Evaluation of soil phosphorus tests for flooded rice soils under oxidized and reduced soil conditions

Abstract

Soil tests have had limited success in predicting the response of rice (Oryza saliva, L.) to phosphorus (P) fertilizer. Phosphorus soil test methods have been developed under oxidized conditions without any consideration of changes in available P due to flooding of rice soils. To determine the potential of various P test to predict P availability in flooded soils 28 rice soils were incubated under oxidized and reduced soil conditions and extracted for P with Bray 1, Olsen, ammonium acetate‐ethylenediaminetetraacetic acid (AA‐EDTA) (Texas A&M test), resin, and water. Phosphorus response experiments were conducted on 19 soils in the greenhouse and eight soils under field conditions. Soil extractable P, yield, and plant P were determined. Reducing conditions increased the amount of P removed by AA‐EDTA and Bray 1 soil test methods. AA‐EDTA and Bray 1‐extractable soil P were highly correlated. Resin extracted the highest amount of P under oxidized conditions. The AA‐EDTA soil test method overestimates the available P for high pH soils. The relationship between extracted P and rice plant growth parameters under oxidized and reduced soil conditions indicated that soil P test methods could be equally effective in predicting rice yield response to P fertilizer only when soils had very low extractable P.