Dynamics of Soil Carbon, Nitrogen, and Phosphorus in a Subtropical Paddy Field After the Abandonment: A Chronosequence Study

ABSTRACT The abandonment of paddy fields has become a significant concern in Asia, particularly, in China's traditional rice‐growing regions. Although it affects the transformation of soil carbon (C), nitrogen (N), and phosphorus (P), its long‐term effects remain unclear. A time‐series comparative analysis was conducted to examine the effects of subtropical paddy abandonment on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and available P (Olsen‐P). A long‐term field experiment (1991–2022) was conducted in a subtropical region of China (Taoyuan, Hunan Province). Before abandonment, fertilization experiments were conducted over 16 years (1991–2006) using four fertilization treatments: no fertilizer (CK), N + P fertilizers (NP), N + K fertilizers (NK), and N + P + K fertilizers (NPK). The fertilizers were applied as urea for N, calcium superphosphate for P, and potassium chloride for K. The results demonstrated that paddy abandonment induced a significant decline in soil TN, TP, DOC, DON, and Olsen‐P concentrations over a 16‐year chronosequence (2007–2022). Notably, SOC exhibited a distinct temporal pattern: a significant reduction in the early abandonment period (2007–2014) was followed by a substantial rebound in the later period (2014–2022). During the early period of paddy abandonment, SOC, TN, and TP significantly decreased by 15.2%, 13.7%, and 12.3%, respectively, resulting in stable stoichiometric ratios of soil C:N, N:P, and C:P of 9.5:1, 4.1:1, and 38.8:1, respectively. In the later period of paddy abandonment, the SOC content increased significantly by 17.4%, leading to significant increases in the soil SOC:TN and SOC:TP stoichiometric ratios. DOC, DON, and Olsen‐P were more sensitive to abandonment, decreasing by 57.5%, 47.8%, and 51.5%, respectively, after paddy abandonment (2007–2022). SOC and TN were more significantly related to TP in high‐P soils (NP and NPK treatments) than in low‐P soils (CK and NK treatments), whereas DOC and DON were more closely related to Olsen‐P. P (Olsen‐P and TP) primarily influenced the changes in SOC and TN. Soils with high P levels exhibited a legacy effect, accelerating the reduction of SOC and TN during the early period of abandonment, while promoting SOC accumulation in the later period through weed restoration, compensating for 92% of the SOC loss.