Cover crops and poultry litter impact on soil structural stability in dryland soybean production in Southeastern United States

This study explored the efficacy of soil aggregate indices in quantifying soil structural development, utilizing 5-year field experiment data from the Southeastern United States. The experiment utilized a split-plot design with cover crops (native vegetation as control, cereal rye (Secale cereale L.), winter wheat (Triticum aestivum), hairy vetch (Vicia villosa), and mustard (Brassica rapa) plus cereal rye as the main factor and fertilizer source (no fertilizer as control, inorganic fertilizer with phosphorus, potassium, and elemental sulfur, and poultry litter) as the secondary factor. Aggregate size fractions were determined using the wet-sieving method, and aggregate stability index (ASI), mean weight diameter (MWD), geometric mean diameter (GMD), and fractal dimension (FD) were calculated to assess soil structural stability. Main effects results indicated that cereal rye (55.11%) and poultry litter (50.97%) exhibited the highest ASI values. The highest MWD, GMD, and FD were observed under mustard plus cereal rye (1.187 mm), cereal rye (0.462 mm), and hairy vetch (2.573), respectively. Principal component analysis revealed that cover crops significantly improved soil aggregate structure and stability, overcoming limitations of sole fertilization practices. Regression analysis suggested that ASI, MWD, and GWD positively correlated with soil organic carbon, whereas FD negatively correlated with MWD, GMD, and ASI. Principal component analysis exhibited that FD decreased with increasing soil organic carbon, ASI, MWD, and GMD, demonstrating that lower FD values indicate enhanced soil aggregation and structure. Assessed indices, FD included, effectively gauged soil structural stability. These metrics should be prioritized in managerial decisions to support soil productivity and health in agricultural systems. The application of cereal rye and poultry litter increased the aggregate stability index (ASI). Poultry litter addition was beneficial to improving mean weight diameter (MWD). ASI, MWD, and geometric mean diameter (GMD) positively correlated with soil organic carbon. Fractal dimension (FD) is negatively correlated with MWD, GMD, and ASI. The evaluated indices (ASI, MWD, and GMD) and FD were effective in assessing soil structural stability.