Exchangeable Aluminum Content Research Articles

Effects of rumen digesta on the physico-chemical properties of soils in Nsukka, Southeastern Nigeria Ifeoma

In tropical and subtropical areas, the importance of organic manure in improving soil physico-chemical properties and crop production for food security cannot be overemphasized. A study was conducted to investigate the effects of rumen digesta on the physical and chemical properties of soils in Nsukka, Enugu State, Nigeria. The soil samples collected from Opi, Nsukka were treated with four rates of rumen digesta (viz. 0, 50, 100 and 150 g/kg soils). Physical and chemical properties of the soil were determined pre- and post-experiment. The results obtained reveal that rumen digesta significantly (p = 0.05) increased the mean weight diameter (0.49 to 1.75 mm), aggregate stability (54.7 to 75.3%), soil pH (3.8 to 7.8), total nitrogen (0.01 to 0.02%), exchangeable sodium and potassium (0.22 to 4.39 cmol/kg for Na + and 0.30 cmol/kg to 4.31 for K + ), CEC (7.2 to 14.9 cmol/kg) and organic matter content (0.97 to 4.29%). It had no significant effect on the texture, micro-aggregate stability (measured as dispersion ratio), exchangeable calcium and magnesium content of the soils. The study found a significant reduction in the exchangeable aluminum (1.5 to 0.0 cmol/kg) and hydrogen content (3.7 to 2.2 cmol/kg) of the soils. It is recommended that farmers can improve the physical and chemical properties of soils by using rumen digesta as an alternative liming material. Key words : Rumen digesta, soil properties, evaluation, rural land, Nsukka-Nigeria.

EFFECTS OF RUMEN DIGESTA ON THE PHYSICO-CHEMICAL PROPERTIES OF SOILS IN NSUKKA, SOUTHEASTERN NIGERIA

In tropical and subtropical areas, the importance of organic manure in improving soil physico-chemical properties and crop production for food security cannot be overemphasized. A study was conducted during 2012/2013 crop years to investigate the effects of rumen digesta on the physical and chemical properties of soils in Nsukka, Enugu state Nigeria. The soil samples collected from Opi, Nsukka were treated to four rates of rumen digesta (viz. 0, 50, 100, and 150 gkg soils). Physical and chemical properties of the soil were determined pre and post-experiment. The results obtained revealed that rumen digesta significantly (p = 0.05) increased the mean weight diameter (0.49 to 1.75mm), aggregate stability (54.7% to 75.3%), soil pH (3.8 to 7.8), total nitrogen (0.01% to 0.02%), exchangeable sodium and potassium (0.22 to 4.39cmolkg for Na + and 0.30cmolkg to 4.31 for K +), CEC (7.2 to 14.9cmolkg -) and organic matter content (0.97% to 4.29%). It had no significant effect on the texture, micro-aggregate (measured as dispersion ratio), exchangeable calcium and magnesium content of the soils. The study found significant reduction in the exchangeable aluminum (1.5 to 0.0cmolkg -) and hydrogen content (3.7 to 2.2cmolkg -) of the soils. It recommended that farmers can improve the physical and chemical properties of soils by using rumen digesta as an alternative liming material.

