I spent hours studying these as a child.
These represent one of our oldest and most highly evolved technologies – starting from a digging stick.
Adapted to the internal combusion engine they were the primary driving force for the post-war Green Revolution but machines don't produce manure and are harder on the ground – compressing it and making it harder to plough. Over the decades since, soils have become depleted of organic matter and more effort is needed to plough them and more fertiliser is needed.
In recent years, farmers across the world have been backing away towards minimum dig approaches – pushed also by rising fuel costs and the availability of herbicides. If we continue down the herbicide path we need to develop ones that are easier on soil life that makes up about four fifths of the land biomass.
I've seen a few more collections over the years