Short-term Changes of pH Values and Aluminium Activity in Acid Soils after the Application of Nitrogen Fertilizers

Laboratory experiments were conducted to investigate the effects of nitrogen fertilizers on the soil pH, Al activity and Al phytotoxicity in 3 acidic soils. The results showed that application of urea and ammonium carbonate caused a significant increase in soil pH, and enhanced with the raising concentrations. However, application of ammonium sulfate induced a distinct decrease in soil pH. Moreover, application of urea and ammonium carbonate caused a profound decline in soil’ exchangeable Al. In contrast, application of ammonium sulfate induced a noticeable increase in soil’ exchangeable Al, and reinforced with the enhanced concentrations when compared with the no-fertilizer control. In our study, urea and ammonium carbonate significantly decreased exchangeable Al in acid soils, therefore reduced Al toxicity to maize seedlings. On the contrary, ammonium sulfate enhanced Al toxicity to maize seedlings and inhibited their growth.