Almost all the paleopedology presented at this Congress was in a symposium entitled Records in Soils of Environmental and Anthropogenic Changes, organized by John Catt and Nicholas Fedoroff on behalf of Commission V (Soil Genesis, Classification and Cartography) and Working Group PP (Paleopedology). The symposium was concerned with the effects of environmental factors on soil properties and with reconstructing past environments from soil properties. These are subjects of increasing importance, the first because of the concern that man’s increasing influence on global environments is seriously limiting the capacity of soils to produce food for a rapidly expanding world population, and the second because knowledge of how environmental changes occurred in the past is important for predicting future global environmental change.

Soils are now regarded as a potentially valuable source of paleoenvironmental data, especially to help construct high resolution climatic curves for the Late Quaternary from loess-paleosol sequences in various parts of the world, and to indicate the effects of early man on the landscape. One objective of the symposium was to identify which soil properties in any situation provide the best means of inferring past environmental factors. Properties considered included carbon isotope ratios (indicating ratios of C3:C4 plants), magnetic susceptibility, depth functions of carbonate, bulk density, porosity, organic C and cation exchange capacity of the soil skeleton; buffering capacity curves; the different forms of organic N; ratios of organic to inorganic P; clay minerals and the types of microfossil remains found (e.g. pollen, diatoms, phytoliths, parasite eggs).

There is a growing realisation that most surface soils show properties that are out of equilibrium with the present environment. Relict features inherited from Cenozoic periods that were distinctly colder or warmer than the present have been recognised for several decades on older deposits and elevated land surfaces in mid- and high-latitude regions, but recent careful study of younger soils and those in lower latitudes has shown that many of their properties reflect later Holocene fluctuations of climate or early human activities. Examples given in the symposium included vertisols in India, red soils in Portugal and the “lithomorphotype soils” of the Russian Plains. Relict features often have considerable significance for macrostructure and water movement, carbonate distribution and pH, salinity, phosphorus sortion/desorption, etc., and also account for much of the short-range soil variability than can present management problems in intensive agriculture (precision farming).

It is one thing to recognise relict features, such as the imprints of past climate change or early human activities, but quite another to date them precisely, especially in surface soils. A terminus antequem is sometimes provided by the age of the parent material, but subsequent events may be less easily related to particular periods. The length of the soil-forming period or a part of it can sometimes be judged from the extent to which some soil features are developed; examples discussed in the symposium included amounts of iron released by weathering processes, the ratios of less mobile elements (e.g. Al) to more mobile ones (e.g. Na), amounts of different humus fractions and the meteoric ¹⁰Be content of surface horizons.

The most reliable pedologcal evidence for paleoenvironments often comes from buried soils, in which a terminus postquem is provided by the date of burial. Examples given in the symposium included the well-preserved chronosequences of stacked soils in the Chinese and Argentinian loess deposits, and those buried beneath funeral mounds of different archeological periods in parts of southern Russia. All of these suggest sequences of rapid climatic change occurring over periods ranging from several thousand years to a few centuries.

Some of the reported studies of soils on archeological sites and comparisons of neighbouring profiles with different recent cultivation histories showed that human activities have profoundly influenced soil properties, sometimes beneficially but more often to the detriment of soil quality. The effects discussed included homogenisation of the upper soil horizons, loss of organic matter, weakening of soil structure and increased erosion, illuviation and gleying as a result of repeated cultivation; increase in organic matter content by manuring or spreading of peat; run-down of soil fertility by cropping or grazing without amendments, leading to podzolisation and ironpan formation, erosion and increased heterogeneity of the soil cover; loss of fertility and reduction in areas of wetlands by drainage; and salinisation, alkalinisation and compaction by irrigation. Several of the papers assessed the rates of these processes, some of which are matters of international concern for future global food production because they are causing rapid soil degradation.