Exogenous Organic Matter Research Articles

Sentinel-2 satellite images for monitoring cattle slurry and digestate spreading on emerging wheat crop: a field spectroscopy experiment

This study is aimed to evaluate the utility of Sentinel-2 imagery for monitoring exogenous organic matter (EOM) applied on winter wheat crop, using two spatial scales: proximal and satellite. From proximal sensing, multi-temporal spectral field measurements were taken on experimental fields consisting of three treatments (cattle slurry, liquid and raw digestates) and a control throughout 46 days. From Sentinel-2 satellites, images were analysed before and after EOM application. For both sensing scales, EOM and vegetation indices were used. On any scale of observation, the digestates spread on emerging wheat were easily detectable in late winter, in contrast to spring spreading events which were hindered by the developed vegetation. The agglomerative hierarchical clustering from the EOM indices divided by EVI achieved to discriminate digestates at early and medium stages of vegetation growth. Our findings did not apply for cattle slurry, presumably because of both lower organic and dry matter contents.

Role of livestock-derived amendments in soil organic carbon stocks in forage crops

The use of organic amendments for forage production has been promoted in recent years due to the adoption of sustainable agricultural practices and the increasing cost of mineral fertilizers. Organic manures can contribute with an extra carbon to the soil to the potential addition of carbon stocks. This study aimed to measure the capacity of different organic amendments commonly available in livestock farms for forage fertilization to influence the rate of soil organic carbon (SOC) under future climate change conditions. For this purpose, on-farm processed exogenous organic matter (EOM) was analyzed for fiber and organic carbon mineralization to obtain the percentage of decomposable EOM and resistant EOM (DEOM and REOM, respectively). The RothC model was run in grasslands and forage maize under different scenarios considering specific DEOM and REOM values. The results showed that the degradability of amendments could influence SOC dynamics. The SOC of grasslands after 38 years of simulation differed by >30 % between compost and the liquid fraction of cattle slurry. Forage crops were simulated under the RCP8.5 scenario and fertilized with amendments at the recommended amounts of nitrogen for these crops. As a result, SOC stocks had a better response to organic fertilization in grassland, except under the application of the liquid fraction, with a decrease in SOC of 16 %. In cropland, only the solid fraction from mechanical separation of slurry and compost applications increased the SOC stock from 13 % to 26 % in the 2020–2090 period. Our study provides insights into how the degradability of EOM can affect simulations of the SOC stock rate over time.

Ecological engineering of iron ore tailings into useable soils for sustainable rehabilitation

Ecological engineering of soil formation in tailings is an emerging technology toward sustainable rehabilitation of iron (Fe) ore tailings landscapes worldwide, which requires the formation of well-organized and stable soil aggregates in finely textured tailings. Here, we demonstrate an approach using microbial and rhizosphere processes to progressively drive aggregate formation and development in Fe ore tailings. The aggregates were initially formed through the agglomeration of mineral particles by organic cements derived from microbial decomposition of exogenous organic matter. The aggregate stability was consolidated by colloidal nanosized Fe(III)-Si minerals formed during Fe-bearing primary mineral weathering driven by rhizosphere biogeochemical processes of pioneer plants. From these findings, we proposed a conceptual model for progressive aggregate structure development in the tailings with Fe(III)-Si rich cements as core nuclei. This renewable resource dependent eco-engineering approach opens a sustainable pathway to achieve resilient tailings rehabilitation without resorting to excavating natural soil resources.

Effect of reduced inherent organic matter on stability and transport behaviors of black soil colloids

Soil organic matter plays an important role in the stability, transport, and fate of soil colloids. At present, studies have mostly focused on the effects of adding exogenous organic matter on soil colloidal properties, while there is very limited research on the effect of reduced inherent soil organic matter on the environmental behavior of soil colloids. This study investigated the stability and transport behavior of black soil colloids (BSC) and black soil colloids with reduced inherent organic matter (BSC-ROM) under different ionic strength (5, 50 mM) and background solution pH (4.0, 7.0, and 9.0) conditions. Meanwhile, the release behavior of two soil colloids in the saturated sand column under transient ionic strength conditions was also studied. The results showed that both ionic strength reduction and pH increase increased the negative charges of BSC and BSC-ROM, and improved the electrostatic repulsion between soil colloids and grain surface, thereby promoting the stability and mobility of soil colloids. The decrease in inherent organic matter had little effect on the surface charge of soil colloids, suggesting that the electrostatic repulsion was not the main force affecting the stability and mobility of BSC and BSC-ROM, and reducing inherent organic matter might significantly reduce the stability and mobility of soil colloids by weakening the steric hindrance interaction. The decrease of transient ionic strength reduced the depth of the energy minimum and activated the soil colloids retained on the surface of the grain at three pH conditions. This study is helpful to predict the potential impact of soil organic matter degradation on the fate of BSC in natural environment system.

