【作者】 孟红旗；

【导师】 吕家珑； 徐明岗；

【作者基本信息】 西北农林科技大学 ， 土壤学， 2013， 博士

【摘要】 为探索农田土壤酸化的时空演变规律，揭示农田土壤酸化的成因，提出农田土壤酸化防治的有效措施，收集了我国6种典型农田土壤（祁阳和进贤红壤、进贤和望城水稻土、重庆紫色土、郑州和昌平潮土、公主岭和哈尔滨黑土、黑河暗棕壤）上10个长期（18~30年）施肥试验的历史观测资料，分析了长期不同施肥措施下耕层土壤pH的演变特征和酸化速率，与其受区域气候和初始土壤理化性质等自然因素的影响；分析了长期不同施肥措施下剖面土壤pH的垂直变异特点；分别从生态系统的表观氮平衡和质子负荷组成、土壤酸中和能力（ANC）和土壤水溶性组分的变化4方面阐述了农田土壤酸化的机制。结果表明：（1）以6年为一阶段，祁阳红壤、进贤红壤、重庆紫色土、公主岭黑土和哈尔滨黑土试验各施肥处理的土壤pH差异明显。长期施肥下农田土壤酸化速率的大小顺序为：N> NPK> NPKM≈CK≈M（成对T检验，P <0.05或0.01）。N和NPK处理的土壤酸化速率分别为0.066和0.046pH/yr，是对照平均值的4.9和3.4倍。化学磷钾肥单施的耕层pH较对照显著下降，土壤酸化速率显著升高。尽管存在区域差异性，长期施肥农田的耕层pH演变存在对施肥措施的共性响应特征。（2）年均气温主导的因子与初始1-6年pH下降量显著负相关。降雨量主导的因子与土壤酸化速率存在显著相关：蒸降比每升高1个单位，土壤酸化速率平均降低0.02~0.04pH/yr。相对土壤酸化速率与海拔因子显著正相关：海拔每增加100m，磷钾处理的相对土壤酸化速率平均增加0.024pH/yr。初始土壤有效磷含量与1-6年pH下降量呈显著正相关。土壤酸化速率受初始土壤pH值和粘粒含量的显著影响：初始pH值越大，土壤年酸化速率越小；土壤粘粒含量越大，土壤酸化速率越大。区域气候和初始土壤理化性质等自然因素对农田土壤酸化存在显著影响。（3）长期施肥下，土壤有效磷的增加效应最为明显（168-599%），其次为有效钾（16-189%），再次为有效氮（9-33%）。在氮或磷钾养分相对不足的生态系统中施入相应养分可有效减缓土壤酸化；而在氮或磷钾养分相对盈余的生态系统中施入相应养分则可明显加速土壤酸化。（4）在农业土壤上，超过作物生物量和土壤积累的过量氮施肥引起了生态系统氮盈余。表观氮平衡的增加加速了土壤酸化。此效应在不同长期试验上依次降低：祁阳红壤>公主岭黑土>哈尔滨高量施肥>黑河暗棕壤>重庆紫色土>哈尔滨常量施肥>望城水稻土。在祁阳红壤试验，每增加10kg/ha/yr氮盈余，土壤酸化速率增加0.01pH/yr。（5）祁阳红壤、进贤红壤、哈尔滨黑土和黑河暗棕壤试验各施肥处理的生态系统质子负荷分别为-3.58~19.84、-2.52~9.96、0.75~13.95和-0.86~10.74kmol/ha/yr。土壤净酸添加率（NAAR）与土壤pH下降速率呈显著线性正相关。这种线性相关在重庆紫色土（-3.17~22.43kmol/ha/yr）和公主岭黑土（-2.24~10.10kmol/ha/yr）试验未达到显著性。长期施肥下农田土壤酸化速率受过量盐基阳离子施肥、生物量移除、生态系统表观氮平衡和有机碳矿化分解4个主要因素的影响。（6）实验室条件下的土壤质子化过程可视作由质子扩散控制的假二级反应动力学过程。在各长期试验，土壤ANC与pH具有高度线性相关性，土壤ANC在指示土壤的酸碱程度上较pH更为灵敏。土壤ANC对土壤有机质（SOM）的变化不敏感。长期施肥措施对土壤ANC的影响因试验点而异，总体上，施用无机氮肥<不施氮组≈有机无机氮配施组。（7）在哈尔滨黑土试验，伴随着土壤pH的显著降低，土壤水溶性组分中碳相关阴离子的比例呈下降趋势，而硝酸根的比例呈上升趋势。在高量施氮处理，硝酸根和钙镁离子在土壤表层（0~5cm）和深层（>20cm）发生明显积累。耕层土壤的可溶性组分中，碳相关阴离子和硝酸根占总阴离子的比例，可溶性有机氮和无机氮占总氮比例均也可指示生态系统碳和氮循环质子负荷占比。（8）在农业生态系统中，土壤中的碱性物质通过淋溶和生物量收获被输出生态系统，形成净质子负荷；作为盐基阳离子的阴离子载体，碳酸氢根、有机酸根和硝酸根输出是生态系统质子负荷的主要形式，分别构成了驱动土壤酸化的碳循环和氮循环效应。为防止农田土壤酸化，除总质子负荷低于3%的土壤ANC上限约束外，10~50%的氮循环质子负荷占比也是重要的约束条件。（9）防治农田土壤酸化应遵从的总体原则是：通过合理的施肥、田间管理和收获模式，促进养分的生物循环，减缓养分的地球化学循环。具体分解为5个方面：合理施用化学氮肥，维持生态系统表观氮平衡；合理施用化学磷钾肥，弥补生物量收获养分输出；合理施用有机肥，保持或逐步提高土壤的基础肥力；合理水分管理，减少土壤养分淋溶和流失；合理田间管理，提高农作物产量。更多还原

【Abstract】 The aims of this study were to characterize the spatial and temporal evolution of soil pHunder long-term fertilizations, and further to understand the mechanisms and effectivemethods against soil acidification in croplands. We collected historical data on ten18–30years long-term fertilization experiments in six typical Chinese cropland soils (red soil atQiyang and Jinxian, paddy soil at Jinxian and Wangcheng, purple soil at Chongqing, alluvialsoil at Zhengzhou and Changping, black soil at Gongzhuling and Harbin and dark brown soilat Heihe). We compared the differences in topsoil pH among experimental stages of six yearsand fertilization treatments, i.e., no-fertilizer control (CK), sole chemical nitrogen fertilizer(N), chemical nitrogen, phosphorus and potassium fertilizers (NPK), manure amendmentswith NPK fertilizers (NPKM) and sole manure (M), calculated soil acidification rates (SAR)and analyzed how the characteristics of soil acidification were affected by natural factorsincluding regional climate and the initial soil properties. On the other hand, we expoundedthe mechanisms for soil acidification in croplands from apparent nitrogen balance, protonbudgets