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

Shixue Zheng , Haichuan Cao , Qiaoyun Huang , Ming Liu , Xiangui Lin ,
Zhongpei Li ,

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 < 0.05). Both principal component analysis (PCA) of calorimetric
indices and metabolic quotient of heat (QT/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 (QT/t), peak power (Pmax) 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, QT/MBC and peak time (tmax) were
greatly increased by the P-deficient treatments. In addition, QT/t as a new introduced parameter was
negatively correlated well with QT/MBC (R2 ¼ 0.93, P < 0.01). Accordingly, integrating microcalorimetric
result analyzed by PCA as well as sensitive indicators of QT/MBC, QT/t and tmax are useful to assess soil
microbial activity. The higher QT/t, lower QT/MBC and tmax 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.



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