Abstract: 【Objective】 In order to prevent red soil acidification by regulating nitrogen fertilization, the changes of several forms of soil nitrogen and soil pH, and the correlations among them were studied under different fertilization.【Method】 Incubation experiments were conducted at the temperature of (30±1)℃. The dynamics of NH4+-N, NO3--N and pH after urea application at different rates or combined with other fertilizers (Control (CK), 20 mgN•kg-1 (25%N), 40 mgN•kg-1 (50%N), 80 mgN•kg-1 (100%N, urea, conventional N application rate), 160 mgN•kg-1 (200%N), 100%N plus chemical phosphorus fertilizer (100%N+P), 100%N+P plus chemical potassium fertilizer (100%N+PK), 100%N+PK plus maize straw (100%N+PKS), 70%N+PK combined with 30% organic N (70%N+PK+30%M), 50%N+PK combined with 50% organic N (50%N+PK+50%M), 30%N+PK combined with 70% organic N (30%N+PK+70%M) and 100% organic N (100%M, pig manure)) were measured. 【Result】 Compared with the control treatment, NO3--N, nitrification potential increased and soil pH decreased in all fertilizer treatments, and difference increased with the urea N application rates and decreased with organic nitrogen application rates. The greatest nitrification potential (335.62 mg•kg-1) was observed in the 200%N treatment and second were 100%N (152.48 mg•kg-1), 100%N+P (153.36 mg•kg-1) 100%N+PK (148.17 mg•kg-1) and 100%N+PKS (148.62 mg•kg-1) treatments. However, k in the treatment 100%N+PKS was 0.039 d-1 and significant lower than 100%N, 100%N+P and 100%N+PK treatments, 0.051, 0.051 and 0.054 d-1, respectively. NH4+-N and soil pH reached their maximum values between the 3rd and 7th day of incubation after application of fertilizers or no fertilizer, respectively, decreased thereafter, and tended to be stable. Compared with the control treatment, soil pH decreased with the urea N application rates, and the greatest decrease of 0.92 units of soil pH in the 200%N treatment. Combination of organic nitrogen with urea-N slowed down the reduction in soil pH. Soil pH was positively correlated with NH4+-N, while negatively correlated with NO3--N and nitrification potential.【Conclusion】 Urea application could increase nitrification of red soil (pH5.7) and decrease soil pH, and the nitrogen application rate is one of the main factors accelerating acidification of red soil. Urea-N combined with corn straw could decrease nitrification rate, and partial urea-N substitution by organic fertilizer nitrogen can decrease nitrification potential, so decreasing NO3--N accumulation and minimizing acidification risk of red soil.

Key words: red soil, different fertilization, pH, urea-N, nitrification potential