Effect Of Natural Clay Materials On Fraction And Availability Of Phosphorus In Soil

In recent years,the situation of farmland heavy metal pollution is becoming increasingly grim in China.Clay,biochar and other materials are widely used in situ remediation practice of heavy metal pollution of farmland soils.However,these materials would change the bioavailability of phosphorus in the soils,and may even further aggravate soil phosphorus deficiency.Therefore,this paper tried to investigate the effects of immobilizing agents on fraction and availability characteristics of phosphorus,and to reveal the mechanism of bioavailability of phosphorus.Results obtained from this thesis is expected to offer scientifical basis for sustainable usefulness and fertility balance of large scale polluted fieldChemical extraction methods were used to investigate the characteristics of P contents and forms in20 type cadmium contaminated soil.The results showed that the content of total P in soil was318.3-2016.2 mg kg^-1,which was generally suitable and rich.The content of available phosphorus in soil was 2.9-128.3 mg kg^-1,and the content of available P in soil was lower than the normal value of50%.In acid paddy soil,the content of inorganic phosphorus was Al-P>Ca-P>O-P>Fe-P,while in alkaline paddy soil,soil inorganic phosphorus content was Al-P>Ca₁₀-P>O-P>Ca₂-P>Fe-P>Ca₈-P.The proportion of total phosphorus in soil was 7.4%-82.3%,and the proportion of total phosphorus in alkaline soil was higher than that in acid soil.Between the soil pH value and Al-P,Ca-P were positively correlated?P<0.01?,and the soil pH value has significant negative correlation with O-P?P<0.05?;there was significant positive correlation between soil total phosphorus and organic phosphorus,Al-P?P<0.01?,and a significant positive correlation relationship with the effective P,Ca-P?P<0.05?between the organic phosphorus content of soil available phosphorus and Al-P,respectively,showed extremely significant and significant positive correlation.The phosphorus soil index?PSI?and degree of P sorption Ssaturation?DPSS?values were 6.77-28.15 and 3.28-30.82.In acidic soil samples,the phosphorus fixation capacity in soil was higher,Al and Fe and soil fixation ability showed a significant positive correlation?R=0.627,P<0.01;R=0.423,P<0.01?.The effects of sepiolite on the availabitily and forms of P were studied in acidic,neutral and alkaline paddy soil contaminated by Cd.It revealed that pH increased with culture time,and thus the free phosphorus and Al,Fe and Ca formation of insoluble phosphate were effectively reduced.The Eh values were decreased with the increasing time,and the high valence state Fe was reduced and activated,which makes the maximum contribution to the fixation of free phosphorus.The activity of phosphorus enzyme was inhibited with with time.As a consequence,the efficiency of organic phosphorus mineralization and the content of available P were reduced.From the first to fourth week,The order of the inorganic phosphorus content was O-P>Fe-P>Al-P>Ca-P?O-P>Al-P>Ca-P>Fe-P?O-P>Al-P>Ca-P>Fe-P and O-P>Ca-P>Fe-P>Al-P.With the time increasing,the contents of Fe-P were decreased,and while the proportion of Ca-P was continue increase.With the sepiolite content increasing,Al-P,Ca-P and Fe-P were inhibited,while O-P was increased.The effects of clay material on the saturated phosphorus absorption in different pH Cd contaminated were studied.The resultes showed that when pH was increased,the content of Al was easy to form by precipitation due to the increasment of OH^-,which resulted in the decrease of phosphorus retention capacity.At the same time,Fe concentration increased,which plays a positive role in the adsorption of phosphorus in soils.The PSI value was greatly affected by sepiolite and biochar,and the maximum PSI value was got at combined treatment of 3%sepiolite+2%biochar.There was no significant correlation between DPSS value and sepiolite and biochar?P>0.05?,while pH had a positive correlation with DPSS,and DPSS was negatively correlated with PSI.