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Research of amendment application on the amelioration of profile cations and zinc pollution in a strongly acidic soil
Strong acid soil (pH < 5.5) is one of the major arable soils in Taiwan. Due to aluminium phytotoxic and calcium deficiency, the growth of the crop root is limited, and the quality and the yield of crops are often influenced in the acid soils. Potassium chloride is the most frequently used potassium fertilizier, however, it might cause the release of soil exchangeable aluminium and an increase in aluminium concentration in soil solution. In the other case, when is soil was polluted by heavy metals, it may cause not only an unfavorable influence to crop, but also give a detrimental effect to human health. Limed the pollued soils with various anions, the adsorption and mobility of heavy metal in the soil profile may be influenced which may result in a decrease in the performance of the limings. This study includes two tests, the first test is to investigate the influences of amendment addition on the acidity, the availabilities of cations, and particularly the changes of exchangeable Al in a KCl treated soil. Our purpose is to establish a suitable practice for both the amelioration of soil acidity and the management of K fertilizer. The second test is to evaluate the effects of Ca amendment on the mobility cation and the amelioration of zinc polluted profile soil.
In the study, Huan-Si strong acid soil was selected to conduct a column leaching experiment. The column was packed in a way similar to the Huan-Si soil profile soil. In the test one, 200 mg K kg-1 potassium chloride was mixed with the top 10 cm soil in each column and incubated for 7 days, then different amendments were mixed with 0 ~ 20 cm soil, the treatments including lime, gypsum, and animal compost. A total of 2500 mm deionized water, which equals the amount of one-year rainfall in Taiwan, were added for 120 days. After the leaching experiment and standing for 7 days, some properties of the soil were determined, including pH, exchangeable Ca, Mg, Na, and Al, solution K, exchangeable K, and non- exchangeable K. In the test two, 650 mg Kg-1 ZnCl2 was mixed with the top 5 cm soil in each column, and was incubated under drying-wetting cycles for three weeks. Then, different amendments were added with mixing, the treatments including lime, gypsum, and calcium citrate. A total of 1250 mm deionized water, which equals the amount of half-year rainfall in Taiwan, were added for 60 days. After the leaching experiment, a portion of soil properties were determined, including pH, exchangeable Ca, Mg, K, Na, and Al, HCl -extraction Zn, total Zn, and the forms of Zn were determined by the sequential extraction method.
The results of test one showed that an increase in the content of exchangeable Al in the subsoil and a decrease in soil pH were observed while soil was treated with KCl. The results indicate that KCl may lead to some detrimental effects for KCl treated soils such as Al toxicity. The lime addition reduced the content of exchangeable Al down to 40 cm depth and increased the content of exchangeable Ca down to the 60 cm depth of the soil profile. Aminal compost treatment also reduced the contents of exchangeable Al down to the 70 cm depth of the soil profile, especially in the soil profile of 0 ~ 30 cm. The results of test two showed that the application of lime and calcium citrate could increase significantly soil pH. Besides, this application could reduce mobility and availability of zinc in soil. Gypsum and calcium citrate could barely elevate soil pH which may keep zinc mobile in the soil and may be easily leached out of the top soil by added Ca. Treatment with Ca nitrate increased significantly in the mobility of znic in soil profile. However, this treatment may simultaneously decrease the exchangeable Mg in the soil profile. As a result, the crop growth could be inhibited due to the lack of Mg.
本研究係以管柱分層方式分別模擬強酸性之關西土壤剖面。試驗一乃先於表土0 ~ 10 cm中添加200 mg kg-1的氯化鉀，待培育7天後再分別於土壤0 ~ 20cm施用石灰、石膏及禽畜糞堆肥，並模擬台灣年雨量約2500 mm，以去離子水淋洗120天，期間測定淋洗液之pH、EC、鈣、鎂、鉀及鈉濃度。待淋洗完成後並靜置7天後，將土壤分層取出，測定各處理各土層土壤之pH、交換性鈣、鎂、鈉、鋁及各型態鉀。試驗二之鋅污染改良試驗中，先將表土0 ~ 5 cm土壤添加650 mg kg-1的氯化鋅，乾濕培育三週後再分別施用石灰、石膏、硝酸鈣及檸檬酸鈣等質材，再以去離子水模擬降雨淋洗土柱，期間測定淋洗液之pH、EC、鈣、鎂、鉀、鈉及鋅濃度，待淋洗完成後，取出各處理各土層土壤，測定土壤pH、交換性鈣、鎂、鉀、鈉、鋁、鹽酸萃出性鋅及總鋅量，並以專一萃取劑連續萃取法測定各型態鋅的含量。
試驗一之結果顯示，於強酸性土壤施用氯化鉀將增加底層土壤之交換性鋁含量，並降低其剖面土壤pH，而加重剖面酸性及交換性鋁含量潛在問題。石灰之施用可降低0 ~ 40公分土壤之交換性鋁含量，並增進0 ~ 60 公分土層土壤之交換性鈣含量。石膏之施用對土壤pH的提昇效應不彰，但能顯著降低整個剖面土壤交換性鋁含量及增進交換性鈣含量。石灰和石膏之處理會降低交換性鎂及鉀之含量，故欲施用此兩種質材來改善強酸性土壤時，宜顧及鎂肥及鉀肥之補充。禽畜糞堆肥處理亦可降低整個剖面土壤之交換性鋁含量，尤其以30公分內土壤最為顯著。由於禽畜糞堆肥本身亦含有鈣、鎂、鉀及鈉，施用禽畜糞堆肥故能增進整個剖面土壤之交換性鈣、鎂、鉀及鈉含量。
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