Phosphorus Characteristics Of Rhizosphere Soil In Different Age Alfalfa On Saline Soil

Saline soil is one of the worldwide poor yield soil resource,and it is also one of the most important factors which lead the ecological environment get worse,many research showed that planting Alfalfa on saline soil could decrease the content of soil salt and improve the availability of soil nutrition element.Phosphorus(P)is an essential nutrition element which limits the yield of Alfalfa seriously.Rhizosphere effect of plant would influence the availability of P remarkably.In this paper,the change characteristic of total P, available P,soil organic carbon(SOC)content and pH between bulk and rhizosphere soils of 2-year-old,3-year-old,4-year-old,5-year-old and 8-year-old alfalfa in Hexi Corridor saline soil were investigated and compared.We also investigated the P fractionation on the basis of the Hedley's P fraction schedule which modified by Tiessen and Sui,and analyzed the correlations among available P,SOC,pH and P fractionations.The results showed that there was no significant difference in total P content between the rhizosphere and the bulk soils in all different cultivating ages,while the available P content in the rhizosphere was significant higher than that in the bulk soils between cultivating ages.There were no regular rules among different ages of alfalfa in total P content in rhizosphere and bulk soils, however,the available P content in both rhizosphere and bulk were increasing with extending of cultivating ages and were highest in first five years plant,which was opposite to 8-year-old alfalfa.The pH of rhizosphere soils was lower than that in bulk soils,but no further acidification was observed in all ages except 4-year-old and 5-year-old Alfalfa. Correlative analyses indicated that there were no significant correlation between total phosphorus and available phosphorus content,pH and available P content in both rhizosphere and bulk soils.In inorganic P portions(Pi),the contents of H₂O-Pi(extracted by deionized water),Dil.HCl-Pi(extracted by diluted hydrochloric acid)in rhizosphere soils of different cultivating ages of alfalfa were lower than that in bulk,but NaHCO₃-Pi (extracted by sodium bicarbonate)and NaOH-Pi(extracted by sodium hydroxide)in rhizosphere were higher than that in bulk significantly,conc.HCl-Pi(extracted by concentrate hydrochloric acid)in bulk soil of 2-year-old alfalfa was higher than that in rhizosphere soils which was opposite to other ages.The content of NaHCO₃-Pi and H₂O increased in both rhizosphere and bulk soils from 2 years to 5 years,but decreased in 8 years,Dil.HCl-Pi increased from 2 years to 8 years gradually,which was opposite to NaOH-Pi,and the change of conc.HCl-Pi had no regular rules.In organic P portions(Po), the contents of NaHCO₃-Po,NaOH-Po and conc.HCl-Po in rhizosphere were higher than that in bulk soil in all ages,as the increasing of growth age,NaHCO₃-Po content decreased obviously both in rhizosphere and bulk soils,.NaOH-Po content increased in rhizosphere from 2 years to 4 years and decreased since 5 years,in bulk soil,NaOH-Po content increased from 2 years to 5 years,but decreased since 8 years,conc.HCl-Po content in rhizosphere and bulk soil has no significant temporal change trend.The Residual-P content between rhizosphere and bulk soil was not different noticeably,but,it decreased rapidly from 3 years to 5 years in both rhizosphere and bulk soil.There were different correlations between different P fractionations.The SOC content in rhizosphere was significant higher than in bulk soil in all ages,and increased with extending of cultivating ages,but this trend in bulk soil was not remarkable,SOC was significant correlated with Po in rhizosphere and Pi in bulk soil which has poor availability.In rhizosphere soil,NaHCO₃-Po and conc.HCl-Po were main factors which influenced the P availability,but in bulk soil,the main factors were conc.HCl-Po and Residual-P.