从不同浸提剂所浸出的磷酸盐形态探讨几种速效磷测定方法的意义

在前一报告中^1],作者通过室内化学分析及生物试验证明,在所试的六种测定土壤有效磷的方法中,以Olsen的0.5M NaHCO₃法与生物反应的相关性最好,马乞金的1%(NH₄)₂CO₃法和Radet的3.5%柠檬酸钠法次之,Egner-Rim的乳酸钙法、Burriel-Hern-ando的混合浸提液法和Joret-Herbert的草酸铵法又次之。另外,从浸提出的磷量看,碳酸氢钠法、马乞金法和柠檬酸纳法相当接近,可以列为同一数量级。乳酸钙法、混合浸提液法和草酸铵法浸出的磷量也很接近,可以列为另一较高的数量级。

APPRAISAL OF THE METHODS OF DETERMINING AVAILABLE FORMS OF PHOSPHATE EXTRACTED FROM SOILS

The forms of phosphate extracted from soils by various methods were established by calculation according to the law of solubility product. Ammonium carbonate solution may extract water soluble phosphates, CaHPO₄·2H₂O, CaHPO₄, Ca₄H(PO₄)₃·3H₂O,aluminum and iron phosphates, a little organic phosphorus and probably a little Ca₃(PO₄)₂, and Ca₅(PO₄)₃OH,similarly sodium carbonate solution may extract the same phosphates except those in organic forms. Sodium citrate solution extracts water soluble phosphates, CaHPO₄·2H₂O, CaHPO₄, aluminum and iron phosphates, and a little organic phosphorus. Lactate solution and Burriel-Hernando's extractant extract all forms of calcium phosphates in soils, but not aluminum and iron phosphates as well as organic phosphorus. Ammonium oxalate solution extracts all the above forms of phosphate from soils.Recovery test made on CaHPO₄, Ca₃(PO₄)₂ and FePO₄·4H₂O confirmed the results from calculation.The difference in the degree of correlation between the available phosphorus content as determined by the various methods and the response of crops to phosphorus fertilization was explained by the forms of phosphate extracted and the present knowledge of their availability.