Fabrication of high performance poly(vinyl alcohol)/straw composite film used for package via melt casting and biaxial stretching.

A high performance poly(vinyl alcohol)/straw (PVA/SP) composite film for package was fabricated in this study by using thermal processing technology of PVA established in our research group and biaxial stretching technology. The introduction of SP disrupted the original hydrogen bonds in modified PVA by forming new hydrogen bonds with the hydroxyl groups of each component in modified system, thus promoting the stable melt casting of PVA/SP composites and also endowing the obtained PVA/SP precursor sheets with good drawability. Upon biaxial stretching, SP reinforced the crystalline structure and orientation of PVA through their hydrogen bonds with PVA, improving the mechanical strength, crystallinity and thermal stability of PVA/SP films. The film with 3.0 × 3.0 stretching ratios demonstrated the exceptional tensile strength (62.2 MPa), tear strength (119.7 kN/m), low heat shrinkage (5.2 %), and oxygen permeability coefficient (1.38 × 10-16 cm3·cm/cm2·s·Pa), which surpassed most conventional plastic films used in food packaging field. This research not only pioneered an environmentally friendly packaging solution, but also offered a novel strategy for solid-state high-value, large-scale and economical utilization of waste crop straw, greatly avoiding the adverse effects of its burning on the environment.

Optimum seeding density and seedling age for the outstanding yield performance of Japonica rice using crop straw boards for seedling cultivation.

Crop straw boards, a novel nursery material, has proven effective for cultivating dense, young rice seedlings suitable for mechanized transplanting, thereby saving labor. However, under high-density nursery conditions, the biomass accumulation and yield formation in rice vary with different seedling ages, necessitating exploration of optimal seeding densities and seedling ages to achieve high yields. This study aims to determine the appropriate seeding densities and seedling ages using crop straw boards to maximize rice yield. Over two years, field studies were conducted using crop straw boards for rice cultivation at seeding densities of 150, 200, 250, 300, and 350 g/tray (labeled as D1, D2, D3, D4, and D5) and seedling ages of 10, 15, 20, and 25 days (labeled as A1, A2, A3, and A4).The results indicated that D4A2 significantly enhanced tiller number, dry matter accumulation, and photosynthetic capacity, resulting in a yield increase of 2.89% compared to the conventional method of D1A3. High-density and short-aged seedlings cultivated with crop straw boards can enhance rice yield by improving photosynthetic capacity and crop quality. This study emphasizes the importance of using crop straw boards for rice nursery practices, as well as selecting the appropriate seeding densities and seedling ages for optimizing rice production.

Cleaner anaerobic fermentation and greenhouse gas reduction of crop straw.

Rice anaerobic fermentation is a significant source of greenhouse gas (GHG) emissions, and in order to efficiently utilize crop residue resources to reduce GHG emissions, rice straw anaerobic fermentation was regulated using lactic acid bacteria (LAB) inoculants (FG1 and TH14), grass medium (GM) to culture LAB, and Acremonim cellulolyticus (AC). Microbial community, GHG emission, dry matter (DM) loss, and anaerobic fermentation were analyzed using PacBio single-molecule real-time and anaerobic fermentation system. The epiphytic microbial diversity of fresh rice straw was extremely rich and contained certain nutrients and minerals. During ensiling, large amounts of GHG such as carbon dioxide are produced due to plant respiration, enzymatic hydrolysis reactions, and proliferation of aerobic bacteria, resulting in energy and DM loss. Addition of FG1, TH14, and AC alone improved anaerobic fermentation by decreasing pH and ammonia nitrogen content (P < 0.05) and increased lactic acid content (P < 0.05) when compared to the control, and GM showed the same additive effect as LAB inoculants. Microbial additives formed a co-occurrence microbial network system dominated by LAB, enhanced the biosynthesis of secondary metabolites, diversified the microbial metabolic environment and carbohydrate metabolic pathways, weakened the amino acid metabolic pathways, and made the anaerobic fermentation cleaner. This study is of great significance for the effective utilization of crop straw resources, the promotion of sustainable livestock production, and the reduction of GHG emissions.IMPORTANCETo effectively utilize crop by-product resources, we applied microbial additives to silage fermentation of fresh rice straw. Fresh rice straw is extremely rich in microbial diversity, which was significantly reduced after silage fermentation, and its nutrients were well preserved. Silage fermentation was improved by microbial additives, where the combination of cellulase and lactic acid bacteria acted as enzyme-bacteria synergists to promote lactic acid fermentation and inhibit the proliferation of harmful bacteria, such as protein degradation and gas production, thereby reducing GHG emissions and DM losses. The microbial additives accelerated the formation of a symbiotic microbial network system dominated by lactic acid bacteria, which regulated silage fermentation and improved microbial metabolic pathways for carbohydrates and amino acids, as well as biosynthesis of secondary metabolites.

