Abstract: Sand samples were collected from Dengkou Section of the Wulanbuhe Desert,Inner Mongolia for analysis of forms and bioavailability of phosphorus with the six-step sequential extraction method and for classification of the sands. Results show that contents of total phosphorus (∑P_i) in the samples ranged from 172.88 to 316.67 μg·g^-1,with a mean of 251.32 μg.g^-1. The mean value of inorganic P(IP) and organic P (Or-P) content was accounting for 96.2% of ∑P_i and for 3.8% of ∑P_i,respectively. Ca-bound P was found to be the most abundant with a mean value being 233.72 μg.g^-1 (accounting for 93.0% of ∑P_i) in sand grains of all particle size fractions. The other forms of P followed a decreasing order of Or-P>Fe-P>Ads-P>Al-P>Obs-P in content. In the sand samples,contents of Ca-P,Fe-P and ∑P_i increased with decreasing of particle size,but Or-P was on the contrary,and no remarkable dependency relationship between content and sand particle size for Al-P,Ads-P and Obs-P was found. The quantity of bioavailable P was estimated at about 6.6% of ∑P_i and this fraction of P pool that actually is bioavailable under natural conditions will vary with natural water systems depending on a number of primarily physical and chemical environmental factors.

Key words: Wulanbuhe Desert, phosphorus, chemical form, particle size, bioavailability