Instead, they say, farmers should switch to no-tillage agriculture, in which once the grain is harvested, the new seeds are simply sown into holes among the leftover plant matter. Leaving the old crop stalks and roots in place holds retains the soil and its moisture, reducing erosion. The rotting vegetation recycles nutrients and attracts microorganisms, worms and insects, which help maintain soil fertility and provide ecosystem services. The practice is gaining popularity in Brazil and across the Americas, but getting the world's poorest farmers to adopt it will take time, partly because of the prohibitive cost of equipment.
I visited Keith Ashby, a farmer who has been using no-till agriculture for the past six years on his wheat fields in Kent, southeast England. "I get a better yield than when I ploughed, and it's slashed my fuel costs," he said. "Instead of having to drive a tractor up and down the field several times, I only have to do it once to drill and sow." Considering that it costs him 9.9 gallons (45 litres) of fuel an hour for 14-hour days over 2 weeks, while his neighbour who still ploughs uses 19.8 gallons (90 litres) an hour for substantially longer, he is making important cuts in costs and carbon emissions.
"We use the sheep to provide manure for the fields, which halves our fertiliser use," he explained. In the next field, Ashby was "resting" his wheat field by growing turnips for the sheep, and nitrogen-fixing peas and beans to help improve his soil.
Back in my office, I reflect that there is more mud on my boots than on parts of the chalk-exposed Kent Downs, which just a few hundred years ago were as lush and fertile as Ashby's fields. We may have spent the past millennia getting rid of valuable soils, but we are now learning ways of retaining it, from the big transcontinental projects to small-scale grass-planting. I have mentioned some of the methods I have discovered on my travels: let me know on our Facebook page of any methods you have found useful.