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In our previous studies, we filtered out fungus (Trichoderma reesei) to have the best ability to transform corn straw into a humic-acid-like substance through laboratory incubation experiments. In order to further verify our former findings, we set up a 360 d field experiment that included three treatments applied under equal carbon (C) mass: (i) corn straw returned to the field (CS), (ii) fermented corn straw treated with Trichoderma reesei returned to the field (FCS-T), and (iii) blank control treatment (CK). Soil organic carbon (SOC), soil labile organic C components, soil humus composition, and the management levels of SOC pools under the three treatments were analyzed and compared. The results showed that the SOC content of CS and FCS-T treatments increased by 12.71 % and 18.81 %, respectively, compared with CK at 360 d. The humic acid carbon (HA-C) content of the FCS-T treatment was 0.77 g kg−1 higher than in the CS treatment. Applying FCS-T appeared to promote a significant increase in SOC content, carbon pool activity index, and carbon pool management index through the accumulation of HA-C, humin carbon, and easily oxidizable organic carbon. Applying fermented corn straw treated with Trichoderma reesei (FCS-T) is more valuable and conducive to increasing soil easily oxidizable organic C (EOC) and humus C content than direct application of corn straw.

In the view of studying humus formation in corn straw under the action of microorganism, three fungi (Trichoderma reesei, Trichoderma harzianum, Phanerochaete chrysosporium) were selected to compar...

Humic substances (HS), which are defined as a series of highly acidic, relatively high-molecular-weight, and yellow to black colored substances formed during the decay and transformation of plant and microbial remains, ubiquitously occur in nature. Humic substances represent the largest stable organic carbon pool in terrestrial environments and are the central characteristic of the soil. However, the validity of the HS concept and the justification of their extraction procedure have been recently debated. Here, we argue that the traditional humic paradigm is still relevant. Humic substances are distinctive and complex because the extracted HS formed during the humification are chemically distinct from their precursors and are heterogeneous among soils. By reviewing the concept, formation pathways, and stabilization of HS, we propose that the key question facing soil scientists is whether HS are soil microbial residues or unique synthesized compounds. Without revealing the distinctiveness of HS, it is impossible to address this question, as the structure, composition, and reactivity of HS are still poorly known owing to the heterogeneity and geographical variability of HS and the limits of the currently available analytical techniques. In our view, the distinctiveness of HS is fundamental to the soil, and thus further studies should be focused on revealing the distinctiveness of HS and explaining why HS hold this distinctiveness.

Straw returning to the field has become a common way to utilize crop residues. This method does not only solve the problem of rational utilization of straw but also improves soil organic ca...

Soils are an important pool for storing organic carbon. Soil organic carbon (SOC) content is generally considered as an important indicator to evaluate farmland soil quality. The loss of SOC causes soil degradation and reduces the sustainability of farmland. In order to reveal the distribution pattern of SOC in the coastal monsoon area of eastern China, and to clarify the macro dominant factors of SOC accumulation caused by temperature and precipitation, this paper analyzed the distribution pattern of SOC in the coastal monsoon area of eastern China by using the SOC data collected from the national soil testing and formula fertilization data set, and discussed the effects of temperature and precipitation on SOC content. According to the provincial administrative divisions, the distribution of SOC in the coastal monsoon areas of eastern China from Heilongjiang Province to Hainan Province was calculated. According to the annual average temperature 20.95℃, annual average precipitation 0 ~ 400 mm, 400 ~ 800 mm, > 800 mm, the study area was divided into different regions, and the effects of annual average temperature and annual average precipitation on SOC content were studied. In the region with annual average temperature less than 10.18℃, the temperature had a negative correlation with the accumulation of organic carbon, and the ratio of precipitation and temperature had a positive correlation with the accumulation of SOC; In the region of 10.18℃~20.95℃, the annual average temperature and annual average precipitation had a significant positive correlation, and the ratio of precipitation and temperature had a positive correlation with the accumulation of SOC; In the region > 20.95℃, the temperature had a negative correlation with the accumulation of organic carbon, and the ratio of precipitation and temperature was not related to the accumulation of SOC. In the range of 0 ~ 400 mm of annual average precipitation, the temperature had a positive correlation with the accumulation of SOC, and the ratio of precipitation and temperature had a negative correlation with the accumulation of SOC; In the range of 400 ~ 800 mm of annual average precipitation, the temperature had a negative correlation with the accumulation of SOC, and the ratio of precipitation and temperature had a positive correlation with the accumulation of SOC; In the region > 800 mm of annual average precipitation, the temperature had a positive correlation with the accumulation of organic carbon before the annual average temperature of 20.95℃, and after the annual average temperature of 20.95℃, the temperature had a negative correlation with the accumulation of organic carbon, and the ratio of precipitation and temperature had no significant effect on the accumulation of SOC. On the macro scale, the annual average temperature and precipitation had significant effects on the distribution pattern of SOC in the coastal monsoon area of eastern China. According to the influence of annual average temperature and annual average precipitation on SOC accumulation, a comprehensive model based on the annual average temperature and annual average precipitation on SOC accumulation is established. Through regression verification of the model, the correlation coefficient, r = 0.9998**, the cubic curve equation could better simulated the relationship between the predicted value and the real value of SOC, r = 0.7048**,the model can reflect the cumulative effect of annual average temperature and annual average precipitation on SOC accumulation Combined with the impact.

