Changes of phosphorous fractions under continuous corn production in a temperate clay soil

Limited efficiency of fertilizer P may be improved through an understanding of soil P fraction changes with time. This study examined sequential changes in soil organic P (Po) and inorganic P (Pi) ina Ste. Rosalie clay (Humic Gleysol; fine, mixed, frigid. Typic Humaquept) under continuous corn with and without P fertilization. Soil P was fractionated into Bicarb-Pi and Po, NaOH-1-Pi and Po, HCl-Pi, NaOH-Pi and Po, and Residue-P. In the non-P fertilized plots, soil total extractable Po declined by 14% of the initial value over five years of corn production, whereas soil Pi fractions were unchanged. The losses of soil Po were mainly from NaOH-1-Po. Added, fertilizer P increased NaHCO3-Pi and NaOH-1-Pi in plots receiving 44 and 132 kg P ha(-1) yr(-1) and increased Residue-P in plots receiving 132 kg P ha(-1) yr(-1). Although NaOH-1-Po decreased slightly in the plots receiving 44 kg ha(-1) yr(-1) P fertilizer total soil extractable Po was maintained in P fertilized plots. Mineralization of from 16 to 29 kg P ha(-1) yr(-1) Po was needed to account for soil Po losses. Bicarb-Pi and NaOH-1-Pi appeared to be most important for assessment of soil P fertility changes in long-term fertilized soils.