Water Extractable Organic Carbon Research Articles

Residual Effect of Compost and Biochar Amendment on Soil Chemical, Biological, and Physical Properties and Durum Wheat Response

The residual effect of compost and biochar amendment on soil properties and durum wheat response was evaluated under field conditions in a Mediterranean environment. The treatments compared in a randomized complete block experimental design with three replications were: mineral fertilizer (100 kg N ha−1), compost applied at the rate of 25 Mg ha−1, biochar applied at the rates of 10 and 30 Mg ha−1, unfertilized control. Wheat was the second crop included in a sorghum–wheat cropping system and did not receive fertilizer supply. A hierarchical statistical analysis was carried out to investigate how different treatments could impact the cropping system performance. The findings highlight the significant influence of soil properties, particularly total N, WEOC, and TOC, on wheat and protein yield. One year after the amendment and fertilizer application, compost and biochar significantly increased soil total organic carbon content. The highest soil water extractable organic carbon was found with the compost application (76.9 mg kg−1), whereas the lowest value (50 mg kg−1) was with the highest rate of biochar. Soil respiration rates and hydraulic properties were not affected by the investigated treatments. This behavior is probably related to the short experimental duration and to the silty clayey soil texture. Significant correlations were observed between bulk density and water content at pressure heads in the −20 and −100 cm range; this range accounts for the effect of soil macro and mesopores. Multiple linear regression analysis revealed strong predictive power for grain (R2_adj = 0.78; p < 0.001) and protein yield (R2_adj = 0.77; p < 0.001). The highest grain yield (3.36 Mg ha−1) was observed with compost, and the lowest (2.18 Mg ha−1) with biochar at a rate of 30 Mg ha−1. These findings lay the basis for understanding how different soil amendment management may impact soil quality and wheat performance, even in consideration of climate change.

Fire Impacts on the Soil Metabolome and Organic Matter Biodegradability.

Global wildfire activity has increased since the 1970s and is projected to intensify throughout the 21st century. Wildfires change the composition and biodegradability of soil organic matter (SOM) which contains nutrients that fuel microbial metabolism. Though persistent forms of SOM often increase postfire, the response of more biodegradable SOM remains unclear. Here we simulated severe wildfires through a controlled "pyrocosm" approach to identify biodegradable sources of SOM and characterize the soil metabolome immediately postfire. Using microbial amplicon (16S/ITS) sequencing and gas chromatography-mass spectrometry, heterotrophic microbes (Actinobacteria, Firmicutes, and Protobacteria) and specific metabolites (glycine, protocatechuate, citric cycle intermediates) were enriched in burned soils, indicating that burned soils contain a variety of substrates that support microbial metabolism. Molecular formulas assigned by 21 T Fourier transform ion cyclotron resonance mass spectrometry showed that SOM in burned soil was lower in molecular weight and featured 20 to 43% more nitrogen-containing molecular formulas than unburned soil. We also measured higher water extractable organic carbon concentrations and higher CO2 efflux in burned soils. The observed enrichment of biodegradable SOM and microbial heterotrophs demonstrates the resilience of these soils to severe burning, providing important implications for postfire soil microbial and plant recolonization and ecosystem recovery.

Three years of cover crops management increased soil organic matter and labile carbon pools in a subtropical vegetable agroecosystem

