Root-zone enrichment of C, N, and soil-test biological activity under cotton systems in North Carolina

Authors: Franzluebbers, Alan

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2021
Publication Date: 6/12/2021
Citation: Franzluebbers, A.J. 2021. Root-zone enrichment of C, N, and soil-test biological activity under cotton systems in North Carolina. Soil Science Society of America Journal. https://doi.org/10.1002/saj2.20290.
DOI: https://doi.org/10.1002/saj2.20290

Interpretive Summary: Soils of the southeastern United States are generally low in organic matter. Root-zone enrichment of organic carbon (C) and nitrogen (N) may be possible with conservation agricultural management, but little is known of how this might be distributed across private farms. A stratified random survey of 120 cotton (Gossypium hirsutum L.) fields from throughout North Carolina characterized root-zone contents of soil organic C (SOC), total soil N (TSN), and soil-test biological activity (STBA). Soils were mostly udults and aquults, but included some udepts, aquepts, aqualfs, and psamments. Depth distribution of soil properties at 0–10, 10–30, and 30–60 cm was fitted to a nonlinear regression model for each soil profile to calculate root-zone enrichment over that of a baseline content estimated from concentration at 30-cm depth. Continuous conservation tillage was practiced on 23% of fields. Root-zone enrichment of TSN and STBA was greater with conservation than with disk tillage (1.30 ± 0.10 vs 0.82 ± 0.04 Mg N ha–1, respectively, p < .001; 209 ± 16 vs 144 ± 6 kg CO2–C ha–1 3 d–1, respectively; p < .001) (mean ± standard error). Difference in root-zone enrichment of SOC between continuous conservation tillage and frequent disk tillage was 8.5 ± 2.5 Mg C ha–1 among eight subregions and was not affected by variations in baseline SOC content, which was greater in the Flatwoods than the Coastal Plain region due to inherent soil formation factors. These on-farm results confirm that continuous conservation tillage is needed to enrich root-zone SOC, TSN, and STBA under cotton production.

Technical Abstract: Soils of the southeastern US are generally low in organic matter. Sequestration of organic C and N is possible with conservation agricultural management, but little is known of how this is expressed on private farms in the region. A stratified random survey of 120 cotton fields throughout North Carolina was designed to characterize sequestration of soil organic C (SOC), total soil N (TSN), and soil-test biological activity (STBA) by sampling at depths of 0-10, 10-30, and 30-60 cm. Soils were typically udults and aquults, but included some udepts, aquepts, aqualfs, and psamments. Depth distribution of these soil properties was fitted to a non-linear regression model unique for each soil profile. Continuous conservation tillage (i.e. strip or no tillage) was practiced on 23% of fields. Estimated TSN sequestration was greater with continuous conservation tillage than with frequent disk tillage (1.30 +/- 0.10 and 0.82 +/- 0.04 Mg N/ha, respectively; p < .001) (mean + standard error). Accumulated STBA was greater with continuous conservation tillage than with frequent disk tillage (209 +/- 16 and 144 +/- 6 kg CO2-C/ha/3 d, respectively; p < .001). Difference in SOC sequestration between conservation tillage and disk tillage was 8.5 +/- 2.5 Mg C/ha among eight subregions and was not affected by base SOC stock, which was greater in the Flatwoods than the Coastal Plain region. These on-farm results confirm that significant sequestration of SOC, TSN, and STBA is occurring, but not likely at maximum achievable levels for the region.