Impact of newly introduced perennial bioenergy crops on soil quality parameters at three different locations in W‐Germany

The land areas used for bioenergy crop cultivation are increasing across Europe. For several years now, various perennial crops have been cultivated, including Miscanthus , switchgrass and reed canary grass, and the newly introduced cup plant, giant knotweed, tall wheatgrass, virginia mallow, and wild plant mixtures. We investigated the impact that many of these perennial bioenergy crops (PECs) have on the soil organic C and N pools, microbial properties, and earthworm activity at three different study sites in W‐Germany with varying soil conditions after an experimental period of five years. Silage maize (Zea maize ) in rotation with green rye (Cecale cereale ) or Triticale was used for comparison (= annual energy crops; AEC). The overall intention of this study was to gain insights into the future trends of soil quality with changes in land‐use towards bioenergy production. Our results emphasized that in general, soil quality was improved through the cultivation of perennials. For example, after five years of investigation, the mean soil organic carbon contents increased, on average, by 1–2% at two of the three study sites, the soil microbial biomass increased from 13% (virginia mallow) to 27% (tall wheatgrass) (p < 0.05) compared to AEC treatment and the mean earthworm activity (cast production) was significantly improved in PECs compared to AEC. These trends were mainly found in silty to loamy soils, but the results were slightly different in sandy soils and dry climate conditions. We suggest that this might be traced back to unfavourable growing conditions for perennial crops during the first years of establishment. To our knowledge, this is the first comprehensive field investigation of the impact of these newly introduced perennial crops on soil quality indicators that considers various site‐ and soil‐specific growth conditions.     

The effect of biochar with biogas digestate or mineral fertilizer on fertility,aggregation and organic carbon content of a sandy soil: Results of a temperate field experiment

Substitution of mineral fertilizers with organic soil amendments is postulated to improve productivity‐relevant soil properties such as aggregation and organic matter (OM) content. However, there is a lack of studies analyzing the effects of biochar and biogas digestate versus mineral fertilizer on soil aggregation and OM dynamics under temperate field conditions. To address this research gap, a field experiment was sampled four years after establishment on a sandy Cambisol in Germany where mineral fertilizer or liquid biogas digestate was applied with or without 3 or 40 Mg biochar ha^?1 (produced at 650°C). Soil samples were analyzed for soil organic carbon (SOC) content, pH, cation exchange capacity, bulk density, water‐holding capacity, microbial biomass, aggregate size class distribution, and the SOC content associated with these size classes. 40 Mg biochar ha^?1 significantly increased SOC content in all fractions, especially free particulate OM and the 2–0.25 mm fraction. The yield of small macroaggregates (2–0.25 mm) was increased by biochar, but cation exchange capacity, water‐holding capacity, and pH were not consistently improved. Thus, high‐temperature biochar applied to a sandy soil under temperate conditions is primarily recommended to increase SOC content, which could contribute to climate change mitigation if this C remains sequestered over the long‐term. Fertilizer type did not significantly affect SOC content or other measured properties of the sandy Cambisol, suggesting that replacement of mineral fertilizer with digestate has a neutral effect on soil fertility. Co‐application of biochar with digestate provided no advantages for soil properties compared to co‐application with mineral fertilizer. Thus, independent utilization of these organic amendments is equally suitable.     

Soil organic carbon temperature sensitivity of different soil types and land use systems in the Brazilian semi‐arid region

Quantifying the sensitivity of soil organic matter decomposition (SOM) to global warming is critical for predict future impacts of climate change on soil organic carbon stocks (SOC) and soil respiration, especially in semi‐arid regions such as north‐eastern Brazil, where SOC stocks are naturally small. In this study, the responses of the labile and recalcitrant carbon components and soil respiration dynamics were evaluated in three different soil types and land use systems (native vegetation, cropland and pasture) of the Brazilian semi‐arid region, when submitted to temperature increase. After 169 days of incubation, the results showed that an increase of 5°C generated an average increase in CO₂ emission of 12.0%, but which could reach 28.1%. Overall, the labile carbon (LC) in areas of native vegetation showed greater sensitivity to temperature than in cropland areas. It was also observed that recalcitrant carbon (RC) was more sensitive to warming than LC. Our results indicate that Brazil's semi‐arid region presents a substantial vulnerability to global warming, and that the sensitivity of RC and of LC in areas of native vegetation to warming can enhance SOC losses, contributing to positive feedback on climate change, and compromising the productive systems of the region. However, further studies evaluating other types of soil and texture and management systems should be carried out to consolidate the results obtained and to improve the understanding about SOM decomposition in the Brazilian semi‐arid region.     

