Release of soil phosphate by sequential extractions as a function of soil properties and added phosphorus |
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| Abstract: | Abstract A study of sequential phosphate (P) extraction by water and iron oxide‐impregnated paper strip procedures was carried out on three Italian soils ranging widely in soil characteristics and enriched with three rates of fertilizer P. The degree of change was dependant on P addition, soil P properties, and type of extraction. For the Fe‐oxide strip procedure, a greater release of P than for water extraction was observed for soils with and without added P. At a given level of added P, more P was released from the soil with the lowest P sorption index (SI). However, at a given level of NaHCO3‐extractable P, less P was released from the soil with lower SI than from soil with a higher SI, indicating that a greater available P content was necessary for low P sorbing soils to maintain a given rate of P release. The variation of SI accounted for 96% and 92% of the variation in amount of water‐extractable and Fe‐oxide strip P at a given P addition. Furthermore, SI accounted for 97% and 98% of the variation in water‐extractable and Fe‐oxide P at a given increase in available soil P. Inclusion in a soil testing program of an estimate of the P Sorption Index, that accounts for the overall effect of soil properties affecting sorption in soils (clay content and type, iron and aluminum oxide content, surface area, etc.), may improve fertilizer P requirements for optimum crop growth for certain soils. |
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