|Frederick, James - CLEMSON UNIV|
Submitted to: Annual Southern Conservation Tillage Conference for Sustainable Agriculture
Publication Type: Proceedings
Publication Acceptance Date: June 5, 1997
Publication Date: N/A
Interpretive Summary: Every spring farmers in the southeastern Coastal Plain deep till, often using special plows that leave the surface undisturbed. This deep soil disruption generally reduces soil strength and improves root growth and yield. Within the past few years more farmers are producing two crops per year on the same fields: summer soybeans and winter wheat. However, spring deep tillage takes time and better yields can be obtained from earlier soybean planting. Some farmers have abandoned the usual spring subsoiling, doing it in fall instead. Others have tried subsoiling before each crop. We set up an experiment to find out whether subsoiling should be done in spring or fall and whether subsoiling should be done once or twice a year. Treatments were subsoiled in spring, fall, both, or neither. Not subsoiling reduced yields of both wheat and soybean by 10 to 20 bu/a. If we depended on last season's subsoiling to keep the soil loose, yields were reduced by 3 to 10 bu/a. If we subsoiled twice a year, yields were improved by 1 to 10 bu/a. This all resulted from the fact that lower soil strengths generally produced higher yields. Economic feasibility of multiple subsoiling has yet to be analyzed.
Technical Abstract: Deep tillage disrupts genetic subsoil hardpans that reform annually in many southeastern Coastal Plain soils. Generally, producers deep till annually, even when double cropping. Our purpose was to find out whether fall tillage, spring tillage, or both would increase yield of a wheat-soybean double cropping system. We planted eight treatments in four replicates. Treatments were surface tillage (disked and not disked) and deep tillage (not deep tilled, paratilled before wheat planting, before soybean planting, and before both). Disked plots that were not paratilled had a disk pan at the 4- to 6-in depth, just below the disked zone. All non-deep-tilled treatments had a hardpan at 8- to 12-in depths (generally associated with the E horizon). Treatments that had been deep tilled most recently had lower mean profile cone indices. Within the range of soil strengths measured, wheat yield decreased approximately 2.3 to 2.6 bu/ac for each atmosphere of increase in mean profile cone index measured at the beginning of the growing season. Soybean yields decreased between 1.6 and 2.7 bu/ac for each atmosphere of increase in mean profile cone index. Deep tillage at the beginning of the season improved yields for both wheat and soybean.