Influence of working depth of a curved rigid tine on the mixture of fragments produced by deep ripping a texture-contrast soil

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A curved, rigid tine with a 50 mm wide point was used to deep rip a texture-contrast soil at different depths of working. The soil had a sandy clay loam A horizon, about 90 mm deep, over a dense clay B horizon; both horizons were drier than their lower plastic limit when ripped. The depth of working varied from 100 to 500 mm and the analysis was done on the loose soil from the lower part of the trough formed by the tine, below the lower boundary of the A horizon. The size and horizon-of-origin of the fragments were measured and their volume recorded as a proportion of the total volume at the water content when ripped. The smaller (0·5 to 2 mm) fragments from the A horizon moved more easily towards the bottom of the trough, but their proportion declined as working depth increased. Fragments from the B horizon with diameter less than a tenth of the point width declined with working depth, whereas soil from the same horizon with more than a tenth of the point width increased with working depth. These different size classes of fragments may have been produced by different soil failure processes induced by the tine. Below a depth of 300 mm the mixture had a relatively constant composition; this depth seemed to correspond to the “critical depth” of working of the tine. The amount of mixing of soil from the two horizons was more than was anticipated from initial visual inspection of the contents of the trough.