Effects of nitrogen application levels on microbiological characteristics of typical Albic soil in mid-temperate zone

Objective  To study changes in microbiological characteristics of Albic soil by regulating nitrogen application levels during the critical periods of maize growth.

Method  Different levels of nitrogen (0, 150, 200 and 250 kg·hm^-2) were applied to the maize field. The dynamic changes in the microbial biomass carbon, microbial biomass nitrogen and the activities of urease, alkaline phosphatase, protease and catalase from typical Albic soil in mid-temperate zone of eastern China under different nitrogen levels during the maize production process were studied.

Result  Urea application increased urease activity in Albic soil at seedling stage by activating microorganisms related with urease release. Higher nitrogen level increased alkaline phosphatase activity at seedling stage. With the growth of maize, phosphatase activity clearly decreased under different nitrogen levels, however, phosphatase activity increased with no nitrogen added. Urea addition at the initial stage was not beneficial for the improvement of catalase activity, but with the growth of maize, catalase activity increased under different nitrogen levels. At seedling stage, protease activity increased with the increase of nitrogen level, but decreased when the nitrogen level reached 250 kg·hm^-2. When the maize was mature, no nitrogen or low amount of nitrogen application was more beneficial for the improvement of protease activity. Urea as a base fertilizer reduced microbial biomass carbon (MBC) content at seedling stage, while with the growth of maize, nitrogen application helped the preservation and stability of MBC. No nitrogen or excessive nitrogen application increased microbial biomass nitrogen (MBN) content, while appropriate amount of nitrogen promoted MBN to turnover and convert into available nutrients for plants.

Conclusion  The concentrated and excessive application of urea is not helpful to the preservation of soil biological fertility. Considering maize yield and soil fertility improvement, the appropriate amount of nitrogen application level in Albic soil is 200 kg·hm^-2.