SOIL MECHANICS

Wairarapa Times-Age, 17 February 1939, Page 3

SOIL MECHANICS

THE ACTION OE EPOST. The loosening action which the mechanical operation of ploughing has is immensely intensified by the action of

frosts. The expansion which takes place when a wet up-turned soil freezes increases temporarily the bulk of the soil, and afterwards when the frozen soil thaws there are many empty spaces which were not there before the frost set in.

These are the, spaces from which frozen water has melted, the place of the water being taken by air and the soil thus benefiting by aeration. Dr E. J. Russel, a noted British authority, points out that frost helps to disintegrate the stubble and roots of plants. I The expansion caused by the freezing of the water they contain splits them up so that they are much more easily attacked by soil organisms. Except when the land is very light, water cannot easily penetrate the soil in the compact state in which it is generally found after harvest, but lies in pools on the surface to be lost by evaporation. Into ploughed land, on the other hand, rain can soak without difficulty, and even if heavy storms come the broken surface checks the flowing off of water and retains it till it has had time to soak in. These effects, states Dr Russel], are easily seen after ploughing has been interrupted by rain. The ploughed land is moist but not waterlogged at the surface, because the water has found its way below, while the unploughed land shows every sign of excess of water at the surface.