Different fall/winter cover crop root patterns induce contrasting red soil (Ultisols) mechanical resistance through aggregate properties

Purpose Red soil (Ultisol) with high clay content and low aggregation results in high soil mechanical resistance and often suppresses crop root growth and productivity. Bio-tillage can be an effective tillage method to reduce the high soil mechanical resistance. This study aims to investigate different bio-tillage plants' root effects on soil mechanical resistance through soil aggregates properties. Methods The experiment designed 5 fall/winter cover crops (2 raps cultivars, lucerne, one-year vetiver (Vet_1Y) and six-year vetiver (Vet_6Y) as bio-tillage before summer maize and one control treatment. Plant root morphological and chemical traits, soil organic carbon (SOC), soil aggregate properties and soil mechanical resistance (measured and fitted values using model) were determined. Results The fibrous-rooted vetiver showed the largest root length density (RLD) (ranging from 2.71 to 4.82 cm cm(-3)), highest root diameter (RD) in deep soil depth, highest percentage of fine roots (0.2-0.5 mm), while lowest root lignin/cellulose ratio than tap-rooted lucerne and rapes. These root properties resulted in the highest improvement in the macroaggregate (> 5 mm and 5-2 mm) percentage for vetiver and especially for perennial Vet_6Y compared to other crops and control. Finally, fibrous-rooted vetiver contributed to the least soil mechanical resistance values followed by lucerne and two rapes compared to fallow. This was attributed to their positive root effect on improvement in macroaggregate and decrease in soil bulk density. Conclusion Our finding suggested that fibrous-rooted vetiver can be selected as a bio-tillage plant to improve soil physical properties, especially to reduce high mechanical resistance in clayey red soil.