A classification based on experimental results is proposed for the suitability of land in Britain for repeated direct drilling of cereals. Chalk and limestone soils and other well-drained loams are classified as equally suited for direct drilling of spring and winter crops; with good management most clay soils are suited for winter crops and may benefit from timeliness of sowing. But direct drilling in spring on some soils can lead to lower yields than those from conventional cultivations.

A sequence of soils is described from a slightly podzolized sandy brown earth to humus-iron podzol. In this gradual degradation sequence morphological and chemical evidence is presented to suggest that the following succession of soil processes is involved :(a) translocation of clay; (b) chemical weathering of the A, horizon resulting in an association of iron with organic matter, and slight eluviation of iron : the stage of podzol intergrade ; (c) strong iron eluviation : the stage of iron podzol;( d ) eluviation of organic matter, which rests on or is incorporated in a previously Pollen analysis has helped to establish that podzolization can occur under oakwood where edaphic environments favour the accumulation of thick, moist, strongly acid organic layers.THE status in classification of many British soils is difficult to assess owing to extensive biotic effects. Deforestation, followed by ploughing and grazing, have altered the soils physically and chemically and changed their ecological relationships. In consequence there are few, if any, areas of natural vegetation, e.g. virgin forest, and relatively few areas of semi-natural vegetation. T h e importance of such sites is therefore often disproportionate to their size, as it is only in sites which most closely approach natural conditions that we can expect to discover the true relationships between natural vegetation and soil morphology.Evidence of podzolization' under oak conflicts with widely held views of the effect of this type of vegetation on soil formation. Dimbleby and Gill (1955), however, refer to mor humus formation under old oaks in the New Forest, where they noticed visible signs of leaching, though at the same time they state that there was no evidence to suggest that continuous oak forest produced a podzol. Anderson (1951) noted signs of degradation on infertile sites under Quercuspetraea and Q. robur, and similar podzolized horizons have been seen by the author under old oaks in Sherwood Forest. In his comprehensive study of the genus Quercus in Britain, Jones (1959) states that on the most nutrient-deficient soils derived from highly siliceous rocks, usually podzols or gley podzols, Quercus petraea is generally the principal species. Betula sp., Sorbus I The definition of podzolization used here involves the reactions concerned in the movement and accumulation in the soil profile of sesquioxides and organic matter in freely drained conditions and under raw humus horizons. These reactions although incompletely understood include (i) the breakdown of clay minerals in the A, horizon leading subsequently to differentiation of silica and sesquioxides, (ii) the mobilization of iron in A horizons in association with acid products of organic decomposition, (iii) the deposition of iron and organic matter in B horizons. developed iron B horizon : the stage of humus-iron podzol.

Data are given concerning four profiles developed in materials of loam or clayloam texture, representative of soils found on moderate or steep slopes in Wales and the Welsh Borderland. Two acid well-drained soils with A(B)C profiles are correlated with sols h n s acides, differences in soluble Fe,O, content probably being the result of more intense weathering in districts of greater rainfall. A humus-iron podzol described differs from typical profiles of this class in being finer in texture, and there is a significant divergence in micromorphology. The remaining soil is regarded as transitional because it has some properties of both classes. It has a prominent brown B horizon of redder hue than the overlying unbleached A horizon ; organic carbon values are distinctly greater than for sols bmns acides, but there is no horizon of accumulation; Si02/R,03 ratios follow the pattern of variation typical of podzols though differences are less marked; the micromorphological characters of the B horizon are very similar to those of the Bs horizon of the humus-iron podzol.

The potential corrosiveness of four soil series was studied in south Oxfordshire by measuring soil properties (resistivity, pH, sulphate content. moisture content and redox potential) thought to be closely connected with ferrous metal corrosion. Fifty random points were located in areas of the soil series map units. Paired measurements of resistivity were made at each sampling point.Analysis of variance over all groups (soil map units) showed that, for all properties except redox potential, between group variance exceeded within group variance. The amount of variance contributed from within the pairs of resistivity measurements was small suggesting little short range variation in this property.There was good association between the properties measured and the soil map units. The kinds of soil identified and the delineations on the soil map therefore represents a useful partitioning of the areas studied in terms of corrosion risk.

Some of the soils on the floors of dry chalkland valleys north of the River Thames in the Marlow area have surface horizons of moderately to very flinty, weakly or non-calcareous, poorly sorted loams, which were deposited in the late Holocene. These overlie typical chalkland gelifluction and periglacial fluvial deposits. Fine calcareous colluvial loams also occur but are less common than in valleys elsewhere on the English chalk. Particle size and mineralogical analyses suggest that the loamy matrix of the flinty surface horizons was derived from loess and early 'I,lames terrace deposits or Clay-with-flints occurring on interfluves between the dry-valleys. On the evidence of their poorly sorted nature, lack of carbonate, abundance of large flints and irregularly ridged surfaces, it is suggested that they originated mainly as valley-side debris flows. Journal of waternary Science

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