Effect of long-term fertilization on spatial distribution and availability of soil phosphorus in Loess Plateau

The spatial distribution and availability of soil phosphorus (P) in Loess Plateau after 20 years of phosphate fertilization was investigated in this study. Phosphorus mainly accumulated in the surface layer after long-term fertilization. Soil total P and Olsen-P increased gradually with fertilization rate, which indicated that long-term continuous fertilization could increase the available phosphorus storage significantly. Ca-P was the main fraction in soil inorganic P, which accounted for above 80% of the inorganic P. The contents of soil Ca2-P、Ca8-P、Al-P and Fe-P increased with the phosphate fertilization rate. Correlation analysis and path analysis showed that soil Olsen-P was significantly correlated with soil inorganic P, Ca2-P and Ca8-P, which can be the source of soil available P. Soil O-P and Ca10-P, the potential sources of soil available P, had low correlations with soil Olsen-P. Soil Al-P and Fe-P had a medium correlation with soil Olsen-P, and in particular, Fe-P affected soil Olsen-P indirectly through other fractions.