Straw from Different Crop Species Recruits Different Communities of Lignocellulose-Degrading Microorganisms in Black Soil.

The biological degradation of plant residues in the soil or on the soil surface is an integral part of the natural life cycle of annual plants and does not have adverse effects on the environment. Crop straw is characterized by a complex structure and exhibits stability and resistance to rapid microbial decomposition. In this study, we conducted a microcosm experiment to investigate the dynamic succession of the soil microbial community and the functional characteristics associated with lignocellulose-degrading pathways. Additionally, we aimed to identify lignocellulose-degrading microorganisms from the straw of three crop species prevalent in Northeast China: soybean (Glycine max Merr.), rice (Oryza sativa L.), and maize (Zea mays L.). Our findings revealed that both the type of straw and the degradation time influenced the bacterial and fungal community structure and composition. Metagenome sequencing results demonstrated that during degradation, different straw types assembled carbohydrate-active enzymes (CAZymes) and KEGG pathways in distinct manners, contributing to lignocellulose and hemicellulose degradation. Furthermore, isolation of lignocellulose-degrading microbes yielded 59 bacterial and 14 fungal strains contributing to straw degradation, with fungi generally exhibiting superior lignocellulose-degrading enzyme production compared to bacteria. Experiments were conducted to assess the potential synergistic effects of synthetic microbial communities (SynComs) comprising both fungi and bacteria. These SynComs resulted in a straw weight loss of 42% at 15 days post-inoculation, representing a 22% increase compared to conditions without any SynComs. In summary, our study provides novel ecological insights into crop straw degradation by microbes.

Degradation of agricultural waste is dependent on chemical fertilizers in long-term paddy-dry rotation field.

The practice of returning straw to agricultural fields is a globally employed technique. Such agricultural fields also receive a significant amount of nitrogen (N) and phosphorus (P) fertilizers, because these two macronutrients are essential for plant growth and development. However, the consequences of such macronutrients input on straw decomposition, soil dissolved organic matter (DOM), key microbes, and lignocellulolytic enzymes are still unclear. In a similar aim, we designed a long-term straw returning study without and with different N and P nutrient supplementation: CK (N0P0), T1 (N120P0), T2 (N120P60), T3 (N120P90), T4 (N120P120), T5 (N0P90), T6 (N60P90), and T7 (N180P90), and evaluated their impact on rice and oilseed rape yield, soil DOM, enzymes, lignocellulose content, microbial diversity, and composition. We found straw returning improved overall yield in all treatments and T7 showed the highest yield for oilseed rape (30.31-38.87 g/plant) and rice (9.14-9.91 t/ha) during five-years of study. The fertilizer application showed a significant impact on soil physicochemical properties, such as water holding capacity and soil porosity decreased, and bulk density increased in fertilized treatments, as compared to CK. Similarly, significantly low OM, cellulose, hemicellulose, and lignin content were found in T7, T4, T3, and T2, while high values were found in CK and T5, respectively. The fluorescence excitation-emission matrix spectra of DOM of different treatments revealed that T3, T7, T4, and T6 showed high peak M (microbial by-products), peak A and peak C (humic acid-like) as compared to others. The microbial composition was also distinctive in each treatment and a high relative abundance of Chloroflexi, Actinobacteriota, Ascomycota, and Basidiomycota were found in T2 and T3 treatments, respectively. These findings indicate that the decomposition of straw in the agricultural field was dependent on nutrients input, which facilitated key microbial growth and impacted positively on lignocellulolytic enzymes, which further aided the breakdown of all components of straw in the field efficiently. On the other hand, high input of chemical based fertilizers to soil can lead to several environmental issues, such as nutrient imbalance, nutrient runoff, soil pH change and changes in microbial activities. Keeping that in consideration, we recommend moderate fertilizer dosage (N120P90) in such fields to achieve higher decomposition of crop straw with a small yield compromise.