Lucerne dry matter and N-fixation, when sown with or without lime and inoculant

This paper quantifies the effect of inoculation and lime on lucerne growth and nitrogen fixation over the establishment and following season. The field experiment at Ashley Dene, in Canterbury, had an initial soil pH of 5.2 and moderate exchangeable aluminium content (4.2 mg/kg). The 15N natural abundance (δ15N) method was used to quantify nitrogen fixation. The pH of the top-soil was increased to ca. 5.5 and the Al content was decreased to 2.0 and 1.3 mg/kg soil by the application of 1 and 2 t lime/ha, respectively. In Year 0 the dry matter yield increased from 3 to 4 t DM/ha with the addition of 2 t lime/ha. The nitrogen content of lucerne plants was 2.2% (w/w), and was unaffected by inoculant or lime in Year 0. Similarly, the δ15N was 0.81‰ and unaffected by inoculant or lime. In Year 1, the N percentage of inoculated lucerne plants was 4.2% (w/w) compared with 3.6% in uninoculated plants. The δ15N value was 0.81‰ in uninoculated plants compared with -0.23‰ in inoculated lucerne plants. The inoculated lucerne yielded 7.8 t DM/ha compared with 2.4 t DM/ha when uninoculated. The calculated proportion of legume N derived from atmospheric N2 (%Ndfa) estimated that 70% of the nitrogen content in the inoculated lucerne shoots was derived from nitrogen-fixation in Year 1. There was no effect of lime on lucerne DM, or δ15N values in Year 1. This suggests lucerne rhizobia tolerated moderate levels of Al in acidic soils. The application of lime and inoculant are therefore recommended for lucerne, particularly in areas where there is no history of lucerne. The available soil N was sufficient to meet crop demand in the establishing year. Lucerne was then reliant on biological nitrogen fixation for yield in Year 1 which suggests lucerne preferentially used soil available N in Year 0, before commencing N fixation. Keywords: Aluminium, lucerne, lime, Medicago sativa L., nitrogen fixation.

Effect of long-term different fertilization on bacterial community structures and diversity in citrus orchard soil of volcanic ash.

This study was conducted to assess bacterial species richness, diversity and community distribution according to different fertilization regimes for 16 years in citrus orchard soil of volcanic ash. Soil samples were collected and analyzed from Compost (cattle manure, 2,000 kg/10a), 1/2 NPK+compost (14-20-14+2,000 kg/10a), NPK+compost (28-40-28+2,000 kg/10a), NPK (28-40-28 kg/10a), 3 NPK (84-120-84 kg/10a), and Control (no fertilization) plot which have been managed in the same manners with compost and different amount of chemical fertilization. The range of pyrosequencing reads and OTUs were 4,687-7,330 and 1,790-3,695, respectively. Species richness estimates such as Ace, Chao1, and Shannon index were higher in 1/2 NPK+compost than other treatments, which were 15,202, 9,112, 7.7, respectively. Dominant bacterial groups at level of phylum were Proteobacteria, Acidobacteria, and Actinobacteria. Those were occupied at 70.9% in 1/2 NPK+compost. Dominant bacterial groups at level of genus were Pseudolabrys, Bradyrhizobium, and Acidobacteria. Those were distributed at 14.4% of a total of bacteria in Compost. Soil pH displayed significantly closely related to bacterial species richness estimates such as Ace, Chao1 (p<0.05) and Shannon index (p<0.01). However, it showed the negative correlation with exchangeable aluminum contents (p<0.05). In conclusion, diversity of bacterial community in citrus orchard soil was affected by fertilization management, soil pH changes and characteristics of volcanic ash.

CARACTERIZAÇÃO QUÍMICA DE DIFERENTES SISTEMAS DE USO DO SOLO

A forma de manejo que se utiliza nos solos amazônicos determina a sua utilização no futuro, assim a caracterização química é fundamental, pois é parâmetro para indicar a fertilidade desses solos. O objetivo deste trabalho foi realizar a caracterização química de diferentes usos de solos no estado do Pará. Foram coletadas quinze amostras simples para formar três amostras compostas com três repetições para cada área nos solos de várzea, capoeira e capoeira em transição para várzea com ampla faixa de variação de características químicas. As análises foram realizadas no departamento de solos na Universidade Federal Rural da Amazônia (UFRA). Foram realizadas as seguintes análises: O pH em água, cálcio, magnésio trocáveis, alumínio trocável e umidade atual. Em relação ao pH, todos os solos apresentaram acidez acentuada. Já para umidade, o solo de várzea foi que apresentou valor mais elevado. Para Ca2+ e Mg2+, os solos de várzea também foram que apresentou valores mais elevados. PALAVRAS-CHAVE: fertilidade, manejo do solo, química do solo.

