土壤酸化是土壤质量退化的重要形式。土壤酸化本是一个自然过程，其速度非常缓慢，但近几十年来，由于工业飞速发展导致酸沉降的增加，人为活动如施肥及耕作作用大大加速土壤酸化进程。目前土壤酸化发生机制、时空演变规律及其恢复重建等已成为土壤退化研究的重要组成部分，成为21世纪国际土壤学、农学及环境科学界共同关注的热点问题。 本文利用江苏地区典型水稻土和潮土长期定位试验，研究了长期不同施肥对酸碱缓冲容量及土壤酸化速率的影响，并结合土壤添加秸秆、猪粪等培养试验、施氮及模拟酸沉降试验，对土壤酸化的关键影响因素、不同致酸因子的贡献进行了较系统的研究。主要结果如下: 1） 与第二次土壤普查结果相比，太湖地区6 类水稻土pH 和CEC显著下降，降幅分别为1.1个单位和8.3 cmol(+) ·kg-1，土壤pH的内梅罗指数分别由1982年的2.69~ 2.91（平均2.82）下降为2004年的1.73~2.41（平均2.05），成为土壤肥力单因子质量指数最低指标；江苏淮北潮土的土壤肥力限制因素也从有效养分低演变为土壤pH的降低，表明土壤酸化已成为影响江苏典型土壤肥力质量的主要限制因子。 2） 太湖地区黄泥土长期定位试验采用裂区设计，主处理为施用有机肥与不施有机肥处理，副处理分别为不施肥、施氮肥、施氮磷肥、施氮钾肥、施氮肥+水稻秸秆、施磷钾肥、施氮磷钾肥，共14个处理。26年长期不同施肥后，不同处理pH降低了0.38~1.39，土壤酸化速率为0.50~1.74 kmol H+ hm-2a-1，酸化修复所需CaCO3用量为24.7~87.1 kg·hm-2·a-1。各处理土壤pH以施磷钾肥处理(CPK)为最高（pH 6.42），纯空白对照（C0）次之（pH 6.38），施氮肥结合有机肥及秸秆处理（MRN）最低（5.41）；各处理土壤酸化速率以施磷钾肥(CPK)处理最低，施氮肥结合有机肥及秸秆（MRN）处理最高，施用氮肥基础上增施有机肥促进土壤酸化，其酸化速率大于单施化肥处理。增施有机肥及秸秆处理土壤缓冲容量保持稳中有升，这主要与土壤有机质的提升有关；而pH的下降则与盐基离子含量的下降有关。 3） 淮北地区黄潮土长期定位试验共设9个处理，采用裂区设计，主处理1：不施有机肥；副处理：①空白对照（CK，不施肥）、②施氮肥（N）、③施氮磷肥（NP）、④施氮钾肥（NK）、⑤施氮磷钾肥（NPK）。主处理2：施有机肥；副处理：①不施化肥（M）、②施氮肥（NM）、③施氮磷肥（NPM）、④施氮磷钾肥（NPKM）。30年连续不同施肥后，徐州石灰性潮土土壤pH降低0.41~0.70；不同施肥处理耕层土壤酸碱缓冲容量为15.82~21.96 cmol·kg-1，施用化肥促进土壤酸化加速，单施氮肥酸化程度最高，而化肥配施有机肥处理则缓解土壤酸化加速。长期不同施肥下石灰性潮土仍处于碳酸钙缓冲体系，该体系下，有机质对石灰性潮土土壤酸碱缓冲体系影响较弱。长期不同施肥显著改变0~40 cm层土壤的碳酸钙和活性碳酸钙含量，且活性碳酸钙含量在剖面中的分异变化比碳酸钙大，其含量与土壤酸碱缓冲容量达到极显著正相关关系，表明长期施肥管理下，土壤活性碳酸钙更能敏感反应土壤基本理化性状的变化。 4） 3年田间小区试验研究了等氮量下不同鸡粪和尿素配比对水稻生长和土壤酸化的影响，鸡粪和尿素配比处理获得较高产量， 50％鸡粪处理产量最高。各施肥处理土壤酸碱缓冲容量为2.07~2.36 cmol·kg-1，随鸡粪施用比例上升而上升，各处理土壤酸碱缓冲容量与土壤有机质含量、CEC变化趋势一致，其相关系数分别达到极显著、显著相关，显示等氮量下，提高鸡粪施用比例导致土壤盐基离子的累积和有机质的提升是导致土壤酸碱缓冲容量增加的主要原因。 5） 室内添加不同氮含量及用量水稻秸秆培养试验表明，各处理土壤0~40 cm层pH降幅为0.01~0.99，总致酸量为56.77~136.18 mmol，对相同氮含量秸秆，致酸量随秸秆用量增加而增加，但相同用量下氮含量不同的秸秆间差异较小，增加外源氮量，总致酸量随施氮量增加而上升；各处理致酸因素中，HCO3—致酸量占总量的比例为82.01%~92.97%、氮淋溶致酸量占总酸量的比例为6.92~13.04%，淋溶致酸随秸秆用量和施氮量的提高而上升，但低氮秸秆和高氮秸秆间HCO3—致酸量相差较小，但氮淋溶致酸量差异较大；有机阴离子循环的致酸比例为0.11~9.98%，其趋势同氮淋溶相一致；而外源H+所占比例较弱，仅为0.001~0.005%。 6） 室内添加不同量猪粪培养试验结果表明，猪粪添加量小于40 mg·kg-1时，土壤盐基离子Ca2+、Mg2+、K+、Na+的净淋失量随猪粪添加量增加而上升。试验土壤的酸碱缓冲容量、有机质含量均随猪粪施用量上升呈上升趋势，添加猪粪后，有机质在试验土壤的酸碱缓冲体系中占有主导作用。 7） 室内比较了3个pH梯度降雨和3水平施氮量对水耕铁渗人为土土壤酸化的影响。不同pH降雨及施氮处理土壤的酸度累积量为4.73~15.57 mmol H+每柱，以pH 6.5降雨不施氮处理、pH 2.5添加高氮量（N2）处理酸化速率为最低和最高，相同pH降雨下，致酸量随施氮量增加而上升；不施氮处理土壤酸度累积随降雨pH降低而增加，但中施氮量（150 mg·kg-1土）和高施氮量（300 mg·kg-1土）下，pH 4.5处理土壤酸度累积量则小于pH 6.5处理；不同降雨及施氮处理NO3—淋溶致酸量为4.32~12.88 mmol每柱，NH4+淋溶消耗H+量为0.01~0.29 mmol每柱；正常酸沉降（pH 6.5）下，中施氮量和高施氮量处理致酸量都大于各梯度pH降雨的致酸量。以上结果表明，单施氮处理的致酸量大于单纯的酸沉降处理，而无论是降雨还是施氮，NO3—淋溶在加速土壤酸化进程中占主导作用。 总之，对于江苏省太湖地区的黄泥土，土壤酸碱缓冲体系处于硅酸盐和盐基离子缓冲体系，该体系下其酸碱缓冲容量的变化受有机质的影响较大，而硝态氮的淋溶和盐基离子的淋失及移出在加速土壤酸化进程中可能占主导作用；江苏淮北潮土则处于碳酸钙缓冲体系，在施用化肥的基础上增施有机肥有减缓土壤酸化的趋势；和模拟不同pH降雨相比，施氮的致酸强度大于降雨，且NO3—的淋溶为致酸量的关键因素。黄泥土酸化的加速可以通过增施石灰、合理的养分管理及轮作方式来缓解或控制。

Soil acidification is a naturally occurring phenomenon and is usually caused by long-term addition of protons to the upper layers of soil and subsequent leaching of exchangeable bases. In recent decades, due to the rapid development of chemical and petroleum industries and frequent agricultural practices including fertilization and crop rotation, soil acidification became more accelerated, which is one of the important soil degradation. In this paper, incubation experiments as well as long-term field experiments in typical paddy soil