AbstractCover crops have been widely adopted to improve soil functions in agroecosystems, including providing carbon (C) inputs that can contribute to soil C sequestration. However, soil C changes may be slow after introducing cover crops in unfavorable environments for soil organic matter (SOM) accumulation, like the Southeast United States subtropical region characterized by a warm humid climate, and coarse‐textured soils. We examined labile C pools as potential early indicators of SOM changes after cover crop introduction in a sandy subtropical vegetable production system. We compared the effects of four cover crop monocultures namely two grasses [sorghum sudangrass, Sorghum bicolor × S bicolor var. Sudanese and pearl millet, Pennisetum glaucum (L.) R. Br.], two legumes (sunn hemp, Crotalaria juncea L., and cowpea, Vigna unguiculata Walp.), and one four‐species mixture on soil organic carbon pools for 3 years. Soil samples were collected at a 15‐cm depth before cover crop planting and post cover crop incorporation to assess changes in SOM, permanganate‐oxidizable carbon (POX‐C), mineralizable carbon (Cmin), and water extractable organic carbon (WEOC). The incorporation of cover crops increased concentrations of SOM, POX‐C, and Cmin in year 3 relative to their baseline values in year 1. Concentration of SOM increased by 0.24 ± 0.05% (mean ± standard error) after 3 years of cover crop management. However, concentrations of WEOC significantly decreased in years 2 and 3 relative to the baseline. Monocultures and the mixture had similar effects on measured C pools, likely due to comparable aboveground biomass production. Our findings highlight the potential of POX‐C and Cmin as early indicators of SOM accumulation driven by cover crops use, as well as the capacity of cover crops to build SOM in similar subtropical systems and coarser textured soils.

Estimation of Carbon Stocks in Soils of Forest Ecosystems as a Basis for Monitoring the Climatically Active Substances

—The eluvozems and soddy eluvozems on two-layered deposits dominating in the soil cover of the Zvenigorod Biostation of Moscow State University, contain, on average, 65–83 t/ha of organic carbon in the organic layer and the upper meter of mineral strata. Carbon stock is minimal (59–68 t/ha) in the coarser-textured soddy eluvozem of the spruce forest and reaches 76–92 t/ha in soils of birch–spruce and pine–spruce forests. Organic layers store 3.3–5.8 t C/ha or 4–9% of the total soil organic carbon stock; the upper mineral layer (0–20 cm) stores 64–69%. Different levels and profile distribution of organic carbon in soils are determined by lithological and textural features of the soil profiles and by the nature of vegetation. The contribution of water-extractable organic carbon to the total organic carbon content in the upper mineral horizons does not exceed 1.3–1.8%; the contribution of microbial carbon is 1.7–2.4%. In acidic loamy soils, the enrichment in calcium and potassium, the cation exchange capacity, the content of exchangeable bases, and the degree of base saturation can serve as indicators of the content and stocks of organic carbon at the ecosystem level. The relationship with the content of clay fractions and oxalate-extractable Al and Fe is manifested to a lesser extent due to the similar origin and properties of soils. The variability of organic carbon stocks in soils is largely determined by its content, the influence of which decreases with depth. Accounting for spatial heterogeneity, field measurements of the soil bulk density and proportion of fine earth, and correct analytical determinations are essential components of the assessment of carbon stocks in soils of forest ecosystems as a part of the national monitoring system for carbon pools and greenhouse gas fluxes.

New insights into the production, characterization and potential uses of vineyard pruning waste biochars

Vineyard pruning waste (VP) can be converted into a useful char using pyrolysis as part of a valorization strategy. This study analyzed the effect of temperature (300 and 600 °C) and residence time (1 and 3 h) on an ample number of properties of VP derived biochars, including potential negative environmental impacts. The results showed a clear influence of temperature on biochar’s properties and a weaker effect of residence time. Increasing temperature raised soil pH, electrical conductivity (EC), ash and C contents, aromaticity, specific surface area, solid density, mesoporosity and partial graphitization. However, higher pyrolysis temperature reduced O/C and N/C ratios, total N, P and Mg, and polycyclic aromatic hydrocarbons (PAHs). Particularly, the concentration of water extractable organic carbon (WEOC) decreased dramatically with pyrolysis temperature. Moreover, the WEOC fraction of biochars pyrolyzed at 300 °C exhibited a larger aromaticity than those pyrolyzed at 600 °C. Prolonged residence time increased ash content and fixed carbon (FC) and decreased H/C and O/C ratios; however, most frequently this parameter affected biochar properties following opposite trends for the two pyrolysis temperatures. Hydrophysical properties were adequate to consider VP derived biochars as growing media component. PAH concentration was much lower than thresholds following international standards. The germination index increased with temperature and decreased with residence time, so that phytotoxicity was observed in VP and in biochars pyrolyzed for 3 h. Our research demonstrates that, besides temperature, residence time can be useful to modulate the properties of biochars and that prolonged time effect is temperature-dependent.

