INFLUENCE OF SOIL MOISTURE AND COMPACTION ON ENERGY FOR SUBSOILING WITH MINIMUM TILLAGE F. M. RHOADS AND D. L. WRIGHT1 Tillage pans were identified and characterized in four Coastal Plain soil series occurring throughout the Southeastern United States (5). Depth to the pan was 11 to 15 cm, pan thickness was 13 to 14 cm, and root growth within the pan was severely restricted.(4) Deep tillage and deep placement of lime, fertilizer, and nematicides have been tested on various crops at several locations with inconsistent results (1, 2, 3, 6, 9, 10, 11, 12). Subsoiling under the row increased seed cotton yields 41% but bedding, deep placement of lime, and addition of a nematicide had no influence on yield (1). Subsoiling increased soybean yields in 7 of 16 experiments, whereas, a nematicide increased yields in 10 of 16 tests (6). However, the combined treat- ment of subsoiling, plus a nematicide, increased yields significantly in 13 of 16 experiments (6). Subsoiling, in New Jersey, with and without deep placement of lime and fertilizer on a Collington sandy loam soil, did not produce significant yield increases of several vegetables (2). However, residual effects of subsoiling significantly increased water movement into this soil for 3 years after the last deep tillage operation. In-row subsoiling before planting produced highest soybean yields in North Florida (7). Depth of rooting of corn was increased with subsoiling (8). Re- sponse to subsoiling on sandy soils appears to be related more to increased nutrient availability than to availability of water. Yield response to subsoiling has been most consistent where under-the-row subsoiling was practiced. Energy requirements for subsoiling are quite high and considerable savings could be achieved if the subsoiling operation was not necessary every growing season. However, under normal tillage operations the soil is recompacted each year and subsoiling is required on an annual basis for maximum crop yields. There is a possibility that recompaction of the soil following subsoiling could be minimized under minimum tillage production of crops. Avoiding travel over crop rows from the previous season with tillage implements and tractor wheels.should reduce soil compaction. This can be accomplished with minimum tillage operations where succeeding crops are planted directly in stubble rows of the previous crop. This report contains test results from experiments designed to measure the effect of soil-moisture content on resistance to soil penetration and the effects of a disc-harrow and a tractor wheel on soil compaction. Power requirements for subsoiling at different levels of soil penetrometer resistance were also estimated. METHODS Eight tillage and compaction treatments were applied to three soil types during the winter of 1979-80. The soils were Orangeburg loamy fine sand, Norfolk loamy fine sand, and Troup sand. All treatments were harrowed with an offset disc- harrow before tillage and compaction treatments were applied. Treatments were 1F. M. Rhoads, Professor of Soil Science, D. L. Wright, Extension Agronomist, AREC, University of Florida, Rt. 3, Box 638, Quincy, Florida 32351.