Land use in agricultural landscapes with chernozems contaminated after Chernobyl accident: Can we be confident in radioecological safety of plant foodstuff?

Agricultural land use in the area of the post-Chernobyl Plavsk radioactive hotspot (Tula region, Central Russia) has raised a problem of radioecological safety of obtained plant foodstuff. Verification of ¹³⁷Cs activities and inventories in components of “soil-plant” systems of the territory has been conducted in 2014–2017 in 10 agrosystems and 2 semi-natural meadows. It was revealed that density of ¹³⁷Cs contamination of arable chernozems and alluvial calcareous soils nowadays varies in a range 140–220 kBq/m² and exceeds radiation safety standard by ˜ 3.5–6 times. Deep plowing of the arable soils up to 30-cm in 1986–1987 resulted in decreasing of ¹³⁷Cs inventories in rooting zone by ≈ 70% for crops cultivated with shallow disk plowing (wheat, barley), and by ≈ 35% for crops cultivated with middle plowing (buckwheat, amaranth, white mustard). The investigated plants and their compartments can be grouped on the basis of transfer factor values as follows: maize (stems and leaves) > amaranth > bromegrass > vegetation of dry meadow, galega, sunflower (seeds), vegetation of wet meadow > maize (grain), soybean (pods), barley (grain), buckwheat (grain), potatoes (tubers) > white mustard (seeds), wheat (grain). It is noticeable that generative plant compartments are characterized by less ¹³⁷Cs activities in comparison with stems and leaves; and that ¹³⁷Cs root uptake is not coincide with total flux of mineral nutrients in “soil-plant” systems. In sum, ¹³⁷Cs soil-to-plant transfer in the area of the Plavsk radioactive hotspot is characterized by considerable discrimination, so ¹³⁷Cs activities in plants are completely in accordance with national standards.     

How many soil samples are neccessary to obtain a reliable estimate of mean nitrate concentrations in an agricultural field?

In Germany, field‐average soil NO₃^‐ measurements are used to identify agricultural risks of groundwater pollution and to evaluate the compliance of land users with environmental regulations. In the present study, it was tested at three typical agricultural sites if common practices of soil NO₃^‐ sampling were appropriate to obtain reliable estimates of the mean field NO₃^‐ content in fall. Three sites of 1 ha area were extensively sampled for NO₃^‐. Ordinary statisticial analyses were conducted on the NO₃^‐ data in order to calculate how many samples per ha were required to predict the mean field NO₃^‐ with a given accuracy. Variograms were derived to assess applicability and relevance of ordinary statistical methods for heterogeneous fields. Results from statistical analysis suggest that at two sites common practices of soil NO₃^‐ sampling would have been adequate to obtain estimates of the actual mean field NO₃^‐ content with a sampling error less than 10 kg NO₃^‐‐N ha^—1 at a 95% probability level. At the other site, common practices obviously would have failed because NO₃^‐ contents varied much more spatially. It remains a problem of soil sampling for NO₃^‐ analysis that information on field heterogeneity is frequently not available a priori.     

Negligible effect of X-ray μ-CT scanning on archaea and bacteria in an agricultural soil

X-ray Microfocused Computed Tomography (X-ray μ-CT) allows a non-destructive and three-dimensional observation of microbial habitats (i.e. pore space) in soil. A major premise for microbiological studies integrating X-ray μ-CT is that soil microorganisms are not affected by irradiation dose in terms of physiology and composition. However, the compatibility of X-ray μ-CT and soil biological experiments has been evaluated controversially.We performed an incubation experiment with packed microcosms to assess the effect of X-ray μ-CT on native microbial populations with emphasis on soil archaea and bacteria. Before (14 days) and after (1 and 14 days) scanning we analyzed (i) respiration, (ii) enzyme activity, (iii) microbial biomass, (iv) abundance and (v) community structure in scanned and control treatments.None of the microbial parameters exhibited significant differences among scanned and unscanned soil samples at all sampling times with the exception of lower archaeal cell numbers subsequent to X-ray μ-CT. Incubation time was the main factor that induced a significant alteration of microbial soil populations while irradiation had no or only very little effect thereupon. Taken together, three-dimensional in situ data obtained via X-ray μ-CT may well be combined with microbiological analyses in soil.     

Do meadow birds profit from agri-environment schemes in Dutch agricultural landscapes?