A three-year field experiment was conducted to analyze the effects of straw enrichment and deep incorporation on the humus composition and the structure of humic acid (HA) in black soil. The differences in the HA structure between different straw returning methods were detected by three-dimensional fluorescence spectroscopy and 13C NMR technology. The purpose of this paper is to provide a theoretical basis and data support for improving the straw returning system. Four different treatments, including no straw applied (CK), straw mulching (SCR), straw deep ploughing (MBR), and straw enrichment and deep incorporation (SEDI: harvested the corn straw from four rows together with a finger-plate rake and then crushed and buried them in one row in the 20∼40 cm deep level in the subsoil with a wind-driven input cylindrical plough), were used in this study. Our results showed that compared to CK treatment, SEDI significantly increased the contents of organic carbon (SOC), soil humic acid carbon (HAC), fulvic acid carbon (FAC), and humin C content (HM-C) in the subsurface soil layer by 27.47%, 34.33%, 19.66%, and 31.49%, respectively. Among all the straw returning treatments, SEDI treatment had the most significant effect in increasing the contents of HEC, HAC, and FAC. Straw returning not only reduced the degree of condensation and oxidation of the HA structure but also increased the proportion of alkyl C and enhanced the hydrophobicity of the HA structure in subsurface soil. Moreover, SEDI treatment significantly increased the proportion of aliphatic C/aromatic C of the HA structure in subsurface soil and improved the aliphatic property of HA, which had a significant effect on the HA structure compared to other treatments.

Agricultural waste can be made into biochar, which serves to raise soil fertility and fix carbon (C). When biochar is added to soil, a small part of biochar could be transformed into soil organic C in a short time to promote soil fertility. However, it is still unknown how much biochar can be stored in the soil as stable C and whether it plays a role in C sequestration. In this study, a 540-day incubation experiment was conducted to evaluate the transformation of maize straw biochar into humus fractions using a 13C isotopic labelling technique. The treatments were CK (no biochar applied) and AB (21.3 g kg-1 of biochar + CK). The results showed that: 1) Compared with those in the CK treatment, the concentrations of organic and humus C in the bulk soil were significantly higher under the AB treatment. 2) The δ13C values of soil humus C were higher (ranging between 0% and 23.45%) in the AB treatment than those in the CK treatment. 3) The proportions of biochar transformed into humic acid (HA), fulvic acid (FA), water-soluble substances (WSS), and water floating substances (WFS) were 2.66–4.30%, 1.11–1.57%, 0.49–0.88%, and 0.68–1.40%, respectively. The remaining biochar (59.44–98.00%) remained in the crude humin form, retaining the inert nature of the biochar itself. Although biochar is relatively stable, approximately 4.22–5.40% of biochar was transformed into extracted humic substances (HA+FA). We concluded that a relatively small amount of biochar could be transformed into soil organic matter under short-term (540 days) incubation conditions.

