Forms And Profile Distribution Of Soil Phosphorus And Its Pedogenic Implication In The Pearl River Delta Plain

Changes in Phosphorus?P? forms and distribution in soil profiles from three different constracting paddy chronosequences developed on marine sediments, fluvial deposits and deltaic deposits in the Pearl River Delta Plain were investigated in this paper.We determined total P?TP?, NaHCO₃-Pi, NaHCO₃-Po, NaOH-Pi, NaOH-Po, Dil.HCl-Pi,Conc.HCl-Pi, Conc.HCl-Po and Residual-P using sequential extraction and the soil P forms in Ap1 horizon were also analyzed by using³¹P-NMR spectroscopy technique. The aim of this study was to understand pedogenic transformation of soil P with increased cultivated ages. The results were as follows:?1? The average TP content showed the order of deltaic deposits > fluvial deposits >marine sediments.soil. TP content was highest in Ap1 horizon soil and decreased rapidly down to Ap2 horizon, and then decreased gradually from Ap2 horizon to B horizon and then it tended to be relatively stable. The change trends of NaHCO₃-Pi, NaOH-Pi and Dil.HCl-Pi content were consistent with TP. Besides, the inorganic and organic P was dominated by Conc.HCl-Piand NaOH-Po respectively, which showed an average proportion of 28.0 % and 6.2 % of TP respectively. The content of the sum of NaHCO₃-Pi and NaOH-Pi??Fe +Al?-P? was higher than that of Dil.HCl-Pi?Ca-P? in deltaic deposits and marine sediments developed soil, but it was opposite in fluvial deposits developed soil.?2? The content of TP in Ap1 horizon increased in the 30⁶00a, 200⁹00a, 50²50a old soils derived from marine sediments, fluvial deposits and deltaic deposits respectively,but the increased amount varies because of different human activities at different growing stages. In Ap2 horizon, it tended to show the same trend with that in Ap1 horizon. With cultivation age increased, the content of TP showed no difference in B and G horizon in marine sediments developed soil and decreased in deltaic deposits developed soil, but it increased in B horizon in fluvial deposits developed soil. The content of NaHCO₃-Pi,NaOH-Pi and Dil.HCl-Pi showed the same change trend with TP with cultivation age increased, but the organic phosphorus fractions changes differently.?3? Changes of TP was mainly attributed to the changes of NaHCO₃-Pi, NaOH-Pi and Dil.HCl-Pi, which accounted for 73.4%?101.1%?102.0% in marine sediments, fluvial deposits and deltaic deposits developed soils respectively. In all, Changes of TP mainly influenced by the changes of inorganic P, but the change of organic P made no difference.?4? Soil P compounds identified by³¹P-NMR spectroscopy was dominated by inorganic orthophosphate which accounted for 75.1%⁹5.7% of NaOH-EDTA extracted P,and followed with orthophosphate monoesters, which accounted for 1.5¹8.9%.orthophosphate diesters or paophosphates accounted for only 0.1%⁴.6%. The proportion of soil P forms identified by³¹P-NMR spectroscopy were affected by land use types. The proportion of orthophosphate in rice planting soil is about 15% lower than that in the vegetables, bananas, sugar cane planting soil, and the single lipid phosphate ratio is about15% higher.The proportions of P compounds changed with cultivation ages increased, but it showed no regular change as it was greatly influenced by anthropogenic activity.?5? Phosphatase activity was declined with soil depth increased. Phosphatase activity in Ap horizon was obviously higher than that in B and G horizon. Acid phosphatase activity was general higher than alkaline phosphatase activity. Phosphatase activity was significantly or extremely significantly positive correlated with TP, NaHCO₃-Pi,NaHCO₃-Po, NaOH-Pi, NaOH-Po, Dil HCl-Pi, Conc HCl-Pi and Conc HCl-Po,but it was not obviously related with Residual-P.