Earthworms change the abundance and community structure of nematodes and protozoa in a maize residue amended rice–wheat rotation agro-ecosystem

The influence of earthworms on nematodes and protozoan communities was determined during the wheat phase of a six year rice–wheat rotation agro-ecosystem. Experimental plots in the rotation had five treatments, i.e. incorporation or mulching of maize residues with or without added earthworms and a control. The addition of maize residues to soil strongly affected the abundance and community structure of nematodes and protozoa in the absence of earthworms. The presence of earthworms gave significantly lower total nematode numbers at all soil depths following maize residue incorporation than the same treatment without earthworms, and also gave lower (although not significantly) total nematode numbers in the upper soil layer following maize residue mulching than the same treatment without earthworms. This was mainly due to a significant decrease in bacterial-feeding nematode numbers. Earthworms also strongly affected the distribution of the number of total nematodes and two trophic groups (bacterial and plant feeders) with soil depth. In the presence of earthworms, total protozoan and flagellate numbers significantly increased at all soil depths following both incorporation and mulching of maize residues, while numbers of amoebae increased only when maize residues were mulched. Additionally, in earthworm casts total nematode numbers (mainly bacterial and fungal feeders) were significantly higher, whereas total protozoa numbers (mainly flagellates and amoebae) were significantly lower than that in soil from 0 to 5 cm layer. results indicated that earthworm activity could affect the abundance and community structure of microfauna, and change their distribution between soil layers and cast material, depending on the mode of application of organic residues.