Comparison of organic carbon properties in extracted soil solutions obtained underneath Cryptomeria japonica and Quercus acutissima and its implication on stream dissolved organic carbon

Dissolved organic carbon (DOC) in soils is released into streams, working as a main component of the carbon cycle. DOC in terrestrial and aquatic ecosystems participates in many biogeochemical reactions and processes such as heterotrophic respiration, sorption of metals, and transport of pollutants. In order to understand the connectivity of organic carbon among soil, soil water, and forest streams, we investigated the concentrations and dual carbon isotope ratios (δ13C and Δ14C) of soil organic carbon (SOC) and water-extractable organic carbon (WEOC) obtained from soils beneath two tree species stands, and compared these with stream Δ14C-DOC of the forest watershed. Soil samples were collected at different depths (0–10, 10–30, and 30–50 cm) beneath Japanese cedar (Cryptomeria japonica) and sawtooth oak (Quercus acutissima). Although the SOC concentration was not significantly different between the two tree species, the WEOC concentration ([WEOC]) of soil at 0–10 cm depth under Cryptomeria japonica was higher than that of Quercus acutissima, in general. The δ13C-SOC and δ13C-WEOC increased, while the Δ14C-SOC and Δ14C-WEOC decreased with increasing soil depth. The Δ14C-WEOC was higher than the Δ14C-SOC, indicating that WEOC could be primarily derived from the young, hydrophilic, and exchangeable fraction of SOC, rather than from SOC strongly bonded to mineral soils. However, the stream Δ14C-DOC was lower than Δ14C-WEOC in general, except during summer storms. The 14C-depleted DOC released from deep soils or groundwater might lower Δ14C-DOC of a stream, suggesting that relatively old DOC could be released into streams during baseflow. This is contrary to the results of previous studies that have reported positive stream Δ14C-DOC from temperate forests. The discrepancy warrants future research on forest stream Δ14C-DOC across entire seasons, particularly under Asian monsoon climates.

Temperature and organic carbon quality control the anaerobic carbon mineralization in peat profiles via modulating microbes: A case study of Changbai Mountain

Peatlands account for a significant fraction of the global carbon stock. However, the complex interplay of abiotic and biotic factors governing anaerobic carbon mineralization in response to warming remains unclear. In this study, peat sediments were collected from a typical northern peatland-Changbai Mountain to investigate the behavior and mechanism of anaerobic carbon mineralization in response to depth (0–200 cm) and temperature (5 °C, 15 °C and 20 °C), by integrating geochemical and microbial analysis. Several indices including humification indexes (HI), aromaticity, and water extractable organic carbon (WEOC) components were applied to evaluate carbon quality, while 16S rRNA sequencing was used to measure microbial composition. Regardless of temperature, degradations of carbon quality and associated reduction in microbial abundance as well as diversity resulted in a decrease in anaerobic carbon mineralization (both CO2 and CH4) towards greater depth. Warming either from 5 °C to 15 °C or 20 °C significantly increased anaerobic carbon mineralization in all depth profiles by improving carbon availability. Enhanced carbon availabilities were mediated by the change in microbial composition (p < 0.01) and an increase in metabolic activities, which was particularly evident in the enhanced β-glucosidase activity and microbial collaborations. A remarkable increase of over 10-fold in the relative abundance of the Geothrix genus was observed under warming. Overall, warming resulted in an enhanced contribution of CH4 emission and a higher ratio of hydrogenotrophic methanogenesis, as evidenced by carbon isotope fractionation factors. In addition, deep peat soils (>100 cm) with recalcitrant carbon demonstrated greater temperature sensitivity (Q10: ∼2.0) than shallow peat soils (Q10:∼1.2) when temperature increased from 15 °C to 20 °C. The findings of this study have significantly deepened our understanding for mechanisms of carbon quality and microbe-driven anaerobic carbon mineralization in peatlands under global warming.

