Determination of the Stability of MSW Compost Using a Respirometric Technique

This paper reports a fully automatic respirometric technique with low maintenance costs that allows the routine determination of the specific oxygen uptake rate (SOUR), as well as the cumulative oxygen demand at 20 h, (OD₂₀). The procedure involves the measurement of the dissolved oxygen concentration in an aqueous suspension of compost that is supplied with various nutrients, none of which contains organic carbon. The proposed method was used to monitor composting in a compost pile consisting of 65% organic matter obtained by selective collection of municipal solid waste (MSW), 30% sewage sludge and 5% plant trimming residues. Based on the results, the maximum SOUR value reached, (SOUR_max), decreases gradually with time, to values near 1 mgO₂/gVS.h after 130 days; indicating that the final product is stable. Linear correlations between OD₂₀ and the absorbances at 465 and 665 nm of aqueous extracts of compost, and its soluble chemical organic demand (COD_sol), and soluble organic carbon (TOC_sol) are significant at the p ≤ 0.01 level. However, the use of such variables instead of respirometric data requires prior experimentation with the type of waste to be composted in order to identify the absolute values at which biological activity ceases.     

Verwertung organischer Substanzen durch mikrobielle Bodenbiomasse als eine Funktion chemisch-thermodynamischer Parameter

Carbon use efficiency of organic substances by soil microbial biomass as a function of chemical and thermodynamical parameters A simple calculation determining carbon use efficiency by soil microorganisms based on chemical and thermodynamical parameters of organic matter is proposed. The use efficiency characterizes carbon fraction of organic matter which is incorporated into the cells of the soil microbial biomass. The proposed approach is based on the transition of the organic matter enthalpy into the microbial biomass enthalpy considering the formation enthalpy of the end products of respiration like CO₂, NH₄⁺ and H₂O. The combustion energy content of organic matter was used for the calculations. This combustion energy content can be determined by simple analytical means. It can be derived from data given in the literature and for various agricultural products. The comparison of organic matter use efficiency data calculated as shown above with literature data produced by diverse methods showed a satisfactory correlation. The calculated enthalpy of formation and maintenance of a C-unit of soil microbial biomass under in situ conditions amounted to —153,3 kJ · gC^—1. This value is compared with the maintenance coefficient used in microbiology. The use of the suggested approach for the calculation of carbon use efficiency based on the substance composition of the organic matter allows a uniform, standardized procedure which is not dependent on specific experimental conditions.     

Short-term partitioning of <Superscript>14</Superscript>C-[U]-glucose in the soil microbial pool under varied aeration status

The effect of soil aeration status on carbon partitioning of a labelled organic substrate (¹⁴C-[U]-glucose) into CO₂, microbial biomass, and extra-cellular metabolites is described. The soil was incubated in a continuous flow incubation apparatus under four different aeration conditions: (1) permanently aerobic, (2) permanently anaerobic, (3) shifted from anaerobic to aerobic, and (4) shifted from aerobic to anaerobic. The soil was pre-incubated for 10 days either under aerobic or under anaerobic conditions. Afterwards, glucose was added (315 g C g^–1) and the soils were incubated for 72 h according to four treatments: aerobic or anaerobic conditions maintained, aerobic conditions shifted to anaerobic conditions and anaerobic conditions shifted to aerobic conditions. Carbon partitioning was measured 0, 8, 16, 24, 48 and 72 h after the glucose addition. In permanently aerobic conditions, the largest part of the consumed glucose was built into microbial biomass (72%), much less was mineralised to CO₂ (27%), and only a negligible portion was transformed to soluble extra-cellular metabolites. Microbial metabolism was strongly inhibited when aeration conditions were changed from aerobic to anaerobic, with only about 35% of the added glucose consumed during the incubation. The consumed glucose was transformed proportionally to microbial biomass and CO₂. In permanently anaerobic conditions, 42% of the consumed glucose was transformed into microbial biomass, 30% to CO₂, and 28% to extra-cellular metabolites. After a shift of anaerobic to aerobic conditions, microbial metabolism was not suppressed and the consumed glucose was transformed mainly to microbial biomass (75%) and CO₂ (23%). Concomitant mineralisation of soil organic carbon was always lower in anaerobic than in aerobic conditions.     

