Effects of Earthworm Activities on Soil Nutrients in Forest Lands of the Qinling Mountains

The effects of earthworm activities on carbon and nitrogen in forest soils of Qinling Mountains were tested to clarify the relationship between earthworm and soil nutrient cycling. Based on the investigations in the field, we conducted a microcosm experiment with Eisenia foetida earthworm and 3 stands (Quercus aliena var. acutesrrata, Pinus tabulaefomis and pine-oak mixed forest) in the Qinling Moutains. The study was set up with 2 treatments: earthworm (E) and no earthworm (CK), 3 replicates per treatment. Soil samples were collected on the 5^th, 10^th, 20^th, 35^th and 60^th day after inoculation. The soil organic carbon, total nitrogen, nitrate nitrogen, ammonium nitrogen content and net nitrogen mineralization rate were determined and analyzed to explore the effects of earthworm activities on soil nutrients. The results show that Eisenia foetida earthworm significantly increased the content of soil organic carbon and total nitrogen in the 3 stands through its own activities. The maximum increase of soil organic carbon was: Q. aliena var. acutessera 7.74 g/kg, P. tabuliformis 3.1 g/kg, pine-oak mixed forest 2.01 g/kg, and the maximum increase of total nitrogen in soil was: Q. aliena var. acutessera 0.77 g/kg, P. tabuliformis 0.15 g/kg, pine-oak mixed forest 0.1 g/kg, and maintained the stability of C/N. The content of NH₄⁺-N, NO₃⁻-N and the mineralization rate of net nitrogen was significantly increased through feeding on litter and decomposition of earthworm. The maximum net nitrogen mineralization rates of the 3 stands were: Q. aliena var. acutessera 3.91 mg/(kg·d), P. tabuliformis 2.39 mg/(kg·d), pine-oak mixed forest 2.72 mg/(kg·d). This study shows that earthworm can significantly increase soil organic carbon, total nitrogen and accelerate the mineralization rate of soil nitrogen, which can promote the circulation of soil nutrients.