Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/1999
Publication Date: N/A
Interpretive Summary: In the southeastern Coastal Plain, producers deep till soil annually, usually in the spring, to disrupt a hard layer that is about a foot deep. The deep tillage is often done with specialized equipment, non-inversion tillage tools that leave residue on the surface. This deep soil disruption reduces soil strength to improve root growth and yield. About half of the producers are growing two crops per year on the same fields: summer soybeans and winter wheat. Deep tillage has traditionally been a spring operation. However, some farmers have started doing it in fall. Others deep till before both crops. We set up an experiment to find out whether deep tillage should be done in spring, fall, both, or neither. Spring deep tillage kept the soil softer throughout the year than fall deep tillage. No deep tillage reduced yields of both wheat and soybean by 10 to 20 bu/a. If producers deep till only once a year, yields for the following season's crop of either wheat or soybean were reduced by 3 to 10 bu/a. If producer deep tilled twice a year, yields were improved by 1 to 10 bu/a. This bottom line is that lower soil strengths generally produced higher yields. The cost-benefit analysis of multiple annual deep tillages has yet to be analyzed.
Technical Abstract: In many southeastern Coastal Plain soils, genetic subsoil pans annually reform to root restricting strengths. To reduce strengths, soils are deep tilled annually, even when double cropping. We used a wheat (Triticum aestivum L.) and soybean (Glycine max L. Merr.) double-cropping system to find out whether deep tillage in fall, spring, or both would increase yield. We applied eight treatments to each of four replicates. Treatment consisted of all combinations of surface tillage (disked and not disked) and deep tillage (not deep tilled, paratilled before wheat planting, before soybean planting, and before both). After soybean and wheat planting, we measured cone indices. Cone index measurements showed that non-deep-tilled plots had a disk pan at the 20- to 30-cm depth, generally associated with an E horizon. Lower mean profile cone indices were measured in more recently and more frequently deep-tilled plots. Based on linear regressions, every megapascal increase in mean profile cone index reduced wheat yields 1.5 to 1.7 Mg/ha and soybean yields 1.1 to 1.8 Mg/ha. Deep tillage at the beginning of either season reduced soil cone indices and improved wheat and soybean yields. Deep tillage only in spring maintained softer soil throughout the year than deep tillage only in fall. Deep tillage at the beginning of both seasons maintained the softest soil.