リン酸Ca, Mg塩生成の影響を受けないリン酸保持容量の測定法ならびにそのリン酸保持容量と活性Al, Feの形態・含量との関係

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Phosphate sorption coefficient (PSC) has long been used to charcterize Andosols and to calculate the P rate for the amendment of poor P status in Andosols. For the determination of PSC, 25 g kg^<-1> of ammonium phosphate adjusted to pH 7 was added to a soil sample at a solution : soil ratio of 2 : 1. However, three problems were pointed out for the PSC as follows : (i) the reactivity of soil and phosphate depends on final phosphate concentrations, (ii) the PSC of most matured Andosols show similar values near the upper limit and (iii) the reason for a solution pH of 7 is not clear. Recently, it was further revealed that PSC was overestimated in Gley soils and Gray lowland soils due to the precipitation of CaHPO_4・2H_2O and MgNH_4PO_4・6H_2O. Hence a new method to determine phosphate retention capacity was developd to solve these problems. In the new method, 0.07 mol L^<-1> sodium phosphate solution adjusted to pH 4.3 using 0.1 mol L^<-1> of acetate buffer was added to soils at solution : soil ratios of 2 : 1, 10 : 1 and 40 : 1. Among them, using two results interposing a final phosphate concentration of 0.05 mol L^<-1>, phosphate retention capacity was calculated at the final phosphate concentration of 0.05 mol L^<-1>. The phosphate retention capacity was free from precipitation of CaHPO_4・2H_2O and MgNH_4PO_4・6H_2O in most Gley soils and Gray lowland soils. A linear relationship was observed between phosphate retention capacity and the content of oxalate-extractable Al (Al_0) plus half iron (Fe_0) for Andosols and non-allophanic Andosols. The atomic ratio of the PSC / (AL_0+Fe_0) was 0.16-0.21 for allophanic Ardosols and 0.32 0.38 for non-allophanic Andosols.
社団法人日本土壌肥料学会の論文
1998-04-05

リン酸Ca, Mg塩生成の影響を受けないリン酸保持容量の測定法ならびにそのリン酸保持容量と活性Al, Feの形態・含量との関係

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