不同pH降雨淋溶对原状水稻土土壤酸化的影响

Effect of Leaching of Simulated Rain With Different pH Values on Soil Acidification of Original Paddy Soil Column

采用原状土柱定时定量淋溶的方法,用pH为2.5,4.5和6.5的模拟降雨淋溶了太湖地区典型的水稻土-黄泥土,淋溶量为5 L/柱,研究原状土柱土壤淋溶后酸碱性变化及盐基离子的淋洗规律。结果显示,不同pH降雨淋溶后,土壤仍处在初级缓冲体系,即阳离子缓冲体系,但大量的盐基离子被淋溶出土体,淋出液的pH都在7.4以上,各淋溶处理淋出量最大的是Ca2+,淋出率最高的则为Mg2+,Na+和K+淋出量明显小于前两者,K+淋出量则最小,各处理间的各盐基离子的淋出量随淋溶液pH的降低而上升。淋溶后的土柱土壤pH和酸碱缓冲容量都出现下降,与淋溶前土壤相比,pH 2.5的处理0-10 cm土层和10-20 cm土层,土壤pH下降0.65,0.30个单位;pH 4.5的模拟降水处理降幅分别为0.42,0.04个单位;pH 6.5的模拟降水降幅为0.08,0.15个单位,各处理20-40 cm土层的pH则受模拟降雨的影响较小;同时采用酸碱滴定法测定了初级缓冲体系下各处理土壤的酸碱缓冲容量,结果显示0-10 cm土层,土壤酸碱缓冲容量降幅最大,和试验前处理土壤对应的土层相比,pH2.5,4.5,6.5的降雨处理降幅分别为31.83%,19.58%,15.59%;各pH 2.5,4.5,6.5的降雨处理10-20 cm土层降幅分别为23.93%,14.73%,7.17%,而各降雨处理20-40 cm土层降幅都小于5%。研究表明,虽然模拟半年度不同pH降雨淋溶处理下,大量盐基离子从土体表层被置换淋洗,导致表层土壤pH的降低,相比之下,不同pH的模拟降雨对土壤的酸化作用随pH的降低而上升。虽然淋溶后各处理土壤仍处在初级缓冲体系,但其表层土壤酸碱缓冲容量的下降必将加速土壤的进一步酸化。

Original Hydromorphic paddy soil columns were used to study cation leaching and soil buffering capacity by simulated acid rain with pH values at 2.5, 4.5 and 6.5 in Tai Lake region. The results obtained were listed as follows. With the leaching amount at 5 liters per column, massive cations were leached out of the soil, causing high pH of 7.4 in the leachate, even though the soil was still in primary buffer system, i. e. cation buffer system. Calcium and potassium were leached out the most and the least in quantity while magnesium was leached out in the highest efficiency. The leaching amounts of cation were increased by the decreased pH of the leachate. The pH values and buffer capacity of the soil in the column were reduced after leaching. Compared to the control treatment, the pH of the 0 to 10 cm soil layer were reduced by 0.65, 0.42 and 0. 08 leached by pH 2.5, 4.5 and 6.5 simulated acid rain, respectively. In the soil layer of 10 to 20 cm, the pH were reduced by 0.30, 0.04 and 0.15 leached by 2.5, 4.5 and 6.5 simulated acid rain, respectively. The pH of 20 to 40cm soil layer was less affected by the simulated rain for all the treatments. The soil buffer capacity of the primary buffer system was determined by acid-base titration. The buffer capacity of 0 to 10 cm soil layer decreased most. Compared to the pretreated soil, the pH 2.5, 4.5 and 6.5 simulated rain lowered the soil pH by 31.83%, 19.58% and 15.41%, respectively. The pH of 10 to 20 cm soil layer was decreased by 23.93%, 14.73% and 7.17%, which were less than 0 to 10 cm soil layer, when leached by pH 2.5, 4.5 and 6.5 simulated rain, respectively. However, the pH of 20 to 40 cm soil layer was reduced less than 5~. The above results suggest the decreased pH in soil surface was caused by the leaching of a large amount of base cations from soil surface. The reduction in soil buffer capacity could accelerate the acidification of the soil, although the simulated rain treated soil was still in primary buffer system.