酸沉降下加速土壤酸化的影响因素

酸沉降对土壤和水域的酸化影响是土壤环境化学研究前沿的热点问题之一。酸沉降的化学组成对酸性土壤的进一步酸化起着催化剂的作用。在酸雨影响下，SO4^2-,NO3^-，有机阴离子是加速土壤酸化和盐基淋溶损失的主要阴离子，外源H^ 的进入会加速铝离子水解。自然因素与人为因素导致土壤酸化的实际酸化速率差异表明：HCO3^－，RCOO^－在土壤剖面中的淋失状况可反映自然土壤的酸化速率，而SO4^2－和N3^- 溶产生的质子负荷揭示土壤受人为因素影响的酸化速率。通过计算酸沉降的主要化学成分进入土壤前后的质子负荷平衡，与酸中和容量（ANC）相结合，反映酸沉降加速土壤酸化的进程。     

土壤酸化成因及其对农田土壤-微生物-作物系统影响的研究进展

自然土壤酸化是一个缓慢的过程,但是农田土壤因频繁的人类活动加速了这一过程,从而给农田土壤-微生物-作物系统带来一系列的负面影响。论文从大气酸沉降、施肥和管理方式、种植作物以及作物移除四个方面介绍了农田土壤酸化的主要原因;重点阐述了土壤酸化对农田土壤肥力、土壤盐基离子以及土壤酸缓冲体系的影响。总结了酸性农田土壤对土壤细菌群落结构、功能性微生物（如氨氧化古菌和氨氧化细菌等）群落结构以及土传病害的影响;分析了土壤酸化对作物的毒害作用,如造成农作物减产、迫使作物根系受到铝毒害等;从外源添加物减缓土壤酸化角度,论述了可持续利用酸性土壤的策略,提出了土壤酸化后的改良措施,展望了土壤酸化需进一步探究的课题。     

酸雨对黄棕壤的致酸作用与对小麦幼苗膜脂过氧化水平的影响

通过模拟酸雨淋洗土壤,造成了土壤酸化和盐基流失。将小麦幼苗栽培于由酸雨致酸的土壤上,导致小麦幼苗的膜脂过氧化水平提高。其中致酸土壤对根系膜脂过氧化水平的影响大于对叶片膜脂过氧化水平的影响。     

微地形作用下紫色母岩发育土壤的酸化特征

为揭示丘陵地区微地形作用下紫色母岩及其不同地形部位发育土壤的酸化特征,在西南丘陵地区采集土壤样品并分析其基本理化性质。结果表明:西南丘陵地区的紫色土已经出现了一定程度的酸化,土壤酸化后使交换性酸含量增加,交换性盐基离子总量和盐基饱和度降低。从丘陵地区的坡顶至坡底,紫色土的发育程度逐渐增加,土壤中维持土壤pH在碱性范围内的碳酸盐遭受到的淋溶作用依次增强。因此,从坡顶至坡底,紫色土的酸化范围逐渐增大。由于酸化后的紫色土pH开始受阳离子交换反应所控制,而在微地形的作用下,受盐基离子遭受淋溶过程和复盐基过程的相对强弱不同的影响,从坡顶至坡底,紫色土的总体酸化程度并未增加。可见,对西南丘陵地区的紫色土的开发利用需考虑到其较为独特的酸化特征。     

