Correlation Between Nitrate and Calcium In Soils with and without Earthworms.

Some of the European earthworm species now endemic in hardwood forests in the northeastern USA produce calcite - a mineral with low solubility - as part of their metabolic activities. Forest soils often show high plant available calcium concentrations when invaded by these so-called calciferous earthworms. We hypothesized that earthworms may engineer the biochemical make up of soil solution to suit their need for Ca. We measured plant available calcium, nitrate and ammonium with Plant Root Simulators (PRS^TM, Western Ag Innovation, Saskatoon, Saskatchewan) in the absence and presence of earthworms in Rhode Island (RI) and Vermont (VT) sugar maple stands. At both sites, soils were siliceous in nature with no CaCO₃ and pH values of 5.5 to 5.8 reported in Soil Survey data. In soils with earthworms, pH were 1 pH unit greater than in soils without them. We found that the ratio of nitrate to ammonium was 4 and 12 in RI and VT, respectively. At the same time Ca concentrations were 5 (VT) and 2 (RI) times greater in the earthworm invaded stands than in the stands without earthworms. At the Vermont site, Ca and NO₃ were positively correlated in the presence of earthworm. In RI, where fewer measurements were conducted over a short period of time, the relationship did not hold. We speculate that nitrification may play a role in maintaining free Ca concentrations to support earthworm metabolic needs.