B horizon criteria used for assessing hydromorphism were of little value in discriminating between the soils under study. Depth to gleying and secondary lithology, were valuable distinguishing properties while the matrix colour value, texture and structure of the B horizons were useful in some instances. Serious consideration of the role of statistical techniques, such as discriminant analysis, is advocated both as a guide to those who design soil taxonomies and as an aid to field identification.

Summary Iron, Al, and Mn were extracted by oxalate and dithionite from two Brown Mediterranean Soils, two Red Mediterranean Soils, one Vertisol and one Gley soil, all derived from basalt or scoria in the sub-humid and humid Mediterranean regions of the Golan Heights. Ratios of oxalate: dithionite extracted iron (Feo:Fed) were low in all soils, indicating that the predominant form of free iron is crystalline. Feo accumulates in the argillic B horizons of the Mediterranean soils, while Fed accumulates in the surface horizons. A large part of the free iron oxide in the surface horizons of Mediterranean soils is associated with non-clay fractions. While manganese behaves in a manner somewhat similar to that of iron, no definite trends could be discerned in the vertical distribution of free aluminium. In the Vertisol, Feo and Mno accumulate in the subsoil. Fed and Mnd increase slightly with soil depth. In the Gley soil, amorphous iron accumulates in the surface horizon, total free iron in the bottom horizon. Both amorphous and total free Mn had been depleted from the upper horizons of the Gley soil.

SUMMARY Six soils on glacial outwash terraces and one on moraine are discussed; four are formed partly in loess of unknown age. Evidence of podzolization is apparent in all profiles, but the vertical drainage under very high rainfall is insufficient to remove surplus water. Gley processes appear to dominate, in a perched-water environment. Podzolic B horizons were identified in the same five profiles following both the Canadian system and that used by the Soil Survey of England and Wales. However, only three of these profiles could be allocated to existing podzolic subgroups in the latter system. Spodic horizons were identified in a different group of five profiles. Differences in classification are discussed with reference to the criteria used and in relation to proposals for revision of the New Zealand Soil Classification.

SUMMARY The properties of contrasting soils occurring under a 1050–1600 mm rainfall gradient are described. The soils range, with increasing rainfall, from Typic Fragiaqualfs to Andic Dystrochrepts. Sand mineralogy of these soils indicates that they have formed in essentially similar parent materials consisting largely of quartzo-feldspathic loess with admixtures of rhyolitic and andesitic tephra. The Fragiaqualfs have high bulk density, impeded drainage in winter, degraded chlorite, argillic horizons, halloysite and vermiculite. The Dystrochrepts have lower bulk density, free drainage, ferrihydrite, allophane, humus-(Al, Fe) complexes and no argillic horizons. An hypothesis to explain differences between these soil groups proposes that the dense horizons in the Fragiaqualfs arise largely from hydraulic suctions exerted by roots during periods of high summer water deficits. The consequent loss of porosity leads to impeded drainage in winter causing gleying and enhanced clay formation. In the Dystrochrepts the summer deficits are lower, consequently the soils have lower bulk densities and remain free draining.

Summary Specific features of a gley soil developed on varved lacustrine clay have been studied by scanning electron microscopy and electron probe microanalysis. Individual clay platelets can be clearly observed in the red-brown parent material but they cannot be resolved in the gleyed surfaces which have a smooth skin-like texture. Ochreous mottles are shown to have a porous blocky structure, the surfaces of the blocks being coated with globular iron oxide. Areas of manganese staining have a characteristic sponge-like morphology.

Summary In 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.

Summary A preselected grid of sixty-five randomly arranged sampling sites was the basis for a preliminary soil survey in south-west Iceland. The soils were divided into freely drained soils and poorly drained soils, the larger group being freely drained, of which many were shallow lithosols and regosols varying in depth from a few cm. to 1–2 m. Visible soil characteristics result mainly from physical effects of climate and recent age of the soil parent material. The combined processes of alternate freeze and thaw and wind deposition have disrupted orderly soil morphology. Colour differences, usually varying shades of brown, are therefore minimized, and the mineral matter shows little sign of horizon differentiation, apart from bands of wind-deposited volcanic ash. The poorly drained soils are mucky in appearance with a non-indurated layer of bog iron above the permanent water-table. Waterlogged conditions do not always lead to general gleying. Under the prevailing sub-arctic climatic conditions grasses and most other species are shallow-rooted, forming a surface mat 5–7 cm. thick. Field texture of freely drained surface soils is usually loamy, but may be extensively conditioned by high organic matter contents. Structure is weak platy, changing to block-like and/or to single-grained structure. On drying, soil aggregates usually disintegrate at the least pressure applied. Many surface features, normally related to frost action, occur, including earth hummocks, scars, V-shaped gullies, polygons, and stone stripes. Perma-frost is absent.

