Dynamic Characteristics And Its Impact Factors Of Soluble Organic Nitrogen In Different Paddy Soils After Astragalus Sinicus Application

Soil soluble organic nitrogen (SON) is one of the most active components in soil nitrogen pool, which plays an important role in the agricultural ecosystem nitrogen cycling. To study the dynamic changes of SON content after turning over Astragalus Sinicus in the paddy field. Waterlogged incubation experiments were conducted with two different types of Fujian subtropical paddy soil (red mud sand field and black mud field) to simulate turning over the same amount of Astragalus Sinicus at 15℃ and 25℃. principal component analysis and structural equation modeling were used to investigate the main influencing factors of paddy soil SON content’s dynamic changes, to reveal the dynamic characteristics, primary and secondary factors and their impact path of different fertility paddy fields soil SON, The main results as followings:1. At 15℃ and 25℃ culture conditions SON content in all treatments of the red mud sand field and black mud field soils showed a general trend of early acute or slow significantly decreased after increasing, later stable or rise slightly. The SON contents of turning over Astragalus Sinicus into two kinds of soil’s treatment were generally significantly higher than the control. In the culture period, the SON content of red mud sand field turning over Astragalus Sinicus group were 22.00%～199.22% higher than control group, black mud field turning over Astragalus Sinicus group were 4.58%～249.36% higher than control group.2. At 15℃ and 25℃ culture conditions, the content mean values of SON in the soil after turning over Astragalus Sinicus are expressed as:black mud field> red mud sand field, the difference between them was significant. The SON contents of same fertility paddy soil at different temperatures culture were also different, and the peak of SON after two kinds of soils turning over Astragalus Sinicus are expressed as 25℃> 15℃, but the two difference in the red mud sand field was not significant, while the two difference in the black mud field was significant. Under different temperature conditions, SON content peaked at different times after turning over Astragalus Sinicus, at 25℃ culture conditions SON content reached the peak time is always earlier than 15℃. 3.Principal component analysis combined with correlation analysisshowed the main factors that affect ofpaddy soil SON dynamics including:urease, microbial biomass C, protease, glutaminase, the initial organic matter, Eh, pH. On this basis, the results of structural equation modeling analysis showed that, direct impact factor of dynamic change of soil SON content in paddy field after turning over Astragalus Sinicus include: initial organic matter, protease, glutaminase and microbial biomass C, path coefficients were 0.652,0.600, 0.499,0.405, in which the largest impact on the SON is the initial organic matter content. In addition to a direct impact on the outer path, each factor influence the content SON’S major indirect effects path are as follows:a) The initial organic matter→microbial biomass C→SON; b) The initial organic matter→ protease→SON; c) The initial organic matter→glutaminase→SON;d) Microbial biomass C→protease→ SON; e) Microbial biomass C→glutaminase→SON; f) The initial organic matter→microbial biomass C→ protease→SON;g) The initial organic matter→microbial biomass C→glutaminase→SON.