Crop rotation British Agricultural Revolution. The rotation between arable and ley is sometimes called ley farming. George Washington Carver (1860s–1943) studied crop-rotation methods in the United States, teaching southern farmers to rotate soil-depleting crops like cotton with soil-enriching crops like peanuts and peas. In the Green Revolution of the mid-20th century the traditional practice of crop rotation gave way in some parts of the world to the practice of supplementing the chemical inputs to the soil through topdressing with fertilizers, adding (for example) ammonium nitrate or urea and restoring soil pH with lime. Such practices aimed to increase yields, to prepare soil
Crop yield of cities meant an increased demand for food stuffs by non-farmers, and their willingness to pay for it. This, in turn, led the farmer to (further) innovation, more intensive farming, the demand/creation of new and/or improved farming implements, and a quest for improved seed which improved crop yield. Thus allowing the farmer to raise his income by bringing more food to non-farming (city) markets. The unit by which the yield of a crop is measured is kilograms per hectare or bushels per acre. Historically speaking, a major increase in crop yield took place in the early eighteenth century with the