Soil strength, cotton root growth and lint yield in a southeastern USA coastal loamy sand

Inverse linear relationships between soil strength and yield in Coastal Plain soils that have subsurface genetic hard layers have previously been developed for corn (Zea mays L.), soybean (Glycine max L. Merr.), and wheat (Triticum aestivum L.) grown under management systems that include annual or biannual non-inversion deep tillage. In a field study in the southeastern Coastal Plains of the USA, we tested this relationship for cotton (Gossypium hirsutum L.) grown in wide (0.96 m) rows, hypothesizing that root growth and lint yield of cotton would increase with a decrease in soil strength associated with annual deep tillage or cover crop. Root growth and yield were evaluated for treatment combinations of surface tillage or none, deep tillage or none, and rye (Secale cereale L.) cover crop or none. Root growth increased (r^2=0.66-0.68) as mean or maximum soil strength decreased. Cotton lint yield was not significantly affected by the treatments. Lack of yield response to tillage treatment may have been the result of management practices that employed a small (3 m wide) disk in surface-tilled plots and maintained traffic lanes, both of which help prevent re-compaction. These results indicate that less than annual frequency of subsoiling might be a viable production practice for cotton grown in traditionally wide (0.96 m) rows on a Coastal Plain soil (fine loamy Acrisol-Typic Kandiudult). Thus, annual subsoiling, a practice commonly recommended and used, need not be a blanket recommendation for cotton grown on Coastal Plain soils.