Potential carbon mineralization assays are confounded by different soil drying temperatures

Measuring carbon dioxide (CO2) produced after re-wetting previously dried soil is an increasingly popular soil health assay, but there is disagreement on the optimal soil drying temperature. We tested whether soil drying temperature impacts water-extractable organic carbon (WEOC) and soil CO2 emissions following rewetting. Soils were collected from corn/soybean croplands and adjacent perennial vegetation at four sites in Iowa, USA. Soil replicates were dried at 22 °C, 35 °C, 55 °C, 85 °C, and rewetted for incubation at 22 °C. Soil WEOC and CO2 emissions after re-wetting increased nonlinearly with drying temperature. Effects on CO2 were largest after four days of incubation, but cumulative differences persisted even after 42 days. Responses of CO2 and its stable isotope ratio (δ13C) to increased drying temperature varied among sites and vegetation types, indicating shifts in C sources. Soil health assays performed with different soil drying temperatures may not be directly comparable, effects of drying temperature may vary idiosyncratically among samples, and drying at 22 °C or 35 °C as opposed to higher temperatures may be preferable to avoid increasing C availability.

Diversifying with grain legumes amplifies carbon in management-sensitive soil organic carbon pools on smallholder farms

Crop diversification with grain legumes has been advocated as a means to increase agroecological resilience, diversify livelihoods, boost household nutrition, and enhance soil health and fertility in cereal-based cropping systems in sub-Saharan Africa and around the world. Soil organic carbon (SOC) is a primary indicator of soil health and there is limited data regarding SOC pools and grain legume diversification on smallholder farms where soils are often marginal. In Malawi, a range of legume diversification options are under investigation, including rotations and a doubled-up legume rotation (DLR) system in which two compatible legumes are intercropped and then rotated with a cereal. The impact of the DLR system on SOC has not yet been determined, and there is a lack of evidence regarding SOC status over a gradient of simple to complex grain legume diversified systems. We address this knowledge gap by evaluating these systems in comparison to continuous sole maize (Zea mays L.) at three on-farm trial sites in central Malawi. After six years of trial establishment, we measured SOC in bulk soils and aggregate fractions and in faster cycling SOC pools that respond more rapidly to management practices, including water extractable organic carbon (WEOC), particulate organic matter carbon (POM-C), potentially mineralizable carbon (C), and macroaggregate C. Cropping treatment differences were not seen in bulk SOC or total N, but they were apparent in SOC pools with a shorter turnover time. The DLR system of intercropped pigeonpea (Cajanus cajan (L.) Millsp.) and groundnut (Arachis hypogaea L.) rotated with maize had higher WEOC, POM-C, potentially mineralizable C, macroaggregate and microaggregate C values than continuous maize. Of the single legume rotations, the pigeonpea-maize rotation had more mineralizable C and microaggregate C compared to continuous maize, while the groundnut-maize rotation had similar C values to the maize system. Overall, this study shows the potential for crop rotations diversified with grain legumes to enhance C in management sensitive SOC pools, and it is one of the first reports to show this effect on smallholder farm sites.