Since 1992 the European Union helps member states to reverse the loss of biodiversity in agricultural landscapes by the financial support of agri-environment schemes. Long-term studies investigating the effects of these schemes are an essential prerequisite for the development of an effective policy to restore biodiversity on farmland. In Dutch meadow landscapes almost all agri-environment schemes focus on the restoration of meadow bird populations by postponement of the mowing date. Between 1990 and 2002 we measured long-term changes in meadow bird densities in areas with and without agri-environment schemes in the Netherlands, both before and after the start of the contract. During these years bird territories were surveyed during five field visits between 15 March and 15 June. Densities of black-tailed godwit (Limosa limosa), and redshank (Tringa totanus) were higher in the areas with management agreements, but these differences were already present before the start of the contracts. After the start of the management contracts densities of black-tailed godwit and oystercatcher (Haematopus ostralegus) did not increase, while those of lapwing (Vanellus vanellus) and redshank even declined relative to the control areas. It is concluded that the current agri-environment schemes are not sufficient to restore meadow bird populations in Dutch agricultural landscapes. In addition to the prescribed postponement of the mowing date, it is probably necessary to raise groundwater levels and to reduce fertilization to allow for the development of an open vegetation structure that will increase chick survival to sufficiently high levels.     

Self-generated microbial population or cultured microflora – an important criterion toward development of an effective and economically viable road map for organic soil management

Huge depletion of soil microflora under conventional farming practice has become the primary contributory factor toward the present depletion of soil and crop productivity. Reconstitution of soil microbial dynamics has been identified as the only way out, but there has been a debate regarding the most effective pathway for soil rejuvenation i.e. whether to create the environment for natural proliferation or opt for inoculation of laboratory generated microbes. In this respect, a study was undertaken at Maud T.E. (Assam) under FAO-CFC-TBI Project, where bio-fertilizer (microbial inoculant, MI), vermicompost (organic food source, OF), vermicompost + bio-fertilizer (OF+MI), and Novcom compost (representing self-generated native microflora in the order of 10¹⁶c.f.u. along with organic food source, SNM); were taken as treatments for a yield target of 1500 kg made tea/ha. The highest crop yield (1500 kg ha^?1) along with high and consistent soil quality development was noted under SNM treatment; while MI influenced lowest yield (1268 kg ha^?1) and minimal soil response. Addition of the organic food source with cultured microbes (MI+OF) was found to improve crop performance (1427 kg ha^?1), but with 7.60 times higher cost (Rs. 39.97 kg^?1 made tea). Economic viability study indicated that except SNM, all other treatments were vulnerable toward crop loss or market downfall.     

Can phosphorus and nitrogen addition affect ammonia oxidizers in a high-phosphorus agricultural soil?

Ammonia-oxidizing archaea (AOA) and bacteria (AOB), which convert NH₃ to NO₂^? in soils, are important for agricultural production. It is well known that N addition can strongly affect soil ammonia oxidizers, but little is known about P addition. Based on microcosm experiments, this study assessed the responses of ammonia oxidizers to chemical P addition in a typically high P agricultural soil with or without N supply. Six treatments examined were neither N nor P, P alone (0.15, 0.45, and 0.75 g P₂O₅ kg^?1 soil, respectively), N alone (0.25 g N kg^?1 soil), and N plus P (0.25 g N and 0.15 g P₂O₅ kg^?1 soil). Quantitative real-time PCR for the abundance and high-throughput sequencing for community structure were applied. The results revealed that P addition did not affect the abundances and community structures of AOA and AOB, but N addition significantly increased AOB abundance and alter its community structure. Without N supply, continuously increasing soil P availability did not affect these two groups of ammonia oxidizers. This study highlights the relationship between soil P availability and ammonia oxidizers and suggests that soil P availability could be as a potential indicator for predicting N-related ecosystem functions in agricultural production.     

Soil Conservation in Europe: Wish or Reality?

Nearly all of Europe is affected by soil erosion. A major policy response is required to reverse the impacts of erosion in degraded areas, particularly in light of the current climate change and water crisis. Soil loss occurs not because of any lack of knowledge on how to protect soils, but a lack in policy governance. The average rate of soil loss by sheet and rill erosion in Europe is 2·46 Mg ha⁻¹ yr⁻¹. To mitigate the impacts of soil erosion, the European Union's Common Agricultural Policy has introduced conservation measures which reduce soil loss by water erosion by 20% in arable lands. Further economic and political action should rebrand the value of soil as part of ecosystem services, increase the income of rural land owners, involve young farmers and organize regional services for licensing land use changes. In a changing World of 9 billion people with the challenge of climate change, water scarcity and depletion of soil fertility, the agriculture economy should evolve taking into account environmental and ecological aspects. © 2016 The Authors Journal of Land Degradation & Development Published by John Wiley & Sons Ltd.     