Potential and benefits of biochar production: crop straw management and carbon emission mitigation in Shaanxi Province, China.

Shaanxi Province is an important agricultural province in western China. Its profit-oriented management of crop residues remains a concern in the agriculture sector. Aiming to accelerate the valorization of agricultural straw and offer potential solutions for profit-oriented use of crop residues in Shaanxi, this study estimated the quantity of resources and collectable amount of crop straw by using the grain-to-straw ratio, analyzed the carbon emission reduction potential considering biochar energy and soil uses with the help of a life cycle assessment (LCA) model, and calculated the economic benefits of biochar production using waste and abandoned straw in Weinan (a city of Shaanxi). The theoretical resources and collectible amount of crop straw in Shaanxi showed an overall growth trend from 1949 to 2021, reaching 1.47 × 107 and 1.26 × 107 t in 2021 respectively. In 2021, straw from corn, wheat, and other grains accounted for 94.32% of the total straw. Among the 11 cities in Shaanxi, Weinan had the largest straw resources of 2.82 × 106 t, Yulin had the largest per capita straw resources of 0.72 t/person, and Yangling had the highest resource density of 7.60 t/hm2. The total carbon emission reduction was 3.11 × 104 t under scenario A with crop straw used for power generation. The emission reduction ranged from 1.25 × 107 to 1.27 × 107 CO2e t under scenario B with biochar production for energy and soil use. By using waste and abandoned straw in Weinan for biochar production, carbon emissions could be reduced by up to 2.07 × 105 t CO2e. In terms of the economic benefit from straw pyrolysis, the actual income was estimated to range from 0.67 × 108 to 1.33 × 108 ¥/a with different carbon prices. This study sheds light on the economic and environmental benefits of agricultural straw valorization through pyrolysis in Shaanxi, and provided an important basis for promoting the agricultural straw utilization in view of its potential for carbon emission reduction.

Optimization of biogas production from straw wastes by different pretreatments: Progress, challenges, and prospects.

Lignocellulosic biomass (LCB) presents a promising feedstock for carbon management due to enormous potential for achieving carbon neutrality and delivering substantial environmental and economic benefit. Bioenergy derived from LCB accounts for about 10.3 % of the global total energy supply. The generation of bioenergy through anaerobic digestion (AD) in combination with carbon capture and storage, particularly for methane production, provides a cost-effective solution to mitigate greenhouse gas emissions, while concurrently facilitating bioenergy production and the recovery of high-value products during LCB conversion. However, the inherent recalcitrant polymer crystal structure of lignocellulose impedes the accessibility of anaerobic bacteria, necessitating lignocellulosic residue pretreatment before AD or microbial chain elongation. This paper seeks to explore recent advances in pretreatment methods for LCB biogas production, including pulsed electric field (PEF), electron beam irradiation (EBI), freezing-thawing pretreatment, microaerobic pretreatment, and nanomaterials-based pretreatment, and provide a comprehensive overview of the performance, benefits, and drawbacks of the traditional and improved treatment methods. In particular, physical-chemical pretreatment emerges as a flexible and effective option for methane production from straw wastes. The burgeoning field of nanomaterials has provoked progress in the development of artificial enzyme mimetics and enzyme immobilization techniques, compensating for the intrinsic defect of natural enzyme. However, various complex factors, such as economic effectiveness, environmental impact, and operational feasibility, influence the implementation of LCB pretreatment processes. Techno-economic analysis (TEA), life cycle assessment (LCA), and artificial intelligence technologies provide efficient means for evaluating and selecting pretreatment methods. This paper addresses current issues and development priorities for the achievement of the appropriate and sustainable utilization of LCB in light of evolving economic and environmentally friendly social development demands, thereby providing theoretical basis and technical guidance for improving LCB biogas production of AD systems.

