Carbon and nitrogen turnover in adjacent grassland and cropland ecosystems

The effects of cultivation and soil texture on net and gross N mineralization, CO₂ evolution and C and N turnover were investigated using paired grassland and cropped sites on soils of three textures. Gross N mineralization and immobilization were measured using¹⁵N-isotope dilution. Grassland soils had high CO₂ evolution and gross N mineralization rates, and low net N mineralization rates. Cropland soils had low CO₂ evolution rates but had high net and gross N mineralization rates. Grassland soils thus had high immobilization rates and cropland soils had low immobilization rates. Cultivation increased N turnover but reduced C turnover. The data suggest that the microflora in grassland soils are N limited, while those of cropland soils are limited by C availability. Increasing clay content reduced N turnover. C turnover was less clearly related to texture. Differences in the immobilization potential of substrates help explain why agricultural soils have higher N losses than do grassland soils.     

The concentration and distribution of 137Cs in soils of forest and agricultural ecosystems of Tula Region

The paper deals with a comparative study of 137Cs contamination in forest, old arable and cultivated soils of Tula Region. Initial interception of Chernobyl derived 137Cs is higher in forest ecosystems: oak-forest > birch-forest > pine-forest > agricultural ecosystems. Vertical migration of 137Cs in deeper layers of soils was intensive in agricultural ecosystems: cultivated soils > old arable soils > birch-forest soils > oak-forest soils > pine-forest soils. In study have been evaluated spatial variability of 137Cs in soil and asymmetrical distribution, that is a skew to the right. Spatial heterogeneity of 137Cs in agricultural soils is much lower than in forest soils. For cultivated soil are determined the rate of resuspension, which equal to 6.1 x 10(-4) day(-1). For forest soils are described the 137Cs concentration in litter of different ecosystems. The role of main accumulation and barrier of 137Cs retain higher layers of soils (horizon A1(A1E) in forest, horizon Ap in agricultural ecosystems) in long-term forecast after Chernobyl accident.     

Distribution, transformation and bioavailability of trivalent and hexavalent chromium in contaminated soil

The purpose of this study was to investigate solid-phase distribution, transformation, and bioavailability of Cr in Cr(III) and Cr(VI) contaminated soils. The effects of EDTA treatment on solid-phase distribution of Cr in soils were also examined. The results show that Cr in both initially Cr(III)- and Cr(VI)-contaminated soils was mainly present in the organic matter bound fraction. Chromium had similar solid-phase distribution and similar overall binding intensity in both Cr(III)- and Cr(VI)-contaminated soils after a growing season. Transformation between Cr(III) and Cr(VI) took place in both Cr(III)- and Cr(VI)-treated soils. Chromium in the Cr(III)-contaminated soils was mostly present as Cr(III), while Cr in Cr(VI)-treated soils was mainly transformed into Cr(III). About 2% of Cr in native non-treated soils was found as Cr(VI). EDTA treatment increased Cr in soluble and exchangeable fraction in Cr(III)-treated soils. In both Cr(III)- and Cr(VI)-contaminated soils, Cr in oxide bound and organic matter bound     

Effects of urea on the germination and early growth of kale,barley, and wheat

Summary Kale was grown in pots in the glasshouse and barley and wheat in bottomless boxes in the open with increasing amounts of urea applied to the soils maintained at various moisture contents. Two sandy soils and two clay soils (one of each containing much and little organic matter) were used in both pots and boxes; in addition four calcareous soils (two developed over chalk, and two over hard limestone) were used in the boxes to compare the effects of the applied urea on the germination and early growth of crops on different soils.The greatest amount of urea applied to the soils containing little organic matter decreased growth of kale in pots, particularly on drier soils, but did not affect growth on soils containing much organic matter; in contrast, with barley and wheat grown in boxes, urea was more damaging in the soils containing much than in those with little organic matter.The various soils used could be grouped according to the amount of urea giving maximum yield. On a soil containing much free calcium carbonate derived from chalk, urea either did not affect yield or depressed it below that of the unfertilised crop.     

