Study Of The Relationship Between Iron Oxide Reduction And Inorganic Phosphorus Availability In Paddy Soils

Incubation method and pot experiments were carried out to study the characteristics that effects of reduction of iron oxides on phosphorus availability. The paddy soil samples were collected from the paddy fields in four province and regions: Jilin, Sichuan, Jiangxi and Guangdong. The primary results were as follows:(1) The concentration of available phosphate of the soils increased significantly with the increasing of Fe(II) during the anoxic incubating process. Under anaerobic condition for 30 days, there are distinct linear correlative relations between Fe(II) and available phosphate. The correlation coefficients of four simples reach the upmost distinct level. It shows that the reduction of iron oxides should be an important factor affecting P availability in paddy soil.(2) Under anaerobic condition for 30 days, the content of Fe-P increased with the decreasing of Al-P and O-P. The reduction of Al-P and O-P were less than the increase in Fe-P in Jilin and Guangdong slurries. It shows that mineralization of organic phosphorus may affect the transformation of inorganic phosphorus. In Sichuan slurries, the total content of Fe-P, Al-P and O-P have decreased. The result indicated that anaerobic condition enhanced the transformation of Fe-P, Al-P and O-P into Ca-P.(3) The reductions of additional ferrihydrite were different in different slurries. The contents of Fe(II) by addition of ferrihydrite are higher than CK in Sichuan and Jiangxi soils, but they are have equal amounts in Guangdong soils under anaerobic condition for 40 days. The process of Iron reduction was more slowly in Jilin paddy than that in other paddy slurries.(4) Addition of iron oxides may decrease the availability of phosphorus. The result shows that iron oxides could fix phosphate, but much of the fixed phosphate could be released during anaerobic incubation process.(5) The concentrations of available phosphate increased by addition of PO43- in paddy soils, but they decreased by addition of PO43- and ferrihydrite. It shows that the additional PO43- may be fixed by ferrihydrite.(6) Addition of PO43- may increase the content of Fe-P, Al-P and O-P in paddy soils. The content of Fe-P increased by 0.51mg/kg-141.61mg/kg, and Jiangxi soil >Guangdong soil >Jilin soil>Sichuan soil. The content of Al-P increased by 11.87 mg/kg-26.73mgkg. The order of O-P is Guangdong soil >Sichuan soil >Jiangxi soil > Jilin soil. Before and after addition of PO43- and ferrihydrite, the variety of Al-P increase and O-P decrease. It means thatferrihydrite enhance the transformation of PO4-3 into O-P, but repress PO43- translate into Al-P.(7) EDTA and fulvic acid may increase available phosphate concentration by advanced the reduction of iron oxides in paddy slurries.(8) Addition of ferrihydrite into paddy slurries may affect the biomass of rice. The content of additional ferrihydrite had notable effects on rice growth. If the lever of ferrihydrite is higher than 50 umol/g in soil, it will inhibit the growth of rice.(9) The pot experiments of addition of EDTA , fulvic acid and acetate shows that 20 u mol/g EDTA may inhibit the growth of upground of rice. The biomass of rice by fulvic acid addition, but additional acetate may promote the growth of rice.