Addition Of Straw Research Articles

Elevated temperature and performance behaviour of rice straw as waste bio-mass based foamed gypsum hollow blocks

The present study explores mechanical, thermal, acoustic, and fire performance evaluation of locally available rice straw as waste bio-mass in foamed gypsum hollow blocks. Two-core hollow gypsum blocks with various agro-waste compositions have been studied in detail and presented. Aluminum sulphate and potassium alum in 1:1 ratio are used as foaming agents in gypsum blocks. The density of two-core hollow blocks varies from 1070 to 730 kg/m3 for 0–15 wt% rice straw addition. The compressive strength of solid cubes and two-core hollow blocks lies in the range of 4.6-1.4 MPa and 2.2–1.1 MPa respectively. Whereas, the thermal conductivity lies between 0.15 and 0.07 W/m.K. exhibiting excellent thermal insulation. The sound transmission class (STC) of straw based foamed gypsum varies over the range of 23 to 20 dB for 20 mm thick with 0–15 wt% agro-waste added samples. The 5 wt% foamed rice straw gypsum sample has shown resistance to the surface spread of flame and the wallette unit of 600 mm × 600 mm has 70.5 kN of load carrying capacity at 800 °C. The foamed agro-waste-based hollow gypsum blocks may be used as a potential building material for non-load bearing wall application owing to its high thermal insulation, moderate acoustic and excellent fire retardant properties.

Microbial gene activity in straw residue amendments reveals carbon sequestration mechanisms in agricultural soils

Land-use practices and their intensity along with climatic conditions alter amounts of soil organic carbon content and consequently influence soil microorganisms. However, land-use management, such as crop residue incorporation to soils has a potential to mitigate losses of soil organic carbon and thereafter promote the diversity of soil microorganisms. To gain insight of microbial functional diversity and activity under organic soil amendments, a glasshouse experiment with arable and grassland soils was performed. Straw was added as a crop residue and microbial activity in the soils was monitored using a captured metatranscriptomics technique. The overall expression of genes related to soil organic matter degradation differed between the two land-use systems. Straw addition enhanced the expression of genes involved in the degradation of organic material, particularly in arable soils. After a month of the amendment, the overall gene expression in arable soils had a similar pattern to that of the grasslands. The straw addition triggered the upregulation of a set of enzyme families catalysing the organic matter degradation in both land-uses but downregulated a higher number of enzyme families in grasslands. However, in the grasslands, the gene families involved in the biosynthesis of carbohydrates were upregulated at straw addition. These findings indicate that arable soils with a low organic carbon content have a potential to get a higher and more active microbial diversity with amendments. In soils such as grasslands the amendments trigger a carbon sequestration process from the added organic material to the soil and can significantly contribute to enhanced soil carbon sequestration.

Maize straw application as an interlayer improves organic carbon and total nitrogen concentrations in the soil profile: A four-year experiment in a saline soil

Soil salinization is a critical environmental issue restricting agricultural production. Deep return of straw to the soil as an interlayer (at 40 cm depth) has been a popular practice to alleviate salt stress. However, the legacy effects of straw added as an interlayer at different rates on soil organic carbon (SOC) and total nitrogen (TN) in saline soils still remain inconclusive. Therefore, a four-year (2015–2018) field experiment was conducted with four levels (i.e., 0, 6, 12 and 18 Mg ha–1) of straw returned as an interlayer. Compared with no straw interlayer (CK), straw addition increased SOC concentration by 14–32 and 11–57% in the 20–40 and 40–60 cm soil layers, respectively. The increases in soil TN concentration (8–22 and 6–34% in the 20–40 and 40–60 cm soil layers, respectively) were lower than that for SOC concentration, which led to increased soil C:N ratio in the 20–60 cm soil depth. Increases in SOC and TN concentrations in the 20–60 cm soil layer with straw addition led to a decrease in stratification ratios (0–20 cm:20–60 cm), which promoted uniform distributions of SOC and TN in the soil profile. Increases in SOC and TN concentrations were associated with soil salinity and moisture regulation and improved sunflower yield. Generally, compared with other treatments, the application of 12 Mg ha–1 straw had higher SOC, TN and C:N ratio, and lower soil stratification ratio in the 2015–2017 period. The results highlighted that legacy effects of straw application as an interlayer were maintained for at least four years, and demonstrated that deep soil straw application had a great potential for improving subsoil fertility in salt-affected soils.