Zinc and cadmium hyperaccumulation by Thlaspi caerulescens from metalliferous and nonmetalliferous sites in the Mediterranean area: implications for phytoremediation

Growth, tolerance and zinc and cadmium hyperaccumulation of Thlaspi caerulescens populations from three metal contaminated soils and three normal soils were compared under controlled conditions. Individuals of six populations were cultivated on five soils with increasing concentrations of zinc (50–25000 μg g⁻¹) and cadmium (1–170 μg g⁻¹). There was no mortality of normal soil populations in the four metal-contaminated soils, but plant growth was reduced to half that of populations from metal-contaminated soils. However, in noncontaminated soil, the growth of individuals from normal soils was greater than that of individuals from metal-contaminated soils. Individuals from normal soils concentrated three times more zinc in the aboveground biomass than those from metal-contaminated soils, but the latter accumulated twice as much cadmium. We conclude that populations of T. caerulescens from both normal and metal-contaminated soils are interesting material for phytoextraction of zinc and cadmium, but to optimize the process of phytoextraction it is necessary to combine the extraction potentials of both type of populations.     

Distinct Weathering Ability and Populations of Culturable Mineral-Weathering Bacteria in the Rhizosphere and Bulk Soils of Morus Alba

In this study, we isolated and compared the weathering effectiveness and population of mineral-weathering bacteria from the rhizosphere and bulk soils of Morus alba grown in a mineral-rich soil. Eighty-four isolates could release Si, Al, K, and Fe from potash feldspar. Weathering effectiveness and pattern of the isolates differed between the rhizosphere and bulk soils. The proportion of the highly effective Si, Al, K, and Fe solubilizers was significantly higher in the rhizosphere soils than in the bulk soils. Notably, the proportion of the highly effective acid-producing isolates was also significantly higher in the rhizosphere soils. The 84 mineral-weathering isolates were affiliated with 15 bacterial genera. Distinct mineral-weathering genera were observed between the rhizosphere and bulk soils. The results suggested that the highly effective mineral-weathering bacteria were selected in the rhizosphere soils and the mineral-weathering bacteria from the rhizosphere and bulk soils might weather potash feldspar through different mechanisms.     

Soil physical properties in relation to rice yield and water consumption under flooded and unflooded conditions

Summary Four paddy soils from Thailand were included in this investigation. The soils are described as marine alluvial, fresh water alluvial, hydromorphic alluvial and hydromorphic non-calcareous brown soil. The hydraulic conductivity of water saturated soil was determined on puddled samples, and soil moisture retention curves were recorded for unpuddled samples. In a pot experiment rice variety RD-1 was grown on the soils under flooded and unflooded conditions. For the soils studied a negative relationship was found between the hydraulic conductivity and the ability of the soil to retain water against a given suction. The grain yield was higher under flooded conditions, while among the various soils studied in this experiment grain yield increased with decreasing water content in the suction range studied and increasing hydraulic conductivity of the soils. Better root development facilitated by more favourable physical conditions in highly permeable soils could be the possible reason for the yield increase.     

Potassium forms in aerated and anoxic soils of different management and potassium fertilizer history

The potassium forms and dominant clay mineralogy were studied in naturally well-drained (Hapludalfs, Eutropept) and poorly-drained soils (Fragiudalfs, Fragiaquept), both composed of the same parent materials (silty-clay or silt loam or clayey-loam). The well-drained soils (i.e. aerated) were cultivated and received larger amounts of K fertilizer; the poorly-drained types (i.e. anoxic) were grasslands and received low amount of K fertilizer. The different aspects investigated-exchangeable and nonexchangeable K, potassium fixation capacity and clay X-ray diffraction diagrams-indicated that the potassium status and the behavior of K-containing clays significantly differed between naturally well-drained aerated soils and anoxic poorly-drained soils. The aerated soils were high in both exchangeable and nonexchangeable K; the K saturation rate was high whereas fixation capacity was moderate. However, the anoxic soils showed a large K depletion and high fixation capacity. The silty-clayey soils studied were more affected by moisture regimes than the silt loam or clayey-loam.The differing K status between aerated and anoxic soils can be explained by several processes and factors, including soil weathering and management and K fertilizer history.     

