Abstract
The physical properties of clay soils are described as they determine root growth and crop behaviour. These include the soil water store, the infiltrability or recharge capacity, and other factors that can limit root growth, e.g. mechanical impedance, salinity and poor aeration. Adequate and accurate estimates of these factors are required for modelling the soil water regime and through this to obtain a description of crop performance on a continuing basis during the growing season. Methods of measurement are proposed. An example is given of a research project where a fourfold increase in the productivity of a difficult clay soil has been achieved by progressively ameliorating limiting physical conditions.