Accumulation of SOC and Carbon Fractions in Different Age Red Fescue Permanent Swards

One of the practices often mentioned to achieve climate change mitigation is the long-term cultivation of perennial plants. The objective of the study was to estimate changes in the accumulation of soil organic carbon (SOC) and its fractions in 0–10, 10–20, 20–30 cm, and within 0–30 cm soil layer of red fescue (Festuca rubra L.) swards that differ in age (5, 10 and 15 years) as well as to compare them with the arable field. Our results show that SOC accumulation at 5-year-old cultivation of red fescue is high, later this SOC increase slowed down from 71% in the 0–30 cm soil layer when land use was converted from arable field to 5-year-old sward to 1% from 10 to 15 years. The level of water extractable organic carbon (WEOC) in the 0–30 cm soil layer of swards was significantly higher compared to the arable field. The positive effect of these swards in the accumulation and stabilization of organic carbon during humification in the soil was also determined. The largest amounts of mobile humic substances (MHS) and mobile humic acids (MHA) accumulated in the 0–10 cm layer of sward soil (3.30–4.93 and 1.53–2.48 g kg−1, respectively). In conclusion, the findings suggest that a conversion from arable to soil under permanent grass cover significantly improves carbon status.

Tree mycorrhizal type controls over soil water-extractable organic matter quantity and biodegradation in a subtropical forest of southern China

Tree mycorrhizal type is believed to be a key factor controlling soil organic matter dynamics in forests, yet its effects on soil dissolved organic matter (DOM) quantity and biodegradation remain unknown, especially in sub/tropical forests. Here, we used soil water-extractable organic matter (WEOM) as a proxy for soil DOM, and measured water-extractable organic carbon (WEOC), total nitrogen (WETN), and total phosphorus (WETP) concentrations, and WEOM chemical composition (i.e., aromaticity and molecular weight) in the 0–10 cm and 10–30 cm mineral soil depths along the gradient ranging from arbuscular mycorrhizal (AM)- to ectomycorrhizal (ECM)-associated tree dominance in a subtropical secondary forest of southern China. Subsequently, we assessed soil WEOM biodegradation using a 42-day aerobic incubation experiment. At each soil depth, WEOC concentration and WEOC:WETN ratio increased with increasing ECM tree dominance, whereas WEOM aromaticity and molecular weight exhibited an opposite changing trend. Moreover, WEOC concentration correlated positively with soil organic C, total N, total P, and sand content, but correlated negatively with soil pH and clay and silt contents. Soil WEOM biodegradation did not change with ECM tree dominance in 0–10 cm depth but decreased with increasing ECM tree dominance in 10–30 cm depth. Soil WEOM biodegradation was negatively related to WEOC:WETP and WETN:WETP ratios, but was positively related to WEOM aromaticity and molecular weight. These findings suggested that tree mycorrhizal type is a potential indicator of soil DOM concentration and biodegradation, and highlight that the shifts in dominance of AM- and ECM-associated trees will influence soil DOM dynamics by altering soil texture, C:N:P stoichiometry, and C quality in subtropical forests.

Amendments of waste ochre from former coal mines can potentially be used to increase soil carbon persistence

There is an increasingly urgent need to remove CO2 from the atmosphere. Increasing C storage in soils has been discussed as a possible method of achieving this. Regardless of whether increasing soil C would result in reduced atmospheric C or not, increasing the amount of organic carbon (OC) stored as organic matter in soils is widely regarded as leading to agronomic benefits such as increased water retention and resistance to erosion. Fe oxides adsorb OC in soil, protecting it from degradation. In this study we investigated the use of waste ochre (Fe oxy-hydroxide) that precipitates from the drainage of former coal mines as a soil amendment to increase C storage in soils via reduced C lability. In preliminary batch experiments, ochres reduced the release of OC from soils into solution. In plant growth experiments with wheat (var. Skyfall, RAGT) 5 wt% amendments of ochre to soils significantly reduced the concentration of hot water extractable OC by approximately 16% and OC lost from the soils in leachate by approximately 43%. Above ground plant biomass was significantly reduced by approximately 50% in the amended soils. There was no evidence for increased uptake of potentially toxic elements in the plants from the ochre-amended soils compared to the study controls but Olsen P extractable phosphate was decreased by the ochre amendments. In subsequent experiments with agronomically realistic additions of KH2PO4 there was no difference in plant biomass between the study controls and the ochre-treated soils suggesting that reduced plant growth was due to reduced P availability; C lability was still significantly reduced. Furthermore, the ochre amendments helped retain th added phosphate in the soil. These results indicate that Fe oxide amendments to soil may be a viable way of changing soil chemistry in order to increase the amount of OC retained in soils. Further experiments investigating the impacts of the ochre amendments on greenhouse gas emissions and soil biology are required followed by field trials where the impact of more variable soil moisture and temperature effects can be assessed and crops grown to harvest. A full Life Cycle Analysis could then be performed. Given the relatively limited quantities of former coal mine ochres available in the UK and the carbon footprint of transporting materials prior to adding them to soils, similar experiments to those reported here, taking into account chemical and mineralogical variations, are warranted to determine the global stock pile of Fe-rich wastes that could potentially be used to reduce C lability in soils.