Comparative analysis of microbial diversity and bacterial seedling disease‐suppressive activity in organic‐farmed and standardized commercial conventional soils for rice nursery cultivation

The outbreak of rice plant diseases can be effectively suppressed in organic farming systems. However, the mechanisms of disease suppression by organic farming systems are not well understood. When Burkholderia‐infected rice seeds were sown and cultivated on nine organic‐farmed soils which were supplied by nine independent organic rice farmers or standardized commercial conventional soils, the emergence of bacterial seedling diseases was suppressed to equivalent degrees in nine organic‐farmed soils, whereas the diseases occurred in two commercial conventional soils. In any organic or commercial conventional soil sown with healthy rice seeds as a control, the diseases did not appear. Upon physicochemical analysis of the nine organic‐farmed soils, component common to these organic‐farmed soils seemed to not be directly associated with disease‐suppressive activity. However, microbiome analyses indicated that the bacterial population in these nine organic‐farmed soils was more diverse than those in commercial conventional soils. Intriguingly, the diverse bacterial population structures of organic‐farmed soils were preserved after irrigating and sowing rice seeds, but that of commercial conventional soils was clearly changed by them. Thus, organic‐farmed soils seem to maintain robust bacterial populations despite the irrigation and seedling growth. Indeed, pathogenic Burkholderia in infected rice seeds also did not proliferate in the seedling grown on organic‐farmed soils. Taken together, the common feature of organic‐farmed soils might be the correlation between bacterial seedling disease‐suppressive activity and higher robustness of the diversified microbiome.     

The Old and Young Amazon: Dung Beetle Biomass, Abundance, and Species Diversity

The Amazon Basin can be divided into two geomorphological regions based on the age of its soils: young (< 30 mya) and old (> 300 mya). We tested the effects of soil age on dung beetle communities by comparing biomass, abundance, and species between reserves in Ecuador on young soils and reserves in Brazil on old soils. Beetle biomass in the old Amazon was one-third that in the young Amazon, and beetle abundance in the old Amazon was one-fourth that in the young Amazon. Species richness, rarefied to equal sample sizes, was not significantly different between old and young soils. These data suggest young soils of the Amazon support a significantly greater biomass and abundance of dung beetles than old soils, but that species richness across the Basin is similar. As dung beetles are bio-indicators of mammals, our data support previous studies indicating a greater biomass of mammals on young versus old Amazon soils.     

Comparative phylogenetic analysis of microbial communities in pristine and hydrocarbon-contaminated Alpine soils

A molecular characterization of pristine and petroleum hydrocarbon-contaminated Alpine soils sampled in Tyrol (Austria) was performed. To identify predominant bacteria, PCR-amplified 16S rRNA gene fragments from five pristine and nine contaminated soils were analysed using denaturing gradient gel electrophoresis (DGGE). Sequencing and phylogenetic analyses demonstrated that the majority of the DGGE bands represented bacteria in the Actinobacteria and Proteobacteria phyla: 18 and 73%, respectively, in pristine soils, compared with 20 and 76%, respectively, in contaminated soils. A different distribution pattern of bacterial classes in the Proteobacteria was observed between pristine and contaminated soils. The relative proportion of microorganisms belonging to the Alphaproteobacteria was larger in pristine (46%) than in contaminated (24%) soils, while Betaproteobacteria and Gammaproteobacteria were detected only in the hydrocarbon-contaminated soils. This result compared favourably with earlier work in which hydrocarbon-degradation genotypes, largely pseudomonads and Acinetobacter, belonging to the Gammaproteobacteria, were enriched following oil hydrocarbon contamination. In contrast, members of the Actinobacteria phylum, represented by Rhodococcus and Mycobacterium, were found in pristine soils where contamination events had not occurred. The results demonstrate a significant shift in the microbial community structure in Alpine soils following contamination. Furthermore, more potentially novel phylotypes were found in the pristine soils than in the contaminated soils.     

Sulphur mineralization and adsorption in soils

Summary Studies were conducted to determine the comparative sulphur mineralizing capacity of selected Malaysian and Iowan soils and to determine the amounts of available and adsorbed sulphate in a number of Malaysian soils. Results of the mineralization study indicated that more sulphur mineralised from Malaysian soils although their average contents of total sulphur were lower compared to Iowan Soils. For both sets of soils, significant correlations between contents of organic carbon and total sulphur existed indicating that most of the sulphur was in organic combination. Phosphate solution consistently extracted higher quantities of sulphate in comparison to chloride solution in the Malaysian surface soils implying that a portion of the sulphate existed in adsorbed form. Adsorption of sulphate in soils was found to be dependent on concentration of sulphate added and followed the Langmuir adsorption isotherm.     

