Tull also invented a horse-drawn hoe for clearing weeds and made changes in the plough that are still visible in modern designs. His interest in ploughing came from his war against weeds and his belief that plants took their nourishment solely from the minerals in the soil and that organic emendation was not necessary. He knew that horse manure was filled with weed seeds and hoped to avoid using it as fertilizer by pulverizing the soil to make the minerals more available.
Although Tull was in error on this latter point -- the error of a pioneer, it should be noted -- overall his innovations form part of the foundation of productive modern farming. His inventions were controversial at the time and were not adopted for many years.