The mechanical properties of soils which are concerned in ploughing are considered under the three heads:
(1) Soil cohesion.
(2) Soil plasticity.
(3) Surface friction between soil and metal.
In each case methods of measurements are discussed and experimental curves are given for representative soils over the whole moisture range with which the practical agriculturist is concerned.
In the case of cohesion Atterberg's method of measurement is followed. A certain difference in character between his results and the author's is discussed.
A new technique is described for measuring one of the plastic constants, which is specially adapted to clays, and throws fresh light on their physical characteristics.
The measurements on soil friction open up a fresh subject, and promise to provide a sensitive means of investigating soil-water relationships from a new angle.