Deep tillage management for high strength southeastern USA Coastal Plain soils

Southeastern USA production is limited in Acrisols (Paleudults and Kandiudults) because they have high strengths and low water holding capacities. Production systems with crop rotations or deep tillage before planting were compared with less intensive management. Production systems included double-crop wheat (Triticum aestivum, L.) and soybean (Glycine max L. Merr.) that were drilled in 0.19 m-row widths and grown in 15 m wide, 150 m long plots with soils of varying hardpan depths. Treatments included surface tillage (disked or none), deep tillage (paratilled or none), deep tillage with winter fallow and maize (Zea mays L.) in rotation, and disked/deep tillage with an in-row subsoiler where soybean was planted in conventional 0.76 m-wide rows. Cone indices were measured near the ends of each plot (120 m apart) to assess soil strength differences among soil types and among treatments. Cone indices were 1.50 MPa higher for non-deep tilled treatments than for deep tilled treatments and 0.44 MPa higher in wheel-track mid rows than in non-wheel-track mid rows. Cone indices were also 0.28 MPa higher for soils with shallower Bt horizons. Cone indices were not significantly different for subsoiled treatments and paratilled treatments. Rainfall was erratic throughout the 5-year experiment with dry periods lasting more than 2 weeks at a time and with annual totals ranging from 520 to 1110 mm. Wheat yields were 0.67 Mg ha(-1) greater for deep-tilled soils (subsoiled and paratilled) than for non-deep-tilled soils. Soybean yields were 0.36 Mg ha(-1) greater for paratilled than for subsoiled or non-deep-tilled treatments partly as a result of the more complete disruption of the paratill and partly because paratilled treatments were managed with narrow rows. Yields did not vary significantly among the soil types despite the fact that they had different cone indices. Tillage was a more dominant factor than soil type. For wheat, lower cone indices from tillage led to higher yields. For soybean, management of uniform loosening from deep tillage and narrow rows led to higher yields. (C) 2005 Elsevier B.V. All rights reserved.