Permanant grassland has 300-500 earthworms per square metre, the biomass of worms is equivalent to the cattle in a field

Arable 50-250 per metre square
Fallow 20-30 per m2
Deciduous wood 100-150/m2
Conifers <50/m2

ley grass, more like arable in numbers

The 92% loss of grassland 1932-1984 resulted in roughly 80% reduction in earthworm biomass in every hectare of grassland lost

85% of UK farms no longer keep cattle, the lack of cow dung has also reduced earthworm biomass

slurry is not beneficial to eartworms high content of

ammonia, salts, anthelmintic drugs, slurry use reduces eartworm biomass

drainage can cause worms to be more often deep in soil unavailable to birds

Pesticides

Hedgehogs and thrushes, waders, all have less food.