Soil Phosphorus Tests for Flooded Rice Grown in Contrasting Soils and Cropping History

Abstract

Soil phosphorus (P) tests for flooded rice (Oryza sativa L.) generally present uncertainties for estimating P availability. Bray 1, 1% citric acid, Mehlich 3, Olsen extractants (dry samples), and Bray 1 extractant after 3 days (BI3) and 7 days (BI7) of anaerobic incubations were evaluated to estimate P availability for rice in 43 Uruguayan soils. Field trials were conduced at each site (0, 13, 26, and 39 kg P applied ha⁻¹). Relative yield and absolute and relative yield increases were determined. Extracted P was variable for the different tests. For silty soils, P availability was better estimated by citric acid, Mehlich 3, and Bray 1, with similar soil P critical concentrations (6−8 mg P kg⁻¹). The BI3 and BI7 tests showed greater soil P critical concentration but poorer correlations with yield indexes. This study contributes to the scientific basis of P fertilization for flooded rice, promoting more effective fertilizer use and minimizing environmental P losses.

Keywords:

• Rice crop
• soil P critical concentrations
• soil P test

Acknowledgments

The present study was carried out with the financial support of the Instituto Nacional de Investigaciones Agropecuarias (INIA) through the Fondo de Promoción de la Tecnología Agropecuaria No. 82. The authors thank the institutions, farmers, and technicians for the field and laboratory work. Also, we sincerely acknowledge Ariel Szogui for the revision of the manuscript.