蔬菜地肥熟表层土壤中各形态磷的可淋洗性研究

肥熟表层是长期培肥形成的富磷表土层.为了解该类土层中积累磷的释放特性,本文选择了酸碱度和质地相差较大的5个代表性肥熟表层土壤样品,采用室内模拟淋洗和磷形态分析方法,研究了该类土层中磷的可淋洗性.结果表明,该类土层有很强的磷释放能力,从中释放出来的磷主要为无机态磷,其占总释放磷的86.68%～94.44%.可释放土壤磷的形态除水溶性磷(H2O-P)外,还有胶体表面吸附的无机磷(NaHCO3-Pi)、钙、镁结合态磷(HCl-P)、有机态P和土壤铁铝氧化物吸附的磷(NaOH-Pi)等形态;在淋洗过程中,H2O-P、NaHCO3-Pi和HCl-P的下降率分别达45.8%～58.1%、30.5%～43.2%和3.6%～49.0%.淋洗过程中磷的稳定性由低到高依次为水溶性磷和NaHCO3-Pi,而后期可能来自HCI-P.

Leachability of various phosphorus forms in vegetable soils with fimic epipedon

Fimic epipedon is a phosphorus-rich surface horizon which was formed in old vegetable soils. In order to understand the leachability of various phosphorus forms in the fimic epipedon, five samples of fimic epipedon with different pH and texture were collected from vegetable soils in Zhejiang province. All samples were packed in columns and leached with de-I-oned water at 0.4 mL/min for 6 h weekly. The forms of P in the soils were characterized and the leachability of different phosphorus forms in the soils was determined. Concentrations of inorganic P, organic P, Ca, Mg, Al, and Fe in the leachate were determined. Samples before and after leaching were subjected to P fractionation. The results showed that those soils had a strong potential to release phosphorus. Results of P-fractionation, solution speciation indicated that P lost from surface horizons during leaching was dominantly in inorganic forms associated with Ca and Mg, and the proportions of total P released from soils as inorganic P ranged from 86. 68% to 94.44%. Releasable P could be originated from water-soluble P ( H_2O-P) as well as NaHCO_3 extractable inorganic P (NaHCO_3-Pi) , HCl extractable P (HC1-P) , organic P and NaOH extractable inorganic P (NaOH-Pi). About 45. 8% -58. 1% of H_2O-P, 30.5%～43.2% of NaHCO_3-Pi, and 3.6% ～49.0% of HCl-P in the soils were lost during sixteen teachings. The release of water soluble P and NaHCO_3-Pi were more rapid than that of HCl-P. The stability of P in the soils increased in the order of water soluble P < NaHCO_3-Pi < HCl-P, organic P < NaOH-Pi < residual P. The stability of P in the soils decreased with increasing pH. The released P may be originated from water soluble P < NaHCO_3-Pi in the initial stage and from HCl-P in the last stage.