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 h as 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 mac ropore area and numbers were quantified by image analysis into three s ize classes (1-8, 8-16 and >16 mm(2)) at three depths (10, 20 and 30 c m) at two locations (between-row, within-row) in corn agroecosystem en closures with manipulated earthworm populations (reduction, not manipu lated, addition). A dilute solution of latex paint was surface-applied to determine pathways for water infiltration. All macropore sizes con tributed to infiltration. Earthworm-treatments had no significant effe cts 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 dep th) then in the other treatments, indicating re-formation of continuou s flow pathways destroyed by tillage practices. The majority of the >1 6 mm(2) size pores were recognized as Lumbricus terrestris (L.) burrow s, 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 existenc e of pre-existing burrows that were not disrupted by tillage or root a ctivity and is due to earthworms concentrating their activity in the r oot-zone, in the within-row location. By increasing soil macroporosity and creating transport pathways of preferential flow, earthworms pote ntially affect the nutrient transport in leachate and nutrient loss fr om the agroecosystem. (C) 1997 Elsevier Science Ltd.