Soil organic matter quality and microbial activities in spruce swamp forests affected by drainage and water regime restoration

The effect of spruce swamp forest (SSF) drainage and water regime restoration on soil organic matter (SOM) quality and soil microbial heterotrophic activities was studied in pristine, drained and restored SSF in the Bohemian Forest, Czech Republic. Sequential chemical SOM fractionation using cold and hot water and hot acid was used to separate SOM fractions according to their mobility and potential lability/recalcitrance, and Fourier transform infrared spectra were used for SOM characterization. Soil physicochemical parameters and heterotrophic microbial activities were also determined. Drainage of SSF had significant long‐term effects (more than 50 yr) on plant communities and SOM quality. On drained sites, cover of sphagnum moss and sedge was much smaller than on pristine locations. A greater proportion of recalcitrant compounds and a smaller proportion of labile compounds were found in drained SSF as compared to pristine sites, which first led to an energy limitation and was followed by a decrease in microbial biomass and heterotrophic microbial activities (CO₂ production, methanogenesis and methanotrophy). Restoration resulted in slow progressive changes in the vegetation cover, including the spread of sphagnum mosses, retreat of mosses typical of drier conditions and increased sedge cover compared with drained SSF. Moreover, soil physicochemical parameters (pH and bulk density), hot‐water‐extractable C and methanotrophic activity tended to evolve towards the pristine SSF and seem to be good indicators of the restoration process. No other SOM fractions changed significantly after restoration. Thus, to change significantly overall SOM quality and most microbial heterotrophic activities following restoration, more than 7 yr are required.     

Humus balances of different farm production systems in main production areas in Austria

The importance of the soil humus content is indisputable. Soil humus plays an important role in preserving soil fertility and exerts great influence on plant production and yield potential. However, proofing that management‐related changes in the stock of soil organic matter (SOM) have taken place against the background of spatial and temporal variation is a difficult task. In most cases, sampling over a long period of time is needed to verify these changes. Alternatively, potential changes in the SOM stock can be estimated using humus balancing models, which help to identify the need for humus reproduction on a farm. In general, a humus balance is the difference between the humus demand of cultivated crops and humus supply through crops and organic fertilizers. In this study, the ‘Dynamic Humus Unit Method' within the modelling program REPRO was applied to calculate the humus balance for 29 model‐farms that are representative of most of the agricultural production in Austria. Each model‐farm represents a specific production type (PT) and farming system in a defined region or main production area (MPA). This approach gives an overview of the humus balances at a large scale and allows a general trend in Austria to be estimated. Besides differing between conventional and organic farming systems, specific site conditions can also be selected in the model. The constructed model‐farms belong to different PTs such as “forage production”, “cash crops”, “refinement”, and “permanent crops”. The PT “permanent crops” refers to the cultivation of wine. The cropping system of each PT was analyzed in detail, while livestock keeping was considered only when applicable. Positive humus balances were found for all PTs except for permanent crops. The results ranged from –122 to 890 kg C ha^?1 y^?1. Regions and farm structure, e.g., forage production compared to cash crop, were found to have a greater influence than the kind of farming system (i.e., organic vs. conventional farming). Comparing the different PTs, forage production had the highest positive humus balances (219 to 890 kg C ha^?1 y^?1), followed by cash crop (24 to 239 kg C ha^?1 y^?1), refinement (–64 to 402 kg C ha^?1 y^?1) and permanent crops (–122 to –38 kg C ha^?1 y^?1). Regarding the farming system, organic farming led to more humus accumulation than conventional farming due to a higher share of fodder legumes and catch crops and more diverse crop rotations. The results were within the range of available empirical data on SOM change, and it was therefore concluded that the results are reasonable. In general, humus reproduction can be regarded as sufficient for agricultural production.     

Can agroforestry improve soil fertility and carbon storage in smallholder banana farming systems?