Trade-offs between fertilizer-N availability and Cd pollution potential under crop straw incorporation by 15N stable isotopes in rice.

Application of crop residues and chemical nitrogen (N) fertilizer is a conventional practice for achieving high yield in a rice system. However, the fallacious combination of N fertilizers with crop straw not only significantly reduces the N use efficiencies (NUEs) but also leads to serious environmental problems. The present study employed five treatments including no N fertilization and no straw incorporation (ck), N fertilization incorporation only (S0), N fertilization with 40% straw (S40), N fertilization with 60% straw (S60), and N fertilization with 100% straw (S100) to improve N use efficiency as well as reduced Cd distribution in rice. The crop yields were largely enhanced by fertilization ranging from 13 to 52% over the straw addition treatments. Compared with ck, N fertilizer input significantly decreased soil pH, while DOC contents were raised in response to straw amendment, reaching the highest in S60 and S100 treatments, respectively. Moreover, straw addition substantially impacted the Cd accumulation and altered the bacterial community structure. The soil NH4+-N concentration under S0 performed the maximum in yellow soil, while the minimum in black soil compared to straw-incorporated pots. In addition, the soil NO3--N concentration in straw-incorporated plots tended to be higher than that in straw-removed plots in both soils, indicating that crop straw triggering the N mineralization was associated with native soil N condition. Furthermore, the NUE increased with 15N uptake in the plant, and the residual 15N in soil was increased by 26.8% with straw addition across four straw application rates. Overall, our study highlights the trade-offs between straw incorporation with N fertilizer in eliminating potential Cd toxicity, increasing fertilizer-N use efficiencies and help to provide a feasible agricultural management.

Effects of straw incorporation and straw-burning on aggregate stability and soil organic carbon in a clay soil of Bangladesh

The clay soil of Bangladesh is typically low in soil organic carbon (SOC) and generally has poor soil aggregate stability (measured as mean weight diameter, MWD). The addition of organic amendments in the field has the potential to increase soil organic matter (SOM) and MWD. However, the influence of organic amendments on aggregation in the clay soils of Bangladesh is largely unknown. A short-term (105 days) field study has been conducted to evaluate the effects of straw incorporation and straw-burning treatments on MWD and SOC in clay soil under eggplant (Solanum melongena L.). This study consisted of three treatments: (i) control (no amendments), (ii) rice straw (straw applied at 21 t ha−1), (iii) rice straw-burning (ash retained after burning at 7.4 t ha−1). Soil samples were collected after plant harvest, and then MWD, SOC, glomalin-related soil protein (GRSP), microbial biomass carbon (MBC), Fe-oxides, and available soil nutrients (e.g., N, P, K, S, Na, Ca, and Mg) were determined. Our results showed that MWD in straw addition treatment was on average 2 times higher, whereas SOC was 1.3 times higher compared to the control and straw-burning treatments, respectively (P < 0.05). Conversely, the straw-burning treatment reduced the MWD by 19% and the SOC by 20% compared to the control treatments (P < 0.05). Significant improvements in the available K, S, and Mg content of soil were found in the straw incorporation treatment (P < 0.05). We did not find any significant influence of the treatments on the MBC and GRSP content of the soil. Soil organic carbon had a significant correlation with MWD (R2 = 0.80**, P < 0.01), while GRSP and Fe-oxides did not show any relationship with MWD (P > 0.05). Our study demonstrates that the incorporation of rice straw has the potential to increase soil aggregation and SOC stock, at least for the short term in the clay soils of Bangladesh.

