SLU news

Only certain types of organic fertilizers increase abundance of soil biota important for soil fertility

Published: 17 May 2021
An insect with long antennae on a brown surface. Photo.

To understand how fertilization regulate soil quality, we need to know more about how fertilization affect soil biota. This has been examined in a new study from SLU. The specific fertilizer was found to be more important in determining the responses of soil biota than whether it was mineral or organic.

Soil organisms provide important ecosystem functions such as decomposition, nutrient and carbon cycling as well as water regulation. Worldwide, the quality of agricultural soils is threatened by the loss of soil organic matter and by soil compaction. A practice commonly used that offsets these threats and enhances soil functions is the application of organic fertilizers.

A need to understand the effects of fertilizers on soil biota

But how does fertilization regulate soil quality? A first step towards understanding that is to examine its effects on the soil biota.

– We used a 17-year-old fertilization experiment at Lanna Field Station to investigate how soil biota responded to four different organic fertilizers. We compared it with two mineral nitrogen fertilizers and a control with no fertilization at all, says Maria.

Soil samples were collected and a wide range of organisms belonging to different functional groups and trophic levels of the soil food web were investigated.

– We found that 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, says Maria.

Multiple factors influence fertilization

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.

– The specific fertilizer was more important in determining the 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, concludes Maria.

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