Soil structural stability assessment with the fluidized bed, aggregate stability, and rainfall simulation on long-term tillage and crop rotation systems

The establishment of long-term tillage and crop rotations studies helps to investigate the cumulative effect and the long-term effect of management practices on soil properties, including those affecting soil health and water quality. In this study, a suite of techniques was used to evaluate the impact of a 28-year long-term tillage and crop rotations on soil structural stability parameters including soil cohesion, aggregate stability, and sediment loss. Fluidized bed experiments to estimate soil cohesion and aggregate stability tests were performed on samples collected from plots managed under chisel tillage (CT) and no-till practice (NT) and four rotations (continuous corn [Zea mays], CC; continuous soybean [Glycine max], BB; corn-soybean, CB; and soybean-corn, BC). At the same site, rainfall simulation experiments were conducted and sediment loss was correlated to fluidized bed and aggregate stability measurements. No-till practice had a positive effect on soil cohesion in the 0-15 cm soil layer; average pressure drop at fluidization (ΔPf) values were 30.8 Pa for NT and 17.0 Pa for CT and a higher proportion of stable macroaggregates was present under NT practice (51.4% vs. 28.9%). In the 15-30 cm soil layer, aggregate stability measurements mimicked those of the surface layer for each tillage practice and crop rotation. In this study, we found no correlation between fluidized bed results and aggregate stability tests. The soil organic carbon content correlated to macroaggregates (R2 = 0.56) and magnitude of cohesion (R2 = 0.51). Corn residues were associated with improved aggregation in both surface and lower soil layers with respectively 18% and 13% more aggregates than soybean residues. Rainfall simulation experiments conducted on the sample sites revealed tillage effect on sediment loss patterns consistent with aggregate stability and fluidized bed measurement results. Chisel-tilled fields yielded 20 times more sediment loss than no-till fields. The effect of corn residue on aggregate stability resulted in 380 and 6.7 kg ha−1 less sediment loss under conventional and no-till practices, respectively.