Type of organic fertilizer rather than organic amendment per se increases abundance of soil biota.

Maria Viketoft,Laura G A Riggi,Astrid R Taylor,Riccardo Bommarco,Sara Hallin

doi:10.7717/peerj.11204

Abstract

Addition of organic amendments is a commonly used practice to offset potential loss of soil organic matter from agricultural soils. The aim of the present study was to examine how long-term addition of organic matter affects the abundance of different soil biota across trophic levels and the role that the quality of the organic amendments plays. Here we used a 17-year-old fertilization experiment to investigate soil biota responses to four different organic fertilizers, compared with two mineral nitrogen fertilizers and no fertilization, where the organic fertilizers had similar carbon content but varied in their carbon to nitrogen ratios. We collected soil samples and measured a wide range of organisms belonging to different functional groups and trophic levels of the soil food web. Long-term addition of organic and mineral fertilizers had beneficial effects on the abundances of most soil organisms compared with unfertilized soil, but the responses differed between soil biota. The organic fertilizers generally enhanced bacteria and earthworms. Fungi and nematodes responded positively to certain mineral and organic fertilizers, indicating that multiple factors influenced by the fertilization may affect these heterogeneous groups. Springtails and mites were less affected by fertilization than the other groups, as they were present at relatively high abundances even in the unfertilized treatment. However, soil pH had a great influence on springtail abundance. In summary, the specific fertilizer was more important in determining the numerical and compositional responses of soil biota than whether it was mineral or organic. Overall, biennial organic amendments emerge as insufficient, by themselves, to promote soil organisms in the long run, and would need to be added annually or combined with other practices affecting soil quality, such as no or reduced tillage and other crop rotations, to have a beneficial effect.

Highlights

Soil biodiversity is highlighted in the European soil thematic strategy as a key component of soil quality (European Commission, 2002), because soil organisms provide key ecosystemHow to cite this article Viketoft M, Riggi LGA, Bommarco R, Hallin S, Taylor AR. 2021
Mineral fertilizers generally increase the microbial biomass in cropping systems (Geisseler & Scow, 2014), and this effect can propagate in the soil food web and increase soil fauna and erase differences between fertilization treatments
Long-term addition of organic and mineral fertilizers had beneficial effects on the abundances of most soil organisms compared with unfertilized soil, but the responses differed between the soil biota groups

Summary

Introduction

Soil biodiversity is highlighted in the European soil thematic strategy as a key component of soil quality (European Commission, 2002), because soil organisms provide key ecosystemHow to cite this article Viketoft M, Riggi LGA, Bommarco R, Hallin S, Taylor AR. 2021. Type of organic fertilizer rather than organic amendment per se increases abundance of soil biota. Organic fertilizers increase SOM and have positive immediate within season effects on the abundance of several soil organisms at different trophic levels, e.g., microorganisms (Birkhofer et al, 2008; Paterson et al, 2011), soil fauna such as nematodes (Ferris & Matute, 2003; Paterson et al, 2011), mites (Axelsen & Kristensen, 2000; Cao et al, 2011), collembolans (Axelsen & Kristensen, 2000; Haubert et al, 2009) and earthworms (Lofs-Holmin, 1983), as well as aboveground predators (Hines, Megonigal & Denno, 2006; Riggi & Bommarco, 2019). While the general within season response to organic fertilization is enhanced diversity and abundance of soil biota when compared with no or mineral fertilization, it is less well known how the overall soil communities react to long-term organic fertilization

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