This is an important technique in modern farming, which was developed as farmers learnt from the mistakes made in the 19th and early 20th centuries. Then many people thought that the Earth’s resources were boundless, and in colonies and other territories around the world, they cleared forests and grasslands to make way for new farms. At first, yields were high, but many farms became infertile. Soil erosion-the rapid removal of fertile topsoil by wind or rain-was the main culprit.
Soil erosion is especially severe on sloping land, when farmers plough furrows straight down the slope. This creates gullies which rain water quicky deepens. Contour ploughing, a way to stop this form of erosion, involves ploughing along contours, so that the furrows follow lines linking points of the same height. Such furrows halt the downward flow of water and so reduce erosion.