Response of carbon and nitrogen dynamics in soil water‐stable aggregates to wheat straw incorporation in the Yangtze River Delta of China#

Abstract Background Research on the changes of organic carbon (OC) and total nitrogen (TN) contents in soil aggregates is crucial for better evaluating C and N dynamics in paddy soil. Aims We investigated the effects of wheat straw incorporation on soil aggregate distributions and stability, the contents of OC and TN in bulk soil, and aggregates as well as their relationships. Methods A rice paddy field experiment in China with four treatments: (1) unfertilized control (CK), (2) mineral NPK fertilizer (NPK), (3) NPK plus medium‐rate wheat straw incorporation (MSNPK), and (4) NPK plus high‐rate wheat straw incorporation (HSNPK). Soil samples were collected from four soil layers (0–5, 5–10, 10–20, and 20–30 cm, respectively) after the rice harvest, and the samples were separated into four classes of aggregates with different sizes (>5, 5–2, 2–0.25, and <0.25 mm). Results The >5 mm fraction dominated aggregate size distribution, but the 2–0.25 mm fraction had the highest OC and TN contents throughout soil profile among treatments. The proportions of >5 and 5–2 mm aggregates, mean weight diameter (MWD), geometric mean diameter (GMD), the proportion of aggregates greater than 0.25 mm ( R 0.25 ), bulk soil organic carbon (SOC) and TN contents, and OC and TN contents in aggregates were highest in HSNPK and lowest in CK at either depth. Both bulk SOC and TN contents positively correlated with R 0.25 , MWD, GMD, and OC and TN contents in aggregates, and positively and negatively correlated with all aggregates ( p < 0.05), except between bulk TN and the proportion of 5–2 mm aggregates. The OC content in the 5–2 mm aggregates (increase in MSE = 23.87%) and the TN content in the 2–0.25 mm aggregates (increase in MSE = 13.89%) were more important than other driving factors for bulk SOC and TN, respectively. Conclusion In conclusion, these results confirmed that the application of HSNPK increased bulk SOC and TN contents, soil aggregates distributions (i.e. >5 mm and 5–2 mm fractions) and stability, and the OC and TN contents in all aggregates at both depths in rice paddy fields of China, which might improve soil C and N sinks in agricultural ecosystems.