Carbon Life Cycle Assessment for Prairie as a Crop in Reclaimed Mine Land

A life cycle assessment with carbon (C) as the reference unit was used to balance the benefits of land preparation practices of establishing tall‐grass prairies as a crop for reclaimed mine land with reduced environmental damage. Land preparation and management practices included disking with sub‐soiling (DK‐S), disking only (DK), no tillage (NT), and no tillage with grazing (NT‐G). To evaluate the C balance and energy use of each of the land preparations, an index of sustainability (I_s = C_O/C_I, Where: C_O is the sum of all outputs and C_I is the sum of all inputs) was used to assess temporal changes in C. Of the four land preparation and management practices, DK had the highest I_s at 8·53. This was due to it having the least degradation of soil organic carbon (SOC) during land‐use change (−730 kg ha⁻¹ y⁻¹) and second highest aboveground biomass production (9,881 kg ha⁻¹). The highest aboveground biomass production occurred with NT (11,130 kg ha⁻¹), although SOC losses were similar to DK‐S, which on average was 2,899 kg ha⁻¹ y⁻¹. The I_s values for NT and DK‐S were 2·50 and 1·44, respectively. Grazing from bison reduced the aboveground biomass to 8,971 kg ha⁻¹ compared with NT with no grazing, although stocking density was low enough that I_s was still 1·94. This study has shown that converting from cool‐season forage grasses to tall‐grass prairie results in a significant net sink for atmospheric CO₂ 3 years after establishment in reclaimed mine land, because of high biomass yields compensating for SOC losses from land‐use change. Copyright © 2014 John Wiley & Sons, Ltd.     

STABILITY,NITROGEN MINERALIZATION CAPACITY AND AGRONOMIC VALUE OF COMPOST-BASED GROWING MEDIA FOR LETTUCE CULTIVATION

Seven composts were used as growing media for lettuce mixed with peat at 25 and 50% (v/v). On the unblended composts and the resulting 14 mixes were determined the main physical-chemical characteristics and the stability by means of a respirometric test in a liquid environment. The potential nitrogen (N)-mineralization capacity of the mixes was measured during the respirometric test solely by the ammonium (NH⁺ ₄-N) determination. The lettuce pot-growing test was performed with and without fertilization; plant biomass and total Kjeldahl nitrogen (TKN) tissue content were measured after cultivation for two months. Compost origin, rate in substrates and fertilization affected plant growth and nitrogen uptake. Multiple regression analysis showed that the stability, proved to be a good predictor for plant growth inhibition. Moreover N-mineralization capacity showed a good fitting with plant uptake. The coupled stability and nitrogen mineralization test gives reliable information about the potential constraints in compost-based growing media.     

Winter wheat carbon exchange in Thuringia,Germany

Eddy covariance measurements and estimates of biomass net primary production (NPP) in combination with soil carbon turnover modelled by the Roth-C model were used to assess the ecosystem carbon balance of an agricultural ecosystem in Thuringia, Germany, growing winter wheat in 2001. The eddy CO₂ flux measurements indicate an annual net ecosystem exchange (NEE) uptake in the range from −185 to −245 g C m⁻² per year. Main data analysis uncertainty in the annual NEE arises from night-time u¹ screening, other effects (e.g. coordinate rotation scheme) have only a small influence on the annual NEE estimate. In agricultural ecosystems the fate of the carbon removed during harvest plays a role in the net biome production (NBP) of the ecosystem, where NBP is given by net ecosystem production (NEP=−NEE) minus non-respiratory losses of the ecosystem (e.g. harvest). Taking account of the carbon removed by the wheat harvest (290 g C m⁻²), the agricultural field becomes a source of carbon with a NBP in the order of −45 to −105 g C m⁻² per year. Annual carbon balance modelled with the Roth-C model also indicated that the ecosystem was a source for carbon (NBP −25 to −55 g C m⁻² per year). Based on the modelling most of carbon respired resulted from changes in the litter and fast soil organic matter pool. Also, the crop and management history, particularly the C input to soil in the previous year, significantly affect next year’s CO₂ exchange.     

