Organic mulching boosts ground-dwelling predators in potato fields

• Organic mulching boosts key carabid and spider predators in potato fields. • Mulching alters predator community composition and increases species richness. • Annual mulch application is needed to maintain the benefits in agroecosystems. • Field trials confirm mulching as a robust tool for conservation biological control. Ground-dwelling generalist predators, such as carabid beetles (Coleoptera: Carabidae) and spiders (Araneae), play a central role in natural pest control, but are threatened by intensive farming. Organic mulching—a practice that increases within-crop habitat diversity—has been proposed for its ability to support beneficial arthropods while also delivering agronomic benefits. To assess its efficacy, three large-scale, replicated field trials were conducted in potato fields in Germany, comparing mulches of triticale/vetch, barley straw, and grass silage against an unmulched control. Arthropods were sampled with pitfall traps during the growing season to assess mulching impacts, and thereafter to test for potential carry-over effects. This was complemented by additional mulch-cleared traps to assess potential biases in capture efficiency. Species-specific responses and community composition were analyzed using generalized linear mixed models, diversity indices, ordination, and indicator species analysis. Across all trials, 11,504 adult carabids (40 taxa) and 2,399 spiders (38 taxa) were collected. Mulching—particularly with triticale/vetch—increased the abundance of several carabid species ( Bembidion lampros , Bembidion quadrimaculatum , Poecilus cupreus ) and linyphiid spiders ( Erigone atra , Erigone dentipalpis ). Mulching also shifted overall community structure, but effects on diversity indices were inconsistent. The benefits were largely limited to the potato growing season, with no evidence of carry-over into the following year. The results highlight organic mulching as a promising tool to enhance biological control in potato agroecosystems.