The Nutritional Dynamics Of Phosphorus In Different Purple Soil Parent Material Under Flooding Conditions

Phosphorus(P) is a key nutrient for the growth of phytoplankton. In the Aquaculture ecosystem, P usually has an important influence on the primary productivity. And the pond bottom soil is an important source of phosphorus nutrients, but the forms and contents of P are greatly differences in various parent material of pond soil. However, to date, the variation characteristics of phosphorus in different soil parent material are rarely reported. Based on the phenomenon that the fish production varied from ponds with different purple soil parent material under the same aquaculture mode and technology in Sichuan basin(an important pond farming area in China), This research studied the characteristics of phosphorus sorption-desorption and their influence factors of different four kinds of purple soil parent material from Sichuan Basin, including Shaximiao(S1), the Suining Group(S2), Penglaizhen(S3) and the Jiaguan group(S4). The changing characteristics of P forms and contents in overlying water and surface pore water were also studied. And the characteristics of algae in the overlying water were analyzed. Moreover, the effects of exogenous phosphorus element on the different purple soil parent material flooding system were compared in this article. The study will provide a basis for revealling the influencing mechanism of purple soil parent material on the primary productivity of aquaculture pond. And it will be help for the development of pond aquaculture according the local conditions. The main results were as follows:1. The soil nutrients and the phosphorus adsorption-desorption characteristics of different parent material were studied. And the resultsshowed as follows:(1) For the four types of purple soil parent material, the total concentrations of major element nutrients and microelement nutrients, the concentration of total phosphorus and available phosphorus were S2>S3>S1>S4, S2>S4>S3>S1, S1>S3>S2>S4, S2>S3>S1>S4, respectively.(2) The P sorption-desorption process of for types of purple soil parent material was conducted in stages. According to isothermal adsorption curve fitting, the Langmuir equation fitting was best. And based on the phosphorus adsorption capacity(Qm), the maximum buffering capacity(MBC) and the adsorption intensity(k), the P sorption amount and intensity of S2 were higher than other three groups.(3) The P nutrient supply capacity was different from purple soil parent material of phosphorus. Considering the dissolved reactive phosphorus(RDP), the equilibrium phosphate concentration(EPC0), the easy desorption phosphorus(DR) and Olsen P, the P contribution of S2 was relatively high.2. The variation characteristics of P forms and contents of different purple soil parent material under flooding condition were studied in this research. The results showed that the contents of different P forms in four types of purple soil parent material were different at the beginning of flooding condition. The contents of exchangeable P(Ex-P) in four parent material soil were S3> S2> S1> S4. And the Iron/aluminum-bound P(Fe/Al-P), Organic P(OP), and Calcium-bound phosphorus(Ca-P) were S1> S4> S2> S3, S1> S2> S3> S4, S3> S2> S1> S4, respectively. The contents of bioavailable P, including Ex-P, Fe / Al-P and OP, were S1> S2> S3> S4. In general, the P supply of S1 and S2 was conducive to the growth of phytoplankton and would be helpfor improving the primary productivity and the fish production of aquaculturepond.3. We also studied the nutritional dynamics of phosphorus and the physicochemical property in different purple soil parent material in flooding system. The research showed that the p H, ORP and DO of overlying water in different treatment groups appears to be on the rise after water covering. However, their variation characteristics were different among the different treatments. And the contents of soluble reactive phosphorus(SRP) were S1>S2>S4>S3 during the whole experiment.And the contents of total phosphorus(TP) were S1>S4>S3>S2.4. We added exogenous P to the four types of purple soil parent material flooding system and studied the phytoplankton of each treatment. In Shaximiao treatment, Chlorophyta was the main phylum with the most species, followed by Bacillariophyta. And in Suining group, Penglaizhen group and Jiaguan group, Bacillariophyta was the main phylum, followed by Cyanophyta. The species of Euglenophyta and Pyrrophyta were less in four groups. In general, Shaximiao group had the most species, while Penglaizhen group had the fewest speces. After the addition of exogenous phosphorus to the overlying water, algae species and dominant species of each group increased. The number and variety of algae in Shaximiao and Suining group were more affected. In conclusion, the species, density and biomass of algae in Suining group were relatively high and stable, therefore, the purple soil parent material of Suining group is more conducive to the aquaculture.