长期施磷黑土中磷的吸附–解吸特征及其影响因素

  【目的】  比较长期不施磷与施磷黑土对外源磷的吸附–解吸特征，为黑土区磷素管理提供理论基础。  【方法】  供试黑土长期定位试验位于吉林省公主岭市，始于1990年。2018年选择其中不施肥(CK)，施氮钾肥(NK)，施氮磷钾肥(NPK)和氮磷钾+有机肥(NPK+M) 4个处理小区，采集0—20、20—40和40—60 cm土层的土壤样品，分析了土壤理化性质，采用恒温平衡法测定了土壤磷的吸附–解吸特征，并由此计算得到磷最大吸附量(Q_m)、吸附亲和力常数(K_Q)、最大缓冲容量(MBC)、磷吸附饱和度(DPS)、最大解吸量(D_m)和解吸率(D_r)。  【结果】  随着平衡溶液中磷浓度的增加，磷的吸附量与解吸量均呈先快速增加后逐渐趋于平衡的过程。与不施磷处理(CK和NK)土壤相比，施磷处理(NPK、NPK+M)减少了磷的吸附量，增加了磷的解吸量。与不施磷处理相比，施磷处理在0—60 cm剖面上的Q_m和MBC值分别降低了4.94%～63.46%和15.90%～75.18%，D_r值增加了8.52%～474.0%，以NPK+M处理变化量最大。施磷处理比不施磷处理在0—60 cm土壤剖面上全磷和有机质含量分别增加了34.40%～145.5%和12.77%～50.07%，游离态铁铝氧化物(Fe_d+Al_d)含量降低了5.14%～11.35%。冗余分析表明，不施磷处理土壤的有机质、Fe_d+Al_d和全磷，以及施磷处理中的Fe_d+Al_d、络合态铁铝氧化物(Fe_p+Al_p)、pH和有机质是影响磷吸附解吸特征参数的主要土壤因子，分别解释了不施磷和施磷处理全部变异的77.59%和90.62%。土壤有效磷(Olsen-P)与磷吸附饱和度(DPS)相关关系表明，所研究的黑土DPS环境界限值为8%左右，NPK+M处理中3个土层的DPS_M-P值(由Mehlich-3 浸提的磷、铁和铝计算)为7.77%～25.96%，DPS_O-P值(由Olsen-P和Q_m计算)为17.24%～24.75%，均高于此环境界限值，具有磷素流失的风险。  【结论】  长期施磷降低了黑土对外源磷的吸附量，增加了磷解吸量。长期不施磷肥，土壤对磷的吸附和解吸主要受有机质、游离态铁铝氧化物的影响。而长期施肥，特别是有机肥与化肥配合处理，土壤中游离态和络合态铁铝氧化物、有机质及pH是影响磷吸附解吸特征的主要因素。

Phosphorus adsorption and desorption characteristics as affected by long-term phosphorus application in black soil

  【Objectives】  Comparison of P adsorption-desorption characteristics in long-term soil treated with and without P fertilizer can provide a theoretical basis for P management in black soils.  【Methods】  The long-term field trial on black soil started in 1990 in Gongzhuling City, Jilin Province. The four treatments were no fertilizer (CK treatment), nitrogen (N) and potassium (K) fertilizers (NK treatment), NPK fertilizers (NPK treatment), and NPK + manure (NPK+M treatment). We analyzed soil physicochemical properties. Soil P adsorption-desorption characteristic parameters maximum adsorption capacity (Q_m), adsorption constant (K_Q), maximum soil P buffering capacity (MBC), degree of P sorption saturation (DPS), maximum desorption capacity (D_m), and desorption ratio (D_r)] in different soil layers were determined using isothermal adsorption and desorption experiment.   【Results】  The adsorbed and desorbed P increased initially and stabilized with increasing P concentration in the equilibrium solution. Compared to the untreated soil, the adsorbed P decreased, and desorped P increased in the soil treated with P fertilizers. Compared to the untreated soil, Q_m and MBC decreased by 4.94%?63.46% and 15.90%?75.18%, while D_r increased by 8.52%?474.0% in the 0?60 cm soil profile. Notably, the most significant changes were recorded in the NPK+M treatment. The long-term P input increased total P and soil organic matter (SOM) by 34.40%?145.5% and 12.77%?50.07%, decreased the free iron and aluminum oxide (Fe_d+Al_d) by 5.14%?11.35% in different soil layers compared to the soil without P fertilizer. SOM, Fe_d+Al_d, and total P in the soil without P fertilizer (P<0.05), as well as Fe_d+Al_d, organic-bound iron and alumina oxide (Fe_p+Al_p), pH, and SOM in the soil with P fertilizers were the main factors influencing the differences in the characteristic parameters of P adsorption and desorption. The main factors explained 77.59% and 90.62% of the total variation in the soil without P and with P fertilizers, respectively. The correlation between Olsen-P and DPS showed that the DPS threshold value for environmental purposes was about 8%. The DPS_M-P (calculated by Mehlich-3 extractable P, Fe, and Al) and DPS_O-P (calculated by Olsen-P and Q_m) ranged from 7.77% to 25.96% and 17.24% to 24.75%, respectively, in 0?60 cm soil profile in NPK+M treatment, which far exceeded the threshold, increasing the risk of P loss.   【Conclusions】  Our research suggests that long-term exogenous P input decreases adsorbed P and increases desorbed P, respectively. SOM and Fe_d+Al_d are the main drivers of P adsorption and desorption characteristics in soil without P fertilizer. In the soil treated with combined P fertilizer, especially NPK fertilizers and manures, Fe_d+Al_d, Fe_p+Al_p, SOM, and pH were the main factors affecting the P adsorption and desorption characteristics.