Soil fertility depletion is a major constraint to agricultural production for smallholder farming households in many sub‐Saharan countries, and it is worsened by climate variability. In order to sustain food security for a growing population, measures have to be taken against C and nutrient losses from soils. This study examines whether banana–coffee agroforestry systems can improve soil fertility and C pools in smallholder farms in E Africa amidst observed climate variability. We selected 20 farms in Central Uganda, where soil samples were obtained from the top and subsoil layers. Samples were analyzed for several soil fertility parameters including soil organic matter (SOM), total soil organic C, pH, total N, plant‐available P, exchangeable K, texture, and bulk density. Soil C stocks were calculated based on soil organic C concentrations and bulky density. We measured tree diameter and height and calculated aboveground plant biomass using allometric equations. Belowground biomass was estimated using equations based on the respective aboveground plant biomass. Our results show that banana–coffee agroforestry farming systems had significantly higher total SOM and total N compared to the banana monoculture. Similar trends were observed for soil C stocks and total C pools. The former contained 1.5 times higher soil C stocks than the latter. Likewise, the mean total C pools for the banana–coffee agroforestry farm plots were 26% larger than that under banana monoculture. However, exchangeable K was higher in the soil of banana monocultures. Plant‐available P levels were limiting under both farming systems. The study demonstrates that beyond socio‐economic benefits banana–coffee agroforestry farming systems have beneficial effects on soil fertility and C sequestration compared to banana monocultures in the study area. However, precautions to avoid P depletion have to be taken under current climate conditions.     

Soil dissolved organic carbon responses to sugarcane straw removal

Global demand for bioenergy increases interest in biomass‐derived fuels, as ethanol from sugarcane straw. However, straw is the main carbon source to soil and its removal reduces C input, affecting active fractions (dissolved organic carbon, DOC) and C storage. To quantify the effects of straw removal on DOC and C stocks, we built lysimeter system using soil (Rhodic Kandiudox) from sugarcane field. We evaluated four soil depths (1, 20, 50 and 100 cm) and four straw removal rates: no removal NR, medium MR, high HR and total TR, leaving 12, 6, 3 and 0 Mg/ha on the soil surface, respectively. After rainfall, drainage water was collected and analysed for DOC content. Soil C stocks were determined after the 17‐month. Total DOC released at 1‐cm depth amounted to 606, 500, 441 and 157 kg/ha in NR, MR, HR and TR, respectively. Net‐DOC suggests straw as the main source of DOC. Most of DOC in NR (50%) was retained within the 1–20 cm layer, resulting in higher C stock (10 Mg/ha) in the topsoil. In HR and MR, DOC retention was higher within 20–50 cm, suggesting differences in DOC composition. DOC in TR was 40% higher at 20 cm than at 1 cm, indicating C losses from topsoil. Low concentrations of DOC were found at 100‐cm depth, but representing 30% in TR. Straw removal for bioenergy production is sustainable, but we should leave at least 3 Mg/ha of straw to ensure DOC production and soil C storage, taking account the DOC contribution to key soil functions.     

Global climate change and its impacts on the terrestrial Arctic carbon cycle with special regards to ecosystem components and the greenhouse‐gas balance

The climatic changes on earth may have serious implications for the carbon (C) cycle in the terrestrial Arctic throughout the 21st century. Arctic vegetation takes up carbon dioxide (CO₂) from the atmosphere producing biomass. In a cold and often moist soil environment, dead organic matter is preferentially preserved as soil organic matter (SOM) due to the inhibition of decomposition processes. However, viable soil microbes exhale huge amounts of CO₂ and methane (CH₄) annually. Hence, Arctic ecosystems exhibit annual fluxes of both carbon‐based (CO₂ and CH₄) greenhouse gases (GHGs) that are in an order of magnitude of millions of tons. Rising Arctic temperatures lead to the degradation of much of today's permafrost in the long run. As a result, large quantities of frozen SOM may become available for decomposers, and GHGs that are entrapped in permafrost may be released. At the same time, warming tends to stimulate the growth, development, and reproduction of many Arctic plants, at least transiently. The present northward migration of boreal shrubs and trees into southern tundra areas may be amplified by that, increasing the ecosystems' gross primary production and, thus, their C sequestration. On the other hand, rising temperatures boost SOM decomposition and microbial respiration rates. In general, soil temperature and soil moisture are key environmental variables to control the intensity of aerobic and anaerobic respiration by microbes, and autotrophic respiration by plants. On the basis of published data on Arctic CO₂ and CH₄ fluxes, the calculations on the terrestrial C‐based Arctic GHG balance made in this review reveal a current annual GHG exchange that ranges between a weak storage of ≤ 225 Tg CO₂ equivalent (eq.) y^–1 and a huge release of ≤ 1990 Tg CO₂ eq. y^–1. Hence, the Arctic GHG balance does apparently already contribute positively to the climatic changes at present. Regarding the future, the relative development of the uptake and release of CO₂ and CH₄ by northern ecosystems is fundamental to the overall GHG status of the Arctic under scenarios of continued climate change.     

