Effect of Soil Variability on Response to Tillage of an Atlantic Coastal Plain Ultisol

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Abstract
Subsoiling and chisel plowing are deep tillage practices which have increased crop yields on soils containing tillage pans. The relationship between crop response to deep tillage practices as influenced by soil property variability is not well understood. This study was conducted to obtain information about the response of corn (Zea mays L.) to selected tillage practices as influenced by soil variability. The effects of selected tillage practices on soil physical properties and corn production were investigated during 1981 and 1982 in a field with a tillage pan. The surface textural class of the Norfolk series (fine‐loamy, siliceous, thermic Typic Paleudults) in the field ranged from loamy sand to sandy loam. Three distinct soil units were delineated on the landscape based on depth to the B horizon. Four tillage treatments were investigated: disking, bedding, subsoiling plus bedding, and chisel plowing. Soil and plant parameters monitored at various times during the study were in situ mechanical impedance, bulk density, corn height, leaf area, barren stalk population, and grain yield. Significant interactions between tillage and soil unit for grain yield indicate a variable response to tillage due to depth to the B horizon. Mechanical impedance and bulk density in the conventional disk and subsoil treatments were negatively correlated with depth to the B horizon, implying that relatively less root restriction occurs when the B horizon is deeper. Grain yield response to deep tillage (subsoiling and chisel plowing) was significant during 1981 but not in 1982; this behavior was attributed to differences in rainfall distribution between the two years. Barren stalk population was significantly decreased by deep tillage both years.