Effect of flood duration on water extractable dissolved organic matter in flood plain soils: A laboratory investigation

Hydrological changes significantly affect organic matter export in flood plains, which is a vital aspect of aquatic food webs and biogeochemical cycles. The frequency and duration of floods are projected to increase; thus, the effects of flood duration on labile forms of organic matter that respond quickly to environmental changes need to be investigated. To better understand the effect of flood duration on dissolved organic matter (DOM), we used columns under controlled laboratory conditions to simulate moderate flooding in riparian forest soils. We monitored changes in physicochemical properties and DOM after 1, 3, 8, 16, and 30 days of flooding (FDs) and up to 30 days after flooding (DAF). pH and electrical conductivity (EC) were significantly affected by flood duration; increasing EC and pH were linked to increasing water-extractable organic carbon (WEOC) after 16 FDs and total dissolved nitrogen (TDN) in soil. The variations included decreased protein-like components after 16 and 30 FDs, increased aromaticity, and TDN in the flood water. In post-flooded soil, WEOC varied with flood duration, that is, 16 > 8 > 3 FDs; however, based on the physical, chemical, and DOM attributes, the principal component analysis distinguished the soil into three groups: initial, early days after flooding (approximately 5 DAF), and 30 DAF, with 30 DAF having a higher fluorophore to WEOC ratio. Flood duration and post-flooding period affected DOM directly and indirectly through changes in physical conditions influencing microorganisms while simultaneously fostering exchange between the soil and flood water during periods of inundation.

Carbon Emission and Biodiversity of Arctic Soil Microbial Communities of the Novaya Zemlya and Franz Josef Land Archipelagos

Cryogenic soils are the most important terrestrial carbon reservoir on the planet. However, the relationship between soil microbial diversity and CO2 emission by cryogenic soils is poorly studied. This is especially important in the context of rising temperatures in the high Arctic which can lead to the activation of microbial processes in soils and an increase in carbon input from cryogenic soils into the atmosphere. Here, using high-throughput sequencing of 16S rRNA gene amplicons, we analyzed microbial community composition and diversity metrics in relation to soil carbon dioxide emission, water-extractable organic carbon and microbial biomass carbon in the soils of the Barents Sea archipelagos, Novaya Zemlya and Franz Josef Land. It was found that the highest diversity and CO2 emission were observed on the Hooker and Heiss Islands of the Franz Josef Land archipelago, while the diversity and CO2 emission levels were lower on Novaya Zemlya. Soil moisture and temperature were the main parameters influencing the composition of soil microbial communities on both archipelagos. The data obtained show that CO2 emission levels and community diversity on the studied islands are influenced mostly by a number of local factors, such as soil moisture, microclimatic conditions, different patterns of vegetation and fecal input from animals such as reindeer.

