Pugging Does Damage

This past weekend I came across the most severe case of animal pugging that I've seen in a long while.

I noticed it while visiting a farmer in the Catlins. He had a hilly winter feed block, most of which he grazed with hoggets. The lower part of it, however, he'd fenced off and used as a feed lot for a herd of cattle. In the process they had churned the heavy clay loam soils into a quagmire.

Looking closely I noticed a remarkable phenomenon. Many of the deep animal footprints were filled with blue-green water, and the sides of the pug marks were in many cases coated with a film of reddish-brown iron oxide. Pressure from cattle hooves had evidently created an anaerobic (oxygen depleted) condition in the soil leading to reduction in soil iron. Iron in its reduced ferrous ion state is soluble (and blue green in colour), and this had leached from the soil into the hoof marks. Once exposed to the air again, however, much of this had converted back to the oxidized or ferric form, producing the rust-coloured coatings on the sides of the hoof marks (see the photo).   

This was one of the more observable effects of pugging on the chemistry of the soil. The physical and biological state of the topsoil was also affected. Soil structure had been destroyed, porosity reduced and most of the biological life killed off. Pugging does damage the soil - there is no question about that. What can be done about it? That's another issue for another time.