The purpose of this study is to analyze the effects of different straw returning modes on the structure of humic acid (HA) in soil by fluorescence spectroscopy and infrared (IR) spectroscopy. Four different straw returning modes, including straw returning to topsoil (St), straw returning to subsoil (Ss), straw mixing with topsoil (Smt), and straw mixing with subsoil (Sms), were used in this study; the soil HA was analyzed after 12 months of corn straw returning by a combination of fluorescence spectroscopy and IR spectroscopy. Based on the results, it was established that IR spectroscopy can estimate the complication and oxidation degree of soil HA and also evaluate its aliphaticity and aromaticity. Monodimensional fluorescence spectroscopy could preliminarily determine the changes in the humification of HA through the fluorescence intensities. The intensity ratio of I456/I380 calculated from synchronous-scan fluorescence spectra could be used to evaluate the humification degree of soil HA. The total luminescence spectra of HAs provided more information on the fluorophores in the structure, including the amount and peak position of lignin-like structures and phenol-like or naphthol-like structures. Among the four straw returning modes, Ss is the most beneficial for reducing the oxidation degree and increasing the aromatization and humification degree of subsoil HA. It is believed that fluorescence spectroscopy and IR spectroscopy are relatively simple and sensitive methods for analyzing soil HA.

The contribution of microbial residues formed on lignin and cellulose to the formation of humus (HS) was investigated. The microbial residues formed by Aspergillus niger (A. niger) in the cultures of cellulose and lignin in a fluid medium were structurally characterized by elemental analysis, differential thermal analysis (DTA), FTIR spectroscopy and CP/MAS 13C NMR spectroscopy. Compared to cellulose itself, the microbial residue from cellulose contains more aromatic compounds and N-containing compounds and fewer carbohydrates and carboxylic compounds. A. niger improved the thermal stability and aromaticity of the cellulose. However, compared with that on lignin, more N-containing compounds, carbohydrates and carboxylic acid derivatives and less aromatic material were found in the microbial residue from lignin. Regardless of whether the carbon source was cellulose or lignin, A. niger utilized the N in the fluid medium to synthesize its own cells, and eventually, they could transfer the N into the microbial residue, in addition, the O-alkyl species dominated over the alkyl and aromatic compounds in the microbial residue. Although the molecular structures of the components of the microbial residue from lignin tended to be simpler, they were more alkylated, more hydrophobic and less aliphatic than those from cellulose. During culture with A. niger, the cellulose underwent degradation and then a polymerization, which led to an increased degree of condensation but a lower degree of oxidation, providing essential precursor substances for HSs formation. However, lignin underwent oxidative degradation. The microbial residue from lignin had a lower degree of condensation and a higher degree of oxidation.

Interaction between soil aggregates and humic substances directly determine soil carbon (C) sequestration and stabilization dynamics. This study investigated the influence of different tillage systems on soil humus composition and humic acid (HA) structural characteristics in water stable soil aggregates in the 0−20 and 20−40 cm soil depths. Tillage systems included no-tillage (NTS) and conventional tillage (CTS) both with corn straw returned, and conventional tillage without corn straw returned (CT). Fluorescence, Fourier transform infrared (FTIR) and 13C nuclear magnetic resonance (13C NMR) spectroscopies were employed to comprehensively characterize soil HA structure in soil aggregate fractions. The results showed that large quantities of humus C was stored in the large macro-aggregates (> 2 mm) and silt/clay ( 2 mm aggregates were dominated by aliphatic, methoxyl, hydrophobic and carboxyl C groups, and this result was more evident in NTS indicating improved soil C stability. Comparing all tillage systems, NTS enhanced aliphatic, methoxyl and hydrophobic C in > 2 mm aggregates, which indicate improved soil C stability. The 13C NMR results of bulk soil demonstrated that NTS enhanced alkyl, O-alkyl and methoxyl/N-alkyl C in the 0−20 cm. We therefore concluded that NTS is the better system to effectively improve soil C sequestration and stability.

