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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 NaHCO_3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。
The results of the determination of phosphorus, lime and aluminum hydroxide show that there are two possible mechanisms that lead to the disappearance of soluble phosphate fertilizer when it is applied to soil: <1> chemical precipitation. When the soil solution is in a neutral to slightly alkaline condition, the phosphate combines with calcium to form hydrated dicalcium phosphate. When the soil solution is strongly acidic (pH <3) (equivalent to the pH of the superphosphate fertilizers) Generate aluminum phosphate precipitate. <2> Adsorption. Under normal natural pH conditions, red soils have a strong ability to adsorb phosphate ions, such as Kowloon red soils, which absorb 138 mg of phosphorus per 100 g of soil. Inferred from the determination results of the iron phosphate aluminum, the fixed phosphorus in the strongly acidic soil is mainly in the form of amorphous aluminum phosphate. The solubility product constant (pK) of amorphous aluminum phosphate is around 28.5 (25 ° C) when the pH of the soil is <2-3, which is greater than that of other known aluminum phosphate salts. It can be inferred that when the superphosphate is applied in the red soil, the initial solid phosphorus salt in the fertilization hole has a higher validity than the insoluble phosphorus salt transformed in the later stage. 3. The huge P fixing capacity of red soils is due to the presence of sesquioxides that are several times higher in soils than other soils. The test result of the ferric hydroxide newly prepared in the laboratory also proves that it has strong phosphorus fixing ability. About 15.8% of the fixed phosphorus is salt-soluble quick-acting phosphorus; about half of the soluble phosphorus is 0.5N NaHCO 3, indicating that half of the fixed-bed phosphorus fertilizers in red soil may be effective for early crop growth. Soil fertilization point of phosphorus decline is a slow process. According to the rate of change of phosphorus in soil presumed, the effectiveness of the superphosphate on the crop will be very high, and then the effect may be lower. From the phosphorus value measured in 40 Zhejiang paddy soil samples, most of the phosphorus salt forms in Zhejiang paddy soil are not calcium phosphate salts. There was no correlation between phosphorus level and rice response to phosphate fertilizer.