Earthworms enhanced winter oilseed rape (Brassica napus L.) growth and nitrogen uptake

A field experiment was conducted to investigate the effects and mechanisms of earthworm (Metaphire guillemi) activities on the winter oilseed rape (Brassica napus L. Zhongshuang 9) growth before winter. Present study included inoculated with (E) or without earthworm (CK) treatments and investigated the dry weights and nitrogen contents of plants, and mineral nitrogen concentrations in 0–5, 5–10 and 10–15 cm depth of soil layers three times (4, 6 and 8 weeks from the beginning of the experiment, respectively). Results showed that earthworm activities significantly increased the dry weights and nitrogen contents of plants compared with CK. These results indicated that earthworm activities enhanced winter oilseed rape growth and nitrogen uptake before winter, which might be due to earthworm activities increased mineral nitrogen concentration in soils, altered the concentration ratio of NO3-N to NH4-N, increased plant root activity and leaf nitrate reductase activity as well as the interactions between them.