The lower labile carbon of surface soils in Chinese semiarid areas

ABSTRACT Hot water extractable organic carbon (HWOC), the labile carbon component, is often used to indicate soil organic carbon (SOC) dynamics. Nevertheless, few studies have been carried out in arid climate areas which affects our full understanding of HWOC. Here, we investigated the change in HWOC in the topsoil of different ecosystems in the southern part of the Loess Plateau in the semiarid region of China and compared it with that in other regions. The HWOC concentrations of the study area (0-10 cm) were 0.27 ± 0.12 g C kg−1 and 0.19 ± 0.04 g C kg−1 in the natural and agricultural systems respectively, and the HWOC proportions were 1.38 ± 0.38% and 2.18 ± 0.22%. The HWOC concentration and proportion in the study area were much lower than the reported data in other areas, which may be affected by drought conditions. Irrigation could weaken the difference in HWOC between agricultural systems in different regions. Since HWOC is easily lost due to the impact of the arid climate, the soil carbon balance and carbon sequestration in arid and semiarid areas are relatively unstable, indicating that soil management should be improved in combination with water management.

Experimental drought increased the belowground sink strength towards higher topsoil organic carbon stocks in a temperate mature forest

Reduced carbon assimilation by trees is often considered to lower the overall carbon sink function of drought-stressed forests. However, soil organic carbon (SOC) stocks may respond differently to drought than ecosystem carbon flux dynamics, leading to imprecise predictions of soil carbon sequestration when one value is inferred from the other. As a major component of soil organic matter, SOC is the largest actively cycling terrestrial carbon reservoir, and thus fulfills various important ecosystem services. Yet, there is uncertainty about how SOC quantity and quality respond to drought in temperate forests. This study addressed the depth distribution of SOC stocks and soil organic matter stability in a forest exposed to artificial drought for five consecutive growing seasons below clusters of temperate mature deciduous beech (Fagus sylvatica L.) and coniferous spruce (Picea abies (L.) Karst.). In addition to SOC stock determination, we measured concentrations of water-extractable organic carbon (WEOC), performed density fractionation, and determined beta values of SOC (slopes of linear regressions between δ13C of soil and log-transformed SOC content throughout soil depth profiles). Following drought, SOC stocks down to 30 cm depth increased by a factor of 1.5 under P. abies while they did not change with drought under F. sylvatica. Under both species, SOC stocks in the mineral topsoil (0–5 cm soil depth) increased by >80 % with drought, increasing the relative contribution of this thin depth section to total SOC from 5 % to >30 %. At 5–15 cm soil depth, SOC stocks decreased with drought under F. sylvatica but not under P. abies. With drought, carbon in the free light fraction (fLF) increased under F. sylvatica but declined marginally under P. abies. Results from density fractionation and beta values suggest decreased soil organic matter stability under F. sylvatica and increased stability under P. abies. Greater SOC accumulation suggests that the belowground carbon sink strength of drought-stressed forests increases, which contrasts with reduced ecosystem carbon uptake under drought.

Solid and Liquid Phases of Anaerobic Digestate for Sustainable Use of Agricultural Soil

Given the growth in the number of biogas power plants and the increase in the generation of waste from energy production, it is relevant to study the sustainable nature of this waste. Digestate is a product of the anaerobic digestion process, and is a valuable bio-fertilizer containing organic matter and nutrients necessary for agricultural plants’ growth. The study showed that different rates of liquid and solid phases of anaerobic digestate influenced the contents of carbon and nitrogen in genetically young soil in alluvial deposits—Fluvisol. The application of solid digestate (SD) considerably increased soil organic carbon content (SOC) in the 0–10 cm soil layer; however, SOC did not reach the 20–30 cm layer. Liquid digestate (LD) significantly increased SOC in the deeper layers. The levels of mineral nitrogen (Nmin) and water extractable organic carbon (WEOC) increased in the 0–10 cm soil layer soon after fertilization with LD and SD. The mobile components of the soil (Nmin and WEOC) were characterized by high variability during the growing season. Within the 2-month period, their concentrations decreased drastically and were close to those of unfertilized soil. The research indicates that anaerobic digestate had a greater effect on mobile forms of carbon and nitrogen in the soil than on their total amounts.