生物炭生产与农用的意义及国内外动态

近年来,生物炭作为土壤改良剂、肥料缓释载体及碳封存剂备受重视。生物炭在土壤中能够保持数百年至数千年,实现碳的封存固定,生物炭还可以改善土壤理化性质及微生物的活性,培肥土壤肥力,延缓肥料养分释放,降低肥料及土壤养分的损失,减轻土壤污染。生物质的热裂解及气化均可产生生物炭,但是慢速热裂解和热水炭化工艺的生物炭产率最大,同时还可获得生物油及混合气,生物油及混合气可升级加工为氢气、生物柴油或化学品,这有助于减轻对化石能源或原料的依赖。生物炭的生产及农用是碳减排的过程,废弃生物质生产生物炭及其农用的效益是多赢的。国外在废弃生物质热裂解生产生物炭及农用方面做了许多研究工作。中国在生物质热裂解获得生物能源方面做了较多工作,但对生物炭的生产及农用重视不够。今后,中国应以废弃生物质生产生物炭,并将生物炭农用作为生物能源、环境及农业可持续发展的战略。     

Simulating SOC changes in long-term experiments with RothC and CENTURY: model evaluation for a regional scale application

Abstract. Predictive, regional use of soil organic matter (SOM) models requires evaluation of the performance of models with datasets from long‐term experiments relevant to the scenarios of interest to the regional scale study, and relevant to the climate of the study region. Datasets from six long‐term experiments were used to evaluate the performance of RothC and CENTURY, two of the most widely used and tested SOM models. Three types of model run were completed for each site: (1) CENTURY model alone; (2) RothC model run to fit measured SOC values, by iteratively adjusting C inputs to soil; and (3) RothC model run using C inputs derived from CENTURY runs. In general, the performance of both models was good across all datasets. The runs using RothC (iteratively changing C inputs to fit measured SOC values) tended to have the best fit to model data, since this method involved direct fitting to observed data. Carbon inputs estimated by RothC were, in general, lower than those estimated by CENTURY, since SOC in CENTURY tends to turn over faster than SOC in RothC. The runs using RothC with CENTURY C inputs tended to have the poorest fit of all, since CENTURY predicted greater C inputs than were required by RothC to maintain the same SOC content. A plausible model fit to measured SOC data may be obtained with widely differing C input values, due to differences in predicted decomposition rates between models. It remains unclear which, if either, modelling approach most closely represents reality since both C inputs to soil and decomposition rates for bulk SOM are difficult to determine experimentally. Further progress in SOM modelling can only be the result of research leading to better process understanding, both of net C inputs to soil and of SOM decomposition rates. The use of default methods for estimating initial SOC pools in RothC and CENTURY may not always be appropriate and may require adjustment for specific sites. The simulations presented here also suggest details of SOC dynamics not shown by available measured data, especially trends between sampling intervals, and this emphasizes the importance of archived soil samples in long‐term experiments.     

The impact of a low humus level in arable soils on microbial properties, soil organic matter quality and crop yield

 In arable soils in Schleswig-Holstein (Northwest Germany) nearly 30% of the total organic C (TOC) stored in former times in the soil has been mineralized in the last 20 years. Microbial biomass, enzyme activities and the soil organic matter (SOM) composition were investigated in order to elucidate if a low TOC level affects microbial parameters, SOM quality and crop yield. Microbial biomass C (C_mic) and enzyme activities decreased in soils with a low TOC level compared to soils with a typical TOC level. The decrease in the C_mic/TOC ratio suggested low-level, steady-state microbial activity. The SOM quality changed with respect to an enrichment of initial litter compounds in the top soil layers with a low TOC level. Recent management of the soils had not maintained a desirable level of humic compounds. However, we found no significant decrease in crop yield. We suggest that microbial biomass and dehydrogenase and alkaline phosphatase activities are not necessarily indicators of soil fertility in soils with a high fertilization level without forage production and manure application. Received: 12 December 1997     

Land‐use change in subalpine grassland soils: Effect on particulate organic carbon fractions and aggregation