Greater humification of belowground than aboveground biomass carbon into particulate soil organic matter in no-till corn and soybean crops

Quantifying the amount of carbon (C) incorporated from decomposing residues into soil organic carbon (C_S) requires knowing the rate of C stabilization (humification rate) into different soil organic matter pools. However, the differential humification rates of C derived from belowground and aboveground biomass into C_S pools has been poorly quantified. We estimated the contribution of aboveground and belowground biomass to the formation of C_S in four agricultural treatments by measuring changes in δ¹³C natural abundance in particulate organic matter (C_POM) associated with manipulations of C₃ and C₄ biomass. The treatments were (1) continuous corn cropping (C₄ plant), (2) continuous soybean cropping (C₃), and two stubble exchange treatments (3 and 4) where the aboveground biomass left after the grain harvest was exchanged between corn and soybean plots, allowing the separation of aboveground and belowground C inputs to C_S based on the different δ¹³C signatures. After two growing seasons, C_POM was primarily derived from belowground C inputs, even though they represented only ∼10% of the total plant C inputs as residues. Belowground biomass contributed from 60% to almost 80% of the total new C present in the C_POM in the top 10 cm of soil. The humification rate of belowground C inputs into C_POM was 24% and 10%, while that of aboveground C inputs was only 0.5% and 1.0% for soybean and corn, respectively. Our results indicate that roots can play a disproportionately important role in the C_POM budget in soils. Keywords Particulate organic matter; root carbon inputs; carbon isotopes; humification rate; corn; soybean.     

Hydrocarbons Emissions from a Municipal Wastewater Treatment Pilot Plant in Vienna

Hydrocarbons emissions were measured from an aerationtank of a municipal wastewater treatment pilot plant. The collected off-gas samples werecharacterised for C₂–C₇ hydrocarbons usingGC-FID analytical technique while the total volatileorganic compounds (TVOC) were measured using acontinuous hydrocarbon gas analyser. Approximately,the estimated emission rates for 1 m³ of wastewaterfrom this aeration tank were 5 mgC of C₂–C₇hydrocarbons, and an average of 7 gC of TVOC. Withexception to toluene, all other measured hydrocarbonsare emitted less than 1 mgC day^-1. The results supportthe view that a significant reduction in annualemissions of hydrocarbons from wastewater treatmentplants in Vienna has taken place.     

Impact of carbon nanomaterials on microbial activity in soil

In this study, effects of an increase in concentration of fullerene-C_60, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) or fullerene soot (FS) on overall microbial activity was investigated over a 21 d incubation period. Microbial utilisation of ¹⁴C-glucose and uptake of ¹⁴C-glucose into the microbial biomass was investigated. For CNM-amended soils, greater extents of ¹⁴C-glucose mineralisation were found in the C₆₀-amended soils compared to MWCNT-, SWCNT- or FS-amended soils. In addition, the 100 and 1000 mg kg⁻¹ were consistently found to have higher extents of mineralisation in C₆₀, MWCNT, SWCNT or FS-amended soils, respectively. Further, the incorporation of ¹⁴C-glucose into the microbial biomass declined slightly with an increase in concentration in the amended soils, but no consistent pattern was observed. As a result, the biophysical quotient (BQ) increased significantly (P < 0.05), as concentrations increased from 1 mg kg⁻¹ to 1000 mg kg⁻¹ in all C₆₀-, MWCNT-, SWCNT- and FS-amended soils. The results obtained from this study showed that the addition to carbon nanomaterials had no profound impacts on the overall microbial activity, and the overall influence of CNMs on soil microbial activity does not reveal a specific pattern in the short term.     