Physico-chemical and agrochemical indicators of typical chernozem and isohumisol under various tillage and fertiliser systems

The relevance of examining the physico-chemical and agrochemical indicators of soils lies in the fact that these properties determine the level and quality of agricultural crops, thus affecting the food security of the country as a whole. In this regard, the purpose of the study is to establish the longterm impact of different soil tillage and fertilisation technologies on the profile distribution of physicochemical and agrochemical indicators of typical chernozem and isohumisol soils. Under conventional tillage (CTu), plant nutrients were evenly distributed within the upper layer of typical chernozem, with the highest values observed in the 10-40 cm depth range. Under soil conservation tillage, with the addition of straw at a rate of 1.2 t/ha+N12+N78P68K68, the content of available hydrolyzable nitrogen, mobile phosphorus, and exchangeable potassium in the typical chernozem soil was highest in the 0-20 cm layer: 192.30±22.44 and 192.51±22 mg/kg; 63.57±5.762 and 62.07±0.312 mg/kg; 527.14±36.204 and 465.27±5.844 mg/kg for shallow (RTu) and deep (DRTu) soil conservation tillage, respectively. In total at 0-100 cm layer of typical chernozem, the highest content of plant nutrients was observed under DRTu followed by CTu. In Chinese isohumisol, a higher accumulation of NH4 + -N and NO3 -N was observed in the 0-10 cm depth range under no-till soil management, while in the 20-40 cm depth range, plowing resulted in greater accumulation of these nutrients. The total phosphorus content did not notably change with depth. Under the application of fertilisers, the content of nutrients and the reaction value of the medium increased for all tillage treatments of typical chernozem. The content of exchangeable calcium and magnesium did not change considerably on the fertilised inputs. The findings of this study indicate the feasibility of using crop residues with nitrogen compensation and cover crops, in conjunction with mineral fertilizers, to maintain the fertility level of chernozem soils under conditions of limited manure utilisation

Straw amendment and nitrification inhibitor controlling N losses and immobilization in a soil cooling-warming experiment

It is common practice in agriculture to apply high‑carbon amendments, e.g. straw, or nitrification inhibitors (NI) to reduce soil nitrogen (N) losses. However, little is known on the combined effects of straw and NI and how seasonal soil temperature variations further affect N immobilization. We conducted a 113-day mesocosm experiment with different levels of 15N-fertilizer application (N0: control; N1: 125 kg N ha−1; N2: 250 kg N ha−1) in an agricultural soil, amended with either wheat straw, NI or a combination of both in order to investigate N retention and loss from soil after a cooling-warming phase simulating a seasonal temperature shift, i.e., 30 days cooling phase at 7 °C and 10 days warming phase at 21 °C. Subsequently, soils were planted with barley as phytometers to study 15N-transfer to a following crop.Straw addition significantly reduced soil N-losses due to microbial N immobilization. Although carbon added as straw led to increased N2O emissions at high N fertilization, this was partly counterbalanced by NI. Soil cooling-warming strongly increased ammonification (+77 %), while nitrification was suppressed, and straw-induced microbial N immobilization dominated. N immobilized after straw addition was mineralized at the end of the experiment as indicated by structural equation models. Re-mineralization in N2 was sufficient, but still suboptimal in N0 and N1 at critical times of early barley growth. N-use efficiency of the 15N tracer decreased with fertilization intensity from 50 % in N1 to 35 % in N2, and straw amendment reduced NUE to 25 % at both fertilization rates. Straw amendment was most powerful in reducing N-losses (−41 %), in particular under variable soil temperature conditions, but NI enforced its effects by reducing N2O emission (−40 %) in N2 treatment. Sufficient N-fertilization coupled with straw application is required to adjust the timely re-mineralization of N for subsequent crops.

Evaluating the properties of compressed soil earth blocks after the addition of bagasse ash, marble powder and paddy straw