Effects of exogenous organic matter addition on agricultural soil microbial communities and relevant enzyme activities in southern China

Soil microbial community composition plays a key role in the decomposition of organic matter, while the quality of exogenous organic matter (EOM: rice straw, roots and pig manure) can influence soil chemical and biological properties. However, the evidences of the effect of combination of crop residues and pig manure on the changes in soil microbial community and enzymes activities are scarce. A greenhouse pot experiment was conducted to investigate the potential effect of EOM by analyzing soil properties, enzyme activities and microbial communities. The experiment consisted of eight treatments: CK (control), S (1% (w/w) rice straw), R (1% (w/w) rice root), SR (1% (w/w) rice straw + 1% (w/w) rice root), and added 1% (w/w) pig manure to CK, S, R and SR, respectively. Results showed that the straw treatment significantly increased the microbial biomass (carbon and nitrogen) and total carbon and nitrogen contents, cellulase and β-1,4-glucosidase activities, bacteria (i.e., gram-positive bacteria and gram-negative bacteria) PLFAs contents relative to CK regardless of whether pig manure was added. Moreover, the interaction between crop residues (e.g., straw and roots) and pig manure significantly influenced the contents of microbial biomass nitrogen and microbial biomass phosphorus, and the ratio of gram-positive bacteria to gram-negative bacteria. Redundance analysis confirmed that pH, nitrate nitrogen, ammonium nitrogen and dissolve organic carbon contents were significantly associated with soil microbial community under crop residues without pig manure addition. Furthermore, the experiment results showed that pig manure application not only provided more abundant nutrients (C, N and P) but also induced higher microbial and enzymatic activity compared with no pig manure addition. Our findings suggest that the combination of above-ground straw and pig manure is a better option for improving the functions of soil ecosystem.

Exogenous-organic-matter-driven mobilization of groundwater arsenic

The potential release capacity of arsenic (As) from sediment was evaluated under a high level of exogenous organic matter (EOM) with both bioreactive and chemically reactive organic matters (OMs). The OMs were characterized by FI, HIX, BIX, and SUVA254 fluorescence indices showing the biological activities were kept at a high level during the experimental period. At the genus level, Fe/Mn/As-reducing bacteria (Geobacter, Pseudomonas, Bacillus, and Clostridium) and bacteria (Paenibacillus, Acidovorax, Delftia, and Sphingomonas) that can participate in metabolic transformation using EOM were identified. The reducing condition occurs which promoted As, Fe, and Mn releases at very high concentrations of OM. However, As release increased during the first 15–20 days, followed by a decline contributed by secondary iron precipitation. The degree of As release may be limited by the reactivity of Fe (hydro)oxides. The EOM infiltration enhances As and Mn releases in aqueous conditions causing the risk of groundwater pollution, which could occur in specific sites such as landfills, petrochemical sites, and managed aquifer recharge projects.

SoilFract: A mechanistic model accounting for the fate of exogenous organic matter in soil carbon and nitrogen cycles

As its use in agriculture grows, the fate of digestate in soil raises concerns on many different levels. In particular, the degradability of its organic matter when spread on soil is still an ongoing topic. In an effort to better understand the processes and dynamics of digestate soil incubation, C and N mineralization kinetics obtained in 358 days long laboratory incubations during decomposition of digestates were simulated using a dynamic model. The model includes twelve compartments related through processes including 18 parameters. The main novelty of this model is the use of accessibility-related variables to describe the fate of exogenous organic matter in soil, thus enabling a detailed understanding of its outcome in soil. Model calibration on cattle manure digestate incubation resulted in the estimation of parameter values. The newly calibrated model was then tested on an energy crop digestate incubation experiment. The model was able to reproduce accurately the experimental behavior of most variables.

