what effectdoes a high proportion of rock fragments have on soil consistency?
A high proportion of rock fragments lightens a soil making it freer draining and easier working. For example a Cotswold Brash soil with granular limestone chunks may contain upto 60% clay, but behaves more like a clay loam. The consistency varies depending on the proportion of clay and rock in the mix together with organic matter content. There are three aspects of soil consistency which can be measured. The shrinkage limit, plastic limit and liquid limit. All are measured on soil which has been dried and ground to less than 2mm in diameter therefore the presence of rock fragments greater than 2mm in diameter will have little effect. The main influences are clay and organic matter contents. Any good soil physics textbook such as Baver, Gardner & Gadner or Kohuke (both called ‘Soil Physics’) will give details of the tests. Engineering textbooks can also be useful.