土壤保肥-供肥机理及其调节 Ⅰ.棕壤型菜园土的P素保持与供应

对辽宁省北部、中部及南部的棕壤型菜园土15对肥、瘦地的保P-供P性能的测定表明,在绝大多数供试土样中,肥地及其各粒级微团聚体的全P量、P解吸量及P解吸率均大于瘦地及其各相应粒级微团聚体的,P吸附量则相反。不论肥地或瘦地,<10μm微团聚体均比>10μm微团聚体具有更大的P吸附能力。供试菜园土的<10μm微团聚体亦具有较大的供P潜势,其P解吸率比其他农用土壤相同粒级微团聚体的大1个数量级。     

Nitrogen mineralization and its controlling factors in various kinds of temperate humid-zone soils

The N mineralization capacity of 41 temperate humid-zone soils of NW Spain was measured by aerobic incubation for 15 days at 28°C and 75% of field capacity. The main soil factors affecting organic N dynamics were identified by principal components analysis. Ammonification predominated over nitrification in almost all soils. The mean net N mineralization rate was 1.63% of the organic N content, and varied according to soil parent materials as follows: soils on basic and ultrabasic rocks < soils over acid metamorphic rocks < soils developed over sediments < soils over acid igneous rocks < soils on limestone. The N mineralization capacity was lower in natural soils than in cropped soils or pastures. The accumulation of organic matter (C and N) seems to be due to poor mineralization which was caused, in decreasing order of importance, by high exchangeable H-ion levels, high Al and Fe gel contents and, to a lesser extent (though more markedly in cropped soils), by silty clay texture and exchangeable Al ions.     

Mountain soils under a changing climate and land-use

Mountain ecosystems are currently experiencing the strongest climatic warming and the largest changes in land-use during the last millennia. The impacts of these changes on soils and their roles in the cycling of carbon and nutrients are, however, largely unknown. Here, we define mountain soils as soils from mountainous areas with cool summers and cold winters and thus, soils from ecosystems that are influenced by snow and ice and where biogeochemical processes are limited by temperature. Because climatic conditions, soil properties, plant species and productivity vary at a small scale in mountains, they provide a unique natural but a seldom used laboratory to study soil processes. In this special issue, we compile different studies on soils from European mountains, reaching from the functioning of mountain soils along natural climatic gradients to responses of greenhouse gas fluxes from mountain soils to experimental warming, soil frost and changes in precipitation.     

Bacterial and fungal community structure in Arctic tundra tussock and shrub soils

Fungal and bacterial community structure in tussock, intertussock and shrub organic and mineral soils at Toolik Lake, Alaska were evaluated. Community structure was examined by constructing clone libraries of partial 16S and 18S rRNA genes. The soil communities were sampled at the end of the growing season in August 2004 and just after the soils thawed in June 2005. The communities differed greatly between vegetation types, although tussock and intertussock soil communities were very similar at the phyla level. The communities were relatively stable between sample dates at the phyla and subphyla levels, but differed significantly at finer phylogenetic scales. Tussock and intertussock bacterial communities were dominated by Acidobacteria, while shrub soils were dominated by Proteobacteria. These results appear consistent with previous work demonstrating that shrub soils contain an active, bioavailable C fraction, while tussock soils are dominated by more recalcitrant substrates. Tussock fungi communities had higher proportions of Ascomycota than shrub soils, while Zygomycota were more abundant in shrub soils. Recent documentation of increasing shrub abundance in the Arctic suggests that soil microbial communities and their functioning are likely to be altered by climate change.     

Effects of Geomorphology and Primary Productivity on Amazonian Leaf Litter Herpetofauna

