Lowland rice production is expanding throughout South-East Asia necessarily onto soils of poorer nutrient status with a resulting decrease in yields. An understanding of the nutrient status of the rice rhizosphere is essential for the development of appropriate management practices to increase rice yields. Phosphorus (P) deficiency is one aspect of rice nutrition. Increased rice root respiration and P uptake efficiency, and an increase in H$ sp{+}$ released from roots and enhanced solubility of calcium phosphates are two possible mechanisms of tolerance to low P levels. These mechanisms were evaluated but could not be used as single tests to differentiate among cultivars for tolerance to P deficiency. Phosphorus reactions in the soil may be confounded by the chemistry of iron (Fe). Iron and P interactions in the rice rhizosphere were investigated using a Philippine paddy soil. Root loss of oxygen (O$ sb2$) into the rhizosphere caused the oxidation of Fe$ sp{2+}$ and the concurrent release of H$ sp{+}$. Root release of H$ sp{+}$ from cation-anion uptake imbalances also contributed to the acidification of the rhizosphere. Accumulation of Fe$ sp{3+}$ was found next to the root plane. Depletion of acid-soluble P coincided with the zone of acidification. Rice plants were able to utilize the acid-soluble P fraction during growth.

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