Studying changes in soil humus composition and humic acid (HA) structural characteristics caused by agronomic practices provide insights into the pathways of soil organic carbon (C) stabilisation dynamics. This five-year field study evaluated the effects of straw returning modes on humus composition and HA structure. Treatments included (i) corn straw returned on the soil surface (NTS), (ii) corn straw incorporated into soil within 0–10 cm (MTS), (iii) corn straw incorporated into soil within 0–20 cm (CTS) and (iv) no corn straw applied (CT). Soil HA was characterised by Fourier transform infrared (FTIR) and fluorescence spectroscopies. The results demonstrated that corn straw returning improved humus C fractions in this order NTS > MTS > CTS > CT in 0–20 cm depth. The FTIR and fluorescence results demonstrated that corn straw returning enhanced aliphatic, hydroxyl, methoxyl and carboxyl groups and simplified HA molecular structure, indicating regenerated and newly formed HA. Among all treatments, NTS was more conducive in simplifying HA molecular structure and enhancing aliphatic and hydrophobic C. Hydrophobicity in aliphatic C is the driving force in the stabilisation of soil C, which is important for sustainable agriculture. Therefore, we conclude that NTS is the better practice to turn arable lands into a sink for C.

Lignocellulase production from straw fermentation has been widely investigated but the research has neglected to quantify fermentation-derived residue transformation to the humus-like substance (HULIS). To investigate the conversion efficacy of corn stalk residue to HULIS, the amount of HULIS associated with chemical composition and structural changes of humic acid-like substances (HAL) was investigated in a 30 L solid-state fermentation tank during a short period of eight days. The results show that the highest decomposition rate of corn stalk and the highest activity of cellulase, xylanase, and &beta, glucosidase appeared at the fourth day. At the end of fermenting process, the amount of humic acid-like substances (HAL) and the percentage of HAL in humus acid (PQ value) increased 17.5% and 8.9%, respectively, indicating Trichoderma reesei facilitates the transformation of corn stalk residue to HAL. Fatty acids decreased while aromatic carbon and carboxyl content significantly increased during the ongoing fermentation, which had a positive impact on the HAL thermal stability. The FTIR spectral and thermal analysis revealed an improvement in HAL degrees of condensation, oxidation, and aromatization. The present study suggests that the residue of corn stalks fermented with T. reesei might be a good fertilizer to improve soil characteristics.

Organic matter (OM) applications can influence the amount and structural characteristics of humic acid (HA). The objective of this paper was to clarify the effect of long term OM application on the changes of structural characteristics in HAs, which provided new information for improving soil fertility by OM application. The experiment was carried out on a brown soil at Shenyang Agricultural University, Liaoning province, China. The experiment included three treatments: zero-treatment (CK br), and two pig manure (PM) treatments (O 1 and O 2) at the rates of 0.9 t·ha−1 and 1.8 t·ha−1 of organic carbon, respectively. The samples of the HA fraction were extracted, separated, purified and characterized by elemental composition, differential thermal analysis (DTA), δlgK value and CP-MAS-13C-NMR. The results indicated that the CP-MAS-13C-NMR spectra of the HA were quite similar to each other. But after OM application, the contents of alkyl C and O-alkyl C increased and the contents of aromatic C and carbonyl C decreased in HAs, indicating that the OM application decreased the content of aromatic C and was simplified the molecular structure in HAs.

International audience; Various organic constituents extracted from wheat and from soil organic matter have been analyzed for their carbon content, their absolute concentration and their stable carbon isotope ratios. Most organic subfractions from plants, or soil, are 13C-depleted by up to 9.4‰ relative to bulk organic matter, mainly as a result of their higher lipid content. Furthermore, soil organic constituents are unexpectedly 13C-enriched by +1.5‰ to +4.3‰ relative to homologous plant constituents. Indeed, the selective preservation of plant lignin and lipids, following incorporation into the soil biomass, should have led to the accumulation of 13C-depleted compounds. Hence, these results favour the in situ formation of soil organic matter either by recondensation of small molecules or by selective preservation of biopolymers from soil microorganisms.

International audience; Two experiments using 13C-enriched substrates have been undertaken to evaluate the relative turnover rates of the main pools of soil organic carbon namely bulk organic carbon, humin and humic acids. Firstly, soil organic matter was labelled naturally during a 5 year field experiment by cultivating Zea mays, a C4 plant, on a soil that had previously grown isotopically distincts C3 plants, e.g. wheat. Secondly, soil organic matter was labelled artificially with either Image-glucose of 13C-enriched Image-glucose during a 21 day laboratory experiment. Isotopic variations observed during both experiments demonstrated the existence of soil carbon pools of decreasing turnover rates: humic acids > bulk organic carbon > humin.