Constructing structures and their establishments with the help of non-toxic and ecological materials that reduce the environmental damages caused in the process and help protect nature can be termed sustainable construction. Red burnt clay bricks are being used for the construction which requires a lot of energy in the process. For the preparation of these bricks, cement is used as a stabilizer and we all are aware that the production of cement releases a lot of energy. Red burnt clay bricks are burnt in kilns which pollutes the environment. Many countries have started using compressed stabilized earth blocks (CSEBs) to overcome these situations. CSBEs are the blocks consisting of clay and one or more stabilizers which are compressed together with the help of a manual press or machines. This study used waste materials like rice straw, marble dust, and bagasse ash as stabilizers. Using waste materials in CSEBs can help us in sustainable development and also will help in reducing the cost of construction. In this study, rice straw is used in the percentages 0.75%, 0.90%, and 1.05%. Marble dust is used in the percentages of 8%, 10%, and 12%. And bagasse ash is used in the percentages of 27%, 32%, and 37%. A total of 27 combinations were selected with these percentages. And for each test, 2 blocks of size 220mm x 100mm x 100mm and beams of size 500mm x 100mm x 100mm were prepared. These blocks were cured by the sprinkling of water for 28 days. Various tests like OMC & MDD, and Flexural Strength were performed in this study.

Utilization of Rice Straw Wastes as Aggregate in Lightweight Concrete Block Production by Using Cold Press Technique

A massive rice straw waste was collected annually after the harvesting period. To reduce the air pollution/PM 2.5 during the burning season and to utilize those straw wastes, the development of rice straw based-lightweight cement block was studied. A Cold press method was selected for block manufacturing as it could gain terrific compressive strength with user-friendly operation. It was found that the saturated surface dry (SSD) condition of the straws achieved higher strength than that of the as-received (AR) condition. SSD of straw had softer and more flexibility to easily disperse in the cement matrix. Moreover, extra water in the wet SSD straws could also allow internal curing for more hydration reactions inside the specimens during their curing period. The optimal proportion for the production of rice straw based-lightweight cement block, achieving 6.43 MPa, is 0.30 of w/c ratio with 2% of straw addition in the SDD state. The outcomes could promote a value-added concept and achieve greener and cleaner production for the development of environmentally friendly alternative construction materials.

Effects of straw returning and nitrogen addition on soil quality of a coastal saline soil: A field study of four consecutive wheat‐maize cycles

AbstractThe effects of different straw returning and nitrogen addition levels on soil quality are important for proper coastal saline soil remediation. However, relatively little is understood concerning the remediation effects, especially, on long‐term effects and mineral composition and microstructures of coastal saline soil. Two maize/wheat straw returning levels [1.0 × 104 kg ha−1(2S) and 5.0 × 103 kg ha−1(S)] and three inorganic nitrogen addition levels [300 kg ha−1(N2), 150 kg ha−1(N) and 75 kg ha−1(N1/2)]—were studied, with 150 kg ha−1inorganic nitrogen and without straw addition treatment as the control (CK), to elucidate the response of soil physical and chemical properties to the two factors. After four consecutive wheat‐maize cycles, different straw and N fertilizer treatments obviously decreased the salinity contents, increased the total nutrient contents, and optimized the soil structure of the saline soil. The saline soil reclamation effects showed significant distinctions among the different straw and N fertilizer treatments. The 2SN2 treatment displayed the greatest effects in regard to reducing salinity, increasing the total soil nutrient contents and optimizing the soil structure, which resulted in the best remediation effect. Straw returning plays a major role in decreasing soil salinity and enhancing saline soil aggregate formation. N fertilizer addition supplies rich nutrients for straw decomposition, and promotes soil microbial growth and reproduction, which brought about C sequestration in coastal saline soil. During the coastal saline soil remediation process in the Yellow River Delta, it is suggested to prioritize straw returning and moderate N fertilizer addition, and live together with moderate P fertilizer application.

Saline soil organic matter characteristics of aggregate size fractions after amelioration through straw and nitrogen addition

