Dynamics of different phosphorus fractions during rewetting and subsequent drying of air-dried calcareous soils

Abstract

Aims The effect of drying and rewetting (DRW) on soil labile phosphorus has been extensively studied, while its effect on the dynamics of metastable phosphorus fractions is poorly understood. This study aims to characterize the changes in the different phosphorus fractions during soil moisture fluctuation and reveal the driving force behind it. Methods Ca2-IP, Ca8-IP, Al-IP and Fe-IP were sequentially extracted during rewetting and subsequent drying of four different air-dried calcareous soils. Ca2-OP, MBP and other soil properties were also determined. Correlation analysis was conducted to study the inter-transition of these fractions during soil moisture fluctuation. Results The sum of all the extracted phosphorus content (Ca2-IP, Ca8-IP, Al-IP, Fe-IP, Ca2-OP, and MBP) increased firstly and then declined to the starting levels at the end of incubation. The metastable phosphorus (Ca8-IP, Al-IP, and Fe-IP) constituted a major fraction of the temporal increase, appearing to be sensitive to the moisture fluctuation. The correlation analysis showed that the soil moisture was likely a master factor controlling the distribution of different phosphorus fractions. Correlation between different metastable phosphorus appeared to be pH-sensitive: in the slightly acidic soil, Al-IP was negatively correlated with Ca2-P, Ca8-IP, and Fe-P; In the alkaline soils, Al-IP was positively correlated with Ca2-IP, Ca8-IP, and Fe-P. Conclusions Our study found that metastable phosphorus was also sensitive to DRW. Considering that metastable phosphorus is also plant-available, detailed study of the dynamics of metastable phosphorus during the drying and rewetting cycles across different soil types is necessary.