Characteristics of macroporosity in a reduced tillage agroecosystem with manipulated earthworm populations: Implications for infiltration and nutrient transport

The effects of macroporosity on the potential for nutrient transport has been extensively studied for no-tillage agroecosystems. The present study was undertaken to quantify macroporosity and to demonstrate the potential for nutrient transport in reduced-tillage systems. Soil macropore area and numbers were quantified by image analysis into three size classes (1–8, 8–16 and > 16 mm2) at three depths (10, 20 and 30 cm) at two locations (between-row, within-row) in corn agroecosystem enclosures with manipulated earthworm populations (reduction, not manipulated, addition). A dilute solution of latex paint was surface-applied to determine pathways for water infiltration. All macropore sizes contributed to infiltration. Earthworm-treatments had no significant effects on infiltration rates, but rates were significantly faster within crop rows than between rows. In the earthworm-addition plots the area of macropores was significantly greater in the surface soil (10 cm depth) then in the other treatments, indicating re-formation of continuous flow pathways destroyed by tillage practices. The majority of the > 16 mm2 size pores were recognized as Lumbricus terrestris (L.) burrows, which represented the greatest per cent area of all size classes at the 10 cm depth. The area of these large macropores was significantly greater in addition-treatments than in the other plots at all depths and locations except for 30 cm-deep between-row locations. The absence of an earthworm effect at this location is attributed to the existence of pre-existing burrows that were not disrupted by tillage or root activity and is due to earthworms concentrating their activity in the root-zone, in the within-row location. By increasing soil macroporosity and creating transport pathways of preferential flow, earthworms potentially affect the nutrient transport in leachate and nutrient loss from the agroecosystem.