白浆土NH4+吸附特征的影响因素

摘要

To explore the rule and its influencing factors of nitrogen ( N) fertilizer adsorbtion on the albic soil for better in-struction of applying N fertilizer, equilibrium adsorption method was performed to study the effects of temperature, content of organic matter, oscillation time and ionic strength on the adsorption of NH4+ on the albic soil. The results shown that (1) with the initial concentrations of NH4+ increasing (0~1 000 mg/L), its adsorption capacity on the albic soil was also enhanced. When the initial NH4 +concentration exceeded 600 mg/L, the adsorption capacity gradually reached the saturated state. The increase of reaction temperature (293~313K) was helpful for the absorption. The changes of apparent thermodynamic param-eters (ΔG<0, ΔH>0, ΔS>0) indicated that the NH4+ adsorption process was spontaneous, endothermic and increased in degree of disorder; (2) The gradual decline of organic matter content with soil depth could lower the NH4+ adsorption capacity;(3) The sorption kinetics was affected by determinable oscillation time, which could be divided into the initial fast phase and the subsequent slow phase after 360 min. This dynamic process was fitted well by all the four selected equations; From the thermodynamic parameters of activation (ΔG≠ >0, ΔH≠ >0, ΔS≠ <0) calculated by the transition state theory, it was shown that the adsorption of NH4+ onto the albic soil was energy-consumed with increasing of the degree of order; (4) The dif-ferent concentrations of coexisting Na+ in a certain range had different influencing mechanisms on the adsorption of NH4+. When the concentration of Na+ exceeded 0. 4 mol/L, the adsorption would be enhanced. In all, the backward-shift N fertilizer application in the albic soil with high fertility could be helpful to enhance its utilization efficiency.%为探究白浆土对氮素的吸附规律及其影响因素,有效指导白浆土氮肥的科学施用,本研究采用平衡吸附法,研究了温度、有机质含量、振荡时间和离子强度等因素对白浆土吸附NH4+的影响,结果表明：(1)随初始NH4+浓度(0~1000 mg/L)的增加,白浆土对其吸附量也增加,当NH4+浓度≥600 mg/L时,吸附渐趋饱和,温度升高(293~313 K)有利于该吸附反应的进行,表观热力学参数(ΔG<0、ΔH >0、ΔS >0)的变化表明, NH4+在白浆土表面的吸附是自发、吸热且混乱度增加的过程。(2)剖面层次所引起的有机质含量递减亦会对白浆土吸附NH4+的数量有所抑制。(3)振荡时间影响白浆土吸附NH4+的动力学过程,该过程可分为起始的快速反应阶段及经过360 min后的慢速反应阶段,所选用的4个动力学方程均能较好拟合这一动态过程。应用过渡态理论所计算的活化热力学参数(ΔG≠>0,ΔH≠>0,ΔS≠<0)表明, NH4+在白浆土上的动力学吸附过程是耗能且体系有序度增高的过程。(4)共存Na+在其不同浓度范围内对白浆土吸附NH4+的影响机制各有不同,当Na+≥0．4 mol/L时,提升其浓度有利于NH4+在白浆土上的吸附。综上所述,在较高土壤养分含量条件下,后移施用氮肥则更有利于其利用率的提升。