Modern agricultural practices emit far more carbon than they sequester. In addition to emissions from tractor fuel, cow burps and petroleum-based fertilizers and pesticides, common practices such as slash-and-burn, and even old-fashioned tillage, release carbon stored in plants and soils into the atmosphere. But minor tweaks to production methods such as planting cover crops, employing no-till cultivation, and converting to rotational grazing-begin to reverse the flow of carbon from the sky back to the farm.
Estimates of the carbon sequestration capacity of the planet's farmland range from a quantity sufficient to cancel out current agricultural emissions, on the low end, up to an amount that would offset all global carbon emissions.
Increasing soil carbon is the same as increasing organic matter content, which every gardener knows is the key to a healthy and productive landscape-pest resistance, water absorption and, ultimately, yields all flow from this "black gold. So switching to climate-friendly growing practices can potentially cut farmers' cost and boost their yields in the long term, but making the transition is difficult for farmers operating on razor-thin profit margins.
Several initiatives have tried selling agricultural carbon credits to companies looking to offset their emissions, including in California’s cap-and-trade system, with little success. The reasons are myriad, though chief among them is that the price per ton hasn’t been high enough to attract the interest of farmers.
There are 3.6 billion acres of cultivated land on earth. The current average of sequestered soil carbon is about 1 percent to 3 percent; and that would equal a trillion tons. Grazing land is an even larger number of acres that also has potential to absorb carbon.