Chemical Action Of Ferric Phosphate And Phosphorus In Flooded Paddy Soil Under Anaerobic Incubation Condition

Available phosphorus is very low in many types of soil that most phosphorus compound is difficutely dissolved. It can be found in practice that phosphorus concentration increase in flooded period in south acid soil that total phosphorus are low and plant don't occure phenomena of shortness. Research found that the increase of available phosphoru was related to reduction of iron in flooded soil. Chemical property of flooded soil was dominated by iron. Dissimilatory Fe(III) oxide reduction under anaerobic condition is a process which is an anaerobic respiration with Fe(III) as the terminal electron acceptor. This anaerobic respiration showed important environmental significances. Dissimilatory Fe(III) reducers can use diverse electron acceptors including many toxic heavy metals and metalloids such as Mn(Ⅳ),Cr(Ⅵ),Co(III) insides Fe(III). So these toxic metals were detoxified or were immobilized reductively. Reductive process stimulate the decomposition of some organic contaminants. Geological significances of anaerobic respiration lie in that reduction of Fe (III) oxides relate change of Si and P. Which increases release of these nutrient elements.In this paper, Through adopting anaerobic enrichment cultivation in which three kinds of water-extracted paddy soil solution were inoculated, effect of phosphate on Ferrihydrite reduction is investigated. And dissimilatory reduction capability of crystal Ferric phosphate is also investigated when using different organic acid as substrates. Water-extracted soil solutions of SiChuan, JiangXi, JiLin and HuNan were incubated under anoxic atmosphere. In the incubation, Ferric phosphate and AQDS were added. The changes of available phosphorus, inorganic phosphorus fraction and phosphatases which indicate organic phosphorus in soil were investigated in anoxic incubation. The primary results were as follows:1. Different phosphate concentration buffer were added in enrichment incubation in which water-extracted paddy soil solution were inoculated. Reaction rate and Fe(II) accumulation were lower than no addition control at phosphate concentration of≥30 mmol/L, even inhibiting Fe(III)oxides induction. While phosphate at concentration of <30 mmol/L would stimulate reduction. Reaction rate and Fe(II) accumulation were most large when adding 5 mmol/L of phosphate in enrichment incubation. But the stimulation and inhibition didn't occur in soil incubation.2. Dissoluble crystal Ferric phosphate could be reducted by microbes. Different substrate and phosphate significantly affected reduction of Ferric phosphate. Microbes directly utilized acetate and pyruvate as only substrate and energy source to reduct Ferric phosphate.