Perennial crops

Once, most of the world's vegetation consisted of perennial plants. Agriculture has largely replaced them with annual crops, which have to be replanted each year.
     Since about 2000, scientists have been able to realize the dream of developing perennial versions of food plants such as maize, wheat, and legumes. Perennials have deeper roots, which prevent erosion and hold onto more minerals from the soil, so that they need less fertilizer and water. They do not need tilling, so the soil instead of exhaling carbon becomes a carbon sink. Yields could be greatly increased in some of the world's poorest regions.
     “Farmers in Malawi are already getting radically higher yields by planting rows of perennial pigeon peas between rows of their usual staple, corn. The peas are a much needed source of protein for subsistence farmers, but the legumes also increase soil water retention and double soil carbon and nitrogen content without reducing the yield of the primary crop on a given plot of land.  . . .  [it has been calculated that] replacing 2 percent of the world's annual crops with perennials each year could remove enough carbon to halt the increase in atmospheric carbon dioxide. Converting all of the planet's farmland to perennials would sequester the equivalent of 118 parts per million of carbon dioxide — enough, in other words, to pull the concentration of atmospheric greenhouse gases back to preindustrial levels.” (Scientific American, Dec. 2011.)
     More research is needed to bring this to the scale of conventional crops, and it will probably take another two decades.

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