in ecosystem, the changes in soil acid-neutralizing capacity (ANC) andwater-extractable components, respectively.1) There were significant differences in topsoil pH among treatments at the experimentalsites of red, purple and black soils but not at the experimental site of purple, alluvial and darkbrown soil. The SARs in the six long-term fertilization experiments were significantlydifferent among treatments (p<0.05or0.01by Paired T-test), and decreased in the order of N> NPK>NPKM≈CK≈M. The SARs under the N and NPK treatments were0.066and0.046pH/yr, and were4.9and3.4times higher than that under the CK treatment, respectively.Moreover, sole chemical P and K fertilizers also significantly decreased topsoil pH andincreased SAR compared with control. Therefore, the evolution of pH in the topsoil wascharacterized as a common response to fertilization with regional differences.2) The factors dominated by average annual temperature were significantly and negativelycorrelated with the decrease in topsoil pH at the first stage of six years. The factors dominatedby precipitation were significantly correlated with SAR. The SARs averagely decreased 0.02~0.04pH/yr over one unit increase in the ratio of evaporation to precipitation (E/P). Therelative SAR under sole PK fertilization averagely increased0.024pH/yr over one unitincrease in altitude of100meters. The factor on the initial available phosphorous content inthe topsoil was significantly and positively correlated with the decrease of topsoil pH at thefirst stage of six years, especially under the N and NPK treatments. The factors on the initialsoil pH and clay content significantly affected SAR. The SARs increased with the decrease ofinitial pH (5.5~8.5) and with the increase of clay content (5~40%). Therefore, the effects ofregional climate and the initial soil properties at each site on the characteristics of soilacidification were significant.3) The increasing responses on fertilization with chemical N, P and K nutrients decreasedin the order of available phosphorous (168~599%)> available potassium (16~189%)>available nitrogen (9~33%) in the topsoil. Soil acidification under long-tem application withchemical N, P or K fertilizers in croplands was effectively alleviated while the correspondingnutrient was deficient in ecosystem, but largely accelerated while the corresponding nutrientwas surplus in ecosystem.4) In the cropland soils, the excess of N fertilization over the N in biomass harvested plusthe N in soil accumulated resulted in the N surplus in ecosystem. The increase of apparent Nbalance may accelerate soil acidification in croplands. The linear correlation between SARand apparent N balance were different among experimental sites, and the slope of linearfitting equation decreased in the order of red soil at Qiyang, black soil at Gongzhuling, highfertilization rate in black soil at Harbin, dark brown soil at Heihe, purple soil at Chongqing,conventional fertilization rate in black soil at Harbin and paddy soil at Wangcheng. In red soilat Qiyang, the SAR increased0.01pH/yr over one unit increase in apparent N balance of10kg/ha/yr.5) By the methods for quantifing soil acidification, total proton budgets under differentfertilization treatments