Recompaction of a coastal loamy sand after deep tillage as a function of subsequent cumulative rainfall

For many coastal plain soils in the southeastern USA, high soil strength within subsurface horizons requires that deep tillage be performed to provide a suitable rooting environment for row crops such as maize (Zea mays L.), wheat (Triticum aestivum L.), and soybean (Glycine max L. Merr.). We hypothesized that water filtering through the soil was recompacting it and that recompaction could be correlated with cumulative amount of rainfall since tillage. We measured cone indices in a structureless, fine loamy Acrisol near Florence, South Carolina, from 7 days to about 6 years after treatments were deep tilled. Measurements were made to a depth of 0.55 m at the point of maximum disruption of a bent-leg subsoiler (Paratill®) that tilled to a depth of 0.35–0.40 m. Regressions of cone indices with cumulative rainfall explained 67–91% of the recompaction and indicated that water filtering through the soil was causing the recompaction. Recompaction was slow, still taking place 6 years after tillage (the end of the experiment) probably because of controlled traffic or excessive disruption by the paratill. Recompaction was also temporarily greater for the 0.1–0.2 m depths when compared with that in the 0.25–0.35 m depths indicating that it was moving down the profile. Recompaction in other climates may be faster or slower depending on their cumulative rainfall relative to an annual amount of 900–1350 mm per year for this study and recompaction for structured soils may be faster or slower depending on whether the structure is stable or not. Though recompaction in this study was slow, tillage may still be necessary annually or seasonally because yield can be reduced even by incomplete recompaction that increases soil strength after a year or less.