Sustainable exploitation and safe utilization of biochar: Multiphase characterization and potential hazard analysis.

Pyrolysis temperature determines the multiphase (solid and dissolved) structure of biochar (BC). In this study, the temperature-dependent evolution of characteristics and potential hazards of three crop (cotton, alfalfa, and wheat) residue BC were systematically investigated. The results showed that pyrolysis temperature significantly affected the elemental composition and morphology of BC. A higher pyrolysis temperature led to a higher aromatization and graphitization degree of BC. A numerical relationship between pyrolysis temperature and BC surface properties (functional groups, carbonization degree) was established. Pyrolysis temperature controlled the content, composition, and functional group evolution of BC-derived dissolved organic matter. Although the amount of potentially toxic elements (PTEs) in BC was concentrated after pyrolysis, the potentially risk of PTEs significantly decreased. The spin concentration of persistent free radicals in BC prepared at 500 °C was the highest. These findings will hopefully offer comprehensive guidance for sustainable utilization of crop straw and fit-for-purpose exploitation of BC.

Mercury and methylmercury in Hg-contaminated paddy soil and their uptake in rice as regulated by DOM from different agricultural sources.

In this study, from the perspectives of structural and compositional variations of soil-dissolved organic matter (DOM), we explored the effects of agricultural DOM inputs on methylmercury (MeHg) accumulation in the soil and mercury (Hg) bioaccumulation in rice grains. Pot experiments with the addition of DOMs from maize straw (MaS), rape straw (RaS), rice straw (RiS), composted rice straw (CRiS), cow dung (CD), and composted cow dung (CCD) were then conducted. Results showed that, relative to the control, the DOM amendment from each agricultural source elevated MeHg concentrations in the soil, with an increase of 18-227%, but only parts of DOMs elevated total dissolved Hg (DHg) and MeHg (DMeHg) concentrations in pore water. Among all DOM species, RiS, CRiS, and CCD significantly increased total Hg (THg) and MeHg contents in rice grains by 34-64% and 32-118%, respectively. Compared with RiS, THg and MeHg contents in rice grains in the CRiS treatment decreased slightly, which was consistent with the distributions of DHg and DMeHg concentrations in pore water and the aromaticity variation of soil DOM. In contrast, the CCD input significantly enhanced the enrichment of THg and MeHg in rice grains relative to CD because it significantly reduced the humification of soil DOM at all rice-growing stages while increasing the low-molecular-weight fractions in soil DOM. The THg and MeHg contents in the rice grains were significantly lower treated by RaS than those by MaS and RiS, which may be related to the higher sulfur-containing compounds such as sulfate and cysteine in rape straw or its DOM solution. Overall, DOM amendment from different agricultural sources resulted in significantly discriminative effects on the MeHg accumulation in soil and Hg enrichment in rice in the Hg-contaminated paddy field by shaping soil DOM properties.

Emerging technologies of employing algae and microorganisms to promote the return-to-field of crop straws: A mini-review.

