Earthworm activity is probably a better indicator of soil biological health than soil organic carbon levels. Organic carbon is not necessarily an accurate indicator of a soil's potential to release nutrients or of soil building benefits. Perhaps the following business analogy is useful. A healthy business is one that has a good cash flow regardless of the assets. If soil assets are carbon and cashflow is microbial activity then zero tillage systems are seeing much more healthy soil businesses despite sometimes static organic carbon levels.
Nitrification is the conversion of ammonium into nitrate.
Booms occur after tillage with busts following shortly after. In contrast, mineralization in no-till soils is more evenly spread over the season. For this reason, spring sown no-till crops should receive adequate fertilizer early in the season to help establish the crop. Nitrification in no-till soils may continue even under dry conditions due to more soil moisture. However, in very wet conditions, nitrification may be inhibited sooner in no-till than in a cultivated soil because of a lack of oxygen.