Root-derived carbon in soil respiration and microbial biomass determined by 14C and 13C

Two approaches to quantitatively estimating root-derived carbon in soil CO₂ efflux and in microbial biomass were compared under controlled conditions. In the ¹⁴C labelling approach, maize (Zea mays) was pulse labelled and the tracer was chased in plant and soil compartments. Root-derived carbon in CO₂ efflux and in microbial biomass was estimated based on a linear relationship between the plant shoots and the below-ground compartment. Since the maize plants were grown on C₃ soil, in a second approach the differences in ¹³C natural abundance between C₃ and C₄ plants were used to calculate root-derived carbon in the CO₂ efflux and in the microbial biomass. The root-derived carbon in the total CO₂ efflux was between 69% and 94% using the ¹⁴C labelling approach and between 86% and 94% in the natural ¹³C labelling approach. At a ¹³C fractionation measured to be 5.2‰ between soil organic matter (SOM) and CO₂, the root-derived contribution to CO₂ ranged from 70% to 88% and was much closer to the results of the ¹⁴C labelling approach. Root-derived contributions to the microbial biomass carbon ranged from 2% to 9% using ¹⁴C labelling and from 16% to 36% using natural ¹³C labelling. At a 3.2‰ ¹³C fractionation between SOM and microbial biomass, both labelling approaches yielded an equal contribution of root-derived C in the microbial biomass. Both approaches may therefore be used to partition CO₂ efflux and to quantify the C sources of microbial biomass. However, the assumed ¹³C fractionation strongly affects the contributions of individual C sources.     

Field-applying an inexpensive, 13C-depleted,labile carbon source to study in situ fate and short-term effects on soils

Background

Labile carbon (C_labile) limits soil microbial growth and is critical for soil functions like nitrogen (N) immobilization. Most experiments evaluating C_labile additions use laboratory incubations. We need to field-apply C_labile to fully understand its fate and effects on soils, especially at depth, but high cost and logistical difficulties hinder this approach.

Aims

Here, we evaluated the impact of adding an in situ pulse of an inexpensive and ¹³C-depleted source of C_labile—crude glycerol carbon (C_glyc), a by-product from biodiesel production—to agricultural soils under typical crop rotations in Iowa, USA.

Methods

We broadcast-applied C_glyc at three rates (0, 216, and 866 kg C ha⁻¹) in autumn after soybean harvest, tracked its fate, and measured its impact on soil C and N dynamics to four depths (0–5, 5–15, 15–30, and 30–45 cm). Nineteen days later, we measured C_glyc in microbial biomass carbon (MBC), salt-extractable organic C, and potentially mineralizable C pools. We paired these measurements with nitrate N (NO₃⁻–N) and potential net N mineralization to examine short-term effects on N cycling.

Results

C_glyc was found to at least 45-cm depth with the majority in MBC (18%–23% of total C_glyc added). The δ¹³C values of the other measured C pools were too variable to accurately track the C_labile fate. NO₃⁻–N was decreased by 13%–57% with the 216 and 866 kg C ha⁻¹ rates, respectively, and was strongly related to greater microbial uptake of C_glyc (i.e., immobilization via microbial biomass). Crude glycerol application had minor effects on soil pH—the greatest rate decreased pH 0.18 units compared to the control.

Conclusions

Overall, glycerol is an inexpensive and effective way to measure in situ, C_labile dynamics with soil depth—analogous to how mobile, dissolved organic C might behave in soils—and can be applied to rapidly immobilize NO₃⁻–N.     

Carbon Isotope Composition, Macronutrient Concentrations, and Carboxylating Enzymes in Relation to the Growth of Pinus halepensis Mill. When Subject to Ozone Stress

We present here the effects of ambient ozone (O₃)-induced decline in carbon availability, accelerated foliar senescence, and a decrease in aboveground biomass accumulation in the Aleppo pine (Pinus halepensis Mill.). Aleppo pine seedlings were continuously exposed in open-top chambers for 39 months to three different types of O₃ treatments, which are as follows: charcoal-filtered air, nonfiltered air (NFA), and nonfiltered air supplemented with 40 ppb O₃ (NFA+). Stable carbon isotope discrimination (??) and derived time-integrated c _i/c _a ratios were reduced after an accumulated ozone exposure over a threshold of 40 ppb (AOT40) value from April to September of around 20,000 ppb·h. An AOT40 of above 67,000 ppb·h induced reductions in ribulose-1,5-biphosphate carboxylase/oxygenase activity, aboveground C and needle N and K concentrations, the C/N ratio, Ca concentrations in twigs under 3 mm, and the aerial biomass, as well as increases in needle P concentrations and phosphoenolpyruvate carboxylase (PEPC) activity and the N and K concentrations in twigs under 3 mm. Macronutrients losses, the limitations placed on carbon uptake, and increases in catabolic processes may be the causes of carbon gain diminution in leaves which was reflected as a reduction in aboveground biomass at tree level. Stimulation of PEPC activity, the consequent decreased ??, and compensation processes in nutrient distribution may increase O₃ tolerance and might be interpreted as part of Aleppo pine acclimation response to O₃.     