The Amazon Basin, representing the largest expanse of intact tropical rain forest on the planet, harbors the largest diversity of amphibians and reptiles in the world. Limited elevation and climate differences across the Basin belie one major division of upland forests – geomorphological soil age and induced nutrient levels. We hypothesized that secondary consumers in the leaf litter herpetofauna community on ancient soils of Central Amazonia would exhibit reduced biomass compared with those found on younger soils of Western Amazonia, and that population densities on ancient soils could be driven below viable thresholds, reducing species richness. We found overall herpetofauna abundance, biomass and richness on young soils in Ecuador were significantly greater than those on ancient soils in the Brazilian Amazon. Separately, amphibians were only slightly more abundant, but their biomass on younger soils was twice that on ancient soils. Even more impressive was the variation exhibited by lizards: abundance was not significantly different, but biomass was five times greater on younger soils. Diversity of both taxa was greater on young soils. The most important driver of differences in herpetofauna biomass, abundance and possibly diversity across Amazonia may be the underlying geomorphologic differences. Reduced primary productivity on ancient soils appears to reverberate up the food chain, leaving fewer resources for higher trophic levels. We suggest that conservation initiatives must compensate for reduced biomass on ancient soils through increased reserve size, especially as forest fragmentation escalates. This study highlights the importance of including biomass as a standard measure in herpetofauna sampling.     

Effects of phosphate sorptivity on long-term plant recovery and effectiveness of fertilizer phosphate in soils

Summary A greenhouse experiment was carried out on 30 soils of eastern Australia in the first year and 15 soils in the following years to determine the effects of soil phosphate sorptivity and phosphate removal in harvested material on effectiveness and recovery of fertilizer phosphate by white clover during a four year period.Phosphate recovery by the clover and fertilizer effectiveness were primarily negative functions of phosphate sorptivity. After the first year there was a progressive decrease in the sorptivity effect such that the subsequent decreases in phosphate recovery and effectiveness were largest on weakly sorptive soils and smallest on strongly sorptive soils. In the long term the cumulative effects of the apparently slow immobilizing reactions on the weakly sorptive soils tended to equalize the effects of faster reactions on strongly sorptive soils so that the actual recovery and effectiveness in the final year were similar on all soils regardless of their sorptivities. The cumulative recovery and cumulative effectiveness in the long term, however, remained strongly negative functions of sorptivity. Phosphate removal in harvested material caused large decreases in phosphate effectiveness on all soils and particularly on weakly sorptive soils.     

栽培番茄的塿土和黄绵土水分和温度变化规律

用土柱试验,研究了栽培樱桃番茄(Lycopersicon esculentum var.cerasiforme Alef.)的塿土和黄绵土水分运移和温度变化规律,水分运移模型选用土壤中水分分布的动力学模型,土壤温度、空气温湿度变化选用正弦曲线模型。结果表明:塿土在各个不同深度的平均含水量均高于黄绵土,塿土的入渗速率高于黄绵土,同一深度塿土温度高于黄绵土,土壤温度随着深度的增加具有明显的滞后性;黄绵土中樱桃番茄的水分利用效率大于塿土,空气温湿度、土壤温度和土壤含水量相互影响。水分运移模型在土壤浅层处可以得到很好的拟合效果,在拟合方程的变量范围内,根据时间可以较准确的确定樱桃番茄盛果期土壤浅层含水量,对于进一步提高农业干旱防御能力、有效制定节水灌溉计划、提高水分利用效率提供了理论依据。     

Status of copper in some calcareous and non-calcareous soils of Egypt

Summary To assess the status of copper in Egyptian soils, surface and subsurface soil samples were collected from various geographical regions of Egypt and of various genesis. The samples were analyzed for the total Cu, water-soluble plus exchangeable as well as the acid-extractable and EDTA-extractable Cu. The total Cu varied between 3.5 and 72.3 ppm. Less than 2% of this copper was in the soluble plus exchangeable form. The highest values of total and soluble plus exchangeable copper were found in the alluvial soils while the sandy soils had the least amounts. This was attributed to the high clay and organic matter content of the alluvial soils in addition to the dominance of montmorillonitic clay minerals in their fine fraction. The calcareous soils showed intermediate values of total and soluble plus exchangeable Cu due to their lower organic matter and clay mineral content. The clay mineralogy of these soils revealed the dominance of illitic and kaolinitic minerals which are relatively poor in Cu and other trace elements.Because of their relatively higher organic matter content, the alluvial soils had a large percentage (up to 43%) of their total Cu in the EDTA extractable form. The calcareous soils, on the other hand, had a large percentage (up to 52%) of their Cu in the acid-extractable form. The EDTA extractable Cu was correlated with the organic matter content of the soils. Since the pH of the EDTA extract was found to be dependent on the CaCO₃ content of the soils, it was suggested that the method be modified so that the final pH of the extract is constant for all soils.