Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 5, 2007
Publication Date: October 15, 2007
Citation: Franzluebbers, A.J., Schomberg, H.H., Endale, D.M. 2007. Soil responses to paraplowing of long-term no-tillage cropland in the Southern Piedmont USA. International Journal of Soil and Tillage Research. 96:303-315. Interpretive Summary: Degradation of cropland with traditional inversion tillage systems has been long documented for soils in the southeastern USA. Conservation tillage systems were developed to improve soil quality for these soils. However, there is concern by producers and technical specialists that lack of mechanical soil loosening could slowly lead to soil compaction under long-term conservation tillage. Scientists at the USDA-Agricultural Research Service in Watkinsville Georgia conducted a 7-year study to investigate changes in soil compaction, nutrient cycling, and soil organic carbon storage under (a) long-term no-tillage and (b) no-tillage planting with paraplowing in the autumn to loosen soil without inverting it. Immediately following paraplowing, soil was loosened without destroying soil organic matter at the soil surface. However, the high energy cost of paraplowing and the short-lived effect of paraplowing on soil loosening (soil density returned to pre-paraplowing level within 1 year), suggests that there may be little advantage to paraplowing to loosen soil. Naturally occurring soil loosening occurs with long-term conservation tillage as a result of surface residue accumulation that feeds soil organisms, thereby creating biopores for adequate root exploration of soil. This information will be valuable to producers and technical specialists across the 41 million acres of land in the Southern Piedmont region of the southeastern USA.
Technical Abstract: The type of conservation-tillage management employed could impact surface soil properties and subsequent processes of water runoff quantity and quality. We determined soil density, organic C and N fractions, plant-available N, and extractable P on Typic Kanhapludults throughout a seven-year period, in which four long-term, no-tillage (NT) water catchments (1.3 to 2.7 ha each) were divided into two treatments: (1) continuation of NT and (2) paraplowing (PP) in autumn (a form of non-inversion deep ripping) with NT planting. Both summer and winter crops were NT planted throughout the study under each management system. Soil bulk density was reduced with PP compared with NT by as much as 0.15 Mg/m3, but the extent of reduction was inversely related to the time lag between PP operation and sampling event. Soil organic C became significantly enriched with time during this study under NT (0.49 Mg C/ha/yr), but not under PP, in which poultry litter was applied equivalent to 5.7 Mg ha/yr. Soil maintained a highly stratified depth distribution of organic C and N fractions under both NT and PP. Inability to perform the PP operation in the last year of this study resulted in rapid convergence of almost all soil properties to similar values, suggesting that PP had <1-year effectiveness. The high energy cost of PP and the lack of sustained improvement in surface soil properties put into question the value of PP for improving upon long-term NT management in sandy loam and sandy clay loam Ultisols of the Southern Piedmont USA, unless large effects on crop yield, water quality, or other ecosystem processes can be documented.