Abandonment of mountain grassland often changes vegetation composition and litter quantity and quality, but related effects on labile soil organic matter (SOM) are largely unknown. The aim of this study was to investigate the impacts of grassland management and abandonment on soil carbon distribution in light (< 1.6 g cm^–3) particulate organic matter (POM) and aggregation along a gradient of management intensity including hay meadows, pastures, and abandoned grasslands. The reduction of management intensity is an interregional phenomenon throughout the European Alps. We therefore selected sites from two typical climate regions, namely at Stubai Valley, Austria (MAT: 3°C, MAP: 1097 mm) and Matsch Valley, Italy (MAT: 6.6°C, MAP: 527 mm), to evaluate effects of land‐use change in relation to climate. Free water‐floatable and free POM (wPOM, fPOM), and an occluded POM fraction (oPOM), were isolated from three water‐stable aggregate size classes (2–6.3 mm, 0.25–2 mm, < 0.25 mm) using density fractionation. Aggregate mean weight diameter slightly decreased with decreasing management intensity. In contrast to absolute POM‐C, fPOM‐C increased in aggregates at both sites with abandonment. Because the oPOM‐C was less affected by abandonment, the ratio of oPOM‐C : fPOM‐C shifted from > 1 to < 1 from meadow to abandoned grassland in aggregates at both sites and thus independent of climate. This suggests that in differently managed mountain grasslands free and occluded POM are functionally different SOM fractions. In bulk soil, the oPOM‐C : fPOM‐C ratio is better suited as an indicator for the response of SOM to management reduction in subalpine grasslands than the total soil C, absolute or relative POM‐C content.     

Assessing the impacts of the establishment of Miscanthus on soil organic carbon on two contrasting land‐use types in Ireland

In recent years the use of biomass for energy production has become an increasingly important measure for mitigating global change. However, the scientific debate has been inconclusive with regard to the risks and benefits of bioenergy use. There is particular concern that land‐use change to bioenergy production can lead to increased CO₂ emissions. These emissions result from the loss of vegetation and the soil disturbance. The use of Miscanthus x giganteus as a bioenergy feedstock offers a possible solution, as it shows a large soil carbon (C) sequestration potential. The aim of the present study was to analyse the impacts of land‐use change to Miscanthus on soil fractions and associated soil organic carbon (SOC). Four young commercial Miscanthus sites, as well as adjacent sites representing the former land‐use, in SE Ireland were analysed for changes in SOC stocks and newly sequestered Miscanthus‐derived C. The fraction with which the SOC is associated significantly influenced its decomposability and turnover time. Using the ¹³C natural abundance method, we found that newly sequestered C was found mainly as particulate organic matter (79.7% of Miscanthus‐derived C) and therefore in a labile state with short turnover times. No significant differences were found in the distribution of the different soil fractions and SOC between the Miscanthus and the control sites, and it was shown that the share of fractions on the bulk soil as well as the proportion of the SOC associated with these fractions in young Miscanthus sites depends mainly on the previous land‐use.     

环境与人为因子对水稻土有机质变化的影响——以长江中下游平原为例

Changes in soil organic matter (SOM) can affect food security,soil and water conservation,and climate change.However,the drivers of changes in SOM in paddy soils of China are not fully understood because the effects of agricultural management and environmental factors are studied separately.Soil,climate,terrain,and agricultural management data from 6 counties selected based on representative soil types and cropping systems in China were used in correlation analysis,analysis of variance,and cforest modeling to analyze the drivers of changes in SOM in paddy soils in the Middle and Lower Yangtze River Plain from 1980 to 2011.The aims of this study were to identify the main factors driving the changes in SOM and to quantitatively evaluate their individual impacts.Results showed that the paddy SOM stock in the study area increased by 12.5％ at an average rate of 0.023 kg m-2 year-1 over the 31-year study period.As a result of long-term rice planting,agricultural management practices had a greater influence than soil properties,climate,and terrain.Among the major drivers,straw incorporation,the most influential driver,together with fertilization and tillage practices,significantly increased the accumulation of SOM,while an increase in temperature significantly influenced SOM decomposition.Therefore,to confront the challenge of rising temperatures,it is important to strengthen the positive effects of agricultural management.Rational fertilizer use for stabilizing grain production and crop straw incorporation are promising measures for potential carbon sequestration in this region.     