As an agricultural waste, crop straw enriched with a variety of nutrients is regarded as an important fertilizer resource. In the past, crop straw return-to-field played a key role in the sustainability of agricultural environment, but some problems, such as ammonia loss in ammoniation, low rate of straw decomposition, and high carbon footprint, attracted researchers' attentions. In this paper, we propose three technical routes, including cyanobacteria-based ammonia assimilation, microorganisms-based crop straw pretreatment, and microalgae-based carbon capture, to address the aforementioned problems. Besides, challenges which may hinder the practical application of these technical routes as well as the potential solutions are discussed in detail. It is expected that this paper could provide new ideas to the practical application of crop straw return-to-field.

Optimization of hydrolysis conditions of crop straw and its effect in Chlorella sorokiniana culture.

Taking straws of corn, wheat, and millet as raw materials, we pretreated them with alkaline hydrogen peroxide, and then hydrolyzed by cellulase and xylanase. We selected the total sugar content in the hydrolysate as the indicator to evaluate the hydrolysis of the straws from three crop species, and further optimized the conditions. Then, the hydrolysates of three types of crop straws were used as carbon source for Chlorella sorokiniana culture to assess their effects on microalgal cultivation. The results showed that the optimal hydrolysis conditions for the three crop straws were identified as solid-liquid ratio of 1:15, temperature of 30 ℃, and treatment time of 12 h. Under such optimal condition, the total sugar contents increased up to 1.677, 1.412, and 1.211 g·L-1 in the corn, millet and wheat straw hydrolysate, respectively. The hydrolysates from the three crop straw could significantly increase both algal biomass and lipid content of C. sorokiniana. Corn straw hydrolysate had the best effect, with high levels of algal biomass (1.801 g·L-1) and lipid content (30.1%). Therefore, we concluded that crop straw hydrolysates as carbon source could significantly promote microalgal biomass and lipid enrichment. The results could lay the foundation for the efficient conversion and utilization of straw lignocellulose raw materials, provide new knowledge for the resource utilization of agricultural wastes, as well as the theoretical basis for the efficient cultivation of microalgae using crop straw hydrolysates.

Elevated methylmercury production in mercury-contaminated paddy soil resulted from the favorable dissolved organic matter variation created by algal decomposition.

Algae-derived organic matter (AOM) may considerably regulate methylmercury (MeHg) production and accumulation in the paddy fields by changing the soil-dissolved OM (SDOM) properties. In this study, a 25-day microcosm experiment was performed to compare the responding mechanisms of MeHg production in the Hg-contaminated paddy soil-water system to the input of algae-, rice-, and rape-derived OMs. Results showed that algal decomposition could release much more cysteine and sulfate than crop straws. Compared with crop straw-derived OMs, AOM input greatly increased the dissolved organic carbon concentrations in soil but resulted in a greater decrease in tryptophan-like fractions while accelerated the formation of high-molecular-weight fractions in soil DOM. Moreover, AOM input significantly increased MeHg concentrations in the pore water by 19.43%-3427.66% and 52.81%-5846.57% compared to rape- and rice-derived OMs, respectively (P < 0.05). And, a similar MeHg changing pattern was also observed in the overlying water (10-25 d) and the soil solid-phase particles (15-25 d) (P < 0.05). Correlation analysis revealed that MeHg concentrations in the AOM-added soil-water system had significantly negative and positive relationships with the tryptophan-like C4 fraction and molecular weight (E2/E3 ratio) of soil DOM, respectively (P < 0.01). These findings suggest that AOM has a higher capacity than crop straw-derived OMs to promote MeHg production and accumulation in the Hg-contaminated paddy soils by creating a favorable soil DOM variation and providing more microbial electron donors and receptors.

Crop Straw Resource Utilization as Pilot Policy in China: An Event History Analysis.

