Earthworm Abundance and Diversity Are Impacted By Long-Term Crop Sequences and Bio-Covers Under No-Tillage.

Earthworms are crucial for improving soil biophysical properties in cropping systems. Consequently, effects of cropping rotation and bio-covers were assessed on earthworm populations under no-tillage. Main effects of 6 different cropping sequences [corn (Zea mays), cotton (Gossypium hirsutum), and soybean (Glycine max)] were rotated in four-year phases for 12 years at two field sites in Tennessee, USA in a randomized complete block design with three split-block bio-cover treatments of hairy vetch (Vicia villosa), wheat (Triticum aestivum), poultry litter, and a fallow control. Earthworms were collected to a 15-cm depth, hand sorted, and identified spring of 2013 and 2015 as one of three species (i.e., Diplocardia caroliniana, Lumbricus rubellus, or Amyntha spp). Population richness and relative abundance were affected by bio-covers and cropping sequences for both years at one site, but only by bio-covers at the other location (P<0.05). Under continuous cotton, overall earthworm populations were reduced 55-68%, and D. caroliniana decreased as much as 88% (P<0.05). Conversely, sequences with soybean and corn had greater populations of D. caroliniana (P<0.05), which did not differ when in rotations, indicating favorable food sources in the rhizosphere of these crops.  Poultry litter supported 2.2 times as many D. caroliniana and L. rubellus across locations and years, compared to cover crops and the fallow control (P<0.05). Consequently, earthworm populations were greatest under nutrient rich bio-covers (poultry litter) and high residue producing, less pesticide-intensive cropping sequences (soybean and corn compared to cotton), suggesting a more dynamic soil ecology under these cropping systems.