INTERNAL STRUCTURE OF TILLED SOIL

Samples of tilled soil were impregnated with paraffin wax and were sectioned by sawing. The distribution of angles of incidence between voids and aggregates on the sections were investigated using random lines in 3 orientations. The angular distributions were isotropic. Incidence angles near to normal were more probable than in idealized beds of spherical aggregates. Distributions of aggregates and voids were examined along horizontal lines on the soil sections using an approach developed in communications theory. Soil structures in the size range 1-5 mm were defined exactly by sets of 16 transition probabilities. Differences were observed in the tilths produced by a moldboard plow, a tine cultivator and a rotary cultivator. The soil structures were different at different depths and changed with time after tillage. Transition probabilities measured in this way can be used in stochastic processes to simulate large tilths in a computer. The techniques described here could be adapted to the study of the distribution of soil structural features at any scale.