AbstractSaline soil organic matter (SOM) composition and distribution are largely unknown. A coastal field experiment was designed to investigate the effects of straw and nitrogen addition on SOM characteristics by diffuse reflectance Fourier‐transform mid‐infrared (FTIR) spectral and amino sugar analysis. In each growing season, maize/wheat straw was applied at rates of 5.0 × 103 kg ha−1 (S5) and 1.0 × 104 kg ha−1 (S10), and inorganic nitrogen was applied at rates of 75 kg ha−1 (N75), 150 kg ha−1 (N150), and 300 kg ha−1 (N300). N150 without straw addition was the control treatment (CK). Dry‐sieving technique was used to fractionate soils into macroaggregates (&gt;0.25 mm, MA), microaggregates (0.053–0.25 mm, MI), and silt‐plus‐clay particles (&lt;0.053 mm, SC). Results showed that SOM and amino sugar contents were efficiently increased in the S5 and S10 treatments compared with CK, which were significantly higher in MA and MI than in SC (p &lt; 0.05). In straw‐addition treatments, SOM and amino sugar contents were significantly higher in S5N300 and S10N300 (p &lt; 0.05). The contribution of microbial necromass C to soil organic C (SOC) was 8.9–17.1%, and the fungal residue was dominant in bulk and aggregate soils. The amount of recalcitrant form of organic C decreased with SOM content increase, and the abundance of aromatic C groups increased under higher salt stress. Therefore, we suggested that microbial necromass accumulation could not be the main pathway of SOC sequestration, and enriching recalcitrant organic C probably led to SOM stability in saline soils.

Investigation on strength behavior of cemented dredged clay with straw at various curing stages

Dredged clay with high water is difficult to use directly in practical engineering due to its extra-low strength. So, a solidifying treatment is often used to improve its engineering properties. In this study, a number of unconfined compression shear tests were conducted to investigate the strength behavior of cemented dredged clay with straw at different curing stages. For cemented dredged clay cured for a few days, the addition of filamentous straw and powdered straw would enhance its unconfined compressive strength (q u). Then, a decrease in q u is observed for samples with a small straw content as the curing time increases, mainly due to the deterioration of the straw. However, solidified soil amended by granular straw sees its q u decreases with increasing straw content decreasing its compactness and integrity. In addition, the failure strain (ε f) varies mostly within the range of (1.0% and 4.0%) and basically decreases with the increasing curing time and straw content. For the cemented dredged clay used in this research, the straw less than 6 mm with a ratio of sample diameter-to-straw length greater than 6.7 is helpful for improving the early-stage strength behavior when the straw content is less than 8%.

Enhancing phosphorus bioavailability in sewage sludge through co-hydrothermal treatment with biomass

The renewable utilization of phosphorus (P) in sewage sludge is greatly hindered by its low bioavailability. In this study, the co-hydrothermal treatment (co-HTT) of sewage sludge and biomass was conducted to enhance P bioavailability. The dehydration and decarboxylation of sludge organic matter were promoted by co-HTT as evidenced by FTIR and elemental analysis. XPS and XRD results showed that co-HTT facilitated the formation of Al/Fe phosphates in sludge. The results of Hedley's sequential extraction demonstrated that HTT at low temperatures (≤ 155 °C) enlarged the relative abundance of bioavailable P in the sludge from 72 % to as high as 80 % because of the decomposition of organic P. In contrast, at a high temperature of 185 °C, more bioavailable P was converted into insoluble and residual forms. The addition of rice straw in sludge during HTT resulted in a two-fold increase in exchangeable P content, suggesting that rice straw can effectively improve sludge P bioavailability. Cellulose exhibited less influence on sludge P bioavailability than lignin. After lignin addition, the relative abundance of bioavailable P in the sludge was further increased to 91 %, which could be attributed to the greater enhancement effect of lignin on the decomposition of sludge organic matter. These findings reveal that the co-HTT of sludge and lignin-containing biomass may be an effective strategy for improving sludge P bioavailability.

Delayed nitrogen application after straw and charred straw addition altered the hot moment of soil N2O emissions