有机物料对不同作物根系土壤腐殖质组成和结构的影响

为探讨施用有机物料后不同作物根系土壤腐殖质各组分含量和胡敏酸元素组成的变化情况,以吉林农业大学试验田培肥2a的黑土为研究对象,试验选取3种作物(玉米、大豆、白菜),每种作物设4种施肥处理,包括化肥(CK)、玉米秸秆配施化肥、树叶配施化肥和鸡粪配施化肥。采用腐殖质修改法提取水溶性物质(WSS)、胡敏酸(HA)、富里酸(FA)、胡敏素(HM),利用重铬酸钾外加热法测定腐殖质各组分有机碳含量,采用分光光度计法测定HA和FA的光学性质,通过光密度E_4/E_6值和元素组成分析HA的结构变化。结果表明:土壤总有机碳(TOC)和腐殖质各组分有机碳含量均表现为白菜玉米大豆。相比CK,配施有机物料后作物根系土壤TOC、WSS、HA含量分别显著增加5%~8%,34%~55%,8%~20%,FA含量变化不明显。相比树叶和鸡粪,秸秆可显著提高TOC含量;WSS在各物料之间差异不明显;HM含量表现为秸秆树叶鸡粪CK。有机物料对PQ值的影响因作物而异,秸秆和鸡粪对玉米、大豆根系土壤PQ值(HA占腐殖酸的比率)的影响相似,而鸡粪对白菜根系土壤PQ值的影响显著高于玉米秸秆。施用有机物料后HA的E_4/E_6未发生明显改变,FA的E_4/E_6显著提高。有机物料使根系土壤HA缩合度升高,分子结构更加复杂,且有利于HA含氮基团的形成,以秸秆处理作用最好。由此可见,有机物料具有良好的培肥效果,其中鸡粪对白菜根系土壤培肥效果最显著,秸秆与鸡粪对玉米、大豆根系土壤培肥效果相似,均显著高于化肥。     

模拟酸雨淋溶下强风化土壤矿物风化计量关系研究

矿物风化计量关系对于定量土壤酸化速率至关重要。我国亚热带地区矿物风化强烈,土壤的酸敏感性高。为获取强风化土壤在矿物风化过程中元素释放特征及其化学计量关系,选取花岗岩发育的富铁土,先用EDTA-乙酸铵溶液洗脱土壤胶体上吸附的盐基离子,然后采用改进的Batch法,将洗脱盐基土壤与未洗脱盐基土壤同时进行模拟酸雨淋溶。结果表明:(1)洗脱盐基土壤与未洗脱盐基土壤的盐基离子(K~+、Na~+、Ca~(2+)和Mg~(2+))释放情况存在显著差异,洗脱盐基后土壤在淋溶中释放的盐基来源为矿物风化,释放缓慢而平稳;(2)未洗脱盐基土壤在淋溶初期,盐基的释放量较大,随着淋溶的进行,释放量迅速下降,淋溶后期的释放速率与洗脱盐基土壤接近,这说明未洗脱盐基土壤在淋溶初期释放的盐基主要来源于阳离子交换过程,后期则主要来源于风化过程;(3)洗脱盐基土壤和未洗脱盐基土壤经酸雨淋溶释放的各盐基化学计量关系(K~+∶Na~+∶Ca~(2+)∶Mg~(2+))以及盐基离子与硅的化学计量关系(BC∶Si)差异较大,由于未洗脱盐基土壤受到阳离子交换的影响,因此只有洗脱盐基土壤的矿物风化计量关系可以作为定量估算土壤酸化速率的依据。     

酸沉降影响下近20年来衡山土壤酸化研究

对不同时期采自衡山东坡垂直带谱上6个典型土壤剖面Ah层和AB层的样品分析,土壤酸化指标研究结果表明,近2 0年来,由于酸沉降的影响,由花岗岩风化物发育的各类土壤,都有不同程度的酸化,表现在pH值下降,交换性酸,尤其是交换性Al3 增加,交换性盐基总量减少,盐基饱和度下降,特别是土壤酸缓冲性能和土壤酸害容量降低。相比之下,山顶的常湿淋溶土和山麓的湿润富铁土酸化更明显,而山体中部的常湿富铁土酸化进程较慢,山体上部的常湿雏形土酸化进程更慢,表明土壤酸化除了与土壤酸沉降量有关外,还与土壤类型有关     

