Land Application of Manure Can Influence Earthworm Activity and Soil Phosphorus Distribution

Earthworms can influence incorporation of animal manures and composts into the soil. As this activity can decrease the potential for phosphorus (P) loss in runoff and increase plant nutrient availability, we evaluated the effect of manure application on earthworm activity. Earthworm activity (as indicated by surface casts of Lumbricus terrestris) and soil P distribution were determined as a function of superphosphate, manure, and compost (dairy and poultry) applied at rates of 0, 50, 100, and 200 kg P ha-1 yr-1. Surface earthworm cast production was greatest in the wet and warm months of May to July. For instance, average annual cast production was 24,520 and 13,760 kg ha-1 with respective applications of dairy manure and compost (100 kg P ha-1) compared with 9,090 kg ha-1 when superphosphate was added. This increased activity was accompanied by lower Mehlich 3 P (130 mg kg-1) at the surface (0-5 cm) of soils treated with 100 kg P ha-1 yr-1 dairy manure than those treated with superphosphate (210 mg kg-1) but greater concentrations at 5 to 10 cm deep (95 and 50 mg kg-1, respectively). While there may have been greater downward movement of organic P added in manure and compost, the stimulation of L. terrestris activity by application of manure or compost has the potential to redistribute surface-applied P within the soil profile to a greater extent than when equivalent applications of P are made in the form of inorganic fertilizer.