The Influence of Long-Term Fertilization on Soil Acidification

Based on the long-term experimental field of Jilin Agricultural University as a platform. Aiming at groping for the influence of long-term fertilized of the acidity changes on soil in research area. The results show that: compared with CK group. The soil pH declined as a result of applying nitrogenous fertilizer chronically. Instead the content of exchangeable acid, exchangeable hydrogen and exchangeable aluminum increased. The content of soil organic matters reduced with the decrease of soil pH application of phosphate fertilizer and potassium fertilizer could achieve the same objective. But the Influence was not as significant as the one fertilized with N.

Extração e quantificação de alumínio trocável em Organossolos

O objetivo deste trabalho foi avaliar diferentes métodos de extração e quantificação de alumínio trocável em Organossolos. As amostras foram coletadas em três perfis de turfeira e, então, secas ao ar e passadas em peneira de malha de 2 mm. Foram feitas extrações com KCl 1 mol L-1 , Ca(OAc2) 1 mol L-1 e CuCl20,5 mol L-1 . Em seguida, os extratos obtidos por KCl e Ca(OAc2) foram analisados por titulação com NaOH 0,025 mol L-1 e por espectrômetro de absorção atômica com forno de grafite (GF-AAE). Os extratos obtidos por CuCl2 foram analisados por GF-AAE. Na quantificação por GF-AAE, os extratores KCl e Ca(OAc2) tiveram capacidade semelhante de extrair alumínio trocável, enquanto o CuCl2 foi capaz de extrair também o Al reativo. Os elevados teores de alumínio trocável observados na titulação após extração com KCl podem estar relacionados aos elevados teores do íon H+ presente nas amostras. O método indicado para determinação do teor de alumínio trocável em Organossolos é a extração com KCl ou com Ca(OAc2) e, para quantificação, a espectrofotometria de absorção atômica com forno de grafite.

No-till and cover crops shift soil microbial abundance and diversity in Laos tropical grasslands

Abstract Agricultural practices affect the physical and chemical characteristics of the soil, which in turn may influence soil microorganisms with consequences on soil biological functioning. However, there is little knowledge on the interactions between agricultural management, soil physicochemical properties, and soil microbial communities, notably in tropical ecosystems with few studies conducted in strongly weathered and acid soils. Here, we investigated the early effect of tillage and crop residues management on top soil physical, chemical, and microbial properties in an acid savannah grassland of northeastern Laos. We initiated a 3-year rotation of rice/corn/soybean under three no-till systems (NTs) distinguished by the cover crops associated prior to and with the main crops, and one conventional tillage-based system (CT). The effect of agricultural management was evaluated 2 years after land reclamation in reference to the surrounding natural pasture (PAS). Our results demonstrate that NTs improve soil physicochemical characteristics (aggregate stability, organic carbon, and cation exchange capacity) as well as microbial abundance (total biomass, bacterial and fungal densities). A significant discrimination of the genetic structure of soil bacterial community was also observed between NTs, CT, and PAS. Interestingly, bacterial abundance and diversity were differently influenced by soil environment changes: microbial density was affected by the quantity and diversity of crop residues, soil organic carbon, and exchangeable base contents, whereas soil bacterial genetic structure was mainly determined by exchangeable aluminum content, pH, cation exchange capacity, and C/N ratio. Altogether, our study represents one of the most complete environmental evaluations of agricultural practices in tropical agrosystems and leads to recommend no-till systems with high residue restitutions to improve the physical, chemical, and microbial properties of tropical acid soils and thus contribute to the sustainability of agriculture in these ecosystems.

