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A series of preferential flow experiments were conducted to investigate the temporal and spatial variability in a large block (5.4 by 3.4 by 1.2 m) of undisturbed soil (Dystric Eutrocrept) situated in mid-Devon, UK. Chloride and nitrate tracers were applied using rainfall sprinklers and the soil water was sampled continuously using 54 ceramic suction samplers installed throughout the block. Two main types of breakthrough curve occurred, a rapid response with a high peak concentration and a slower response with a lower peak concentration. Analysis of the spatial patterns of these characteristics confirmed the importance of the horizontal and vertical heterogeneity of flow. Peak concentration and time to peak concentration were related to depth in one quadrant but no relationship was found when the entire block was considered. Preferential flow paths occurred at intensities above 2 mm [h.sup.-1] and were less important for intensities of 1 mm [h.sup.-1]. A delayed leaching experiment was conducted in which a nitrate tracer remained in the soil for 10 d before leaching commenced. The pattern of response to the 5-mm [h.sup.-1] rainfall application was similar to the earlier experiments. Analysis of the shape of the breakthrough curves and time to peak suggested that nitrate movement was minimal in the wet soil during the intervening period. The spatial variability, noted even at this limited block scale, suggests that simplified approaches to understanding water and chemical transport are unable adequately to describe field behavior.

The condition or quality of soils determines its ability to deliver a range of functions that support ecosystem services, human health and wellbeing. The increasing policy imperative to implement successful soil monitoring programmes has resulted in the demand for reliable soil quality indicators (SQIs) for physical, biological and chemical soil properties. The selection of these indicators needs to ensure that they are sensitive and responsive to pressure and change e.g. they change across space and time in relation to natural perturbations and land management practices. Using a logical sieve approach based on key policy-related soil functions, this research assessed whether physical soil properties can be used to indicate the quality of British soils in terms of its capacity to deliver ecosystem goods and services. The resultant prioritised list of physical SQIs were tested for robustness, spatial and temporal variability and expected rate of change using statistical analysis and modelling. Six SQIs were prioritised; packing density, soil water retention characteristics, aggregate stability, rate of erosion, depth of soil and soil sealing. These all have direct relevance to current and likely future soil and environmental policy and are appropriate for implementation in soil monitoring programs. [ABSTRACT FROM AUTHOR]