Nematodes are important indicators for soil life. An Agroscope study shows that nematode numbers and species diversity are significantly higher in organic vegetable fields than in conventionally farmed fields.
Nematodes, also called roundworms or eelworms, are invaluable indicators for the soil ecosystem, since there are countless species playing a wide variety of roles in the food chain: some are bacterivores, fungivores, herbivores or omnivores, whilst others are predators. Some nematode species are also major plant parasites and may reduce yields. Nematodes also have a great influence on the decomposition of organic material as well as on the nutrient cycle.
Field experiments have shown that organic farming, i.e. the forgoing of synthetic pesticides and fertilisers, has a positive impact on nematodes. These trials, however, focus mostly on individual sites and crops. The general impact of organic farming on nematode communities has hardly been studied at all.
Greatest density of nematodes in grassland
In this study, 20 organically farmed and 20 conventionally farmed vegetable fields were investigated. Vegetable production is of particular interest, since crops are often produced highly intensively. Twenty extensively managed meadows were included for purposes of comparison. In total, over 30,000 nematodes were analysed and 98 different genera were identified.
The study shows that nematodes are most common in extensively managed grassland, followed first by organic and then by conventionally farmed vegetable fields (Fig. 1). In other words, the more intensive the management, the fewer nematodes are present.
Signs of a more extensive food web in organic soils
There were also clear differences between organically and conventionally farmed fields, with the former containing significantly more nematodes than the latter. In particular, herbivores, bacterivores and omnivores were more numerous. Moreover, the metabolic performance of the entire nematode community in organically farmed fields was higher than in conventionally farmed fields. This suggests that the food web is more extensive and soil fertility is greater in organic soils.
Crops not standardised
In summary, the results show that the management method – organic or conventional – strongly influences the nematode community in the soil. However, the fields were only sampled once, at the end of the growing season, and the type of crop was not standardised, i.e. the exact same crops were not grown on the organically and conventionally managed fields. Further investigations are therefore necessary in order to confirm the results.
Furthermore, there are also plant-parasites among the nematodes which attack vegetable crops. Control strategies against these pests are needed.
- The nematode communities in 20 organically farmed and 20 conventionally farmed vegetable fields were investigated. Twenty extensively managed grasslands served as a standard of comparison.
- Nematodes are most numerous in extensively managed grassland, followed first by organically farmed and then by conventionally farmed vegetable fields.
- The organically farmed fields contained significantly more and a greater variety of nematodes than conventionally farmed fields.
- The results suggest that the food web is more extensive and soil fertility is greater in organically farmed vegetable fields.
- The results must be interpreted carefully, since the same crops are not grown on the organically and conventionally farmed vegetable fields.