SEASONAL-VARIATIONS IN INFILTRATION-RATE UNDER NO-TILL AND CONVENTIONAL (DISK) TILLAGE SYSTEMS AS AFFECTED BY LUMBRICUS-TERRESTRIS ACTIVITY

Lumbricus terrestris activity can improve water how into soils, but th e effects of L, terrestris (nightcrawlers) on infiltration and runoff rates throughout the growing season have not been quantified. Our obje ctive was to quantify and describe the effects of L. terrestris on inf iltration rates under an established no-till and a disk tillage system on a silt loam Alfisol (fine-loamy, mixed, mesic Aquollic Hapludalf) in west central Indiana. Under each tillage practice there were areas within the field that had L. terrestris activity and other areas that had no activity as indicated by the presence or absence, respectively, of middens. Infiltration was measured using a portable sprinkling inf iltrometer which delivered 7 cm of water h(-1) to a 1.4 m(2) area. Inf iltration was measured five times during the growing season, for the d isk tillage treatment: (1) before any spring field work began; (2) imm ediately after tillage but before planting; (3) immediately after plan ting; (4) 3 weeks after planting; and (5) after harvest. For no-till t reatments, the measurement times were the same as times 1, 3, 4, and 5 of the tilled site. Results showed that in early spring before any ti llage was performed, the tilled treatment without middens had the high est infiltration rate and the tilled treatment with middens had the lo west. Immediately after planting and 3 weeks after planting, no-till w ith middens had the highest infiltration rates, but disk tillage treat ments had the lowest infiltration rates. Measurements after harvest sh owed that no-till with middens again had the highest infiltration rate s. The presence of L. terrestris, as indicated by the presence of midd ens, appears to have increased infiltration rates in a no-till system on this soil. In the disk system, however, the activity of L, terrestr is and the presence of their middens apparently was not persistent eno ugh to affect infiltration rates, and the amount of surface residue co ver may be a more important factor in this system. (C) 1997 Elsevier S cience Ltd.