TILLAGE AND CROP-ROTATION EFFECTS ON SUBSURFACE DRAINAGE RESPONSE TO RAINFALL

A field study was conducted to determine if tillage and crop rotation affected subsurface drainage response to rainfall. An instrumentation system collected subsurface drain flow data from thirty-six, 0.4 ha pl ots during the 1993, 1994 and 1995 growing seasons. Response time, tim e-to-peak drainflow rate, drainage volume, peak drainflow rate and per cent preferential flow were compared between two tillage systems (no-t ill and chisel plow) and two crop rotations (continuous corn and com-s oybean)for 23 drainage events over the three-year study. The influence of preferential flow was estimated for each drainage event using a hy drograph separation procedure based on subsurface drainflow rate chang es. Drainage event parameters. were not consistently different between crop and tillage systems during this study. Drainage parameter data w ere highly variable and little correlation was observed between parame ters. Percent preferential flow wasfound to be greater than 10% of the total subsurface drainflow only four times for the 23 drainage events . The highest average percent preferential flows for an event did not correlate with the highest rainfall intensity and varied among crop an d tillage systems. Annual averages of drainage parameter data indicate d that drainage volume and peak drainage rate may have been influenced more by the experimental plot than by the crop. Overall results indic ated that changes occurring in the soil flow system during the growing season may have more influence on preferential flow and subsurface dr ainflow compared to tillage and crop rotations for these loam soils.