施用生雞糞之土壤中銅、鋅之型態變化及移動性

Abstract

近年來農民大量開墾蘭陽溪上游河灘地與台地且施用大量生雞糞。由於生雞糞中含有重金屬銅及鋅，其濃度分別達到99.7 mg/kg及440.8 mg/kg，施用於農地後會有累積或溶出之虞，因此本研究針對重金屬銅及鋅利用序列萃取方式，了解重金屬於土壤中的型態，並利用動態模式模擬重金屬施用於土壤後型態的轉換及其移動，最後估計出最大的施用容許量。 蘭陽溪上游長期施用雞糞的河床地土壤測得的銅及鋅的濃度分別為154.9 mg/kg 及353.1mg/kg ，長期施用雞糞的台地土壤測得的銅及鋅分別為139.4 mg/kg及462 mg/kg，重金屬的濃度均超過台灣食用作物農地的監測標準（銅為120 ppm, 鋅為260 ppm），顯示農地有重金屬累積的情形。根據生雞糞序列萃取的結果顯示有53％的的銅及49％的鋅會與有機物結合。根據土壤農地的序列萃取結果顯示，在長期施用生雞糞的河床土壤有35％的銅會與有機物結合，長期施用生雞糞的台地土壤有40 ％的銅會與有機物結合，然而大部分的鋅會與土壤中的鐵錳氧化物結合。實驗室土壤管柱淋洗試驗之結果顯示，銅及鋅會從生雞糞上的有機結合態，轉換到土壤中的交換態、有機物結合態或是鐵錳結合態；或者是隨著灌溉水及入滲水移動而離開土壤系統中。因此土壤有機物質的分解會影響土壤中重金屬的移動。利用動態模式模擬出最佳的生雞糞土壤施用率為每年每平方公尺可施用1.35 公斤的生雞糞。

The speciations of copper and zinc, repectively, in poultry manure and soils from Yi-lan River basin have been investigated in order to establish a model to predict the movement of these two metals and to estimate the allowable rate of application of manure to farmlands. The total concentration of copper in tableland(LTt) and in riverbed(LTr) are 139.4 mg/kg and 154.9 mg/kg, respectively, which are higher than the concentration of copper in manure, 99.7 mg/kg. This observation indicates that there is accumulation of metals in the farmland soils due to the application of manure. Fifty three percent of copper and 49% of zinc in manure are associated with organic matter. Thirty five percent (35%) of total copper in riverbed soils and 39.9% of total copper in tableland soils are associated with organic matter, while most of zinc are in the form of oxide in soils. There are dynamic changes among different forms of metals in laboratory-scale soil columns with different treatment of manure.Copper and zinc were transformed from the organic form in amended manure to the exchangeable, organic or oxide-bound forms in soils, or removed from soil by infiltrating rainfall or irrigation waters. The rate of the decomposition of organic matter was strongly influence the movement of metals. By using a calibrated mathematical model, the amount of manure allowed to apply on the field was estimatedto be 1.35 kg/m2 per year, which is much less than the current application rate, 14 kg/m2 per year.