Physicochemical Properties and Carbon Storage of Forest Soils on Cambodian Basalt: A Preliminary Study with a Density Fractionation Approach

Forest soils in the basalt region of Southeast Asia are important natural resources, due to their high agricultural potential and high capacity for carbon sequestration. To characterize the physicochemical properties and the components of the soil organic carbon of forest soils in the basalt region, five evergreen sites (E1–5) and one deciduous forest site (D1) were selected in Cambodia at elevations ranging from 132 to 908 m. The components of the soil organic carbon of each site were separated using a density fractionation approach, i.e. high(≥ 1.6 g cm−3) and low( 600 m), were strongly weathered and characterized by a lower pH, a lower level of exchangeable bases, and a more reddish color than the other evergreen forest soils. The soils of sites E3 and E4, located on a hillside and at the base of a hill, respectively, had a high soil effective cation exchange capacity in the B horizons compared to those at sites E1–2 and E5. The soil of site E5 in the isolated basalt region had characteristics resembling those in sites E1–2 except for its high exchangeable aluminum content. The site D1 soil on a hillside was relatively young and shallow, and black in color. The carbon stock in the six forest sites (0–30 cm in depth) was 40.8– 113.7 Mg C ha−1 for high-density fractions and 3.3–7.6 Mg C ha−1 for low-density fractions, respectively. The differences in vegetation types (deciduous vs. evergreen forests), mean annual temperature and free aluminum contents among forest sites were considered factors affecting the carbon content and carbon to nitrogen (C/N) ratio of high-density fractions. It was considered that the variously weathered parent materials, regulated by the relative position in the basalt plateau, were responsible for the gradient of soil morphology and soil nutrient conditions and characterized the soil carbon stock in the study area. Discipline: Forestry and forest products Additional key words: tropical monsoon forest * Corresponding author: e-mail jtori@affrc.go.jp Received 29 May 2012; accepted 19 September 2012.

ARBUSCULAR MYCORRHIZAE IN AGRICULTURAL AND FOREST ECOSYSTEMS IN CHILE

Arbuscular mycorrhizal (AM) association plays a key role in the sustainability of terrestrial plant ecosystems, in particular those presenting limitations for the establishment and subsequent growth of plants. In Chile, more than 50% of arable soils are originated from volcanic ashes, showing in general several constraints to crop production, such as low pH, high exchangeable aluminum content and low levels of available P. Under these conditions, the management of AM fungal propagules using adequate cultural management practices emerges as a successful alternative in order to maximize the positive effects of AM symbiosis on plant growth in these types of soil. This review presents the results of several years of research about the effect of different agronomic and forest management practices on the density and functionality of the native fungal populations in volcanic soils from Southern Chile, and their subsequent effect on the improvement of soil characteristics. These investigations have contributed to a better understanding of the role played by AM symbiosis in such soils and provide guidance on the most appropriate alternatives to increase its presence and functionality.

Analysis on Formation Factor of Sclerotia of Cenococcum geophilum in Picea abies Forest, Harz Mts., Germany

Cenococcum geophilum Fr. is one of the most frequently encountered mycorrhizal fungi in nature. It reveals tolerance to low pH and forms abundant number of sclerotia. In this study, distribution of sclerotia of C. geophilum was investigated in a single stand forest of Picea abies, Harz mountains, Germany to analyze their forming factors. Surface soil samples were collected to examine density of sclerotia based on weight and count of grains, soil pH(H2O, KCl), content of exchangeable aluminum, total carbon and nitrogen, and humification degree based on melanic index and Pg index. Elemental composition of sclerotia was examined by SEM-EDS analysis. 14C age of sclerotia was determined by AMS measurement. The averages of sclerotia density by weight and counts throughout all points were 0.54 mg g−1 and 1.3 count g−1, respectively. The distributional correspondence of sclerotia to micro-topography was not clear and demonstrated the formation of sclerotia as a nearly constant phenomenon in the investigated forest soil. However, a large amount of sclerotia tended to distribute in soils with scarce floor vegetation. Content of exchangeable aluminum in soil was an effective factor on accelerating formation of large sclerotia and Al and Fe content in sclerotia were likely to increase in lower pH soils. The existence of sclerotia in forest soil may stand as an indicator of soil chemical properties such as strong acidity and high Al3+ content.

