菜园土壤磷素解吸模型与淋溶流失预测

Modeling desorption of soil phosphorus and prediction of leaching loss of P from gardening soils

为减少菜园土壤P面源污染,通过土壤解吸试验和种植叶菜的盆栽渗漏水收集试验,得到土壤P解吸模型,并建立解吸特征值与土壤渗漏水P浓度的关系.6种供试土壤的解吸试验表明,土壤镉解吸模型需经过修正才能较好地拟合土壤P解吸曲线,并求得土壤P可解吸量Q、土壤溶液初始P浓度和缓冲系数等解吸特征值.提出"双速率转折点"概念预测土壤P流失潜能,当耕层土壤P解吸特征值超过"双速率转折点"时,土壤渗漏水P浓度将以非线性形式显著增加.若以城镇污水处理厂污染物排放标准的二级标准(3mg/L)作为土壤渗漏水P的限值,则Q(水土比为20:1时的水溶性P)应<10.5mg/kg,并进一步得出各土壤的"环保施肥量".

In order to reduce non-point source pollution of phosphorus （P） leached out from the soils of vegetable gardens, a study employing both batch desorption and potted culture techniques was initiated. Data from batch desorption experiments were utilized to establish regression models for the desorption of P in soils. Desorption experiments with 6 types of soils showed that a previous published desorption model for cadmium （Cd） could be modified for better modeling of P desorption in soils. In fitting data with the modified model, parameters such as the quantity of desorption-liable P （QDLP）, the initial P concentration in the soil solution and the soil buffering coefficient were obtained. A new concept called ＂transition point for double-rate＂ （TPDR） was postulated to predict P loss potential from soils based on results from the potted experiments. Whenever the desorption characteristic values exceeded the TPDR, the P concentrations in tillage soil leachates experienced significant and rapid non-linear increases. If the second tier P concentration （3 mg/L） of the China national pollutant discharge standards for municipal sewage treatment plants is set as the upper limit for P concentration in garden soil leachates, QDLP can be calculated to be less than 10.5 mg/kg, assuming a water solution to soil solid ratio of 20 to 1. Accordingly, the highest permissible rates for P fertilization for different soils can be established and termed ＂environment-friendly fertilization rates＂ .