and alluvial soil in Jiangsu Province were carried out to study acid deposition and nitrogen application on soil acidification rates, the key factors of soil acidification, the characteristics of various factors and their contributions to soil acidification. Analysis on the 198 soil samples among 6 categories of paddy soil in Tai Lake region in 2004, showed that the organic matter content, total N, available P and K concentration were significantly improved while pH and CEC were reduced by 1.1 unit and 8.3 cmol·kg-1, respectively, compared to the results obtained from the Second National Soil Survey. The pH index of fertility, decreased from 2.69~2.91in 1982 to 1.73~2.41in 2004, becoming the lowest single soil fertility index. Soil limiting factor of low contents of available nutrients in the Second National Soil Survey is now replaced by those of shallow cultivated horizon, increased soil density and reduced soil pH in North Huai in Jiangsu Province. Over 26 years of different fertilization, the acidification rate of the paddy soil in Tai Lake region was 0.50~1.74 kmol H+ hm- 2a-1, and lowest and highest soil acidification rates appeared in the control treatment (no fertilizer) and the treatment of urea plus pig manure and rice straw application, respectively. The required amounts of CaCO3 were 24.7~87.1 kg·hm- 2·a-1 among all treatments. The pH of major plot of chemical fertilizer (6.10) was 0.33 higher than the main plot of organic fertilizer addition. Na+, K+, Ca2+ and Mg2+ concentrations in chemical fertilizer plots were 5.24, 2.05, 39.87 and 9.04 mmol·kg-1, which were 2.7%, 54.1%, 3.1% and 13.4% higher than the corresponding organic fertilizer addition plots, irrespectively. Significant differences were found in K+ and Ca2+ concentration between the two major plots. The soil pH was highest in P and K fertilizer application treatment (pH 6.42), followed by the control treatment (pH 6.38), the treatment of N plus organic fertilizer and rice straw addition was the lowest (pH 5.41), and the main plot with pig manure additional got a low concentration of cation, indicating that the lower pH in the major plot of organic fertilizer amendment might be due to transfer of base cations from soil to plant. The exhaustion of base cations occurred when the yield increased. The buffer capacity of soil amended by organic fertilizers (2.18 cmol kg-1) was slightly higher than the chemical fertilzer treatment (2.14 cmol·kg-1). Soil buffer capacity was positively correlated to soil organic matter content, and soil pH value decline was due to the cation depeletion. Soil pH, CaCO3 and active CaCO3 contents, soil buffer capacity significantly changed over continuous 30-year fertilization on Alluvial soil in Xuzhou City. The topsoil pH was decreased by 0.41-0.70. The soil buffer capacity, ranging from 15.82 to 21.96 cmol·kg-1, was lowest in sole N treatment and highest in the treatment of manure plus NPK. The soil buffer capacity of chemical fertilizer treatments (except NP) was lower than the control, while the manure treatments had higher soil buffer capacity than the control. The soil buffer capacities of the treatments of MN, MNP and