Highly efficient transformation of slowly-biodegradable organic matter into endogenous polymers during hydrolytic fermentation for achieving effective nitrite production by endogenous partial denitrification

The utilization of slowly-biodegradable organic matter (SBOM) to provide nitrite efficiently for anaerobic ammonia oxidation (anammox) process is an essential topic. High nitrite concentration without inhibition of exogenous organic matter is optimal condition for anammox process. In this study, hydrolytic fermentation (HF) of SBOM was applied to drive an endogenous partial denitrification (EPD) process (nitrate to nitrite) during an anaerobic-anoxic operation in a starch-fed system. With a limited production of exogenous organic matter (22.3 ± 4.9 mg COD/L), 79.0% of SBOM was transformed into poly-hydroxyalkanoates (PHA) through a pathway of simultaneous HF-absorption and endogenous polymer synthesis, corresponding to a hydrolytic fermentation ratio of 86.0%. A high nitrate to nitrite transformation ratio of 85.4% was achieved under an influent carbon to nitrogen ratio of 4.8. Denitrifying glycogen-accumulating organisms (DGAOs) was enriched from 0.6% to 10.9%, with an increase from 0.7 to 1.0 of nitrate reductase genes to nitrite reductase genes ratio. Subsequently, nitrate reduction rate was 5.6-fold higher than the nitrate reduction rate. A prominent migration of exogenous complete denitrification to EPD was accomplished. Furthermore, the starch-fed system exhibited performance with significant adaptability and stability in the presence of different SBOMs (dissolved protein and primary sludge). Therefore, the HF-EPD system achieved efficient nitrite production through EPD with the addition of various SBOMs, providing a potential alternative to anammox systems for the treatment of SBOM-rich wastewater.

The fate of N released from the fixed NH4+ pool in response to different straw application doses

Ammonium (NH4+) can be fixed by clay minerals and subsequently released, and this process plays a vital role in promoting soil nitrogen retention and supply in agriculture. However, the process of fixed NH4+ release and its driving forces remain unclear, especially under inputs of exogenous organic matter. In this study, the fixed NH4+ pool of an Udoll (based on the USDA Soil Taxonomy System) in Northeast China was labelled using a 15N tracer under chloroform-fumigated conditions, and then the labelled soil was mixed with unlabelled (unfumigated) soil at four levels of straw incorporation: S0 (without straw), S4 (4 t ha−1), S8 (8 t ha−1), and S12 (12 t ha−1). By monitoring the tracer, we found that 20 %–24 % of the labelled fixed NH4+ was released at the end of the incubation period (288 d), and the release of fixed NH4+ was significantly affected by the straw addition rate. Generally, S4 promoted the accumulated release and fixation amounts, but S8 and S12 showed inhibitory effects compared with the S0 treatment. Moreover, microbial immobilization played a predominant role in the release of fixed NH4+ during stage 1 (0.5–72 d), while both nitrification and immobilization played important roles in promoting fixed NH4+ release during stage 2 (72–288 d). In addition, more than 47 % of the labelled fixed NH4+ released was incorporated into the nonmicrobial organic nitrogen pool after microbial turnover, reducing N loss and prolonging the N supply, and this proportion increased under increasing rates of straw application. This study clarifies the fate of fixed NH4+ derived N under different rates of straw addition, which is critical for our understanding of soil N cycling and to optimize straw application in agricultural soils.

Prediction of CO2 emission from arid soil after addition of exogenous organic matter

Organic amendment application is an efficient technique that could contribute to stock organic C in soil reducing CO2 and enhancing soil fertility. However, some types of amendments increase CO2 emission from soil such as soil respiration. Modeling soil respiration after addition of exogenous organic matter will help to provide carbon fates and then to choose the most efficient amendment.Empirical method was used to develop a pseudo-empirical model based on soil wealth and organic matter composition. These data were obtained during an incubation experiment. The obtained model simulated immediate CO2 emission from the soil in controlled and natural conditions following carbon input based on the chemical and biochemical compositions of the organic matter applied in the soil. The simulated values showed an excellent correspondence with the amounts of CO2 emitted from an arid soil after organic matter application. This model allowed a good prediction of the exogenous organic matter mineralization. Moreover, it can be used to predict CO2 emission, as a greenhouse gas, from the soil following exogenous organic matter input. Nevertheless, this empirical model can only be applied in areas with the same climatic characteristics.