Summary The relative productivity of certain soil series has been determined from an evaluation of certain physical characteristics of the soil profile which are measurable in the field. The evaluation has been based on the assumption that the most important physical properties of a soil affecting its productivity are its texture, its depth, and the goodness of its drainage. The basis of the evaluation formula is that a rating is given to each textural class, ranging from 20 for a medium loam to 3 for a gravel and 5 for a heavy structureless clay, and this rating is given for each inch down to the bottom of the profile, or to an arbitrary depth of 30 in., whichever is the shallower. These ratings are added together to give a textural value, V, for the soil. If there is any gleying in the top 30 in. this value is then reduced by multiplying by a factor G, which is less than unity and which is smaller the higher the top of the gley horizon. The yield, of wheat, P, as. measured by the weight of ears produced per unit area at any spot in the field was calculated by the formula P = cVG, where c is an arbitrary constant. This prediction formula accounted for 90–7 per cent, of the variance of the wheat yield in 1947, a year in which accurate estimates of the yield were made, but only 68 per cent, of the variance in 1948, a year in which the yield figures were subject to large errors. The formula was less satisfactory for the yield of straw. The formula P = cVG was more accurate than P = cVG where VG is the textural value to the top of the gley horizon, a result interpreted as showing that wheat roots make some use of gleyed soil.

Summary The clay separates (

Summary The study is primarily concerned with the very extensive loamy podzols showing imperfect drainage in the eluvial horizon (Crampton, 1963a). The preferential preservation of Polypodium spores and the less complete floristic sequence recorded by pollen grains in podzols on warm slopes with W. or S. aspect, and greater prominence of Ericaceae and birch in the vegetational history of podzols on cold slopes with N. or E. aspect, suggest that those soils on the colder slopes were both the wetter and more acid in the past. Gleying and the development of associated structures in the eluvial horizon probably began under Ericaceae during early medieval times, and are continuing. In the spoil tips occurring across the north crop of the Coal Measures, where undisturbed for over 100 years, these structures and gleying have developed only in cold, damp pockets associated with Ericaceae on slopes with NW., N., or E. aspect. A similar but less rigid relationship occurs in places of high relief outside the spoil tips. The essential elements of these structures may develop remarkably quickly, and can be seen on opencast sites fifteen years after restoration under pastures which have become impoverished through neglect.

Summary This investigation concerns a topographic sequence of iron pan podzols developed on loamy and silty parent materials in a zone of high relief and rainfall. The upper ridge flanks are occupied by a soil designated podzol with gleying; a‘Podzol’, except that the eluvial horizon is characterized by a fine prismatic structure. Each prism contains a thin, cup-shaped iron pan defining the prism core which is anaerobic because of saturation by moisture held within the overlying organic layer for a greater part of the year. Iron oxide concretions occur throughout the remainder of the profile which is kept better aerated through structural cracking within the narrow eluvial horizon. The ridge crests are occupied by the peaty gleyed podzol. Under the thicker organic layer anaerobic conditions exist throughout the eluvial horizon and the iron pan does not occur within the structural units but is confined to the base of this horizon. Iron has probably been mobilized in these soils by microbial action within an anaerobic environment. From the pollen present it appears that the earliest vegetation was high forest dominated by oak, and podzolization probably began under this cover, which was subsequently replaced by a more open forest environment with ferns, initially on the ridge crests, probably resulting from a deterioration of the climate. Gleying probably occurred under an ericaceous flora which succeeded the forest. Grassland has now extended across the ridges, except occasionally on upper ridge flanks.

Summary A catena on the Mid-Tertiary surface near Salisbury, Southern Rhodesia, has developed over granite. Both land form and rock form indicate a two-cycle landscape. The climate is sub-tropical with a 33-in. rainfall and the vegetation is a variant of Braclzystegia savannah woodland. Profiles of good and imperfect drainage have three main horizons, namely, M (mineral); over, F/S (ferricrete and stones); over, W (weathered rock) horizons. Poorly drained soils exhibit G (gley) horizons. The W horizon of a hill-top soil comprises material at an early weathering stage below 12 ft having a platy structure, well-developed clayskins, and fresh minerals, but older material above that depth does not correspond to Van Wambeke's criteria for ante-Pleistocene materials. Dynamic soil-forming processes include lateral movement of the M horizon by sheetwash and truncation of the W horizon by insect activity.

