Effects of land use patterns on soil phosphorus fractions in the Longzhong part of the Loess Plateau

We investigated the soil phosphorus fractions in croplands(planted and fallow,which had a history of traditional cultivation for at least 50 years)and grasslands(fenced and grazed,which had been restored from cultivation for 24 years) on the Loess Plateau.1) Different land use patterns changed soil phosphorus fractions.The contents of active inorganic phosphorus(H2O-Pi,NaHCO3-Pi),potential active inorganic phosphorus(NaOH-Pi),and stable inorganic phosphorus(DHCl-Pi)in the 0-10 cm soil layer and highly stable inorganic phosphorus(HHCl-Pi)in the 30-60 cm soil layer in the croplands were significantly higher than those in the grasslands due to long-term fertilization of the croplands;2) The conversions between soil phosphorus fractions mainly occured between moderately stable inorganic phosphorus(DHCl-Pi)and other phosphorus components,and also mainly in the 0-20 cm soil layer in the croplands;3) Available phosphorus and total phosphorus were significantly correlated with H2O-Pi,NaHCO3-Pi,and NaOH-Pi.There were significant correlations between total soil nitrogen,soil organic carbon and NaOH-Pi,NaOH-Po,and HHCl-Pi(P0.01).Soil pH was significantly and negatively correlated with NaHCO3-Po(P0.05),H2O-Pi,NaHCO3-Pi,NaOH-Pi,NaOH-Po,and HHCl-Pi(P0.01).