Residual Effects of Deep Tillage vs. No‐Till on Corn Root Growth and Grain Yield

Tillage pans occur in many coarse‐textured soils and must be ripped by a form of deep tillage to maximize yields. This study compared the longevity of slits produced by subsoiling and slit‐till (both to 16 in.) to a no‐till treatment, and related slit longevity to corn (Zeu mays L.) grain yield and root development. The soil was a Typic Kandiudult with a tillage pan. Both deep tillage treatments were last performed in 1989; this study was conducted from 1990 through 1992. Roots were examined at tasselling each year, and in 1992 thin sections were examined to determine the effects of the tillage slits on root penetration. Corn grain yields were not significantly different among the three tillage treatments in any of the 3 yr. Concentrations of roots in soil profiles did not differ significantly among treatments and roots extended to depths > 40 in. Root observations indicated that the tillage slits affected root development 2 yr after tillage was performed. Residual effects of both subsoiling and slit‐tillage on root growth could be seen for up to 2 yr after tillage was imposed, but the effects were gone by the third year. The residual effects of tillage did not affect yield in any year. Research Question Deep tillage methods are the best management practices to use to break tillage pans and deepen root development. While annual subsoiling is recommended, some growers are concerned that such frequent deep tillage is harmful because it brings acidic soil material to the surface, and in the long run may simply cause compact layers to form deeper in the soil. Slit‐till is another deep tillage method that cuts a very thin slit in the pan layer. We investigated how long the slits made by the subsoiler and slit‐till implements persist in the soil and affect corn root growth and yield over a 3 yr period. Literature Summary Numerous studies have shown that annual subsoiling will increase the yields of corn, tobacco, soybeans, and other crops in soils with tillage pans. The yield increases vary with rainfall, and on sandy soils are greatest during the dry years. Little work has been done to show whether deep tillage must be done annually in order to increase yield, and virtually no work has been done to examine whether slit‐tillage works best when done every year. In addition, no work has shown that subsoiling is actually harmful. Study Description We studied a single field that had been deep‐tilled for 3 yr prior to our experiment. The tillage treatments that were imposed prior to our study included: subsoiling to 16 in. below the row each year, slit‐tilling to 16 in. below the row each year, and no‐till. Corn was planted using a notill system for the 3 yr of this study, such that no deep tillage was performed in any of our plots. Root distribution was measured in each treatment at tasselling each year, and soil core samples were collected to assess compaction. Corn grain yields were determined each year as. well. Applied Questions Do the slits formed by subsoilers or slit‐till implements persist for more than one growing season? The slits formed by these tillage implements could be seen for up to 2 yr after the tillage treatments were imposed. They also had roots growing in them during this period. By the third year, the slits were difficult to find, and they appeared to have only a small affect on root growth. The tillage pan appeared to have reformed by the third year. How do the residual slits formed by tillage one, two, and three years earlier affect corn grain yield? Corn grain yields were not significantly different among the tillage treatments in any of the 3 yr studied. We interpreted this to mean that the deep tillage slits collapse or fill‐in within a year of formation, and don't influence root development to the same degree as freshly made slits do. Using deep tillage every year appears to be the best way to ensure that it will increase yields on soils containing tillage pans.