Soil Organisms (Aug 2020)
Soil Oligochaeta communities after 9 decades of continuous fertilization in a bare fallow experiment
Abstract
Mineral and organic fertilizers and amendments modify soil characteristics and impact beneficial soil organisms. However, conventional fertilizer experiments cannot separate impacts mediated through changes in crop productivity and through changes in soil chemical properties. We assessed populations of earthworms and enchytraeids (Oligochaeta, Annelida) in the surface horizons of a loess Luvisol of a world-unique long-term bare fallow experiment of INRAE (Versailles, France) to test the trophic and edaphic limits of existence for these soil taxa. Continuous annual applications since 1928 of 16 different treatments including nitrogen, phosphorus, potassium fertilizers but also basic (alkaline) and organic amendments, led to strongly diverging physical and chemical properties in the soil’s surface layer. The feeding activity of soil organisms was also assessed using the bait lamina method, assuming that lower bait consumption rates would be observed in treatments where fewer terrestrial Oligochaeta persist. We showed that compared to conventionally managed cultivated soils, both taxa were much less abundant in these extreme soil treatments, but enchytraeids were relatively more abundant than earthworms, ascribed to the enchytraeids’ higher tolerance to low pH soil conditions and a different feeding ecology. Most of the enchytraeid and earthworm individuals were found under horse manure inputs and basic amendments, suggesting that organic matter contents and/or pH would drive most of the Oligochaeta communities. Moreover, the bait-lamina feeding activity was significantly positively correlated with enchytraeid abundance. This study underlines the usefulness of historic long-term trials to improve knowledge on the ecology of soil organisms, and it presents an example of long-term soil biological resilience in highly degraded soils.
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