Field‐scale potassium and phosphorus fluxes in the bioenergy crop switchgrass: Theoretical energy yields and management implications

Our understanding of how mineral nutrition affects productivity and composition of bioenergy crops grown on marginal lands remains fragmented and incomplete despite world‐wide interest in using herbaceous biomass as an energy feedstock. Our aim was to determine switchgrass (Panicum virgatum L.) biomass production and maize (Zea mays L.) grain yield on marginal soils used previously to evaluate the effect of soil phosphorus (P) and potassium (K) fertility on alfalfa (Medicago sativa L.) forage production. Grain yield of maize was reduced on P‐ and/or K‐limited plots that also impaired alfalfa forage yield, whereas switchgrass biomass yields were high even in plots possessing very low available P (4 mg kg^–1) and K (< 70 mg kg^–1) levels. Linear‐plateau regression models effectively described the relationship of soil test P and K to tissue P and K concentrations, and tissue P and K concentrations accurately predicted removal of P and K in harvest biomass. However, neither soil‐test P and K, nor tissue P and K concentrations were effective as diagnostics for predicting switchgrass biomass yield nor could soil tests and their change with cropping predict nutrient removal. Concentrations of cellulose, hemicellulose, lignin, and ash were not influenced by P and K nutrition. Predicted bio‐ethanol production was closely associated with biomass yield whereas high biomass K concentrations reduced estimated bio‐oil production per hectare by as much as 50%. Additional research is needed to identify diagnostics and managements to meet the bioenergy production co‐objectives of having high yield of biomass with very low mineral nutrient concentrations (especially K) while sustaining and improving the fertility of marginal soils.     

Humus balancing in Central Europe—concepts,state of the art,and further challenges

Humus‐balancing methods are simple tools for the assessment of interactions between agricultural land use and soil organic matter (SOM). Aside from this commonality, approaches for humus balancing differ considerably with regard to their specific aim, scope, and methodical approach. The term “humus balance” covers both simple models to quantify SOM change in arable soils, or soil organic C (SOC) change in particular, and models that refer to the optimization of soil productivity in arable soils by calculating organic‐fertilizer demand, without quantifying SOM or SOC change. This situation naturally has caused much discussion and misunderstandings. Against this background, the aim of this review is to systematically explore the different methodical approaches to humus balancing in order to contribute to a more sophisticated discussion of this model family, its opportunities, and limitations. As humus balancing has long history as well as special actual relevance in Germany, and, lately Switzerland, we focus on these countries and discuss the different approaches that are presently available and applied there. We argue that humus balances can be roughly categorized into “ecological” and “agronomical” approaches based on their specific concepts and methodology. Ecological humus balances comprise a strong link to quantitative SOM change, while humus balances of the agronomical family refer to the maintenance of soil productivity without a quantitative link to SOM change. Lately, some models have been presented that link the two concepts. However, we identify that humus‐balancing methods often are insufficiently validated, partly because the validation of agronomical humus balances is not easily possible without a very comprehensive field‐experimental basis. Further, the comparability of different approaches even within the two concept families is low at present, indicating the need for a comparative model evaluation for a proper assessment of the methods.     

Direct effect of fertilization on microbial carbon transformation in grassland soils in dependence on the substrate quality

Response of microbial metabolism (growth, substrate utilization, energetic metabolism) to fertilization by N and P and resulting changes in soil‐organic‐matter (SOM) decomposition (priming effect) were studied in grassland soils with relatively high organic‐matter content. Treatments with and without glucose addition were studied to simulate difference between rhizosphere and bulk soil. Our expectation was that fertilization would decrease soil respiration in both treatments due to an increased efficiency of microbial metabolism. At first, fertilization activated microbial metabolism in both treatments. In glucose‐nonamended soils, this was connected with a short‐term apparent priming effect but if glucose was available, the higher energetic demand was covered by its mineralization in preference against SOM, causing significant SOM savings as compared to unfertilized soils. After a relatively short period of 1–3 d, however, the phase of deprived microbial metabolism occurred in both treatments, which was characterized by lower soil respiration in fertilized than in unfertilized soils. Fertilization further decreased net microbial growth following glucose addition, shortened turnover time of microbial biomass and changed the partitioning of assimilated glucose within microbial biomass (decreased accumulation of storage compounds and increased the proportion of mineralized glucose). As a result, fertilization reduced soil respiration mainly due to a deprivation of microbial metabolism. The rate and range of microbial response to fertilization and also the amount of saved soil C were larger in the soil with higher SOM content, likely driven by the higher content of microbial biomass.     

