The roots of the Austrian Winter Pea cover crop.  You can see the many, many nodules of nitrogen that the plant puts back into the soil, rebuilding the soil for the benefit of the next crop.  
We planted about a quarter acre of Winter Pea this year, both row and scatter method.  Scattering works best and plenty of rabbit, chicken and duck manure.  To make the potato rows we hilled up the manure/compost mixture covering over the winter peas.

The potatoes are doing well with our first year soil building technique…see the potato time post.