AbstractThe combination of nitrogen (N) fertilization and straw incorporation has complex influences on soil N transformations and derived nitrous oxide (N2O) emissions. This study aimed to reveal the coupled effects of straw returning forms and N fertilizer management on soil N2O emissions. Here, carbon (C) sources with varied availabilities were supplied by different straw returning forms, including straw, charred straw, and combined application of straw and charred straw. The time gaps between additions of exogenous N and C sources were carried out by managing the timing of N fertilization, including N application simultaneous with or delayed after straw return. Soil N2O emissions under different straw returning forms and their response relationships to soil C, N, microbial biomass, as well as soil pH and oxygen (O2) were explored. Co‐application of straw and N fertilizer provided sufficient C and N sources, enhanced the microbial biomass, and consequently increased N2O emissions. Delayed N fertilization could decouple the response of N2O emissions to straw addition, because of constrained N availability and limited pH decline, which decreased the cumulative N2O emissions significantly. Possibly due to straw induced N immobilization coupled with charred straw induced pH elevation, the combined application of straw and charred straw constrained soil N2O emissions compared with straw only application, regardless of N fertilizer management. By shaping the microbial biomass and soil C, N, and O2 dynamics, delayed application of N fertilizer could further enhance the inhibition effect of the charred straw and straw combination on soil N2O emissions. Therefore, the varied straw returning forms and the timing of N fertilization could affect the supply of available C and N, influencing the hot moments of N2O emissions, and the joint addition of straw and charred straw with a few weeks delayed N application could possibly reduce the risk of soil N2O emissions from straw return systems. Such mitigation potential should be evaluated further under field conditions.Highlights Delayed N fertilization attenuated the magnitude of N2O emissions after straw additions. Combination of charred straw with straw mitigated N2O emissions, further enhanced by delayed N fertilization. Soil pH was the chief regulator for N2O emissions under different straw returning forms and N application.

Active polysaccharides from Lentinula edodes and Pleurotus ostreatus by addition of corn straw and xylosma sawdust through solid-state fermentation

In this study, Lentinula edodes and Pleurotus ostreatus were selected as representatives to explore the effects of corn straw and xylosma sawdust on the production and activity of polysaccharides by edible fungi during solid-state fermentation. The results clearly indicated that the addition of lignocellulose could promote the polysaccharide content compared to the control group. Meanwhile, the hydroxyl radical scavenging activity of polysaccharides reached the maximum when the glucose concentration was 1.5 %, and among them, the xylosma sawdust groups for two fungi (L. edodes-32.37 %, P. ostreatus-25.86 %) both performed better than corn straw groups (L. edodes-24.96 %, P. ostreatus-20.80 %). In addition, structural characterization and degradation mode analysis were carried out. The results showed that the structure of the xylosma had a stronger destruction than corn straw. The activities of lignocellulolytic enzymes such as carboxymethyl cellulase, filter paper enzyme, β-glucosidase and xylanase increased rapidly in the early stage of fermentation, which could degrade the cellulose and hemicellulose as raw materials for the synthesis of active polysaccharides.

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.

The changes of chemical molecular components in soil organic matter are associated with fungus Mortierella capitata K.

Fungi play essential roles in the turnover of soil organic matter (SOM). However, it is unclear how fungi affect the chemical molecular composition of SOM. This study examined the effect of saprophytic soil fungus Mortierella capitata K on different soil carbon components and their molecular components. Genome sequencing revealed the ability of the strain to synthesize and degrade heterocycles, heteropolysaccharides, alkenes, terpenoids, steroids, amides, lipids, and amino acids. Subsequently, the turnover of SOM in M. capitata K inoculation with straw (KS) or without straw (K) addition was investigated via an aseptic microcosm experiment for 240 days. Pyrolysis gas chromatography-mass spectrometry analysis (Py-GCMS) showed that the molecular composition of SOM significantly changed with culture time in the two treatments. M. capitata K inoculation increased the relative abundance of tetradecanentitrile, dotriacontane, n-hexadecanoic acid, and n-dodecyl methacrylate in SOM during day 5–180. In contrast, the proportion of components in SOM (oxidizable by potassium permanganate) reduced after M. capitata K inoculation. Similarly, M. capitata K inoculation decreased the relative abundance of alkanes, alkenes, and alcohols in the original SOM on the 240th day. However, the above decline was effectively alleviated after straw addition. Straw addition significantly improved the abundance of n-hexadecanoic acid. RNA sequencing on the 30th day revealed the association between genes encoding alcohol dehydrogenase and SOM ester formation. Therefore, this study may provide insights into the complex feedback loops between microbial activities and molecular composition changes in SOM.

