Effects of earthworm (Metaphire guillelmi) density on soil macropore and soil water content in typical Anthrosol soil

Abstract

The burrowing activities of earthworms can change the soil macropore structure in terrestrial ecosystems. Studying the burrows structure and their effects on soil water movement may be crucial for exploring earthworm ecological functions and improving water use efficiency in farmlands in semi-humid areas. It was an experiment taken to assess the impact of anecic earthworm Metaphire guillelmi on the characteristics of soil macropore and soil water content (SWC). Earthworms with different densities (0, 3 and 10 in. in each column) were introduced in soil columns (height 38 cm, diameter 23 cm) for 33 days. The macropore characteristics were determined by X-ray computed tomography (CT). Results showed that increasing earthworm density increased the macroporosity and macropore number. The macropore number in the high-density earthworm treatment (HDE) was 1.3 times larger than that in columns with low-density earthworm (LDE). The diameter of soil macropores ranged from 2.12 mm to 7.30 mm. The mean macroporosities in HDE and LDE treatments were 1.35 % and 0.61 %, respectively. The soil pore morphology (mean macropore circularity, branch, junction and connectivity) was also improved by earthworms. The high number of macropores (45.30/N) and connectivity (0.05 cm−3) were observed in the column with high density of earthworms. Earthworms improved the soil macropores and macroporosity. The SWC linearly decreased with increasing earthworm density. A significant difference (P < 0.05) of SWC was observed between columns with earthworm (LDE and HDE) and those without earthworm (CK), especially at the 10–30 cm soil depth. The burrows generally open to the soil surface and increased water vapour transfer channels, thus accelerated soil evaporation. In areas with uneven rainfall, high earthworm density could aggravate the risk of seasonal drought at the plough layer, which is an important threaten for crop growth and yield.