Soil compactibility in relation to physical and organic properties at 156 sites in UK

The variation of soil compactibility and its relationship to plasticity, texture, organic matter and particle density is considered for 156 sites and for one intensively sampled site. These sites were concentrated in east Scotland and were the locations of Scottish Agricultural College (SAC) field experiments and surveys related to tillage and compaction. Compactibility was determined by a rammer method on sieved soil. The coefficient of variability of compactibility (as maximum dry bulk density) was relatively low between sites (9.5%) and within site (4%). The soils covered a wide range of textures; sand contents ranged from 1.7 to 93.5 g 100 g−1 and clay contents ranged from 2.5 to 49.1 g 100 g−1. However, liquid limit was more important than particle size fractions in the prediction of compactibility. Loss-on-pretreatment prior to measurement of particle soil distribution was taken as a measure of readily oxidisable soil organic matter. This fraction was more variable and more relevant than total organic matter in determining mechanical behaviour. Compactibility was predicted adequately by a combination of loss-on-pretreatment and liquid limit. Maximum dry bulk density and liquid limit were identified as important characteristics of the dataset and would be suitable parameters for measurement of soil physical/behavioural quality. Although particle density was not particularly important in predicting compactibility, it ranged from 2.36 to 2.87 Mg m−3. Awareness of this variability is important for properties estimated by a calculation involving particle density.