Soil-test biological activity associates with soil aggregation characteristics under different land uses in North Carolina

Authors: Franzluebbers, Alan

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2022
Publication Date: 11/18/2022
Citation: Franzluebbers, A.J. 2022. Soil-test biological activity associates with soil aggregation characteristics under different land uses in North Carolina. Soil Science Society of America Journal. 86:1639-1651. https://doi.org/10.1002/saj2.20474.
DOI: https://doi.org/10.1002/saj2.20474

Interpretive Summary: Soil erosion continues to be a serious threat to the sustainability of agriculture. Conservation management is needed to protect the valuable soil resources around the country. An ARS scientist in Raleigh North Carolina conducted an evaluation of soil aggregation characteristics among soils managed with conventional-till cropland, no-till cropland, grassland, and woodland across 25 research stations in North Carolina. Resistance to water erosion was enhanced with no-till compared with conventional-till cropland. Perennial grasslands and woodlands that had no recent disturbance were more strongly aggregated than any of the croplands. Soil biological activity measurements were strongly associated with soil aggregation characteristics, reflecing the role that soil microorganisms play in gluing soil particles together, even in relatively sandy soil conditions. Results from this study can be used by farmers, extension advisors, and policy makers to make better decisions to protect soil with relatively simple, specific management changes or possibly through broader systems-level changes.

Technical Abstract: Soil erosion is a major constraint to agricultural sustainability. Land management that protects soil from water erosion can be assessed from the fraction of aggregates stable upon water immersion. Conservation management with minimal soil disturbance is known to enhance water-stable aggregation, but how annual vs. perennial vegetative cover affects soil biological activity and aggregation from soils varying in texture remains relatively unexplored. This study assessed the effects of long-term conventional-till and no-till cropland, grassland, and woodland on dry-stable and water-stable mean-weight diameter (MWD) from 25 research stations across North Carolina. Soil clay concentration varied from 36 to 279 g kg^–1 and sand concentration varied from 392 to 904 g kg^–1 (5–95% distribution). Across locations, water-stable MWD followed the order: conventional-till cropland (0.64 mm) < no-till cropland (0.87 mm) < woodland (1.12 mm) = grassland (1.15 mm). Soil stability index (i.e., water-stable MWD/dry-stable MWD) followed a similar order: conventional-till cropland (0.59 mm mm^–1) < no-till cropland (0.76 mm mm^–1) < grassland (0.92 mm mm^–1) = woodland (0.96 mm mm^–1). Although water-stable MWD was positively associated with clay concentration (r = .50, p < .001, n = 310), soil-test biological activity had the strongest association with water-stable MWD (r = .80). Soil-test biological activity reflected biological manipulation of surface-concentrated organic matter, as mediated by conservation land uses. This study revealed the large impact of surface organic C and N resources on water-stable aggregation through soil biological manipulations interacting across a textural gradient.