Relação entre atributos de solos e oxidação de enxofre elementar em quarenta e duas amostras de solos do Brasil

O uso do S-elementar como fertilizante pode reduzir custos de produção. É necessária, porém, a sua oxidação a S-sulfato, forma disponível à planta. Poucas informações são encontradas na literatura sobre a capacidade de solos brasileiros em oxidar S-elementar. Este trabalho foi realizado com os objetivos de determinar a taxa de oxidação de S-elementar em amostras de 42 solos coletadas em vários Estados do Brasil e verificar como atributos de solos podem afetar a oxidação. O estudo foi realizado com amostras coletadas no horizonte A, na camada de 0 a 20 cm, que foram incubadas com S-elementar na dose de 10 g kg-1 de S0 no solo por 90 dias em estufa na temperatura de 27 ± 1 ºC, em frascos de vidro com capacidade para 150 mL. As amostras dos 42 solos apresentaram taxas de oxidação do S-elementar a S-sulfato que variaram de 1,95 a 21,89 µg cm-2 dia-1 de S0. A taxa de oxidação do S-elementar se correlacionou positivamente com o teor de matéria orgânica (MO) e negativamente com os teores de Al trocável e o teor inicial de S dos solos. O pH e os teores de argila, P, K disponíveis, Ca e Mg trocáveis não afetaram a taxa de oxidação do S-elementar dos solos.

2,4-D sorption in iron oxide-rich soils: role of soil phosphate and exchangeable Al.

This study examined herbicide retention in iron oxide-rich variable charge soils (Ultisols) under no cultivation (forest), agriculture (farm), and turf maintenance (golf course) to explore the following hypothesis: inorganic phosphate accumulation from soil fertilization and liming to decrease exchangeable aluminum (Al) content will influence carboxylic acid herbicide sorption onto soils and leaching into groundwater. A suite of soil properties, including mineralogy (particularly soil iron and aluminum oxide content), exchangeable Al content, and soil phosphate content, influenced sorption of the anionic, 2,4-D. In general, 2,4-D sorption was lower in the presence of phosphate, possibly due to competition between phosphate and 2,4-D for surface sites or increase in surface negative charge resulting from phosphate sorption. Additionally, 2,4-D sorption was greater in the presence of exchangeable Al. It appears that 2,4-D may form surface complexes with or be electrostatically attracted to exchangeable aluminum in the soil. Our results suggest that carboxylic acid herbicides may be more easily leached in intensively managed Ultisols subject to continued phosphate fertilization and liming.

Distribution and development of sclerotium grains as influenced by aluminum status in volcanic ash soils

The distribution of sclerotium grains, which are considered to be the resting bodies formed by fungi species, was studied in 5 Andosol profiles in central Japan. Sclerotium grains were detected in the surface A and buried A horizons of nonallophanic (Alp / Alo > 0.5) soils but not in allophanic (Alp / Alo < 0.5) soils. The maximum density of the sclerotium grains in each profile was approximately 2.5 g kg−1. A highly positive relationship was observed between the mean weight of the sclerotium grains and the content of exchangeable aluminum (Al3+) in soils. Aluminum concentration inside of the sclerotium grains was confirmed by energy dispersive X-ray spectrometer (EDS) analysis. The results obtained suggest that the status of active Al in soils is an important factor for sclerotium development.