The use of individual tree statistics to quantify effects in an ‘acid mist’ experiment with mature trees

Mature trees of a single clone of Sitka spruce (Picea sitchensis (Bong.) Carr.) growing in the field were exposed to simulated acid mist at pH 2.5 over three successive years. The growth of each tree in the acid mist treatment, in terms of the stem area increment, was related to the pattern of growth of the untreated trees at the site during 1991 and 1992. In 1993, the effects of stopping the acid mist treatment on half of the treated trees was investigated by comparing the actual growth against that predicted relative to the untreated trees on the basis of the previous years' data. The prediction of growth from one year to the next was consistently too small for the smallest acid-misted trees, suggesting that the growth rates relative to the untreated trees were increasing with time. Relative to the trees which continued to receive acid mist, however, the smaller trees which received no further acid mist in 1993 grew less than predicted, but there was a significantly greater growth than predicted for the largest recovering trees. Results from the individual tree modelling approach showed that a 10% change in relative stem area increment would be detectable at the 5% level, using a block of 4 trees as a treatment unit. The statistical techniques used are alternatives to conventional ANOVA calculations in determining statistically significant treatment effects where numbers of replicates are small.     

Effect of cycloheximide on N2O and NO3– production in a forest and an agricultural soil

The present work aims at evaluating the effect of cycloheximide at concentrations of between 0.5 and 5mgg^–1 on N₂O and NO₃ ^– production in two slightly alkaline soils, sampled from deciduous woodland and arable cultivation. In the first experiment, peptone was used as the “inducing substrate” for heterotrophic activity, and soil was incubated with cycloheximide (at different concentrations) and/or acetylene (1mll^–1) to block induced eukaryotic protein synthesis and ammonia monooxygenase activity, respectively. Peptone addition stimulated N₂O and NO₃ ^– production significantly in woodland soil, whereas arable soil showed no significant N₂O emissions and low NO₃ ^– production. Low cycloheximide concentrations drastically reduced N₂O emissions in woodland soil, suggesting a potential role of fungi in N₂O emissions. However, acetylene was equally effective in blocking N₂O emissions and part of NO₃ ^– production, so that a possible role of ammonia monooxygenase in an organic-inorganic pathway of N nitrification in fungal metabolism can be hypothesized. A second experiment was carried out on the woodland soil to check if low cycloheximide concentrations had non-target biocidal effects on soil microorganisms. Attention was focused on the range of concentrations which had reduced N₂O emission in the woodland soil. The results suggested that at concentrations of cycloheximide between 0.5 and 2mgg^–1 any biocidal effect on microbial biomass was negligible in the first 48h; therefore only selective inhibition of protein synthesis could be expected. The whole nitrifier population seemed to be particularly sensitive to cycloheximide concentrations higher than 2.5mgg^–1. Received: 4 July 1997     

Changes in organic matter and enzymatic activity of an agricultural soil amended with metal‐contaminated sewage sludge compost

Abstract

The effect of organic amendment with sewage sludge composts of varying heavy metal content on the organic matter content and enzymatic activity of an agricultural soil supporting barley (Hordeum vulgare L.) or lettuce (Lactuca sativa L.) crops was studied. The organic amendments did not improved lettuce growth, the contaminated composts having a negative effect on yield. However, all organic amendments improved barley straw yields although they did not affect grain yields. The addition of the organic materials increased the total carbohydrate content of the soil although this content decreased with cultivation. There was a clearly observed effect of crop type and the degree of heavy metal contamination of the amendment on the most labile carbon (C) fractions (water‐soluble C, carbohydrates, and polyphenolics). In general, soil enzymatic activities were stimulated by addition of sewage sludge compost with low heavy metal content. The compost containing high level of cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) inhibited protease‐BAA activity with respect to the other composts. After cultivation, urease activity increased in soil amended with the high dose of composts, regardless their degree of metallic contamination. Both crop type and metallic contamination contained in the organic materials added influenced phosphatase and ß‐glucosidase activity.     