MNPK were 3.23, 1.56 and 4.33 cmol·kg-1 higher than those of N, NP and NPK, irrespectively. The soil buffer capacity was significantly positively correlated to soil CaCO3 content, but had no significant correlation with organic matter content and CEC, indicating that Alluvial soil was still in the CaCO3 mediated buffer system, in which organic matter had a small role over long term fertilization. Different long term fertilizations altered CaCO3 and active CaCO3 contents notably in the 0-40 cm soil layer, and the contents of active CaCO3 which was very significantly positively correlated to soil buffer capacity, showed a greater variation along soil profile than that of CaCO3, suggesting that soil active CaCO3 could more sensitively reflect variation of soil physical and chemical properties than CaCO3, and the CaCO3 mediated buffer system could be subdivided into the active CaCO3 mediated buffer system. A 3-year field experiment was carried out to study the effects of different ratios of chicken manure to urea under the same N input on rice grow and soil acidification. The mean rice yields of the treatments of chicken manure/ urea ratio of 75%, 50% and 25% were increased by 4% than the chemical fertilizer treatment and 0.4%~45.3% higher than that of the control. Chicken manure / urea ratio of 50% (7978.5 kg·hm-2) had the highest rice yield, followed by the ratio of 25% (929.0 kg·hm-2). No significant difference in rice yields was found between the chicken manure/urea ratios of 75%, 50% and 25%. Soil CEC increased with the increasing of the proportion of chicken manure, the ratios of 75% and 100％ had significantly higher CEC than other treatments, while only urea treated soil had the lowest CEC. With the increasing of chemical fertilizer, soil pH showed a significant declining tendency. The decline of soil pH was significantly and linearly related to increasing of the proportion of urea (R2＝0.998**). Soil buffer capacity ranged from 2.07~2.36 cmol·kg-1 and was increased with the increasing of the proportion of chicken manure. Soil buffer capacity showed a similar trends to soil organic matter contents and CEC, with the correlation co-efficiency of 0.903** and 0.859*. The above results indicated that under the same N input, soil base cation accumulation and improved organic matter contents caused by the elevated proportion of chicken manure should be an important reason for enhancing soil buffer capacity. Application of rice straw with different N concentrations led to a 0.01~0.99 reduction in pH of 0-40 cm soil layer. The total amounts of induced acid ranged from 56.77 to 136.18 mmol, which was increased with the increasing of rice straw input under the same N contents. However, little difference existed between treatments of the same rice straw amounts under different N contents. The total amounts of induced acid were increased with the increasing of exogenous N input. The proportion of HCO3－ induced acid amount accounted for 82.01%~92.97%, and N leaching took up 6.92~13.04%. The amount of acid induced by N leaching increased with the increasing of straw and N input. Little difference was found in HCO3— induced acid amount, while