Slash and burn, an early type of crop culture, remains today a widespread form of agriculture in developing countries, that is independent of fossil fuel energy. In such a system, about ten hectares of productive land is held in fallow for each planted hectare. With this rotation system, a hectare is planted once every 20 years, allowing the soil to reaccumulate vital plant nutrients. Although the practice requires large acreages and large labor inputs, the crop yields are adequate for a family unit. For example, corn with ample rainfall can yield about 2000 kilograms per hectare (kg/ha).