Massively generated crop straw can be utilized and valorized with great economic and environmental benefits. The Chinese government has adopted the pilot policy of crop straw resource utilization (CSRU) for disposing of the straw and practicing waste valorization. This work took 164 counties in the Hebei Province of China as a case study, mapped the temporal and spatial characteristics of the diffusion of the CSRU pilot policy in this province, and conducted an Event History Analysis by establishing a binary logistic regression model to identify the specific factors that determine the diffusion of the CSRU pilot policy in China from the aspects of resource availability, internal capacity, and external pressure. It indicates that: (1) the CSRU pilot policy diffuses rapidly in Hebei Province, although it is still at the early stage of this policy diffusion; (2) the model explains 95.2% of the variance in adopting a pilot county, indicating the effectiveness of this model; (3) straw resource density has a positive impact on CSRU pilot selections, and it can increase the possibility of one county being selected as a CSRU pilot by 23.2%, while population density has shown a negative effect; (3) policy support from local government is a major internal factor that determines CSRU performance, and it can increase the possibility of one county being selected as a CSRU pilot nearly tenfold; proximity pressure from neighboring counties has a positive effect on the diffusion of the CSRU policy, and it also greatly increases the possibility of being selected as a CSRU pilot.

Cascade utilization of rice straw for biogas production.

To improve the biogas yield of rice straw, an innovative cascade utilization process for biogas production was proposed using a method referred to as "the first digestion + NaOH treatment + the second digestion" (labeled FSD). Both the first digestion and the second digestion of all treatments were conducted at the initial total solid (TS) loading of straw of 6%. A series of lab-scale batch experiments were conducted to investigate the effect of first digestion time (5, 10, and 15 days) on biogas production and lignocellulose structure destruction of rice straw. The results showed that the cumulative biogas yield of rice straw using the FSD process was increased by 13.63-36.14% compared with the control (CK), and the highest biogas yield of 233.57 mL g-1 TSadded was obtained when the first digestion time was 15 days (FSD-15). The removal rates of TS, volatile solids, and organic matter were increased by 12.21-18.09%, 10.62-14.38%, and 13.44-16.88%, respectively, compared with those of CK. The results of Fourier transform infrared spectroscopy analysis revealed that the skeletal structure of rice straw was not significantly destroyed after the FSD process, but the relative contents of functional groups in rice straw were changed. The FSD process accelerated the destruction of crystallinity of rice straw, and the lowest crystallinity index of 10.19% was obtained at FSD-15. The abovementioned results indicated that the FSD-15 process is recommended for cascade utilization of rice straw in biogas production.

Effects of biochars derived from four crop straws on a Cd-polluted cinnamon soil.

Crop straw biochar is an efficient and low-cost alternative amendment for heavy metal immobilization in acidic soil. However, reports on the effect of these biochars on the amendment of actual Cd-polluted calcareous soil are limited. Therefore, four biochars, derived from peanut, rice, maize, and wheat straws, were applied to determine the changes in the chemical properties of alkaline cinnamon soil and effects on Cd immobilization. The results showed that the cation exchange capacity and the contents of organic C, Mehlich-3 K, and Mehlich-3 P in the biochar-amended soil increased by 4.87-22.02%, 68.78-218.83%, 1.9-10.3 times, and 19.18-74.40%, respectively, indicating the potential high performance of biochar in improving soil fertility and productivity. The Community Bureau of Reference sequential extraction results showed that decrease in acid-extractable Cd resulted in a reduced availability of Cd. Thus, crop straw biochar could be a promising alternative for soil Cd decontamination and fertilization.

[Properties of Biochars Prepared from Different Crop Straws and Leaching Behavior of Heavy Metals].

