Soil organic carbon and nitrogen pools impacted by long-term tillage and fertilization practices

A long-term field experiment, started in 1983, was carried out on a clay loam soil (Ferric/Haplic Luvisols, FAO) in Jurong Agricultural Institute, Jiangsu Province, China, to study changes of organic carbon (C) and nitrogen (N) pools in the topsoil under a rice/wheat rotation system. Treatments included conventional tillage (CT) and no tillage (NT) combined with various fertilizer treatments. The fertilizer treatments were control (no fertilizer), chemical fertilizer only, straw plus chemical fertilizer, and pig manure plus chemical fertilizer. With the exception of the control treatment, all treatments received the same level (in kg ha(-1)) of N (150), phosphorus (P) (50), and potassium (K) (155). Results showed that soil organic C, N, and microbial biomass carbon (MBC) and nitrogen (MBN) were higher in the top 5 cm layer after 18 years of no tillage than that under CT, whereas the reverse trend was observed in 5 to 10- and 10 to 20-cm layers. The application of organic manures with a reduced amount of commercial chemical fertilizer increased the content of soil organic C, total and available N, and MBC and MBN compared to the treatment with inorganic fertilizer alone. Organic C and total N contents of soils from different treatments were found in the order of pig manure plus inorganic fertilizer > straw plus inorganic fertilizer > inorganic fertilizer > control. Microbial biomass C and MBN showed a similar trend to organic C and total N. These results indicate that a combination of NT and application of pig manure is the best way to sustain soil fertility in the experiment.