Changes in aluminum pools of andisols due to soil acidification

Aluminum concentrations in soil solutions are not only controlled by inorganic clay minerals but also by organically bound aluminum. The objective of this study was to determine which pools contribute to Al dissolution. Soil samples were taken at various distances from tree trunks and at various depths at the Rolling Land Laboratory (RLL), Hachioji, Tokyo. Selective dissolution techniques were used to analyze the changes in pools of solid-phase aluminum. Soil pH values around Hinoki cypresses were in the aluminum buffer range. Exchangeable aluminum contents in soils under Hinoki cypresses were 104 mmolc kg-−1 on the average. This value was similar to that of the cation exchange capacity (CEC) of Andisols at RLL at a soil pH of 4. The relationship between the soil pH and exchangeable, organically bound, and amorphous aluminum pools showed that dissolved aluminum ions in the soil solution were primarily derived from the amorphous Al pool. Dissolved aluminum ions were substituted with base cations of soils, resulting in the increase of the content of exchangeable Al and/or the formation of complexes with organic matter which increased the proportion of organically bound Al pools. Increase in the proportion of organically bound Al pools indicated the importance of complexation with soil organic matter for controlling the aluminum concentration in the soil solution.

Measurement of the acid neutralizing capacity of agroforestry tree prunings added to tropical soils

Laboratory incubation in the UK of an Oxisol from Burundi and an Ultisol from Cameroon with 3·1% by weight of prunings of young shoots of Calliandra calothyrsus, Cassia siamea, Flemingia congesta, Grevillea robusta, Gliricidia sepium, Leucaena diversifolia and Leucaena leucocephala resulted in increased soil pH and decreased exchangeable aluminium content. The greatest increase in pH and corresponding decrease in exchangeable aluminium occurred during the first 14 days of incubation and the decrease continued at a slower rate until 42 days incubation. The acid neutralizing effect decreased after 42 days but was still important at the last sampling time at 98 days. Polyphenol to nitrogen ratio was not well correlated with observed change in soil pH whereas the total base cation (calcium, magnesium and potassium) content proved to be a good predictor of these changes in the Ultisol, but not in the Oxisol. The proposed mechanism giving rise to acid neutralization is complexation of protons and aluminium by organic anions. The total base cation content of the prunings ranged from 0·94 to 2·25 molc/kg and the buffer capacity of the Oxisol was 48 mmol OH−/pH/kg.

Effect of liming and phosphate application on sudangrass growth and phosphorus availability in two temperate acid soils

A pot experiment was carried out in the greenhouse with two loamy sand Dystric Cambisols derived from schist to investigate the effect of liming and phosphorus (P) application on plant growth and P availability and its assessment by four soil test methods: 0.01M calcium chloride (CaCl2), cation anion exchange membrane (CAEM), Egnér‐Riehm, and Olsen procedures. Soils were first incubated for two weeks with lime at four levels, depending on their content of exchangeable aluminum (Al). Phosphorus was added at two rates (75 and 150 mg P kg‐1) and the incubation proceeded for an additional two‐week period. Sudangrass (Sorghum sudanenses cv. Tama) was then planted and harvested four weeks later. During incubation and plant growth, soils were maintained at 70% of field moisture capacity. Although pH value and soil extractable P in original soils were similar, the results showed a significant difference on the effect of liming and P application. Acidity was the major limitation for DM yield in the soil with the highest amount of exchangeable Al, while P availability was the main constraint in the other soil. Liming above pH (0.01M CaCl2) 5.3–5.5 did not increase DM yield in either soil and showed a negative effect on one soil (9.7 to 6.9 and 10.2 to 7.8 g pot‐1). Phosphorus content and uptake by sudangrass increased with liming, revealing a positive effect of lime on the availability of P to plants. Added P showed a lower efficiency in the soil with highest amounts of Al compounds. Soil tests performed after the execution of the pot experiment showed variable tendencies to predict P availability, according to the nature of the procedures and soils. Soluble‐P in 0.01M CaCl2 increased with the rise of soil pH. Extractable CAEM‐P and Egnér‐Riehm‐P also increased with liming, but reflected the soil depletion caused by plant uptake. Extractable Olsen‐P presented the most inconclusive results, suggesting the limitation of this method for acid soils which have been limed.