Summary The formation of podzols with well-marked iron pans on boulder clay soils overlying chalk is described. A sub-peat soil at Goodland is to be regarded as a fossil soil with two podzol profiles superimposed. The upper podzol formed in a relatively short time prior to the growth of the overlying blanket bog following tillage which helped to accelerate the rate at which podzolization occurred. A well-marked iron pan in a podzol at Torr has developed during the past hundred years. The formation of an impermeable humuslayer within the top few inches of such soils leads to waterlogged conditions suitable for the development of blanket bog over them. This humus layer effectively seals the underlying podzol from waterlogged or gleying conditions. Accepting the hypothesis that the podzol at Goodland is a fossil soil, a chronology for soil development is proposed using archaeological material as dating evidence.

Summary Total air-space values are related to the hydrologic sequence of soils as described by Glentworth and Dion. The greatest differences within the profile are found in freely drained soils, where from a value of approximately 50 per cent. air space in the B2 horizon there is a drop to 25–35 per cent.(depending on the type of parent material) in the indurated B3 horizon. Imperfectly drained soils have a slightly lower air space in the B2 horizon and values decrease below. Poorly drained soils commonly have values between 35 and 40 per cent. and very poorly drained soils values between 30 and 35 per cent. The tendency for values to decrease in the lower horizons of a gley profile becomes less as the natural drainage conditions deteriorate.

Summary Cultivating grassland changes the physical state of the soil. The paper describes observations and measurements made in the field and the laboratory on a wide range of soils (with series names) in England over a period of 25 years. Dry sieving showed that natural weathering of grassland aggregates after three months'exposure was very considerable. The drawbar-pull on ploughing soil recently out of grass, as compared with old arable, increased with the number of years out of grass. The number of earthworms per hectare on old grassland was 6 to 9 times that on old arable of the same soil series: after three years'cultivation it was reduced by about a half. The possibility of erosion by wind increased with the number of years out of grass. Old arable land on gentle slopes had its resistance to flowing water (sheet erosion) much increased by as little as 2 years under grass. The apparent densities of soils were at a minimum under old grass and increased under cultivation. On some soils arable for many decades, the apparent densities were near those considered limiting for root penetration. The volurne of water per cent in the soil at the sticky point decreased as the years out of grass increased, suggesting a decrease in the number of days the soil could be cultivated without smearing. The water-stability of soil aggregates decreased as the number of years after ploughing old grassland increased. Whatever the texture, on ploughing old grassland, the water stability of air-dry aggregates feil sharply in the first – years and then approached the value corresponding to that of old arable soils more slowly, apart from soils of low clay content in which it differed little from old arable land after 2 years. Measurement of changes in water stability and field observations in a 6-course rotation (3 years ley, 3 years cereal) on a loam which had been in a similar rotation for about a decade after old grassland, suggested that this balance was probably right for maintaining such a soil at a good cropping level. Puddling (poaching) by animals of wet arable loam soils overlying clay resulted in gleying to the surface: ferrous iron was detected chemically. On putting down to grass there was little increase in water stability of the aggregates after 4 years. The reduction in the total pore space caused by harvesting machinery and also as a result of some years'cultivation of grassland was considerable. The ease of penetration of soils when taking cores was compared by counting the number of blows to drive in a corer: the number was much less in a soil recently out of old grass compared with old arable. The root development of cereals was poor in old arable silt soils very unstable to wetting and drying and with few visible biopores (> 10–00 μm). On soils with many visible pores, root development was much greater and yields with similar rates of nitrogen were double. The total N in the soils feil when old grassland was ploughed, sometimes by as much as 75 per cent in about 20 years. There was sometimes a significant corre-lation between total N and the reduction in water-stable aggregation during the years following ploughing grassland: the correlation coefficient was much higher on ploughing old grassland rather than leys. The N level dropped much more quickly in the first few years after ploughing old grassland than later. All single-property measurements give only a limited assessment of the physical state of a soil. Soils can be assessed satisfactorily only by making a range of measurements appropriate to the farming System.