【摘要】 1.磷位、石灰位和氢氧化铁铝位等的测定结果表明,当磷肥施入土壤后,导致溶性磷肥消失的机制可能有二:<1>化学沉淀。当土壤溶液处于中性至微碱性条件下,磷酸根与钙结合,生成水化磷酸二钙;当土壤溶液出现强酸性（pH<3）时（相当于过磷酸钙施肥穴的pH）,生成磷酸铁铝沉淀。<2>吸附作用。在一般自然pH条件下,红壤具有强大吸附磷酸离子的能力,例如九龙红壤,每百克土壤吸附磷量达到138毫克。2.从磷酸铁铝位的测定结果推理,在强酸性土壤中的固定磷,主要呈无定形磷酸铝铁形态存在。当土壤pH<2—3时,无定形磷酸铝的溶度积常数（pK）大约在28.5上下（25℃）,较其他已知的各种磷酸铝盐溶度为大。由此推论,红壤施用过磷酸钙时,施肥穴中最初出现的固态磷盐比之后期转化形成的难溶性磷盐有较高的有效度。3.红壤的巨大固磷能力是由于土壤中存在着比其他类土壤高出数倍的倍半氧化物。用实验室新制备的氢氧化铁试验结果也证明它有强大固磷能力。被固定的磷约有15.8%是盐溶性速效磷;约半数为0.5N NaHCO₃可溶性磷,表明红壤中由于活性铁所固定的磷肥可能有半数对作物早期生长有效。4.土壤施肥点磷位下降是个缓慢过程。根据土壤中磷位变化的速度推测,过磷酸钙对当季作物的有效度将会相当高,而后效则可能较低。5.从40个浙江水稻土样测得的磷位值看,浙江水稻土的磷盐形态,大多数不是磷酸钙盐。磷位和水稻对磷肥反应之间无一定的相关性。更多还原

【Abstract】 1. A comparison of the solubility diagram of the phosphate compounds in soils with the measured curves showing the actual relationships between phosphate potentials and lime potentials and between phosphate potentials and aluminum （or ferric） hydroxide potentials reveals that there may exist two mechanisms of phosphate fixation.（1） Chemical precipitation: In the near neutral to slightly alkaline range, the soluble phosphates may combine with calcium to form dicalcium phosphate, CaHPO₄·2H₂O （near neutral soil）, and calcium octaphosphate, Ca₄H（PO₄）₃·3H₂O. But under strongly acid conditions （pH<3.1. Such a low pH may be found near the point of placement of superphosphate）, precipitation of phosphates with iron and aluminum may be expected.（2） Adsorption （mostly chemi-sorption）: In their natural acid range, the high phosphate fixation capacity of red earths may be ascribed mainly to the presence of the active adsorption surface of sesquioxides （or their hydroxides）.As the pH value increases, the role of adsorption mechanism tends to decrease.2. The removal of active sesquioxides from red earths by dithionite and fluoride treatments resulted in a marked decrease in phosphate fixation capacity. It is evident, hence, that the high fixation capacity of red earths is primarily due to the abundance of active sesquioxides. Laboratory studies showed that only about 15.8% of the sesquioxides adsorbed phosphorus was salt soluble, while as much as half of the adsorbed phosphorus was extracted by 0.5 N NaHCO₃ solution. The results suggest that much of the phosphorus fixed by acid red earths may still be available to crops for their early growth.3. Judging from the change of phosphate potential values, it appears that the main forms of fixed phosphates under strongly acid conditions are amorphous iron and aluminum phosphates （the latter being probably predominant）. The chance for the formation of strengite at the initial stage of fixation seems to be rare.The solubility product （pK） of amorphous aluminum phosphate as calculated from its potential values was about 28.5 at 25℃. Owing to its greater solubility than other forms of aluminum phosphates which may form in the latter stage of fixation, it would be more available to plants for their early growth even though it is a product of phosphate fixation in the region of fertilizer placement.4. Studies on the phosphate potential of 40 paddy soils collected from zhejiang province showed that their phosphate potentials were mainly controlled by the adsorbed phosphate. No definite correlation was found between the measured phosphate potential and the response in the yield of rice to phosphorus fertilization.更多还原