Coupling effect of inorganic nitrogen and cabbage waste onsoil nitrogen mineralization

A 100-day laboratory incubation experiment was conducted under controlled conditions (25 °C and 65% moisture content) to determine the effect of addition of waste cabbage leaves B1: 200 g?kg^-1(soil), B2: 400 g?kg^-1(soil), B3: 550 g?kg^-1(soil) coupled with inorganic nitrogen N0: 0 mg(N)?kg^-1(soil), N1: 25 mg(N)?kg^-1(soil), N2: 50 mg(N)?kg^-1(soil), N3: 100 mg(N)?kg^-1(soil) on amended soil nitrogen (N) mineralization. Results showed that soil net accumulated N mineralization under different inorganic N treatments were 4~5 times of that under the control (CK). Furthermore, net accumulated N mineralization under N1 treatment was significantly higher than those under other N treatments. Net accumulated N mineralization under waste cabbage leaves treatments were 3~5 times of that under CK. Net accumulated N mineralization under B2 treatment was significantly higher than those under B1 and B3 treat-ments. Statistical analysis showed no significant interaction effect was noted (P=0.275) between inorganic N and waste cabbage leaves treatments. Waste cabbage leaves addition was the dominant driving factor (Eta²=0.16) of amended soil N mineralization while inorganic N supply was only a secondary factor (Eta²=0.07). In the early period (0~20 d) of the incubation treatment, net accumulated N mineralization gradually increased and then maintained a steady trend in the later stage under B1 treatment. However, N mineralization, immobilization and re-mineralization occurred in the early period of incubation (30 d) while net accumulated N mineralization increased gradually in the later stage under B2 and B3 treatments. The results of N mineralization rate showed that N mineralization mainly occurred in the first 30 days as affected by waste cabbage leaves addition. Also during incubation, a ?rst-order kinetics equation of amended soil net accumulated N mineralization fitted well with the days of incubation (R²=0.62~0.89).