were-3.58~19.84、-2.52~9.96、0.75~13.95和-0.86~10.74kmol/ha/yrin red soil at Qiyang and Jinxian, black soil at Harbin and dark brown soil at Heihe,respectively. The net acid addition rate (NAAR) was significantly correlated with the rate ofsoil pH decline relative to the initial value. However, this correlation was not significant inthe purple soil at Chongqing and black soil at Gongzhuling. Therefore, the SAR underlong-term fertilization was affected by four major factors, i.e., fertilization with excess basecations over acid anions, biomass removal, apparent N balance in ecosystem and thedecomposition of organic carbon.6) Under laboratory conditions, the process of soil protonation was considered as thepseudo-order reaction kinetics controlled by the proton diffusion in soil particles. At each long-term experiment, there were significant correlation between ANC and pH in the topsoil.Soil ANC was more sensitive to soil acid-base status rather than pH, but not to soil organicmatter (SOM). Significant differences in soil ANC among long-term fertilizations at theexperimental sites were in the order of inorganic nitrogen <non-nitrogen≈organic plusinorganic nitrogen with variations at each site.7) In black soil at Harbin, the decrease in C-related anions percentage and the increase innitrate percentage were along with the decrease in topsoil pH under the control, conventionaland high rate of mineral N treatments. The accumulations of nitrate and bivalent base cationspresented both at the top (<5cm) and sub (>20cm) soil depths under high rate of mineral Nfertilization. In the water-extractable components, the percentages of C-related anions andnitrate may indicate the percentages of proton budgets from carbon and nitrogen cycles inecosystem, respectively, and so as the components of dissolved organic N and inorganic N.8) The excess output of base cations over acid anions via soil leaching and biomass harvestproduced the net proton budgets in agricultural ecosystem. As the companied anions withbase cations, the output fluxes of bicarbonate, organic acid anions and nitrate were the mainperformances of proton budgets in ecosystem, and constituted the effects of carbon andnitrogen cycles for driving soil acidification, respectively. To prevent soil acidification incroplands in the long-term scales, the limitations of proton budgets included total amountbeing less than3%of soil ANC and the percentage of nitrogen cycle effects ranging10~50%.9) The general principle against soil acidification in croplands was summarized that thebiological cycle of nutrients in ecosystem should be accelerated but the geochemical cycle ofnutrients in ecosystem should be alleviated under the suitable mode of fertilization, fieldmanagements and biomass harvest. The effective methods against soil acidification incroplands were summed up from five aspects: suitable amount of chemical N fertilizer tokeep apparent N balance in ecosystem; suitable amount of chemical P and K fertilizers tooffset the output via biomass harvest; suitable amount of organic manure to keep or enhancesoil basic fertility gradually; suitable water managements to reduce the leaching losses of soilnutrients; suitable field managements to improve crop production.更多还原