In this study, rice straw, soybean straw, wheat straw, and corn straw were chosen as raw materials, and biochars were prepared through the pyrolysis method at 550℃ under oxygen-limited conditions to investigate the physicochemical properties of biochars derived from the straws, the migration and transformation characteristics of heavy metals (HMs) (Cr, Ni, Cu, As, Cd, and Pb) after pyrolysis, and their leaching behaviors in different leaching solutions. The results showed that the physicochemical properties and elemental composition of the biochars were basically consistent. However, compared with that of biochars derived from other straws, biochar derived from wheat straw had a higher ash content (22.48%) and H/C radio (0.06). Meanwhile, biochar derived from corn straw had a smaller micropore volume (0.006 cm3·g-1) and a correspondingly smaller specific surface area (110.120 m2·g-1), which was consistent with the SEM image. After pyrolysis, the content of HMs (except Cd) increased by 14.04% to 410.81%, especially that of Cu and As. However, the content of Cd in soybean straw and corn straw decreased by 20.49% and 8.20% after pyrolysis, respectively, due to the low boiling point of Cd. Furthermore, most of the HMs (except Cd and Pb) tended to transform from unstable (acid-soluble/exchangeable and reducible forms) to stable forms (oxidizable and residual forms), implying that pyrolysis facilitated the stabilization of the HMs. The HMs in biochar were not leached or were leached in small amounts in ultra-pure water and buffered salt solutions, as opposed to leaching in relatively larger amounts in acetic acid solution and humic acid solution. Cr and Ni showed low leaching capacity in all leaching solutions. Cu showed relatively high leaching capacity in acetic acid solution, with the leaching amount ranging from 2.601 mg·kg-1 to 4.224 mg·kg-1, and As showed a relatively high leaching capacity in humic acid solution, with the leaching amount ranging from 0.074 mg·kg-1to 0.166 mg·kg-1. After pyrolysis, the environmental quality index (PIi) and the Nemerow pollution index (NPI) values of various HMs increased by different degrees. However, the pollution of single HMs remained at a safe level, and the integrated pollution of biochars was at the level of "clean". Due to the significant increase in potential ecological risk factors (Er) of Ni, Cd, and Pb after pyrolysis, the potential ecological risk index (RI) of biochar derived from the rice straw increased slightly. However, the potential ecological risk indexes of biochars derived from other straws significantly decreased after pyrolysis, owing to the stabilization of HMs.

Potential of crop straw incorporation for replacing chemical fertilizer and reducing nutrient loss in Sichuan Province, China.

Sichuan Province is rich in crop straw, yet little is known about its spatial distribution pattern, potential in replacing chemical fertilizer and mitigating nutrient loss. Based on the statistical data and literature review, the spatial distribution and potential of nutrient resources in crop straw for replacing chemical fertilizers was evaluated in this study. The nutrient loss with both crop incorporation and chemical fertilizer application were examined using a nutrient release coefficient method and compared. Results showed that Chengdu Plain, Northeast and South Sichuan produced more than 95% of the total straw nutrient resources during the period of 2016-2020. The potential of crop straw to substitute potassium (K), nitrogen (N) and phosphorus (P) fertilizer were K2O 33.08-285.95 kg hm-2, N 9.52-82.32 kg hm-2 and P2O5 4.91-28.71 kg hm-2, respectively. If chemical fertilizer was substituted by all the available straw nutrient resources, N and P loss can be decreased by 55.12% and 65.84% in average in Sichuan Province. 343.93 t of N loss and 20.05 t of P loss can be reduced in plain areas, 122.88 t of N loss and 46.29 t of P loss can be reduced in mountainous and hilly areas, and 5.65 t of t N loss and 3.54 t of P loss can be reduced in plateau areas. It can be concluded that there were rich crop straw nutrient resources in Sichuan Province with obvious spatial variability, solid consideration should be put on to the proper use of crop straw nutrient resources, with the aim of chemical fertilizer reduction, nutrient loss reduction and sustainable development.

Straw incorporation interacting with earthworms mitigates N2O emissions from upland soil in a rice-wheat rotation system.