积盐对设施栽培土壤酸度及酸组成的影响

[目的]探讨盐渍化对土壤酸度的可能影响,为了解设施栽培土壤的酸化过程提供依据。[方法]采集了不同酸化特征的设施栽培土壤、露天栽培土壤和自然酸性土壤等3类表层土壤和剖面分层土壤样品,通过化学分析和室内添加肥料盐及土壤洗盐模拟试验,比较研究设施栽培土壤、露天栽培土壤与自然酸性土壤中活性酸、潜性酸、盐基饱和度之间关系差异及其受土壤盐分积累的影响。[结果]与自然酸性土壤相比,设施栽培土壤的酸是人为输入式,其酸化主要发生在表层,土壤剖面呈自上而下下降。在相同交换性酸水平的条件下,设施栽培土壤的pH值最低,其次为露天栽培土壤,而自然酸性土壤的pH值相对较高。在相同土壤pH值的情况下,自然酸性土壤的盐基饱和度明显低于设施栽培土壤和露天栽培土壤,而设施栽培土壤的盐基饱和度高于露天栽培土壤;设施栽培土壤的交换性酸中活性酸组成比例高于自然酸性土壤。增加中盐的积累可显著降低设施栽培土壤pH值;设施栽培土壤的盐分淋洗过程在降低土壤盐分的同时也降低了土壤的活性酸(提高了土壤的pH值)。[结论]盐分的积累增强了设施栽培土壤中潜性酸向活性酸的转化,高量施用化肥不仅可直接通过酸性物质的输入促进土壤pH值的下降,同时由此引起的盐分也可在一定程度上进一步降低土壤的pH值。     

有机–无机肥长期配施对潮土土壤肥力和作物产量的影响

以24年（1981－2004年）的肥料长期定位试验为基础，分析探讨了有机无机肥长期配施对潮土土壤肥力和作物产量的影响。研究结果表明，除增施秸秆外，增施化肥也能提高土壤有机质的含量，但同时增施化肥和秸秆更有利于土壤有机质的积累。在提高有机质复合量方面，施用化肥的效果好于施用秸秆，而有机无机结合效果较单一施用秸秆或化肥都要高；随秸秆或化肥施用量的增加有机质的复合度逐渐降低，但有机无机结合施用可以提高有机质的复合度。有机无机结合有利于改善土壤的物理性状，降低了土壤容重，提高了土壤田间持水量和饱和含水量，增加了土壤总孔隙度和毛管孔隙。单施秸秆肥和单施化肥均有显著的增产效应，而化肥的增产幅度远远大于秸秆肥，有机无机结合的增产幅度在同等施肥量下较单独施用秸秆或化肥的产量都要高。结果表明，有机无机结合较单一施用秸秆肥或化肥能更有效的提高潮土的土壤肥力，提高作物产量。     

抑菌剂浇施与不均匀施肥对玉米马铃薯生长和产量的影响

农业生产中,肥料和抑菌性农药施用是两种重要的农业生产技术。在施肥过程中,点状和条状施肥是主要的施肥方式,易导致作物生长期内土壤养分以斑块状分布,因此根系趋肥性对农田中作物获取养分具有重要性。而在施用抑菌性农药时,药剂能够通过淋溶等过程进入土体中,对土壤生态环境和根-土过程产生直接或间接的影响。然而目前有关农药施用是否影响作物根系趋肥性,进而改变产量表现还不清楚。本研究选用旱地主要粮食作物玉米和马铃薯为研究对象,通过等量肥料下隔行施用的方式构建土壤养分斑块,在此基础上进行广谱性杀菌剂浇施土壤,研究抑菌性农药对作物利用异质性养分的影响。两年的大田试验数据表明,一定程度上,抑菌剂浇施和隔行施肥能够显著地影响作物的植株生物量、产量,根系生物量及分布,且对玉米生物量影响具显著交互效应,表现为隔行施肥对生物量的显著提高发生在抑菌剂浇施条件下,而抑菌剂对玉米生物量的提高则主要表现在隔行施肥条件下。同时,抑菌剂浇施能够提高作物的根系觅养精确度,其中在马铃薯上达到显著水平,表明抑菌剂浇施对作物适应土壤养分斑块具有一定的促进作用。当然,抑菌农药和养分斑块在影响作物生长过程中的显著性受作物类型和种植年份的影响,具有复杂性。因此,进一步针对不同作物、生态环境和栽培措施,探讨抑菌剂农药在作物适应养分斑块中的作用以及对作物根系趋肥的影响机制,对于了解农药施用对化肥利用的影响具有潜在的价值。     