Soil microbial biomass and nitrogen supply in an irrigated lowland rice soil as affected by crop rotation and residue management

 Processes that govern the soil nitrogen (N) supply in irrigated lowland rice systems are poorly understood. The objectives of this paper were to investigate the effects of crop rotation and management on soil N dynamics, microbial biomass C (C_BIO) and microbial biomass N (N_BIO) in relation to rice N uptake and yield. A maize-rice (M-R) rotation was compared with a rice-rice (R-R) double-cropping system over a 2-year period with four cropping seasons. In the M-R system, maize (Zea mays L.) was grown in aerated soil during the dry season (DS) followed by rice (Oryza sativa L.) grown in flooded soil during the wet season (WS). In the R-R system, rice was grown in flooded soil in both the DS and WS. Three fertilizer N rates (0, 50 or 100 kg urea-N ha^–1 in WS) were assigned to subplots within the cropping system main plots. Early versus late crop residue incorporation following DS maize or rice were established as additional treatments in sub-subplots in the second year. In the R-R system, the time of residue incorporation had a large effect on NO₃ ^–-N accumulation during the fallow period and also on extractable NH₄ ⁺-N, rice N uptake and yield in the subsequent cropping period. In contrast, time of residue incorporation had little influence on extractable N in both the fallow and rice-cropping periods of the M-R system, and no detectable effects on rice N uptake or yield. In both cropping systems, C_BIO and N_BIO were not sensitive to residue incorporation despite differences of 2- to 3-fold increase in the amount of incorporated residue C and N, and were relatively insensitive to N fertilizer application. Extractable organic N was consistently greater after mid-tillering in M-R compared to the R-R system across N rate and residue incorporation treatments, and much of this organic N was α-amino N. We conclude that N mineralization-immobilization dynamics in lowland rice systems are sensitive to soil aeration as influenced by residue management in the fallow period and crop rotation, and that these factors have agronomically significant effects on rice N uptake and yield. Microbial biomass measurements, however, were a poor indicator of these dynamics. Received: 31 October 1997     

黄土高原人工油松林土壤碳氮对短期氮添加的响应

为了更好地理解土壤碳氮元素对氮添加的响应,通过短期原位模拟氮沉降试验,揭示黄土高原子午岭人工油松(Pinus tabulaeformis Carrière)林土壤碳氮对外源氮添加的响应过程和机制。从2015—2016年设置4个氮添加水平,分别为对照(0kg/(hm~2·a),N0)、低氮(50kg/(hm~2·a),N50)、中氮(100kg/(hm~2·a),N100)和高氮(200kg/(hm~2·a),N200),研究人工油松林地不同深度土层土壤有机碳和全氮以及土壤碳氮储量对模拟氮添加的响应。结果表明:土层对土壤有机碳、全氮和碳氮储量有显著影响,上层土壤有机碳、全氮和碳氮储量显著高于下层土壤;氮添加水平对土壤有机碳、土壤碳储量影响不显著,但可显著影响土壤全氮和氮储量。此外,土壤有机碳、全氮和碳氮储量和土壤碳氮储量比受地下生物量碳氮比的影响显著。因此,短期氮添加对人工油松林地土壤碳的影响不显著,但可显著影响土壤氮,地下生物量碳氮比是影响土壤碳氮的重要因素。     

Recycling of Two-Phase Olive-Mill Cake “Alperujo” by Co-composting with Animal Manures

