2.2. Percolation below the solum Unlike studies conducted using shallow lysimeters, the 4.3 m long, 1.7 m wide by 2.4 m deep monolith lysimeters at the NAEW give us the capability to evaluate the effects of tillage on percolation below the solum. The entire undisturbed soil profile is contained within these lysimeters and the bottom 1-1.5 m is composed of the fractured sandstone and shale bedrock from which the soils were derived (Fig. 3).
In a 4 year comparison with a Keene silt loam soil (FAO - Haplic Luvisol; USDA -fine-silty, mixed,
mesic Aquic Hapludalf), conventionally tilled monolith lysimeters consistently yielded more surface runoff than no-till lysimeters with an average annual difference of 57 mm and a range of 10-114 mm (Chichester, 1977). Consistent differences in percolation, however, were not apparent among tillage treatments. The no-till lysimeters annually yielded from 39 mm less to 75 mm more percolate than the tilled lysimeters. During the 4 years, the no-till lysimeters yielded an average of only 6% more percolate than the tilled lysimeters. Although significant differences in percolation among tillage treatments might have been detected had more lysimeter years of data been collected, it is apparent that the relatively large differences in percolation detected at shallow depths in the aforementioned studies were not reflected in the deep percolation results. Moreover, unlike the shallow lysimeters, percolation from the deep lysimeters was rarely affected by storms during the growing season and only 14% of the total yearly percolation from the tilled and no-till lysimeters occurred during the months of May-October.