Vegetation-derived pyrogenic carbon degradation and stabilisation in UK peatlands†

Background Strongly varying timescales of pyrogenic carbon (PyC) degradation have been observed across depositional settings. To date, PyC degradation in UK peatlands has had limited investigation. Aims This study aims to evaluate how PyC recalcitrance relates to differing production characteristics, fuels and duration of exposure in UK peatlands. Methods PyC samples produced from key peatland vegetation types were exposed on a peatland surface to assess molecular (by Fourier-transform infrared), leachable carbon (water-extractable organic carbon) and elemental (C, H, N, O) changes occurring over a year. Key results PyC degradation phases were observed: (1) very rapid (≤1 month) loss of leachable carbon; (2) longer-term (1–12 months) changes to PyC characteristics indicative of soil interactions. ‘Severity’ had a significant effect on all measured variables. Conclusions This study indicates that PyC is susceptible to changes within short timescales in UK peatlands, particularly low-temperature PyC, but that stabilisation through soil matrix interactions may occur over longer periods (&gt;1 year). Implications The findings indicate that UK peatland wildfire carbon cycling research should consider early pulses of carbon to the wider environment, as well as longer-term C storage in PyC.

Variation of Soil Nitrogen, Organic Carbon, and Waxy Wheat Yield Using Liquid Organic and Mineral Fertilizers

Biogas slurry is widely used to fertilize crops. However, their impact on soil parameters and waxy winter wheat (Triticum aestivum L.) nutrition is poorly understood. The aim of this research was to determine the influence of liquid anaerobic digestate and pig slurry applied to waxy winter wheat on the dynamics of soil organic carbon (SOC) and total nitrogen (Ntot) in different forms on grain yield, and to compare them with the use of ammonium nitrate. The nitrogen rates (kg N·ha−1) used for fertilization were N0, N60, N120, and N120+50. The study showed that the variation of nitrate nitrogen (N-NO3) and water-extractable organic carbon (WEOC) in the soil during the growing season depended on N fertilizer rates, meteorological conditions of the year, and, to a lesser extent, on fertilizer forms. Meteorological conditions were responsible for the demand and supply of nutrients from the soil by the waxy winter wheat variety. This determined the wheat yield and the variation in the soil parameters studied. Over the 2 years, the soil C:N ratio decreased, especially at the medium and high N fertilizer rates. The lowest changes were observed in the unfertilized and fertilized plots at a rate of 60 kg N·ha−1.

Temporal changes in the nutrient content of cattle dung in the Nebraska Sandhills ecosystem

Dung excreted by cattle composes a significant portion of the nutrient inputs in a grazed ecosystem and can have wide-ranging effects on soil properties and vegetation. However, little research has been conducted on the nutrient dynamics of excreted dung in situ that has not been disturbed prior to field sampling. In this study, we analyzed 294 dung pats (1–24 days old) collected from a Nebraska Sandhills meadow to determine water-extractable organic carbon (WEOC), water-extractable nitrogen (WEN), water-extractable phosphorus (WEP), and percent dry matter (DM) changes over time. In addition, we investigated if sample handling - frozen storage – and the formation of surface crust during dung field drying affect dung nutrient concentrations. Dung WEOC and WEN both followed exponential decay curves of nutrient loss over time and were modeled as a function of age. In contrast, WEP was poorly correlated with age. The percent dry matter in conjunction with sample WEOC concentration were stronger determinants of WEP than age alone. Freezing samples prior to analysis increased WEOC (37–98%) and WEN (37–123%), but lowered WEP (0.8–65%) compared to the samples from the same dung pat analyzed fresh. The dry surface crusts of dung pats had higher WEOC (98–112%) and WEN (112%) compared to moist interiors (on average, 3 cm from surface). This research provides evidence that dung nutrient concentrations decreased by 73% (WEOC) and 76% (WEN) over 24 days and shows that frozen storage and subsequent thawing for analysis, as well as crust formation during field drying, can significantly affect dung nutrient concentrations and spatial partitioning of dung nutrients.