The use of poultry manure or goat/sheep manure in the co-composting of the two-phase olive-mill cake “alperujo” (ALP) with olive leaf (OL) is compared by studying organic-matter mineralization and humification processes during composting and the characteristics of the end products. For this, two different piles (P1 and P2) were prepared using ALP with OL mixed with poultry manure (PM) and goat/sheep manure (GSM), respectively, and composted by the turned windrow composting system. Throughout the composting process, a number of parameters were monitored, such as temperature, pH, electrical conductivity (EC), organic matter (OM), OM losses, total organic carbon (C_org), total nitrogen (N_t), C_org/N_t ratio, and the germination index (GI). In both piles, the temperature exceeded 55 °C for more than 2 weeks, which ensured maximum pathogen reduction. Organic-matter losses followed a first-order kinetic equation in both piles. The final composts presented a stabilized OM and absence of phytotoxins, as observed in the evolution and final values of the C_org/N_t ratio (C_org/N_t < 20) and the germination index (GI > 50 percent). Therefore, composting can be considered as an efficient treatment to recycle this type of waste, obtaining composts with suitable properties that can be safely used in agriculture.     

Optimization of Medlar Pruning Waste Composting Process by Cattle Manure Addition

In this study, medlar pruning waste (MPW) was composted with and without cattle manure (CM). Two piles were prepared: one contained only MPW (pile 1) and one contained MPW augmented with CM (pile 2). Both piles were composted in an enclosed composting vessel with passive aeration and aeration by turning. During the composting process, temperature, pH, electrical conductivity (EC), organic matter (OM), OM losses, total organic carbon (C_org), total nitrogen (N_T), C_org/N_T ratio, and germination index (GI) were measured. Pile 2 produced a faster increase of the temperature and had a longer thermophilic phase than pile 1. However, the rate of OM degradation was faster in pile 1 than in the pile containing CM (pile 2). The addition of CM also resulted in an increased pH and salt content. In both piles, C/N ratio decreased throughout the process, presumably as a result of the faster organic carbon degradation compared to N mineralization. However, only pile 2 had a final C/N ratio <20, the limit accepted for compost by the Spanish legislation on fertilizer. Also, both composts had GI > 50 percent, indicating an absence of phytotoxicity.     

Crop yield and carbon sink potential with precipitation in maize and potato cropland ecosystems over the summertime monsoon transition zone of China

China has significantly enhanced vegetation coverage and terrestrial carbon sink functions through ecological restoration. However, cropland ecosystems are sensitive to a changing climate over the summertime monsoon transition zone of China (SMTZC), which has implications for carbon cycling. For example, it is unclear how changes in precipitation will affect the cropland ecosystem carbon sinks (CS_e) and carbon sink potential (CS_p), and the mechanisms of tradeoffs that develop between plant and soil organic carbon (SOC) are unclear. Here, we integrated crop yield, total biomass (TB) and water coefficient in a combined field and modelling experimental. We explored the mechanisms of ecosystem carbon cycling and CS_p in the SMTZC under different precipitation scenarios. We found that soil organic carbon sink (SOC_s) was strongly correlated with the plant organic carbon sink (POC_s) and discovered. Significant differences in CSp between ecosystems resulting from interannual precipitation. The C₄ (maize, Zea mays) and C₃ (potato, Solanum tuberosum L) carbon sinks (CSs) were 68.59, 190.73, 160.37 Mt and 10.21, 30.97, 14.59 Mt for the 3 years, respectively. Precipitation effectively increased TB and yield, but excessive precipitation in them, which was most obvious in C₃ ecosystem (R² > 0.60) and reduced POC_s, evident in C₄ ecosystem (R² > 0.16). This study provides data and a scientific basis for increasing CS and achieving carbon neutrality in cropland.     

Plant canopy effects on litter accumulation and soil microbial biomass in two temperate forests

The objective of this study was to determine whether differences in canopy structure and litter composition affect soil characteristics and microbial activity in oak versus mixed fir-beech stands. Mean litter biomass was greater in mixed fir-beech stands (51.9t ha⁻¹) compared to oak stands (15.7t ha⁻¹). Canopy leaf area was also significantly larger in mixed stands (1.96m² m⁻²) than in oak stands (1.73m² m⁻²). Soil organic carbon (C _org) and moisture were greater in mixed fir-beech stands, probably as a result of increased cover. Soil microbial biomass carbon (C _mic), nitrogen (N _mic), and total soil nitrogen (N _tot) increased slightly in the mixed stand, although this difference was not significant. Overall, mixed stands showed a higher mean C _org/N _tot ratio (22.73) compared to oak stands (16.39), indicating relatively low rate of carbon mineralization. In addition, the percentage of organic C present as C _mic in the surface soil decreased from 3.17% in the oak stand to 2.26% in the mixed stand, suggesting that fir-beech litter may be less suitable as a microbial substrate than oak litter.     