Water-soluble organic matter in incipient podzols: accumulation in B horizons or in fibres?

To elucidate the mechanism of podzolization in its first stages we studied the fate of the water-soluble organic matter (WSOM) in incipient podzols in sandy soils by comparing the composition of the WSOM from L, F and H horizons with that in the bulk of the Bh horizons and fibres of three profiles. The WSOM appeared to consist significantly of ligno-cellulose and proteins, but these biopolymers were hardly present in the Bh horizons. The material of the fibres, however, greatly resembled the WSOM composition, thereby suggesting that in these soils most of the WSOM is transported through the B horizon and accumulates hardly changed in thin bands where the water stops moving. This implies that in the early steps of podzolization, accumulation of organic matter in the B horizon is not likely to be caused by water-soluble material.     

Does variability in litter quality determine soil microbial respiration in an Amazonian rainforest?

Tree species-rich tropical rainforests are characterized by a highly variable quality of leaf litter input to the soil at small spatial scales. This diverse plant litter is a major source of energy and nutrients for soil microorganisms, particularly in rainforests developed on old and nutrient-impoverished soils. Here we tested the hypothesis that the variability in leaf litter quality produced by a highly diverse tree community determines the spatial variability of the microbial respiration process in the underlying soil. We analyzed a total of 225 litter-soil pairs from an undisturbed Amazonian rainforest in French Guiana using a hierarchical sampling design. The microbial respiration process was assessed using substrate-induced respiration (SIR) and compared to a wide range of quality parameters of the associated litter layer (litter nutrients, carbon forms, stoichiometry, litter mass and pH). The results show that the variability of both litter quality and SIR rates was more important at large than at small scales. SIR rates varied between 1.1 and 4.0 μg g⁻¹ h⁻¹ and were significantly correlated with litter layer quality (up to 50% of the variability explained by the best mixed linear model). Total litter P content was the individual most important factor explaining the observed spatial variation in soil SIR, with higher rates associated to high litter P. SIR rates also correlated positively with total litter N content and with increasing proportions of labile C compounds. However, contrary to our expectation, SIR rates were not related to litter stoichiometry. These data suggest that in the studied Amazonian rainforest, tree canopy composition is an important driver of the microbial respiration process via leaf litter fall, resulting in potentially strong plant-soil feedbacks.     

Chemical Fractions of Zinc and Their Contribution toward Its Availability under Long-Term Integrated Nutrient Management in Rice–Wheat Sequence in an Acidic Alfisol

This study was carried out in an ongoing field experiment initiated during the 1991 kharif season (May–October) on an acidic soil in the Western Himalayas of India to evaluate the effect of integrated nutrient supply on transformation of zinc (Zn) into various chemical pools. The continuous use of chemical fertilizers alone for 20 years brought about marked depletion in different pools of Zn compared to buffer plots, while integrated use of organic and chemical fertilizers recorded greater content than chemically treated plots. Nonspecifically adsorbed exchangeable Zn (Zn I) was the most important fraction of Zn contributing to diethylene triamine penta-acetic acid (DTPA)–extractable Zn. Content of DTPA-extractable Zn also increased in soil with integrated application of chemical fertilizers and organics over the years. Residual Zn was the most dominant form of Zn, contributing about 55% to total Zn, whereas nonspecifically adsorbed exchangeable Zn was the most important fraction of Zn contributing to DTPA Zn.     

Collembola in ecotoxicology—Any news or just boring routine?

Despite the uncontested significance of soils for human nutrition and drinking water quality, the majority of ecotoxicological testing is confined to aquatic test systems. Among the standardised tests for soils, the reproduction test with the springtail Folsomia candida is among the most widely used ones. First steps towards its standardisation were undertaken in the late 1980s. Here we review major advances that have been made since then, with respect to mechanistic, pragmatic and ecological aspects. Specifically we address the ecological relevance of any modifications of the standardised tests. We introduce a miniaturised version of the reproduction test which allows reducing the amount of soil per test unit to one third and the number of synchronised individuals to 40% as compared to the standard test. In addition, we developed an assay using Collembola eggs instead of synchronised adults. First results of a three-species test indicate that the presence of other species may affect choice behaviour. We point out a potential biased view of existing ecotoxicological data with Collembola due to the fact that most results refer to metal contamination. Finally, recommendations for future research are given, with special reference to avoidance and microcosm tests involving Collembola.     