Intensive attentions have been paid to the positive effects on nitrous oxide (N2O) production under straw return or the presence of earthworms. Straw return as a sustainable practice can promote earthworm growth, how the interactions between straw and earthworms affect N2O production is still not well known. A split-plot field experiment (straw return as main plot and earthworm addition as subplot) was performed to quantify the interactive effects of straw and earthworm on N2O emissions from a wheat field and to determine the underlying mechanisms from nitrification and denitrification processes. The results showed that straw return significantly increased N2O emissions by 41.0 % under no earthworm addition but decreased it by 19.0 % under earthworm addition compared with straw removal (P < 0.05). The significant interaction between straw and earthworm benefits the mitigation of N2O emissions. Random forest model showed that denitrification and nitrification were dominant processes to affect N2O emissions at the jointing and booting growth stages of wheat, respectively. The interaction between straw and earthworm significantly decreased the abundances of N2O-producing bacterial genes such as nirS and nirK at the jointing stages, and AOB at the booting stages. The contrasting mechanisms in regulating N2O emissions at different growth stages should be considered in nitrogen recycling models to accurately predict available N and N2O dynamics. Our findings suggest that N2O emissions under straw return can be weakened with the increasing earthworm populations under the scenario of widely used conservation practices (e.g., straw return and no-till) due to significant interaction between straw and earthworms.

Decreased in vitro bioaccessibility of Cd and Pb in an acidic Ultisol through incorporation of crop straw-derived biochar.

Studies analyzing the in vitro bioaccessibility (BAc) of heavy metals in biochar-amended soils are currently lacking. The present study aimed to assess the metal BAc in Cd- and Pb-spiked acidic Ultisol samples treated individually with 2% (w/w) maize, rice, wheat, soybean, and pea straw-derived biochar. The results indicate that the Cd-BAc simulated in gastric phase (GP) decreased from 78.4% to 66.5-72.3% and the Pb-BAC decreased from 74.3% to 67.2-69.2%; however, the Cd-BAc in the intestinal phase (IP) decreased from 35.6% to 27.9-33.5% and the Pb-BAc decreased from 34.7% to 29.7-32.9% after 120 d of incubation with biochar application compared to the un-amended Ultisol. The Cd- and Pb-BAc in both GP and IP were significantly negatively correlated with soil pH, CEC, and organic carbon (P < 0.05), which increased after biochar application. The soybean straw-derived biochar amendment has the greatest potential to decrease the BAc of Cd and Pb in the GP and IP, owing to the highest level of CEC, SOC, TC and TN among all soil samples. Moreover, the BAc was positively correlated with the exchangeable, and exchangeable + carbonate-bound Cd and Pb fractions (P < 0.05), indicating these fractions had a dominant influence on the BAc of cationic heavy metals. Therefore, crop straw-derived biochar amendment can decrease the BAc of Cd and Pb in acidic Ultisol, and thus mitigate the health risks posed by these metals from incidental ingestion.

Practice, pathways, and performance for resource utilization of crop straw: A case study of Xinyang City in China.

The open-air burning of the massive generated crop straw in rural areas has been a troubling problem in China in recent decades, and the utilization and valorization of crop straw have provided promising solutions to it. However, due to the limitations in straw resources, economic, social, and technological conditions, different regions vary greatly with each other in the technological pathways and performance of straw utilization. By taking ten counties and districts of Xinyang City in Henan Province of China as examples, it analyzed the spatial distribution of straw yields and the adoption of five pathways of crop straw utilization in Xinyang City, and summarized three typical combination modes. In addition, it also provided the integrated model of FBWM-TOPSIS-PROMETHEE to evaluate the performance of crop straw utilization in the ten counties and districts, to provide local decision-makers with the pathways for promoting the utilization and valorization of crop straw. The results indicated that: (1) The endowment of straw resources and the straw utilization pathways in the ten counties and districts of Xinyang City vary greatly with each other; (2) Returning crop straw to the fields as fertilizer after being crushed is the mainstream mode of resource utilization of crop straw, although five technological modes have been adopted in Xinyang City; (3) Among the 10 counties, Huaibin and Xixian have the best performance of resource utilization of crop straw, and Shangcheng is the worst performer.