Last week I went out to our long-term tillage plots to observe comparisons of 41 years of no-till, chisel-disk, and moldboard tillage. I was impressed by the difference in earthworm activity between plots of conventional tillage and long-term no-till. This year is our soybean year in a wheat-corn-soybean rotation (with either hairy vetch or crimson clover as a cover crop after wheat). The soybeans had just dropped their leaves. In the conventional tillage plot I noticed very few earthworm middens, however in the long-term no-till field I found many.
Pencil-sized nightcrawler burrows can be observed under the middens. (Credit: Sjoerd Duiker)
Middens are the small mounds that anecic earthworms make on top of their deep, vertical burrows. These burrows can easily go as deep as 3 or 4 feet. Middens consist of crop residue pulled into the burrow by the earthworm (in this case mostly soybean leaves) and earthworm casts that the earthworms deposit at the soil surface. When you carefully remove the midden, you can see the pencil-size earthworm burrow underneath.
Very few nightcrawler middens were found in conventional tilled soil plots compared to long-term no-till soil plots. (Credit: Sjoerd Duiker)
These burrows are coated by organic substances. In our type of climate, these deep burrows are important pathways for root growth into the subsoil. In a study in Wisconsin, researchers observed that the average rooting depth of no-till corn was 49 inches, but that of tilled corn was 26 inches. The difference was attributed to the prolific nightcrawler activity in no-till: there were no nightcrawler burrows in the tilled fields, but on average 2.3 middens per square foot in the no-till fields – that is about 100,000 middens per acre. The average length of the burrows made by the nightcrawlers was 49 inches or more than 4 feet! In one study in Australia, researchers found that below a depth of 2 feet, almost all roots grew into pores and cracks. These deep roots are very important for facilitating water uptake in dry years.