Intensification of Upland Agriculture in Thailand: Development or Degradation?

The large scale conversion of extensive swidden agriculture to intensive market oriented production of maize in upland areas of South East Asia is a cause of environmental concern. This study investigates how intensive maize cultivation affects soil quality in an upland area of Northern Thailand by comparing commonly used indicators of soil quality in soils from maize fields used at various intensities. Relations between these indicators and concentration of permanganate oxidizable carbon (Pox‐C) – a low cost proxy for soil quality – are also examined. The extent, type and drivers of land use changes between 2002 and 2012 are investigated by classification of high resolution satellite images, interviews, participatory mapping and questionnaires. We document a widespread change from traditional swidden agriculture to intensive cultivation of maize that is mainly brought about by economcic and political drivers. We show that the concentration of Pox‐C in the top soil of the maize fields is closely related to common indicators of soil quality and to farmers' perceptions of soil quality. Most of the other soil quality indicators are negatively – albeit not significantly – related to intensity of maize cultivation. There is a strong negative correlation between intensity of maize cultivation and concentration of Pox‐C in the upper 5 cm of the soil where the Pox‐C concentration declines with a rate of 40 mg year under maize⁻¹. We conclude that Pox‐C is a sensitive indicator of effects of land use intensity on the soil and a useful integrative measure of soil quality. Copyright © 2016 John Wiley & Sons, Ltd.     

Selenium in agriculture: a nutrient or contaminant for crops?

Selenium (Se) is an essential nutrient for animals, humans, and microorganisms, but its role in the plants needs further exploration. It is considered beneficial at low levels, but is toxic at higher levels, and there is a fine boundary between these concentrations. Generally, Se levels less than 1 mg kg^?1 have been found to be beneficial for the plants while higher levels cause toxicity in most of the agricultural crops. At low concentrations, Se can act as a plant growth regulator, antioxidant, anti-senescent, abiotic stress modulator, and defensive molecule against pathogens in plants. At higher concentrations, plants show various toxic symptoms, which include stunting of growth, chlorosis, withering, and drying of leaves, decreased protein synthesis premature and even death of the plant. The roles of selenium as enhancer and inhibitor of plant growth in various agricultural crops are discussed here with recent updates. Biofortification of some crops with Se using agronomic and genetic approaches is being explored to cultivate them in the regions having Se-deficiency in foods. Strategies of phytoremediation of Se in hyperaccumulators and transgenic plants overexpressing enzyme/proteins to increase Se tolerance are also described.     

Can a diazotrophic endophyte originally isolated from lodgepole pine colonize an agricultural crop (corn) and promote its growth?

Several diazotrophic Paenibacillus strains were isolated from extracts of surface-sterilized lodgepole pine seedling and tree tissues. One strain, Paenibacillus polymyxa P2b-2R, was found to fix high amounts of nitrogen when reintroduced to the gymnosperms, lodgepole pine and western red cedar. We wanted to determine if P. polymyxa P2b-2R could colonize rhizosphere and internal tissues, fix N and promote growth of corn (Zea mays L), an important agricultural crop. We inoculated corn seeds with P. polymyxa strain P2b-2R and grew seedlings for 30 days. Corn seedlings were harvested 10, 20 and 30 days after inoculation for evaluation of endophytic and rhizospheric colonization as well as nitrogen fixation and growth promotion. P2b-2R successfully colonized the rhizosphere as well as internal root tissues of corn (i.e., endophytically) with population densities near 10⁶ cfu. Corn seedling growth was promoted significantly by inoculation with P2b-2R with an increase of up to 35% in length and up to 30% in biomass after 30 days of inoculation. Seedlings inoculated with P2b-2R derived up to 20% of foliar nitrogen from atmosphere after 30 days of inoculation, which is significant considering the fact that this was a short growth trial. These results suggest that P. polymyxa P2b-2R might have a broad range of plant hosts and is able to fix N and promote the growth of at least one important agricultural crop i.e. Corn.     

Contaminants in Norwegian fjord sediments: industrial history or future source?

Norwegian fjords have been accumulating contaminants since early industrialisation. The key question for sediment management in Norway is whether the sedimentary contaminant record is an archive of industrial history or a future source of contaminants to the fjord environment. Innovative sediment management strategies are being developed in Norway to find solutions which are both cost-effective and sustainable.