Soil macrofauna connections with subdrain functionality and leaching in regenerative farming

The aim of the study is to find out whether the deep burrows of the earthworm Lumbricus terrestris (the dew worm), affect subdrain flow in agricultural fields. Dew worms are common in the field soils of Finland and often become more abundant under regenerative farming. Based on our previous findings, we assume that the burrows enhance soil water permeability above the subdrains and direct percolation of water into the drains thereby increasing drain flow. Our second assumption is that at the same time the leaching of substances from the topsoil into the subdrains may increase.

The maintenance of functional drainage is an important part of field soil management, and its importance is likely to be emphasized under changing climate. Adequate drainage of arable land requires periodic renewal or supplementation of subdrainage systems, which causes significant costs for farmers. If our first assumption turns out to be correct, regenerative farming activates an earthworm population, which naturally maintains subdrain function and potentially produces cost savings. Based on the results of the study, it can also be assessed whether the phenomenon has harmful effects on the environment, for example by increasing leaching of nutrients.

The study produces novel information on the connections between soil biodiversity and soil processes. Since the vast majority of fields in Finland are subdrained and dew worms are found throughout the agricultural area of the country, the results will apply to large arable areas and are applicable in practical land management.

The study will utilize a long-term experimental leaching field at Jokioinen, SW Finland. In the field's current experimental design, the most important regenerative measure is no-till - which is particularly advantageous for dew worms - with traditional autumn plowing as the comparison point. The field has previously been inoculated with dew worms, and the clear differences in their abundance between and within tillage treatments offer an exceptional opportunity for field-scale examination of the study hypotheses.

We will combine the long-term data on the field's plot-specific subdrain discharge, the monitoring data on the spread of the dew worm population, and a new data set collected in the initial phase of the study on the variation of the abundance of dew worms and their burrows in the field. With the help of chemical markers, we will study the leaching of substances from the topsoil soil into the drainage system by analyzing samples taken from drainage water, surface run-off and soil. In the statistical modeling of the data, we will investigate the relationships between the abundance of dew worms and their burrows with the quantity and quality of subdrainage discharge over time and in different parts of the field.

The movement of substances is studied in collaboration with Åbo Akademi (Turku PET Centre). University of Central Lancashire (Preston, UK) is the partner in the collection of new dew worm field data. The research is funded by Salaojituksen Tukisäätiö sr and Teknillis-Yhteiskunnallinen Tutkimussäätiö sr foundations. The research will be carried out during 2022–2024.