Straw addition increases enzyme activities and microbial carbon metabolism activities in bauxite residue

Recovery of microbial functions is one of the critical processes in the nutrient cycling of bauxite residue for improving revegetation. Straw is considered to be effective to increase microbial diversity and drive the development of the microbial community, but its effect on microbial carbon metabolism has not been illustrated. The present study evaluated the effects of phosphogypsum (PG), straw (SF) and phosphogypsum plus straw (PGSF) on physicochemical properties, enzyme activities, and microbial carbon metabolism activities in bauxite residue. After 180 days incubation, PG, SF and PGSF treatment significantly reduced the residue pH from 10.85 to 8.64, 9.39 and 8.06, respectively. Compared to CK treatment, SF treatment significantly increased the content of total organic carbon (TOC) and organic carbon fractions (DOC, MBC, EOC, and POC). In addition, straw addition significantly increased glucosidase, cellulose, urease, and alkaline phosphatase by 7.2-9.1 times, 5.8-7.1 times, 11.1-12.5 times, and 1.1-2.2 times, respectively. The Biolog results showed that straw addition significantly increased microbial metabolic activity (AWCD) and diversity in bauxite residue. Redundancy analysis indicated total nitrogen (TN) and carbon fractions (POC, MBC and DOC) were the most important environmental factors affecting microbial metabolic activity and diversity in bauxite residue. These findings provided us with a biogeochemical perspective to reveal soil formation in bauxite residue and suggested that nutrient supplement and regulation of salinity-alkalinity benefit the establishment of microbial communities and functions in bauxite residue.

Study on the suitability of rice straw and silicate cement

In order to study the feasibility of preparing cement particle board by compounding silicate and rice straw shavings, this paper explored their compatibility by detecting the heat of hydration of both by HPLC and characterized by FTIR, SEM and XRD. The results suggested that rice straw contained a certain amount of sugars soluble in water as well as organic carboxylic acids, having toxic effects on the hydration of silicate cement and could retard the hydration reaction of silicate cement. The addition of rice straw would inhibit the generation of crystals of hydration products in the early stage of silicate cement hydration, which makes it difficult for the C-S-H gel to build a dense spatial mesh, resulting in the poor compatibility of rice straw with silicate cement. The verification experiments exhibited that the static flexural strength of straw cement particleboard was far lower than the standard value of CB/T 24312–2009 cement particleboard, indicating that rice straw was unsuitable for direct apply for the preparation of rice straw silicate cement particleboard, and the compatibility regulation of rice straw and silicate cement was required.

Combined anaerobic digestion of chicken manure and corn straw: study on methanogenic potential and microbial diversity

PurposeTo explore the methane production potential and microbial community changes of combined anaerobic digestion of chicken manure and corn straw. Increase methane production, reduce the environmental pollution caused by the burning of livestock manure and straw, and provide some theoretical references for the construction and operation of actual biogas projects.MethodsDifferent proportions (3%, 5%, 10%) of corn straw were added to the anaerobic digestion systems of chicken manure in order to improve the C/N ratio and to evaluate the feasibility and potential synergistic effect on the co-digestion. The key point was to use 16S rDNA sequencing to analyze the relationship between the microbial diversity and the hydrolase activity during the anaerobic digestion.ResultThe results showed that the volumetric gas production of methane in the 3% straw addition group was 227.66 ml/gVS, which was 18% higher than the cumulative methane production in the pure chicken manure experimental group. However, with the increase of straw concentration, methane production and the utilization rate of the raw materials continued to decrease. The change in activity of each hydrolase was in agreement with changes in hydrolytic acidifying bacteria, and the activity of the main hydrolase also increased with the addition of straw; the correlation coefficient was 0.9943. Sequencing results showed that the dominant strains of methanogenic archaea were Methanosarcina, Methanosaeta, Methanobacterium, and Methanospirillum. Mainly for hydrogen-eating, acetic acid-eating methanogens, its role is to use H2, methanol and acetic acid, and other substances to metabolize methane, and convert it into CH4 and CO2.ConclusionThe addition of a small amount of straw enhanced the production capacity of hydrogen-nutritive methane to some extent, and the species richness and evenness were also improved, reducing the pollution caused by livestock manure to the environment while controlling the pollution caused by straw burning.Graphical