Response to Phosphorus of Cranberry on High Phosphorus Testing Acid Sandy Soils

Abstract

The fertilized sand‐grown cranberry (Vaccinium macrocarpon Aiton cv. Stevens) could be at risk for water contamination by P during seasonal flooding and drainage, especially in high‐P soils. The P diagnosis is usually conducted from soil and tissue tests but should also include water‐extractable P (PW) as an environmental index. Although the Bray‐1 P (PBray1) test is the current test for cranberry soils, the Mehlich‐III (M‐III) test is now commonly used in Quebec and the mid‐Atlantic USA as an agri‐environmental index with specified thresholds. Our objective was to relate the (P/[Al+Fe])M‐III molar ratio to PW and PBray1 and to evaluate this ratio against yield and tissue P responses to added P in high‐P sand‐grown cranberry crops. Fertilizer trials were conducted during the 2001 to 2004 period at rates of 0, 13, 26, and 39 kg P ha−1 yr−1 on permanent plots at five locations in central Quebec. The slope of the relationship between the (P/[Al+Fe])M‐III molar ratio (range: 0.024–0.094) and PBray1 (60–235 mg P kg−1) was 0.0004 (R2 = 0.92). There were significant site and year effects but no significant effect of added P on berry yield. There were significant linear effects of added P on tissue P concentration in the range of 0.9 to 1.4 g P kg−1 but no critical value could be defined. The simulated (P/[Al+Fe])M‐III environmental threshold (9.7 mg PW kg−1) was 0.113. The (P/[Al+Fe])M‐III molar ratio could be used interchangeably with PBray1 in Quebec sand‐grown cranberry crops but the provisionary environmental threshold must be ascertained from drainage water monitoring.