Yet, in an impossible equation, as cultivable soils are gradually depleted, crop production levels must keep rising. FAO estimates that farmers will have to produce 40 percent more grain in 2020 to feed the world population. Using conservation tillage, farmers leave crop residues on their fields after harvest, instead of ploughing them in or burning them off. They plant new crops with specially designed planters. These guide the seeds down into a slot in the soil underneath the protective layer of mulch formed by rotting residues.
Cover crops have additional benefits according to the species planted.
For instance, legumes enrich the soil with nutrients, while plants with strong, deep roots break up compacted soil. To maintain healthy numbers of such animals, agro-chemicals must be used with special care and kept to a minimum. The modern plough was invented and perfected for weed control. When farmers first begin to practise conservation agriculture, herbicides are often necessary to control the weeds - but they must be used judiciously to protect the soil life. Experience has shown that after a few years, the quantities of agro-chemicals necessary tend to decline.