[Effects of long-term fertilization on soil particulate organic carbon and nitrogen in a wheat-maize cropping system]

0-20 cm soil samples were collected from an 18-year wheat-maize rotation field on the North China Plain to study the effects of long-term fertilization on the contents and storages of soil particulate organic carbon (POC), particulate organic nitrogen (PON), incorporated organic carbon (IOC), and incorporated organic nitrogen (ION). The long-term fertilization experiment was designed to include 7 treatments, i.e., chemical NPK (NPK), organic manure (OM), 1/2 organic manure plus 1/2 chemical NPK (1/20 MN), chemical NP (NP), chemical PK (PK), chemical NK (NK), and control (CK). After 18 years experiment, all the fertilization treatments showed higher contents of soil POC, PON, IOC and ION, higher proportions of soil POC to soil total organic carbon (TOC) and of soil PON to soil total nitrogen (TON), and higher C/N ratio of soil particulate organic matter. The storages of soil POC and PON under fertilization treatments were increased by 11.7%-196.8% and 13.0%-152.2%, respectively, compared with the control. The contribution of soil POC to the increased storage of soil TOC ranged from 31.5% to 67.3%, and that of soil PON to the increased storage of soil TON ranged from 14.3% to 100.0%. The storages of soil IOC and ION under fertilization treatments increased by 2.0%-75.0% and 0.0%-69.8%, respectively, compared with the control. Among the fertilization treatments, treatment OM had the highest storages of soil POC, PON, IOC and ION, followed by treatment 1/20 MN, and the treatments of applying chemical fertilizers alone. Balanced application of chemical fertilizers (treatment NPK) showed higher storages of soil POC, PON, IOC and ION than imbalanced application (treatments NP, PK, and NK). It was suggested that applying organic manure or its combination with chemical NPK and the balanced application of chemical NPK could be the keys for the increase of soil POC, PON, IOC and ION contents and storages.