Using Soil P Tests and P-Sorption Index to Predict P Requirement for Cassava Grown in Tropical Upland Sandy Soils

• Published in: Communications in Soil Science and Plant Analysis 2023-02, Vol.54 (3), p.311-325
• Main Authors: Ratanavirakul, Pinyaluk, Thanachit, Suphicha, Anusontpornperm, Somchai, Kheoruenromme, Irb
• Format: Article
• Language: English
• Subjects: Availability; Biological fertilization; Calcium chloride; Cassava; Fertilization; Fertilizer application; Fertilizers; Loamy sand soils; P availability indices; P fertilizer rate estimation; Phosphorus; Phosphorus pentoxide; Sandy soils; Soil; Soil fertility; Sorption; upland soils
• ISSN: 0010-3624; 1532-2416; 1532-4133
• DOI: 10.1080/00103624.2022.2112591

The phosphorus (P) sorption index and efficiency of P extracting methods were investigated to quantify the available P content for accurate recommendations regarding cassava P fertilizer application in the sandy soils of Thailand. Phosphorus sorption isotherms were examined to predict the response of soils to the P fertilizers applied. Six rates of P fertilizers (0, 12.5, 25, 37.5, 50 and 62.5 kg P 2 O 5 ha −1 ) were applied in a randomized complete block design at five field sites in major cassava-growing areas. The efficiency among the Bray II, CaCl 2 and Mehlich III extracts was also tested by comparing their capacity to predict crop response. The P adsorption capacities of all soils were in the range 39.4-106 mg kg −1 ; therefore, there were classified as low P-sorbed soils. Phosphorus fertilizer produced significantly higher aboveground biomass than did zero-P fertilization. The critical P level adequate for 95% of the maximum yield was in the range 0.14-0.26 mg P L −1 . The equation for calculating P fertilizer using soil P extracted based on the Bray II, CaCl 2 and Mehlich III methods had accuracy levels of 73, 65 and 72%, respectively. Bray II was slightly superior to Mehlich III for use in soil-P availability indices, both of which were recommended for P fertilizer assessment.