A GIS-based method for modeling methane emissions from paddy fields by fusing multiple sources of data

Quantification of regional methane (CH4) gas emission in the paddy fields is critical under climate warming. Mechanism models generally require numerous parameters while empirical models are too coarse. Based on the mechanism and structure of the widely used model CH4MOD, a GIS-based Regional CH4 Emission Calculation (GRMC) method was put forward by introducing multiple sources of remote sensing images, including MOD09A1, MOD11A2, MOD15A2H as well as local water management standards. The stress of soil moisture condition (f(water)) on CH4 emissions was quantified by calculating the redox potential (Eh) from days after flooding or falling dry. The f(water)-t curve was calculated under different exogenous organic matter addition. Combining the f(water)-t curve with local water management standards, the seasonal variation of f(water) was obtained. It was proven that f(water) was effective in reflecting the regulation role of soil moisture condition. The GRMC was tested at four Eddy Covariance (EC) sites: Nanchang (NC) in China, Twitchell (TWT) in the USA, Castellaro (CAS) in Italy and Cheorwon (CRK) in Korea and has been proven to well track the seasonal dynamics of CH4 emissions with R2 ranges of 0.738–0.848, RMSE ranges of 31.94–149.22 mg C/m2d and MBE ranges of −66.42- -14.79 mg C/m2d. The parameters obtained in Nanchang (NC) site in China were then applied to the Ganfu Plain Irrigation System (GFPIS), a typical rice planting area of China, to analyse the spatial-temporal variations of CH4 emissions. The total CH4 emissions of late rice in the GFPIS from 2001 to 2013 was in the range of 14.47–20.48 (103 t CH4-C). Ts caused spatial variation of CH4 production capacity, resulting in the spatial variability of CH4 emissions. Overall, the GRMC is effective in obtaining CH4 emissions from rice fields on a regional scale.

Multi‐modelling predictions show high uncertainty of required carbon input changes to reach a 4‰ target

AbstractSoils store vast amounts of carbon (C) on land, and increasing soil organic carbon (SOC) stocks in already managed soils such as croplands may be one way to remove C from the atmosphere, thereby limiting subsequent warming. The main objective of this study was to estimate the amount of additional C input needed to annually increase SOC stocks by 4‰ at 16 long‐term agricultural experiments in Europe, including exogenous organic matter (EOM) additions. We used an ensemble of six SOC models and ran them under two configurations: (1) with default parametrization and (2) with parameters calibrated site‐by‐site to fit the evolution of SOC stocks in the control treatments (without EOM). We compared model simulations and analysed the factors generating variability across models. The calibrated ensemble was able to reproduce the SOC stock evolution in the unfertilised control treatments. We found that, on average, the experimental sites needed an additional 1.5 ± 1.2 Mg C ha−1 year−1 to increase SOC stocks by 4‰ per year over 30 years, compared to the C input in the control treatments (multi‐model median ± median standard deviation across sites). That is, a 119% increase compared to the control. While mean annual temperature, initial SOC stocks and initial C input had a significant effect on the variability of the predicted C input in the default configuration (i.e., the relative standard deviation of the predicted C input from the mean), only water‐related variables (i.e., mean annual precipitation and potential evapotranspiration) explained the divergence between models when calibrated. Our work highlights the challenge of increasing SOC stocks in agriculture and accentuates the need to increasingly lean on multi‐model ensembles when predicting SOC stock trends and related processes. To increase the reliability of SOC models under future climate change, we suggest model developers to better constrain the effect of water‐related variables on SOC decomposition.Highlights The feasibility of the 4‰ target was studied at 16 long‐term agricultural experiments. An ensemble of soil organic carbon models was used to estimate the uncertainty of the predictions. On average across the sites, carbon input had to increase by 119% compared to initial conditions. High uncertainty of the simulations was mainly driven by water‐related variables.