Effects of Climate Changes and Pollution with Heavy Metals on the Transformation of Carbon Compounds in Different Soil Types of Agroecosystems in the Forest-Steppe of Baikal Region

The results of long-term (1992–2005) monitoring of the carbon compounds transformation in soils of forest- steppe agroecosystems polluted by heavy metals in the Baikal region in the years different from the “climatic norm” are discussed. The influence of environmental factors on the functioning of microbial community was estimated by the C_micr content and CO₂ emission. The changes in the ecophysiological parameters (C_micr/C_org and C-CO₂/C_micr, mg/(g h) related to the availability of the substrate and intensity of carbon (re)immobilization in different soils revealed the differences in the formation of a stable microbial community dependent on the environmental factors, especially in anomalous years. The use of a systemic approach and analysis of the carbon compounds transformation based on the proportion between the flows of net-mineralized and (re)immobilized carbon (NM: RI) allowed to evaluate integrally the functioning regime of the agroecosystems and the ecological impact on them. The differences in the functioning of agroecosystems on different heavy metal-polluted soils identified on the background of climatic changes are suitable for forecasting the current state and development of agroecosystems. For agroecosystems of this region, C-CO₂ emission was estimated for the first time; it was more intense from the soils with the high humus content than from the soils poor in humus (141 and 101 g C/m², respectively).     

Changes in the organic matter forms in chernozems of the Kamennaya Steppe under different land uses, locations, and hydromorphism degrees

The soils of the Kamennaya Steppe (Voronezh oblast) were studied. The rate of changes in the contents of C_org and the particular forms of organic matter (labile, microbial, and stable) were revealed in the quasi-natural soils of the fallows and shelterbelt and in the arable soils (rainfed farming for 12, 55, 85, and 115 yrs and irrigated farming for 40 yrs) of different positions on the watersheds and slopes. The effect of the increased soil moistening in the recent decades was also studied. In the upper 50 cm of the fallow soils that were not plowed since 1882, the relative C_org accumulation in the recent 30 yrs has amounted to 5%. The soils of the shelterbelt planted in 1903 were similar to the fallow soils. As compared to the soil of the unmown fallow, the C_org loss from the 1-m soil layer under the shelterbelt and the 12-year-old cropland were less than 9%; the losses from the plowed soils (used for 55–115 yrs) were 21–27% on the watersheds and 37–46% on the slopes. In the first decade, the rate of the Corg losses in the 0- to 20-cm layer of the cultivated chernozem was 120 g C/m². With the increasing duration of the soil plowing (from 55 to 115 yrs), the C_org losses decreased from 45 to 28 g C/m² per yr in the watershed soils and from 51 to 35 g C/m² per yr in the soils on the slopes. The maximum loss of C_org was found for the soils on slopes, waterlogged soils, and irrigated soils. In the slope soils, the C_org loss due to erosion was 9–18% of the total. In the upper horizons of the old agrogenic soils, compared to the soil of the unmown fallow, the C_ha/C_fa increased, since the content of fulvic acids (FA) faster decreased than that of the humic acids (HA); the C content of the nonhydrolyzable residue was reduced. The slope and waterlogged soils differed from the watershed soils in the smaller amounts of HA and FA and in the greater content of humin carbon. In the 0- to 20-cm layer of the soils studied, the rate of the basal respiration (BR) was 0.2–0.5 μg C/g soil per h, the content of the microbial biomass (C_micr) was 326–1073 μg C/g, and the share of C_micr amounted to 1.0–1.9%. These values were minimal in the irrigated soil and maximal in the fallow ones. A high correlation coefficient (r = 0.88–0.92) was found between the C_micr content and the BR, between the contents of C_org and HA, and between the contents of C_org and mobile C. The correlation coefficient between the contents of C_org and FA and C_org and humin C was 0.67.