Higher soil carbon and nitrogen sequestration in rice than non-rice soils following land reclamation

Long-term rice and non-rice cultivation following coastal tidal flat reclamation can significantly influence the soil organic carbon (SOC) and total nitrogen (TN) sequestration. However, the impacts of cultivation patterns and time on SOC and TN sequestration after coastal tidal reclamation remain poorly understood. This study aims to investigate the dynamics of SOC and TN sequestration in long-term rice and non-rice cultivation following the tidal flats reclamation. Rice paddy (RP) and non-rice soils (NR) were sampled from soils aged 50 (RP50 and NR50), 100 (RP100 and NR100), 300 (RP300 and NR300), and 700 (RP700 and NR700) years to elucidate the responses of SOC and TN to long-term cultivation. Results indicated that SOC and TN increased over time under rice cultivation in the cultivated layer, reaching peaks of 34.2 g kg-1 in SOC (RP700) and 2.0 g kg-1 in TN (RP300). Moreover, SOC was 0.7-1.4 times higher in rice paddy soils than in non-rice soils, and TN was 0.6-1.1 times greater than in rice paddy soils than in non-rice soils. SOC and TN in the deeper layers remained relatively stable compared to the cultivated layer. The CDE (the difference in the SOC at a depth of D and the SOC under the steady-state condition) and NDE (similar to CDE) of rice paddy soil reached their maximum at RP300 measuring 37.6 and 2.1 g kg -1, respectively, significantly higher than those of non-rice soils. In addition, SOC density and TN density increased with rice cultivation time, peaking at RP300 (1.7 g cm-2) and RP700 (0.2 g cm-3), respectively. Overall, SOC and TN sequestration rate were 67.0 % and 62.7 % higher under rice cultivation than under non-rice cultivation, reaching steady-state equilibria after 300 years and 700 years of rice cultivation, respectively. Stabilization mechanisms associated with the depth of the cultivated layer, thickness of obstacle horizons, and specific microbial communities should be considered in future studies on the dynamics of soil carbon and nitrogen sequestration dynamics over long time scales in rice and non-rice cultivated soils.