Effect of humic acid derived from leonardite on the redistribution of uranium fractions in soil.

Humic acids (HAs) are complex organic substances with abundant functional groups (e.g., carboxyl, phenolic-OH, etc.). They are commonly distributed in the soil environment and exert a double-edged sword effect in controlling the migration and transformation of uranium. However, the effects of HAs on dynamic processes associated with uranium transformation are still unclear. In this study, we used HAs derived from leonardite (L-HA) and commercial HA (C-HA) as exogenous organic matter and C-HA as the reference. UO2, UO3, and UO2(NO3)2 were used as the sources of U to explore the fractionations of uranium in the soil. We also studied the behavior of the HA. The incubation experiments were designed to investigate the effects of HA on the soil pH, uranium fraction transformation, dynamic behavior of exchangeable, weak acid, and labile uranium. The observations were made for one month. The results showed that soil pH decreased for L-HA but increased for C-HA. Under these conditions, uranium tended to transform into an inactive fraction. The dynamic behavior of exchangeable, weak acid, and labile uranium varied with the sources of HA and uranium. This study highlighted that HA could affect soil pH and the dynamic redistribution of U fractions. The results suggest that the sources of HA and U should be considered when using HA as the remediation material for uranium-contaminated soils.

Distinct response of arsenic speciation and bioavailability to different exogenous organic matter in paddy soil

Land application of organic waste has been increasingly encouraged since it could sequester carbon to mitigate climate change. Considering the susceptibility of arsenic (As) bioavailability in soils to organic matter, understanding the influence of different exogenous organic matter on As biogeochemical behavior in rice-soil system is crucial to reasonably recycle organic waste on soils and ensure the food safety. In this study, impacts of two typical organic matter amendments, rice straw and humic substance, on the As speciation and bioavailability in paddy soil were investigated. Results showed that addition of both rice straw and humic substance could increase the dissolved organic carbon (DOC) content in soil solution by 16.4%–34.4% and 21.7%–53.2%, respectively, but the response of As speciation and bioavailability was quite different, showing the decoupling between As release and DOC. Rice straw addition increased As release to porewater by 28.0%–28.4%, particularly at the initial 0–18 days after the soil was flooded, but humic substance presented the opposite effect, decreasing As release by 27.4%–43.1% which was mainly attributable to the AsIII immobilization. This study suggests that the organic matter with high contents of labile heteroaliphatic/aliphatic carbon, being easily to be biodegraded, should not be applied on As contaminated soils.

Soil Fertility Improvement and Carbon Sequestration through Exogenous Organic Matter and Biostimulant Application

One of the main tasks in the search for environmentally friendly crop-growing methods is to increase soil fertility by improving its physical, chemical and biological parameters. The aim of this study was to determine the effect that the long-term annual application of different types of soil fertility agents (exogenous organic matter: 1. manure, 2. straw in combination with nitrogen fertilization and liming and 3. the addition of biostimulants) had on organic matter properties, including humic acid (HAs) properties. The research was carried out on the basis of soil samples from a ten-year pot experiment which was set up as single-factor pot experiment with four replications. PVC pots with perforated bottoms were filled with soil samples taken from the tilled layer of an arable field where winter wheat was grown in monoculture. The pots were exposed directly to the weather and were left without vegetation. The soil samples were assayed for the content of total organic carbon (TOC), total nitrogen and fractional composition of humus. HAs were extracted with the Schnitzer method and analyzed for the elemental composition, spectrometric parameters in the FT-IR and UV-VIS range and hydrophilic and hydrophobic properties. In addition, EPR spectra were produced. The results showed that the content of organic matter compared to soil without additives increased with the use of manure and the use of straw in the CaO variant and in the form of a mulch. The content of dissolved organic carbon (DOC) ranged from 124.6 to 286.1 mg kg−1 and had strong positive correlation with TOC content. The values of the ratio of carbon content in humic acids to carbon content in fulvic acids (CHAs/CFAs) ranged from 0.71 to 0.99. The use of a biostimulator—with or without the addition of straw—increased carbon sequestration in humic acid molecules, as well as their oxidation level and their share of hydrophobic fractions with the longest retention time. Thus, the addition of UGmax intensifies humification processes, leading to the formation of stable humic acid molecules.

