Effects of earthworm ecotype and density on comprehensive quality of watered land soil

【Objective】To explore effects earthworms of different ecotypes and inoculation density of earthworms on soil physical indexes, pH, nutrient indexes and cation exchange capacity through indoor culture experiments, so as to provide reference for improving soil quality of watered land in South China.【Method】The control soil without earthworm (CK), low-density Eisenia fetida treatment(E1:20 earthworms, about 10 g), high-density Eisenia fetida treatment(E2:40 earthworms, about 20 g), low-density Amynthas aspergillum treatment(A1:2 earthworms, about 10 g) and high-density Amynthas aspergillum treatment(A2:4 earthworms, about 20 g) were set, and their mechanical composition, pH, nutrient and cation exchange capacity were measured.【Result】Compared with CK, earthworm treatment significantly reduced sand content of the soil(P<0.05, the same below), and increased the content of silt and clay in the soil. However, there was no significant difference in mechanical composition between different ecotypes under the same density and no significant difference was found between different density treatments under the same ecotype(P>0.05). Under low density earthworm inoculation, E. fetida significantly reduced soil pH and increased soil exchangeable magnesium content, A. aspergillum significantly reduced soil conductivity and effective phosphorus content. In addition, A. aspergillum had higher soil pH and lower conductivity, effective phosphorus and exchangeable magnesium content compared to E. fetida. Under high density earthworm inoculation, E. fetida significantly reduced soil conductivity, A. aspergillum significantly reduced soil conductivity and effective phosphorus and increased soil pH, organic carbon and carbon-nitrogen ratio. In addition, A. aspergillum had higher soil pH, organic carbon and carbon-nitrogen ratio and lower effective phosphorus content compared to E. fetida. The results of the principal component analysis showed that earthworms had increased nutrient, cation exchange properties, silt and clay content of the soil; high density earthworm treatments had higher carbon to nitrogen ratio, organic carbon, silt and clay contents, and low density earthworm treatments had higher sand and available phosphorus contents; E. fetida treatment had higher cation exchange capacity, conductivity, available phosphorus, total nitrogen and alkaline nitrogen, and A. aspergillum treatment had higher pH, carbon-nitrogen ratio and organic carbon content. Based on the results of the principal component analysis, the soil comprehensive quality was calculated and the results showed that the low density of E. fetida treatment significantly improved the soil comprehensive quality.【Conclusion】For the ecological management of watered land in southern China, low-density inoculation of the epigeic E. fetida is beneficial to improve soil texture and enhance the soil comprehensive quality.