Research was undertaken to determine the capacity of organic inputs and practices to restore soil organic carbon (SOC) stocks and other soil health indicators in Norfolk sandy loam soils, a widely farmed soil series of the southeastern coastal plain, characterized by low SOC and fertility. Soils from forest and from organically and conventionally farmed annual cropland were tested for active and total SOC, microbial respiration, total protein, and N mineralization. Field trials were conducted at two sites in a tilled corn-soy-sweetpotato rotation with or without winter cover crops (crimson clover, rye, crimson clover, total 2.7 tons organic C/ac), and amended with compost, biochar, or 50-50 mix in one-time or split annual applications totaling 3.6 tons C/ac.

Findings include:

• Soils under row crop farming averaged 66% lower total SOC than adjacent forested soils, and had 10% higher bulk density (evidence for compaction).
• Cropland did not show increasing total SOC over time (1-15 years) under organic management compared to conventional.
• Organic cropland had 62% higher active (permanganate-oxidizable) SOC, and higher pH, cation exchange capacity, biological activity, and fertility than conventional fields.
• Cover crops and amendments each enhanced total SOC in the top 6 inches.
• Over 3 years, compost, biochar, or mix added 2.3-2.7 tons total SOC/ac (~70% retention), cover crops added 0.85 tons SOC/ac (~30% retention) and cover crops + amendments accrued SOC in an additive manner.
• Cover crops and compost enhanced active SOC, microbial respiration, N mineralization, and total soil protein, while biochar did not.
• Compost + legume cover crop + organic fertilizer released surplus N, stimulated weed competition, and reduced corn and sweetpotato yields.
• Soybean with compost + rye cover (no fertilizer), or crops amended with biochar + cover crop + fertilizer did not suffer increased weed pressure or yield loss.