Deciphering the Effectiveness of Humic Substances and Biochar Modified Digestates on Soil Quality and Plant Biomass Accumulation

The effective use of digestate as exogenous organic matter to enhance soil carbon sequestration depends on the balance between labile and recalcitrant organic carbon, which is influenced by the type of feedstock, the fermentation process, and the fraction (liquid, solid) of the fermented product used. In this work, in order to change the ratio of labile to stable carbon in the resulting fertiliser, the digestate was mixed with organic carbon-rich supplements: biochar and Humac (a humic acid-rich substance). The pot experiment was carried out under controlled conditions with maize (Zea mays L.) in soil amended with the digestate (D), which was incubated with Humac (H), biochar (B), or a combination of both (D + B + H) before the application. Digestate enriched with Humac showed improved short-term nutrient (carbon, phosphorus, nitrogen) transformation, as indicated by soil enzyme activity and the highest maize biomass production of. Total carbon content, C:N ratio, short-term respiration activity, and nitrification were most enhanced by digestate enriched with either biochar or combined biochar + Humac). Long-term nitrogen mineralization was mostly enhanced by digestate + Humac, as indicated by amino-acid-induced respiration and urease activity. Short-term positive effects of digestate + biochar (eventually + Humac) on catabolism were proven, whereas their long-term effects on nutrient mineralization were negative (i.e., biochar-mediated immobilization, sequestration), which should be the focus of further research in future.

To what extent can soil moisture and soil Cu contamination stresses affect nitrous species emissions? Estimation through calibration of a nitrification–denitrification model

Abstract. Continental biogeochemical models are commonly used to predict the effect of land use, exogenous organic matter input or climate change on soil greenhouse gas emission. However, they cannot be used for this purpose to investigate the effect of soil contamination, while contamination affects several soil processes and concerns a large fraction of land surface. For that, in this study we implemented a commonly used model estimating soil nitrogen (N) emissions, the DeNitrification DeCompostion (DNDC) model, with a function taking into account soil copper (Cu) contamination in nitrate production control. Then, we aimed at using this model to predict N2O-N, NO2-N, NO-N and NH4-N emissions in the presence of contamination and in the context of changes in precipitations. Initial incubations of soils were performed at different soil moisture levels in order to mimic expected rainfall patterns during the next decades and in particular drought and excess of water. Then, a bioassay was used in the absence or presence of Cu to assess the effect of the single (moisture) or double stress (moisture and Cu) on soil nitrate production. Data of nitrate production obtained through a gradient of Cu under each initial moisture incubation were used to parameterise the DNDC model and to estimate soil N emission considering the various effects of Cu. Whatever the initial moisture incubation, experimental results showed a NO3-N decreasing production when Cu was added but depending on soil moisture. The DNDC-Cu version we proposed was able to reproduce these observed Cu effects on soil nitrate concentration with r2 > 0.99 and RMSE < 10 % for all treatments in the DNDC-Cu calibration range (> 40 % of the water holding capacity) but showed poor performances for the dry treatments. We modelled a Cu effect inducing an increase in NH4-N soil concentration and emissions due to a reduced nitrification activity and therefore a decrease in NO3-N, N2O-N and NOx-N concentrations and emissions. The effect of added Cu predicted by the model was larger on N2-N and N2O-N emissions than on the other N species and larger for the soils incubated under constant than variable moisture. Our work shows that soil contamination can be considered in continental biogeochemical models to better predict soil greenhouse gas emissions.

The The Kinetics of Carbon and Nitrogen Mineralization of Different Organic Amendments in the Soil

The exploitation of exogenous organic matter from fresh or composted livestock manure in agriculture is an effective source that addresses the problem of soil depletion and provides essential nutrients to plants. It can also cause worry about environmental degradation, such as CO2 emissions and nitrate leaching. The rational use of these organic soil amendments requires additional research, which still remains limited in terms of articles and books in Morocco.  The objective of our research is to study the kinetics of carbon and nitrogen mineralization of the different organic amendments, sheep manure (SM), cattle manure with straw (CM), two composts (CA, CF), and poultry manure laying hen (PL), by an incubation method under controlled laboratory conditions, and characterize the organic matter (OM) by biochemical fractionation. In the light of these results obtained, it can be seen that laying hen droppings induced the highest level of carbon and nitrogen mineralization, followed by sheep manure and cattle manure with straw which recorded an intermediate rate of carbon mineralization. And high nitrogen immobilization, these two materials are considered to be a transition point between the manure and the two compost, which recorded slow and low carbon and nitrogen mineralization. Statistical analysis endorsed a correlation between the kinetics of carbon mineralization and biochemical fractionations of organic matter in EOMs.

