Long-term effects of inorganic fertilizers on microbial biomass and community functional diversity in a paddy soil derived from quaternary red clay

Long-term effects of inorganic fertilizers on microbial biomass and community functional diversity were investigated in a paddy soil derived from quaternary red clay in the Red Soil Ecological Experimental Station of the Chinese Academy of Sciences. The original soil is extremely eroded, characterized by low pH and deficiencies of available nutrients, particularly phosphorus and nitrogen. After 13 years application of inorganic fertilizers for flooded double rice crops, the number of cultivable microorganisms was significantly larger, and microbial biomass and community functional diversity were significantly higher in the treatments fertilized with P than those in the treatments without P fertilization. The significant effects of P application were mainly due to enhanced growth of rice crops and. accumulation of soil organic carbon through increased root turnover and rhizodeposition. The soil was also deficient in N, but stimulation by N application of microbial biomass and community functional diversity as well as rice crop yields could be achieved only after improvement of the P supply. K application had no effect on rice crop yield or on microbial parameters. Most microbial parameters were mainly correlated with soil organic carbon content rather than P and N, indicating that the application of P and N did not directly affect microbial parameters in the soil, but did so indirectly by increasing crop yields, thus promoting the accumulation of soil organic matter. (c) 2006 Elsevier B.V. All rights reserved.