traditionally called crop rotation. Companion planting can be used to improve the health and growth of crops, and also as another form of intensive planting, which uses vertical space more efficiently by mixing shallow rooting plants with deep rooting plants or slow growing plants with fast growing plants. In order to achieve sustainable fertility on a closed system basis, the biointensive method uses carbon and calorie farming, an aikido-style of work (using the least amount of energy or effort to achieve the greatest amount of work or production), composting—including safe and legal human waste recycling—the use of open pollinated seeds, and limited land use, which allows farmers and gardeners to retain more of the land in a wild state for genetic diversity and an ecosystem balance. If carbon or compost crops are grown in about sixty percent of the cultivated land, they can provide the compost materials that maintain the fertility for one hundred percent of the cultivated land. Many cereal crops qualify as compost crops, but provide both food and abundant compost. Some of the compost crops may be grown during the winter, when the land would be otherwise unused. Certain compost crops are higher in carbon while others are higher in nitrogen and/or fix nitrogen in the soil, and the desired proportion of each must be grown for the compost to achieve maximum effectiveness. Also, certain compost crops take particular desired nutrients from the subsoil and concentrate them in the compost, thus allowing a redistribution of those nutrients to the food crops. This proportion of 60% compost crops is crucial to the sustainability that is the goal of the biointensive method, and to the fertility of the garden. In calorie farming, care is given to growing enough food energy (and other nutrients) to live on in a minimal area. Root crops are often used in calorie farming because they allow biointensive farmers and gardeners to grow more nutrients in smaller areas, resulting in less labor per calorie, and more space for wilderness and other people. These crops—which have both a high calorie content per pound, and a high yield per area—include potatoes, sweet potatoes, garlic, leeks, burdock, Jerusalem artichoke and parsnips. These crops can produce as much as 5 to 20 times the calories per unit of area per unit of time. In biointensive farming, 30% of the land cultivated for food is used for root crops. The