Soil preparation methods in U.S. agriculture reached a watershed in 1997. Nationally, conservation tillage acres outstripped conventional acres for the first time ever last season, with 37.3% of the cropland planted in no-till, ridge till, and mulch till systems, reports Purdue University, West Lafayette, Ind. That compares with the 36.5% that was conventionally tilled or plowed. The annual national survey is conducted on a county-by-county basis by U.S. Dept. of Agriculture Natural Resources Conservation Service and soil and water conservation districts, and is released by the Conservation Technology Information Center. Conservation tillage, which minimizes soil disturbance, typically leaves at least 30% of the field covered with residue from previous crops. That reduces erosion, strengthens earthworm populations, and cuts down on tractor trips across a field.