On Tuesday I went to a field day on no-till tobacco production. Tobacco is a warm season solanaceous crop -- like tomatoes or peppers -- that is usually transplanted into freshly-tilled soil in late spring. After fall harvest the remaining stubble is usually left to decompose in the bare soil until the next spring, when the plow comes around again.

In recent decades people have started to recognize that soil suffers when it's left bare, or routinely disturbed by cultivation. Bare soil is susceptible to wind and water erosion. Cultivation destroys the soil structure, further increasing its susceptibility to erosion. Cultivation also introduces a lot of oxygen to the soil very quickly, resulting in a brief boom in the microbial population, and a rapid depletion of the soil organic matter that the microbes eat. (Organic matter is a valuable component of soil because it holds on to the nutrients and water that plants need; soil microbes help release nutrients into the soil solution, making them accessible to plants, and exude sticky material that holds soil particles together, reducing soil's susceptibility to erosion.) In the long term, cultivation reduces soil organic matter content and soil microbial populations.

No-till grain production is now fairly common, but very few farmers grow transplanted crops, like tobacco, without cultivating. It turns out that one of them happens to be a sixth-generation Kentucky farmer who took the 'Introduction to Sustainable Agriculture' course that I co-taught last semester. The field day was at his farm.

We saw a nice demonstration of how soil that hasn't been tilled holds together better than soil that is routinely cultivated. Clods of soil collected from sections of the farm that hadn't been cultivated for 10 years were suspended in water next to a clod collected from a routinely cultivated section. You can see the clod on the left disintegrating while the clod in the middle holds firm:

After harvest the land is seeded to a winter cover crop that protects the soil from winter erosion, saves nutrients that might leach out of the soil in the absence of plants, and feeds soil microbes. The farm is experimenting with different winter cover crop mixes, most of which include a nitrogen-fixing legume species.

At the Kentucky State University Research and Demonstration Farm we often use a mixture of rye, which grows quickly and out-competes weeds; and hairy vetch, which fixes nitrogen and twines its way up the rye. Here are the two plants together, towering over a yardstick:

Nitrogen-fixing crops like hairy vetch harbor bacteria in their roots that are able to convert nitrogen gas from the air around us into nitrogen that is available to plants. A winter cover crop of hairy vetch can add more than 100 pounds of nitrogen to the soil per acre (Kansas State University pdf), enough to feed a nitrogen-demanding crop like corn.

Of course organic farmers have been using nitrogen-fixing cover crops for decades; the organic standards don't allow synthetic nitrogen fertilizer. Conventional farmers have known about the advantages of cover cropping, but using nitrogen fertilizer has long been cheaper than managing cover crops. Soaring fertilizer prices have changed that. Suddenly tactics like no-till production and cover cropping aren't just better for the soil; they're cheaper, too.

Michael Bomford provides research and extension services related to organic agriculture and small-scale renewable energy production through Kentucky State University's Land Grant Program.