Organic matter, they say, just can't accumulate in southern soils. But from the Coastal Plain Research Station in Florence, South Carolina, the latest word is that organic matter can accumulate--if you reduce tillage.
Patrick Hunt, a soil scientist there, has been monitoring fields for 15 years. His records show that organic matter, which started at about 0.6 percent, has doubled in the no-till fields. In his comparison fields (which are tilled surprisingly little--a few passes to work in crop residues before planting), the organic matter level has stayed the same. (In the northern half of the country, 5 percent organic matter is considered a good level to shoot for and maintain.)
Here's what's going on. Hunt has calculated that the crop residues are sufficient to raise organic matter in the top inches of the soil by 0.3 percent a year, and that a modest amount of tillage is enough to burn it all off. But though decay also uses up most of the orgainc matter in the no-till plots, enough remains to accumulate about .05 percent each year. "We see the most dramatic change in the top 2 inches," says Hunt. ''We see a little improvement in the next 2 inches, and from 4- to 6 inches there is very little change at all. But my feeling is that if we continue this observation for, say 50 years, we'll see the organic matter going deeper."
A key point here is that the changes are very slow. You may not be able to see much improvement in your soil from one year to the next, but if you do things right, the levels will go up steadily. Hunt says gardeners should continue to work in organic matter but till only enough to get the job done.