Soil organic carbon and aggregation in response to thirty-nine years of tillage management in the southeastern U.S

Authors: SINGH, SURENDRA - University Of Tennessee; NOURI, AMIN - University Of Tennessee; SINGH, SHIKHA - University Of Tennessee; Anapalli, Saseendran; LEE, SJAIOHOON - University Of Tennessee; Arelli, Prakash; JAGADAMMA, SINDHU - University Of Tennessee

Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2019
Publication Date: 12/18/2019
Citation: Singh, S., Nouri, A., Singh, S., Anapalli, S.S., Lee, S., Arelli, P.R., Jagadamma, S. 2019. Soil organic carbon and aggregation in response to thirty-nine years of tillage management in the southeastern U.S. Soil and Tillage Research. 197:1-9. https://doi.org/10.1016/j.still.2019.104523.
DOI: https://doi.org/10.1016/j.still.2019.104523

Interpretive Summary: Tilling the soil for rising crops leaves the soil disposed to to its organic matter and fertility losses to water and wind erosions. Soil management practices known as ‘no-tillage’ promote growing crops with minimum soil disturbance and leaving crop residues on the soil surface (NT) has often been promoted as a remedy for this problem. The NT can bring savings on soil-cultivation costs and better water use efficiency in irrigated cropping systems. However, the location-specific viability of the system, especially, in producing sustainable crop yields depend upon the growing season climate and soil properties Long-term cropping system experiments offer a great opportunity to understand the magnitude and direction of soil organic carbon (SOC) change in response to management practices. Such information is very limited in the southeastern US. Therefore, researchers with the USDA ARS Sustainable Water Management Research Unit at Stoneville, MS; USDA-ARS, Crop Genetics Research Unit, Jackson, TN; and the Department of Biosystems Engineering, University of Tennessee, Knoxville, TN, investigated SOC changes with a long-term chisel plow (CP), disc plow (DP), moldboard plow (MP), and no-tillage (NT) practices in soybean cropping system in which winter wheat was used as a cover crop. Results showed that NT system with cover crops increased SOC significantly over CP, DP, and MP tillage practices. In conclusion, soil tilling practices in the long-term can strongly compromise organic carbon storage in soils under soybean based cropping systems in the southeastern US.

Technical Abstract: Agricultural management practices control soil organic carbon (SOC) content in croplands. Long-term cropping system experiments offer a great opportunity to understand the magnitude and direction of SOC change in response to management practices. Such information is very limited from the southeastern US, a region with warm and humid climatic conditions that typically favor SOC decomposition over accumulation. Therefore, this study was conducted to assess the effect of 39 years of chisel plow (CP), disc plow (DP), moldboard plow (MP), no-tillage (NT), NT with winter wheat (Triticum aestivum L.) cover crop (NTW), and NT with wheat-soybean (Glycine max L.) double crop (NTWD) on total SOC and SOC fractions including permanganate oxidizable C (POXC), water extractable C (WEC), resistant C (RC), and aggregate associated SOC in a continuous soybean system. Additionally, aggregate size distribution, mean weight diameter (MWD), and wet aggregate stability (WAS) were determined. Results showed that NTW and NTWD significantly increased SOC and POXC compared to MP with mean SOC (g kg-1 soil) of 12.2 (NTW) = 10.9 (NTWD) > 7.2 (MP) and mean POXC (mg kg-1 soil) of 465 (NTWD) = 418 (NTW) > 252 (MP). The WEC and RC fractions did not differ among treatments. Across the treatments, the greatest aggregate associated SOC concentration was found in microaggregates (0.053-0.25 mm) and the lowest in silt and clay sized particles (<0.053 mm). Additionally, WAS under NT systems were significantly higher (45.5-52.3%) than tilled treatments (21.9-29.1%). Total SOC correlated significantly with POXC (r = 0.68, p <0.01), RC (r = 0.46, p <0.05), WAS (r = 0.65, p <0.01) and aggregate associated SOC concentrations (r > 0.6, p <0.01). Overall, this study revealed that NT enhanced SOC and POXC accumulation and macroaggregation compared to tilled treatments. Cover cropping and double cropping further improved SOC accumulation. In conclusion, long-term adoption of different tillage intensities can strongly alter SOC dynamics in bulk soil and aggregates under continuous soybean production systems of the southeastern US.