there was great difference in N leaching induced acid between treatments. The proportion of organic anion cycling induced acid took up 0.11~9.98%, and showed a similar trend to N leaching. The proportion of exogenous H+ induced acid was little, only 0.001~0.005%. Results from the indoor experiment on different application rates of pig manure showed that soil organic matter content was significantly correlated to soil buffer capacity and pH, with the correlation co-efficiencies of 0.6726 and 0.5363, respectively. Increased application of pig manure caused increased leaching of Ca2+ and Mg2+. Indoor simulation experiment was carried out to compare the effects of 3 pH values and 3 nitrogen application rates on soil acidification. Soil acidification accumulation varied from 4.73 to 15.57 mmol H+/column, among which the highest and lowest soil acidification accumulation occurred on the treatments of pH 6.5 depositions without N and pH 2.5 depositions with high N input, respectively. Soil acidification accumulation was elevated with the increase of N input under the same pH deposition. Soil acidification accumulation increased with the decrease of pH in zero N application treatment, when the same amounts of N were provided. However, within medium (150 mg·kg-1soil) and high (300 mg·kg-1soil) N input, soil acidification accumulation was lower in pH 4.5 deposition than pH 6.5 deposition. Nitrate-induced soil acidification accumulation was 4.32~12.88 mmol per column, and ammonia leaching consumed H+ by 0.01~0.29 mmol per column. In case of normal deposition (pH 6.5), soil acidification accumulation was greater than other pH deposition treatments under medium and high N inputs. The above results indicated that soil acidification accumulation induced by N input was greater than acid deposition. Nitrate leaching played a leading role in the acceleration of soil acidification. In conclusion, Hapli-Stagnic Anthrosols was silicate and cations buffering system, soil acidification induced either by matter single application of chemical fertilizer, or of chemical fertizer, or by combined appliacation of chemical fertilizer and organic fertilizer, or by mixed application of organic fertilizer, rice straw and chemical fertilizer, was influenced by soil buffering capacity which in turn was affected by soil organic matter content; Accumulation or depletion of base cations was a major factor to the in-consistent acidification trend between different fertilization treatments. The content of calcium carbonate was a key factor affected pHBC for the sandy loam calcareous fluvor-aquic soil, and the active calcium carbonate more sensitively response to different fertilizer treatments, calcium carbonate buffering system can be further broken down into the soil active calcium carbonate buffering system. Compared to different pH rainfall, nitrogen application contributed more to soil acidification and nitrate was the key acidity inducing factor. Rice straw addition induced acidification in neutral soils was mainly affected by bicarbonate ion caused by soil respiration and nitrogen leaching, and bicarbonate ion induced acidity amount was the major factor.