Long-term Evolution Characteristics Of Phosphorus Molecular Morphology Left In Farmland Soils And Microstructure Characterization Of New Organic Phosphate Fertilizers

The development of modern agriculture depends greatly on the consumption of chemical fertilizers.Phosphorus(P)from chemical fertilizers usually exists as soluble form,then the majority of fertilizer P is fixed by soil solid matrix in agricultural lands within the short term after application.Over the past decades,the large accumulation of surplus P in cropland soils due to the excessive and intensive application of chemical fertilizers,termed soil legacy P,has threatened agricultural profitability and water quality.Therefore,it is recommended to reduce chemical fertilizer application to draw down soil legacy P by maximizing plant utilization,and develop new organically bound P fertilizer to enhance the resistance to soil fixation,in order to alleviate and prevent further accumulation of legacy P in agricultural lands.Using multiple molecular spectroscopic techniques(P K-edge bulk/μ-XANES,μ-XRF,P-NMR),This study focuses on the investigation of the speciation and transformation of legacy P in the black and alluvial soils,representing two typical agricultural regions of Northeast and North of China,as well as the synthesis and characterization of a new organically bound P fertilizer(starch bound P fertilizer).The main achievements are as follows:(1)Phosphorus in the black soil was predominantly as organic P and hydroxyapatite(HAP),as well as a certain of Ca(H2PO4)and Fe-associated P(Fe-P).Withholding P fertilization for 27 years,Ca(H2PO4)and HAP significantly decreased compared to the reference soil collected in 1989,which indicated these P species supported crop growth.Soil legacy P transformations among treatments suggested that the release of orthophosphate from labile orthophosphate diester could be triggered by soil P deficits.Additionally,P fertilization enriched some inorganic[Ca(H2PO4)and Fe-P]and organic P(orthophosphate diesters)forms.(2)The majority of P in the alleviate soils existed as Ca3(PO4)2,in addition to a certain of Fe-P and organic P.Without P fertilization for 26 years,significant decrease in the concentration of Ca3(PO4)2 in the 2015-NK soil relative to the 1990-referrence soil highlighted the availability of Ca3(PO4)2 to crops.Moreover,continuous application of Ca superphosphate resulted into the formation of HAP in addition to Ca(H2PO4).Compared to the 1990-reference soil,orthophosphate monoesters and diesters were accumulated in the 2015-NPK soil,while these P species did not show depletion in the 2015-NK soil.(3)A new starch-bound organic P fertilizer with total P at 5218 mg kg-1 was synthesized,and P in this fertilizer was mainly presented as orthophosphate monoester,representing 75.8%of total P.Orthophosphate diester accounted for 17.3%of total P,while inorganic P only 6.9%.This results provide an important basis for further studies on the high phyto-availability mechanisms of organically bound P fertilizers.