Effects of rhizosphere of rice plant on the native inorganic phosphorus fractions in the paddy soils of north of Iran were investigated in a greenhouse experiment. The study was performed as a 14×2 factorial experiment in a randomized complete block design with 2 factors of soil (10 calcareous and 4 noncalcareous), and cultivation (cultivated and uncultivated), each level with 2 replicates. Bags of soil samples, buried in experimental pots (cultivated and uncultivated), were taken out simultaneously after a 3 month period, and their inorganic P fractions measured by the sequential extraction methods of Jiang and Gu (1989) in calcareous soils, and Kuo (1996) in noncalcareous soils. The available P in all soils was measured by Olsen method. In a different experiment, a special pot of 1 m2 × 30 cm depth was designed to measure the variation in available P with distance from the plant stem. In this pot, the plant spacing was 25 cm, and bags of soil samples were buried in the soil at different distances from the plant stem. The results of these experiments are as follows: 1- In all 14 soils, the Olsen-P in the rhizosphere of rice was significantly lower than that in the uncultivated soils. 2- In calcareous soils, the dicalcium phosphates, the octacalcium phosphates, the Al-phosphates, the P in apatites, and the occluded-P in the rhizosphere of rice were significantly lower than those in the uncultivated soils; whereas the Fe-phosphates was not significantly different in the two conditions. 3- In noncalcareous soils, the readily soluble-P, the Fe-phosphates, and the Al-phosphates in the rhizosphere of rice were significantly lower than those in the uncultivated soils; whereas the occluded-P and the apatites were not significantly different in the two conditions.4- The Olsen-P of the soil between the two hills of rice plant in the special pot experiment, did not vary with the distance from the plant stem, whereas, the Olsen-P in the cultivated soil was significantly lower than that in the uncultivated soil. 5- In all soils, the pH of the water on the surface of the soils in the cultivated pots was significantly lower than that in the uncultivated pots at the end of the growth period
)