Suppression of Fusarium solani f. sp. phaseoli on Bean by Aluminum in Acid Soils

ABSTRACT The severity of bean root rot caused by Fusarium solani f. sp. phaseoli in vitro was studied with regard to exchangeable soil aluminum for 25 soil samples collected from northeastern Honshyu island, Japan. Of these, 24 were Andosols, typically acidic and of volcanic ash origin. Disease severity was assessed based on the number of lesions produced by the pathogen on a 6-cm section of bean stem buried and incubated for 8 days at 25 degrees C in artificially infested soil samples. The number of lesions differed considerably among soil samples. In all soils in which disease incidence was very low, macroconidial germination was strongly inhibited. The inhibition was observed in all soil samples with exchangeable aluminum contents of at least 0.4 meq/100 g of soil, although it is unclear if this concentration is the lowest limit for inhibition. When soil pH was 5.6 or lower, higher amounts of exchangeable aluminum were detected from soils in which the major clay mineralogy was chloritized 2:1 minerals, while no or limited amounts of aluminum were detected from soils in which the major clay mineralogy was allophane/imogolite. Macroconidial germination and disease incidence are thus closely related to clay mineralogy, which regulates the behavior of exchangeable aluminum.

Effet à court terme de la mise en culture sur le statut organique et l’agrégation d’un sol ferrallitique argileux du Congo

Cultivation of oxisols of the Niari Valley (Congo) leads to considerable decline in the soil organic carbon content and structural stability in a few years. The objective of this study was to estimate the very short-term effects of cultivation on organic status and macroaggregate (&gt; 0.2 mm) stability of a soil which had been under savanna for 20 yr. Another objective was to identify the determinants of macroaggregate stability.On one hand, after 5 mo of manual or mechanized cultivation, stable macroaggregate content MA decreased significantly in the 0- to 10-cm layer (7% on average); soil organic carbon stock S did not (6% on average), whereas the decrease in soil organic carbon content C was significant only under mechanized cultivation (13.5% on average, vs. 7% under manual cultivation). On the other hand, the influence of cultivation on MA, S and C was not significant in the 10- to 20-cm layer (variations &lt; 5%, on average).MA was correlated with exchangeable aluminum content (r = 0.6), though its contribution to stability was low, but was neither with "free" or "amorphous" iron and aluminum contents (r &lt; 0.3), nor with C (r &lt; 0.1); moreover, the influence of hot water-extractable compounds on MA was not significant. Therefore, macroaggregation did not seem to be controlled by organic matter. Key words: Macroaggregate stability, soil organic carbon, oxisol, setting into cultivation, exchangeable aluminum, hot water pretreatment

Acidification and nutrient imbalance in forest soils subjected to nitrogen deposition

Emission of nitrogen oxides (NO x ) and ammonia (NH 3 ) from a fertilizer factory and the resulting input of nitrates (NO 3 - ) and ammonium (NH 4 + ) into the soil were the main reasons of nitrogen (N) cycle disturbance in forest ecosystems near Novgorod, North-Western Russia (50°31' North 31°17' East). Total N atmospheric input was about 100 kg/ha annually. NH 3 was a dominant pollutant, causing the increase of atmospheric precipitation pH within the polluted region compared to background territories (6.0 - 6.5 and 4.5 - 5.0, respectively). Soil acidification through NH 4 + nitrification was observed. N-NO 3 - concentrations in soil solution reached 20-30 mg/l, and proton (H + ) production was equal to 4.1 keq/ha per warm season (from April to October). Compared with soil status in 1983, pH decrease by 0.2 pH units was found in A horizon. The content of exchangeable calcium (Ca) and magnesium (Mg) decreased by the factor of 2 - 3 and 1.5 - 2 in A and B horizons, respectively. Triple increase of exchangeable aluminium (Al) content was detected in A horizon. Through recent decrease of pollutant emission, the polluted territory is now a suitable subject for recovery studies.