Passage III

The presence of earthworms in forest soil can affect the amount of phosphorus (P) in the soil. Studies were done in 2 adjacent oak forests: Forest W, an old forest, and Forest Z, a young forest. Both forests had the same type of soil.

Two 100 m² plots were selected in each forest: one that had been invaded by earthworms several years before the studies began, and one that had no earthworms (see Table 1).

Study 1

Three holes were dug in each plot. In each hole, a 10 cm³ volume of soil was collected from the wall of the hole at the surface and also at 3 cm, 6 cm, 9 cm, and 12 cm depths. All the soil volumes collected from the holes in a plot were combined into a single sample, and all particles larger than 2 mm in diameter were removed. The sample from each plot was oven dried and then analyzed to determine the total soil P, in mg P/cm³ (see Figure 1).

Study 2

In each plot, samples of the soil solution (aqueous solution present between soil particles) were collected using a pair of lysimeters that had been installed 2 years before the studies began. One lysimeter collected a sample of soil solution from a depth of 12 cm (shallow), and the other collected a sample from a depth of 36 cm (deep). For each sample, the concentration of soluble reactive P (SRP; one of several different forms of P found in soil solution), in micrograms of P per liter (μg P/L), was determined (see Figure 2).