Acidification in the Rhizosphere of Rape Seedlings and in Bulk Soil by Nitrification and Ammonium Uptake

Ammonium salts used as fertilizers may cause soil acidification by two different processes: nitrification in soil and net release of protons from roots. Their influence on soil pH may vary depending on the distance from root surface. The aim of this study was to distinguish between these two processes. For this purpose rape seedlings were grown 10 d in a system which separated roots from soil by a fine-meshed screen. As a function of distance from the plane root layer formed on the screen, pH, titratable and exchangeable acidity and NO₃- and NH₄-nitrogen were determined. The soil, a luvisol from loess, was supplied with no N or (NH₄)₂SO₄ either with or without a nitrification inhibitor (DCD). The bulk soil pH remained unaffected when no N or 400 mg NH₄? N kg^?1 soil plus DCD was applied but it decreased from 6.6 to 5.8 without DCD. In contrast, rhizosphere pH decreased in all cases, mainly within a distance of 1 mm from the root plane only, but with gradients extending to between 2 and 4 mm into the soil. The strongest pH decrease, from 6.6 to 4.9, occurred at the root surface of plants treated with both NH₄-N and DCD where most of the mineral N remained as ammonium. In this case Al was solubilized in the rhizosphere as indicated by exchangeable acidity. Total soil acidity produced in the NH₄ treatment without DCD was mainly derived from nitrification compared to root released protons. However, acidification of the rhizosphere was diminished by nitrification because nitrate ions taken up by the roots counteracted net proton release. It is concluded that nitrification inhibitors may reduce proton input from ammonium fertilizers but enhance acidification at the soil-root interface which may cause Al toxicity to plants.     

Soil Acidification as Affected by Phosphorus Sources and Interspecific Root Interactions between Wheat and Chickpea

A pot experiment was conducted to determine the effects of chickpea/wheat intercropping and two phosphorus (P) sources on soil acidification and to explore a new way of ameliorating soil acidification. Wheat and chickpea roots were grown in compartments separated either by a solid barrier to prevent any root interactions or by a nylon mesh (30 μm) to permit partial root interactions, or with no separation between the compartments. Two P sources were applied at 60 mg P kg^?1 soil either as sodium phytate or ferrous phosphate (FePO₄). The decline of soil pH after growing plants for 42 days was alleviated by supplying organic P or intercropping while receiving organic P. The ameliorating of soil acidification resulted mainly from a decrease in excess cations over anion uptake of both wheat and chickpea under phytate supply, compared to FePO₄ supply. The excess cation uptake of chickpea was reduced by root interactions.     

Nutrient management on crop productivity and changes in soil organic carbon and fertility in a four–year-old maize-wheat cropping system in Indo-Gangetic plains of India

The aim of this investigation was to prepare and evaluate organic manures (vermicompost, compost and FYM) and mineral fertilizers on crop productivity and changes in soil organic carbon (SOC) and fertility under a four-year-old maize-wheat cropping system. The results demonstrated that yields and nutrient uptake by crops increased significantly in plots receiving manures and mineral fertilizers either alone or in combination than unfertilized control. Application of manures and fertilizers also enhanced SOC, mineral N, Olsen-P and ammonium acetate-extractable K (NH₄OAc-K) after both the crops. Surface soil maintained greater build-up in SOC, mineral N, Olsen-P and NH₄OAc-K than sub-surface soil. Plots amended with manures at 5 t ha^?1 and 50% recommended dose of fertilizer (RDF) had pronounced impact on improving SOC and fertility after both the crops indicating that integrated use of manures and mineral fertilizers could be followed to improve and maintain soil fertility, increase crop productivity under intensive cropping system.     

