Abstract: In 2010-2012, this paper studied the accumulated amounts of available phosphorus (P), water-soluble P, and bioavailable P in a cinnamon soil under long-term (1988-2012) fertilization, and analyzed the correlation between the soil water-soluble P and P saturation degree. Long-term application of P fertilizer and organic fertilizer increased the contents of the soil available P, water-soluble P, and bioavailable P significantly, which was most significant in the treatment of applying high amount organic fertilizer combined with chemical P fertilizer. In treatment 45000 kg·hm^-2 of organic fertilizer plus 75 kg·hm^-2 of P₂O₅, the soil P saturation degree in 2012 was >25%, which enhanced the P loss risk of cinnamon soil remarkably. There existed extremely significant correlations between the soil available P, water-soluble P, and bioavailable P, of which, the first two were of exponential relationship. In addition, there was an extremely significant exponential relationship between the soil P saturation degree and water-soluble P.

Key words: the middle and lower reaches of the Yellow River, riparian zone, soil properties, redundancy analysis.