Seasonal influence of climate manipulation on microbial community structure and function in mountain soils

Microbial communities drive soil organic matter (SOM) decomposition through the production of a variety of extracellular enzymes. Climate change impact on soil microbial communities and soil enzymatic activities can therefore strongly affect SOM turnover, and thereby determine the fate of ecosystems and their role as carbon sinks or sources.To simulate projected impacts of climate change on Swiss Jura subalpine grassland soils, an altitudinal soil transplantation experiment was set up in October 2009. On the fourth year of this experiment, we measured microbial biomass (MB), microbial community structure (MCS), and soil extracellular enzymatic activities (EEA) of nine hydrolytic and oxidative extracellular enzymes in the transplanted soils on a seasonal basis.We found a strong sampling date effect and a smaller but significant effect of the climate manipulation (soil transplantation) on EEA. Overall EEA was higher in winter and spring but enzymes linked to N and P cycles showed higher potential activities in autumn, suggesting that other factors than soil microclimate controlled their pool size, such as substrate availability. The climate warming manipulation decreased EEA in most cases, with oxidative enzymes more concerned than hydrolytic enzymes. In contrast to EEA, soil MB was more affected by the climate manipulation than by the seasons. Transplanting soils to lower altitudes caused a significant decrease in soil MB, but did not affect soil MCS. Conversely, a clear shift in soil MCS was observed between winter and summer. Mass-specific soil EEA (EEA normalized by MB) showed a systematic seasonal trend, with a higher ratio in winter than in summer, suggesting that the seasonal shift in MCS is accompanied by a change in their activities. Surprisingly, we observed a significant decrease in soil organic carbon (SOC) concentration after four years of soil transplantation, as compared to the control site, which could not be linked to any microbial data.We conclude that medium term (four years) warming and decreased precipitation strongly affected MB and EEA but not MCS in subalpine grassland soils, and that those shifts cannot be readily linked to the dynamics of soil carbon concentration under climate change.     

Soil organic matter composition and soil lightness

Relationships between soil lightness, soil organic matter (SOM) composition, content of organic C, CaCO₃, and texture were studied using 42 top‐soil horizons from different soil types located in southern Germany. SOM composition was determined by CPMAS ¹³C NMR spectroscopy, soil color was measured by diffuse‐reflectance spectrophotometry and given in the CIE L*a*b* color coordination system (Commission Internationale de l'Eclairage, 1978). Multiple‐regression analysis showed, that soil lightness of top‐soil horizons is principally determined by OC concentration, but CaCO₃ and soil texture are also major variables. Soil lightness decreased with increasing OC content. Carbonate content had an important effect on soil lightness even at low concentrations due to its lightening property. Regressions between soil lightness and organic C content were strongly linear, when the soils were differentiated according to texture and CaCO₃ content. The aryl‐C content was the only SOM component which correlated significantly with soil lightness (r_S = –0.87). In the linear regressions carried out on the different soil groups, soil aryl‐C content was a more significant predictor for soil lightness than total OC content.     

Remediation of Fly Ash Dumpsites Through Bioenergy Crop Plantation and Generation: A Review

Utilization of fly ash, a byproduct of coal combustion in thermal power plants, is a sustainable use of waste for power generation. Discarding fly ash as waste in landfills/ash ponds may not only be regarded as a loss of valuable land and essential nutrients, but also pose a significant health hazard due to fine air-borne particles and leaching of heavy metals. The presence of essential macro- and micronutrients and its porosity make fly ash an excellent soil amendment for plant growth as an organic nitrogen (N) and carbon (C) supplementation. As harmful heavy metals make fly ash unsafe for agronomy, bioenergy crop plantation and energy generation from different thermochemical conversions of the biomass would be an ideal method for coal fly ash utilization through which carbon-neutral fuel can be generated from fossil fuel, thus reducing climate change impact. This review summarizes the development of bioenergy plantation and silviculture at fly ash dumpsites with an integrated phyto-bio-rhizo-mycoremediation approach and assesses utilization of the valuable biomass for thermal energy, electricity, and biofuel generation with inclusion of a SWOT analysis (a strategic technique typically used to help identify the strength, weakness, opportunities, and threat). Bioenergy crop production through integrated phytomanagement can generate billions of dollars of wealth from waste and provides a sustainable solution for fly ash management, with environmental, economic, and social benefits.