Soil Acidity Changes in Bulk Soil and Maize Rhizosphere in Response to Nitrogen Fertilization

The capacity of nitrogen (N) fertilizers to acidify the soil is regulated principally by the rate and N source. Nitrogen fertilizers undergo hydrolysis and nitrification in soil, resulting in the release of free hydrogen (H⁺) ions. Simultaneously, ammonium (NH₄ ⁺) absorption by roots strongly acidifies the rhizosphere, whereas absorption of nitrate (NO₃ ^?) slightly alkalinizes it. The rhizosphere effects on soil acidity and plant growth in conjunction with N rate are not clearly known. To assess the impact of these multiple factors, changes in the acidity of a Typic Argiudol soil, fertilized with two N sources (urea and UAN) at two rates (equivalent to 100 and 200 kg N ha^?1), were studied in a greenhouse experiment using maize as the experimental plant. Soil pH (measured in a soil–water slurry), total acidity, exchangeable acidity, and exchangeable aluminum (Al) were measured in rhizospheric and bulk soil. Plant biomass and foliar area (FA) were also measured at the V₆ stage. Nitrogen fertilization significantly reduce the pH in the bulk soil by 0.3 and 0.5 units for low and high rates respectively. Changes in the rhizosphere (the “rhizospheric effect”) resulted in a significant increase in soil pH, from 5.9 to 6.2. The rhizospheric effect × N source interaction significantly increased exchangeable acidity in the rhizosphere relative to bulk soil, particularly when UAN was added at a low rate. Only total acidity was significantly increased by the fertilizer application rate. In spite of the bulk soil acidification, no significant differences in exchangeable aluminum were detected. Aerial biomass and FA were significantly increased by the higher N rate, but N source had no effect on them. Although changes in acidity were observed, root biomass was not significantly affected.     

Aluminum-Enhanced Proton Release Associated with Plasma Membrane H+-Adenosine Triphosphatase Activity and Excess Cation Uptake in Tea (Camellia sinensis) Plant Roots

Cultivated tea (Camellia sinensis) plants acidify the rhizosphere, and Aluminum (Al) toxicity is recognized as a major limiting factor for plant growth in acidic soils. However, the mechanisms responsible for rhizosphere acidification associated with Al have not been fully elucidated. The present study examined the effect of Al on root-induced rhizosphere acidification, plasma membrane H⁺-adenosine triphosphatase (H⁺-ATPase) activity, and cation-anion balance in tea plant roots. The exudation of H⁺ from tea plant roots with or without Al treatment was visualized using an agar sheet with bromocresol purple. The H⁺-ATPase activity of plasma membranes isolated from the roots was measured after hydrolysis using the two-phase partition system. The Al treatment strongly enhanced the exudation of H⁺, and the acidification of tea plant roots by Al was closely associated with plasma membrane H⁺-ATPase activity. The root plasma membrane H⁺-ATPase activity increased with Al concentration. The Al content, amount of protons released, and H⁺-ATPase activity were significantly higher in roots treated with Al than in those untreated. The results of the cation-anion balance in roots showed an excess of cations relative to anions, with the amount of excess cation uptake increasing with increasing Al concentrations. These suggest that Al-enhanced proton release is associated with plasma membrane H⁺-ATPase activity and excess cation uptake. Findings of this study would provide insights into the contributing factors of soil acidification in tea plantations.     

Soil acidification used as a management strategy to reduce nitrate losses from agricultural land

pH is known to be a primary regulator of nutrient cycling in soil. Increasing soil acidity in agricultural systems has the potential to slow down N cycling and reduce N losses from leaching thereby enhancing sustainability and reducing pollution. We conducted a field experiment to investigate the impact of acidity on N leaching in arable and grassland agricultural systems. The results showed that nitrate (NO₃⁻) concentrations in soil water were greater under arable than under grassland. Soil acidification significantly lowered NO₃⁻ concentrations in soil water over winter and spring under grassland, whilst in cereal plots a similar effect was only observed in spring. Our results suggest that soil acidification decreased nitrification causing an accumulation of NH₄⁺ which was not subject to leaching. Dissolved organic nitrogen (DON) concentrations in soil water were significantly greater under arable than grassland. Soil acidification lowered concentrations of DON in soil water, usually to a greater extent in grassland than in arable plots. It was concluded that it may be possible to use careful soil pH management as a tool to control NO₃⁻ leaching without compromising the quality of drainage water, and that this may be more effective on grassland than on arable crops.     