Effects of drilling waste combined with exogenous organic matter on physicochemical properties of aeolian sandy soil and growth of spinach

An indoor potted experiment was carried out to study the application effects of water-based waste drilling mud (WBDM) and drill cuttings combined with humic acid and woody peat in aeolian sandy soil.We analyze their effects on the growth of spinach, in order to provide a reference for the resource utilization of drilling waste and the improvement of aeolian sandy soil. A total of three individual experiments were set up: 4 treatments in the basic group, taking aeolian sandy soil as the control (CK), mixing aeolian sandy soil and drill cuttings at a mass ratio of 1:1, then added with 0, 2%, and 4% WBDM (dry basis) respectively. The basic group treatment was added with 1% humic acid, 1% humic acid+3% woody peat mixture respectively, as the humic acid group and woody peat group. The results showed that in the basic group, drilling waste application significantly increased soil organic matter content (SOM), pH and electrical conductivity, the 2% WBDM significantly promoted the growth of spinach. Humic acid and woody peat reduced soil pH and increased SOM content and electrical conductivity. Plant growth indicators such as plant height, total leaf area, fresh weight and dry weight of the humic acid group were higher than the corresponding treatments in the basic group. The mixed addition of humic acid and woody peat did not affect plant growth. The treatment with the best performance was to add 2% WBDM to the humic acid group, and the SOM was 13.1 g·kg-1, spinach's plant height, total leaf area, fresh weight and dry weight significantly increased by 49.7%, 93.4%, 83.3%, and 34.6% than CK after 40 days of sowing. The application of drilling waste with organic matter could significantly increase SOM content and promote spinach growth. Aeolian sandy soil + drill cuttings + WBDM (2%) + humic acid (1%) was the best combination mode.

Resistant soil carbon is more vulnerable to priming effect than active soil carbon

The newly added exogenous organic matter may change the decomposition rate of native soil organic matter (SOM) by the priming effect (PE) and further impact the terrestrial carbon (C) balance. Earth system models have not yet considered the distinct responses of soil C pools with different stability and turnover rates to PE. We addressed this knowledge gap by incubating three soils (from the same site but at different stages of SOM decomposition) developed under C3 vegetation with or without the addition of maize straw (C4) and its pyrolysis product-biochar (C4) in a 180 d-incubation at 22 and 32 °C. The three soils were sampled from 15-year old-field, 15-year bare-fallow, and 23-year bare-fallow plus additional laboratory 815-d incubation, representing active (old-field soil) and relatively resistant (two bare-fallow soils, with more stable fraction and less labile fraction) soil C pools, respectively. Soil-derived CO2 was distinguished by a two-component mixing model using a natural 13C isotopic tracing method (C3 vs. C4). The PE was by 30%–239% higher in two bare-fallow soils than in old-field soil regardless of types of new C input (straw and biochar) or temperatures (22 and 32 °C), and the straw-induced PE was by 90%–297% higher than the biochar-induced PE regardless of soils or temperatures. Moreover, the straw-induced PE was not altered with warming in the three soils, but the biochar-induced PE was significantly decreased by warming, especially in old-field soil. These results suggested that the PE varies with soil C pools with different stability. The relatively resistant soil C pool is more vulnerable to PE than the active soil C pool, but the resistant soil C pool can sequestrate more exogenous C and result in higher soil C storage than the active soil C pool, at least in the short term. In addition, more biochar-C can be retained in these soils than straw-C, but this difference would decrease with warming. Overall, this study suggests that future experimental and modeling studies should pay attention to the distinct vulnerability of soil C pools with different stability to PE and warming for accurately predicting soil C dynamics.