Long-term fertilization of P coupled with N greatly improved microbial activities in a paddy soil ecosystem derived from infertile land

Microcalorimetry was used to study the effects of long-term (20 years) fertilization regimes on microbial activities in a paddy soil in southern China derived from infertile land. Managements of phosphorus fertilizer coupled with nitrogen fertilizer significantly promoted the contents of total and available P, mineral N and microbial biomass C (MBC) ( P Q T /MBC) showed that fertilization of P coupled with N, P-deficient fertilization and non-fertilized control significantly separated from each other. Redundancy analysis plot showed that rate of heat output ( Q T /t), peak power ( P max ) and constant of growth rate ( k ) were significantly correlated with soil total and available P, total and mineral N, which were greatly increased by the P fertilizer coupled with N fertilizer. In contrast, Q T /MBC and peak time ( t max ) were greatly increased by the P-deficient treatments. In addition, Q T /t as a new introduced parameter was negatively correlated well with Q T /MBC (R 2 = 0.93, P Q T /MBC, Q T /t and t max are useful to assess soil microbial activity. The higher Q T /t, lower Q T /MBC and t max indicate higher microbial activity and soil quality. In conclusion, long-term fertilization of P coupled with N, especially combined organic fertilizer greatly improved soil fertility and microbial activity; in contrast, deficiency of soil P had lower microbial activity in the paddy soil derived from infertile land.