Carbon sequestration and mineralization of aggregate-associated carbon in an intensively cultivated Anthrosol in north China as affected by long term fertilization

Abstract

Understanding organic carbon (OC) sequestration in aggregates and OC stability under different fertilization practices is of key importance in improving soil quality and crop productivity and in mitigating the causes of climate change. A long-term field experiment established in 1990 was used to assess the influence of organic and inorganic fertilizers on aggregate-associated OC and its mineralization and on the SOC stock at a soil depth of 0–20cm under an intensive wheat-maize cropping system on Anthrosol in North China. The study involved three treatments: CK, control without fertilization; NPK, nitrogen (N), phosphorus (P) and potassium (K) fertilizers; MNPK, manure (M) combined with N, P and K fertilizers. Soil samples were collected and analyzed to determine the size distribution of aggregates, which were separated by dry sieving; the concentrations of OC and N in aggregates (>2, 0.25–2 and <0.25mm) and bulk soils; and respiration from aggregates and bulk soils in the 0–10 and 10–20cm layers after 21years. Fertilization did not affect the size distribution of aggregates in the surface soil layer, but there was a significant change in the subsurface layer in response to manure addition. Application of NPK and MNPK significantly and evenly augmented OC and N sequestration in the three aggregate classes tested. However, the OC mineralization rate was substantially higher in micro- than in macro-aggregates. Application of NPK and MNPK considerably increased OC mineralization in both aggregates and bulk soils; MNPK yielded the highest values. OC mineralization rates in bulk soils were comparable among the three treatments for the surface layer, but they increased in the subsurface layer because of adding manure. Overall, soils treated for 21years with NPK and MNPK showed increases in the OC pools in the top 20cm of 7.42 and 22.83MgCha−1, respectively, compared with the control treatment, and had average sequestration rates of 353 and 1087kgCha−1yr−1 respectively. Thus, appropriate application of NPK, alone or in combination with manure, can lead to improved OC sequestration by evenly augmenting aggregate-associated OC and providing the same degree of protection for OC in both macro-aggregates and micro-aggregates under a winter wheat-summer maize rotation on Anthrosol.