包膜尿素对芹菜产量、品质及氮素平衡的影响

通过盆栽试验研究了包膜尿素(自制)和尿素等肥料在两种质地灰潮土上对芹菜产量、品质、氮素吸收和氮平衡的影响。结果表明,施用包膜尿素较尿素使当季芹菜增产11.5％-15.2％,氮素吸收增加5.9％-9.5％,氨挥发损失N减少14.2％-14.9％,淋失和反硝化氮损失减少25.5％-28.3％,氮素利用率提高19.2％-27.1％,土壤持留氮增加32.0％-37.3％。芹菜植株硝态氮含量降低44.2％-58.9％,维生素C含量显著提高,品质改善;后茬作物生菜增产14.4％-35.2％。     

Root-induced changes in the rhizosphere: Importance for the mineral nutrition of plants

Root-induced changes in the rhizosphere may affect mineral nutrition of plants in various ways. Examples for this are changes in rhizosphere pH in response to the source of nitrogen (NH₄-N versus NO₃-N), and iron and phosphorus deficiency. These pH changes can readily be demonstrated by infiltration of the soil with agar containing a pH indicator. The rhizosphere pH may be as much as 2 units higher or lower than the pH of the bulk soil. Also along the roots distinct differences in rhizosphere pH exist. In response to iron deficiency most plant species in their apical root zones increase the rate of H⁺ net excretion (acidification), the reducing capacity, the rate of Fe^III reduction and iron uptake. Also manganese reduction and uptake is increased several-fold, leading to high manganese concentrations in iron deficient plants. Low-molecular-weight root exudates may enhance mobilization of mineral nutrients in the rhizosphere. In response to iron deficiency, roots of grass species release non-proteinogenic amino acids (?phytosiderophores”?) which dissolve inorganic iron compounds by chelation of Fe^III and also mediate the plasma membrane transport of this chelated iron into the roots. A particular mechanism of mobilization of phosphorus in the rhizosphere exists in white lupin (Lupinus albus L.). In this species, phosphorus deficiency induces the formation of so-called proteoid roots. In these root zones sparingly soluble iron and aluminium phosphates are mobilized by the exudation of chelating substances (probably citrate), net excretion of H⁺ and increase in the reducing capacity. In mixed culture with white lupin, phosphorus uptake per unit root length of wheat (Triticum aestivum L.) plants from a soil low in available P is increased, indicating that wheat can take up phosphorus mobilized in the proteoid root zones of lupin. At the rhizoplane and in the root (root homogenates) of several plant species grown in different soils, of the total number of bacteria less than 1 % are N₂-fixing (diazotrophe) bacteria, mainly Enterobacter and Klebsiella. The proportion of the diazotroph bacteria is higher in the rhizosphere soil. This discrimination of diazotroph bacteria in the rhizosphere is increased with foliar application of combined nitrogen. Inoculation with the diazotroph bacteria Azospirillum increases root length and enhances formation of lateral roots and root hairs similarly as does application of auxin (IAA). Thus rhizosphere bacteria such as Azospirillum may affect mineral nutrition and plant growth indirectly rather than by supply of nitrogen.     

Der Einfluß unterschiedlicher Kalium- und Nitraternährung auf pH-Änderungen in der Rhizosphäre

The Influence of potassium and nitrate nutrition on pH changes in the rhizosphere Seedlings of winter wheat, barley, sunflower, peanut and field bean were grown in soils differing in K and nitrate content. pH changes of the rhizosphere soil were measured periodically with antimony electrodes. In soils relatively poor in K the lowest pH values were measured at the root surface of the dicots (maximum pH decrease from 5 to 4.2), while soil pH increases from 5 to 5.4 in contact with roots of the monocots. Increasing K addition caused decreasing pH near peanut and field bean roots. In soils fertilized with K, monocot roots also decreased soil pH. In a K-rich soil the roots of the dicots decreased pH even after addition of 6.6 mg NO₃-N/100 g soil, while the roots of the monocots did not change pH. The pH changes are explained by an imbalance between anion and cation uptake, causing release of protons or hydroxyl ions. The reason for the differences in behaviour between monocots and dicots may be due to the differing cation-exchange capacity of the plant roots, causing a higher cation uptake by dicots and therefore greater proton release.