Rice Straw Residues Research Articles

Half substitution of mineral N with fish protein hydrolysate enhancing microbial residue C and N storage and climate benefits under high straw residue return

The widespread utilization of straw return was a popular practice straw disposal for highly intensive agriculture in China, which has brought about some negative impacts such as less time for straw complete biodegradation, aggravation of greenhouse gas evolution, and lower efficient of carbon accumulation. It was urgent to find an eco-friendly N-rich organic fertilizer instead of mineral N as activator to solve the above problems and lead a carbon accumulation in long tern management. Besides, microbial necromass was considered as a crucial contributor to persistent soil carbon (C) and nitrogen (N) pool. How organic fertilizer activators influence microbial residue under different amount of crop residues input remained unclear. Thus, soils incorporating moderate and high rate of rice straw residue with additions of half and full of organic activators (fish protein hydrolysates vs. manure) were incubated for measuring carbon dioxide (CO2) and nitrous oxide (N2O) emission, microbial community and necromass. It was found that soil CO2 emission was rapidest during the first 13 days of straw decomposition but remained lowest in the treatments of 50% mineral N substituted by fish protein hydrolysate. There were that 81%–89% of total CO2 release and 59%–65% of total N2O emission occurred within 60 days of incubation period, and bacterial community and nitrate positively affected soil CO2 and N2O release respectively. Straw incorporation amount and organic activator application interactively influenced soil CO2 emission but not affected soil N2O emission. After 360 days of incubation, the difference of bacterial necromass was noticeable but fungal necromass remained almost unaltered across all treatments. All treatments showed generally comparable contribution of microbial necromass N to the total N pool. The treatment of 50% mineral N substituted by fish protein hydrolysate under high rate of straw input (HSF50) promoted the highest proportion of microbial necromass C in soil organic C because of alleviating N limitation for microorganisms. Finally, HSF50 was recommended as an eco-friendly strategy for enhancing microbial necromass C and N storage and climate benefits in agroecosystems.

Response of Bacterial Community Structure in the Bulk Soil and Rice Straw Residues under Different Crop Rotation Systems

This study investigated the effect of upland crop rotation on soil bacterial community in bulk soil and rice straw residues in the alluvial soils. Soil samples and rice straw residues in two crop rotation models including triple rice and rice-upland crops were collected for incubation under anaerobic and aerobic conditions. Data were analyzed from Denaturing Gradient Gel Electrophoresis band patterns. The results showed that the composition and diversity of communities colonizing the rice straw residues differed from those inhabiting the bulk soil. The bacterial community composition and diversity were only moderately affected by rice straw residues in the bulk soil. Especially, this study indicated that the composition of the bacterial community associated with the bulk soil and rice straw residues was dynamic in two incubation conditions (aerobic or anaerobic) and the different crop rotation models. The findings of this study demonstrated that the bacterial diversity was not affected by the difference in continuous paddy rice cultivation compared to the upland crop rotation system.

Recent advances in xylitol production in biorefineries from lignocellulosic biomass: a review study

The progression of sustainable practices in biorefineries is pivotal in mitigating carbon emissions and optimizing the utilization of natural resources, thereby preserving the environment. Biorefineries, which convert lignocellulosic biomass into a variety of products, distinguish themselves by efficiently transforming waste into high-value products. Xylitol stands out among biorefinery products. Derived from the conversion of xylose present in lignocellulose, it not only offers health benefits but is also considered an intermediate molecule in the production of valuable chemical products. Microbiological methods for xylitol production are increasingly acknowledged as efficient and environmentally friendly alternatives. These are some of the main factors discussed in this review, which aims to demonstrate the biotechnological route for producing xylitol through lignocellulosic materials. Several studies were observed to characterize various lignocellulosic residues, and it was noted that Eucalyptus globulusand banana leaves exhibit high levels of xylose. By analyzing the most recent researches related to xylitol production, the possibility of co-production of bioethanol using the same biotechnological route of xylitol production was identified. For instance, studies have shown that a combination of bagasse and sugarcane straw, as well as rice straw residue, are capable of producing substantial levels of xylitol and ethanol. The yields reached 30.61 g/L of xylitol and 47.97 g/L of ethanol, and 34.21 g/L of xylitol and 2.12 g/L of ethanol, respectively. These innovations not only promote sustainability but also have the potential to generate positive impacts on the global economy.

Bacterial assisted sustainable production of Three-Dimensional defective carbon from rice straw for supercapacitor

Defective carbon nanomaterials with three-dimensional (3D) structure are showing great potential for advanced electrochemical storage and conversion devices, but its application is restricted by the synthesis, which is usually involved with complicate and energy-intensive processes. Herein, pyrolysis of rice straw (RS) residue, of which is collected from the bacterial assisted hydrolysis, is proposed by us here, and the obtained bio-char is defective with 3D structure and rich in oxygen-containing functional groups. Compared to the pristine one, specific surface area of the representative RS carbon (RSC2) was increased from 428.8 to 1131.7 m2 g−1. The assembled supercapacitor with RSC2 showed a high specific capacitance of 331F g−1 at a charge–discharge current density of 0.5 A g−1, and a capacity retention of 97.6% was maintained at 5 A g−1 even after 10,000 cycles.

Sodium Hydroxide Hydrothermal Extraction of Lignin from Rice Straw Residue and Fermentation to Biomethane

The purpose of the NaOH pretreatment of rice straw with a recycling strategy was to enhance the economic efficiency of producing biomethane. Anaerobic digestion is used for converting rice straw into biogas. In this work, 5% NaOH and rice straw mixed samples were autoclaved at 121 °C for 20 min for lignin removal. The NaOH black liquor was separated using filtration for the subsequent treatment cycle. The NaOH liquor was utilized in one more subsequent recycling procedure to test its ability to remove lignin from the rice straw. The 5% NaOH treatment results in a reduction in rice straw (RC) lignin of 73.6%. The lignin content of the recycled NaOH-filtrated rice straw samples (RCF1) was reduced by 55.5%. The 5% NaOH-treated rice straw sample yields a total cumulative biogas of 1452.4 mL/gVS, whereas the recycled NaOH-filtered (RCF1) samples generate 1125.2 mL/gVS after 30 days of incubation. However, after 30 days of incubation, the untreated rice straw (RCC) bottle produced a total of 285.5 mL/gVS of biogas. The total increase in methane output after NaOH treatment is 6–8 times greater, and the biogas yield improves by 80–124%. We show here that the recycled NaOH black solution has still the effectiveness to be used for successive pretreatment cycles to remove lignin and generate methane. In the meantime, the NaOH black solution contains useful materials (lignin, sugars, potassium, and nitrogen) that could be purified for commercial purposes, and more importantly recycling the NaOH solution decrease the chances of environmental pollution. Thus, recycling NaOH decreased chemical consumption, which would provide net benefits instead of using fresh NaOH solution, had a lower water consumption, and provided the prospect of producing an optimum yield of methane in anaerobic digestion. This method will decrease the chemical treatment costs for biomass pretreatment prior to anaerobic digestion. Recycling of NaOH solution and the integration of pretreatment reactors could be a novel bioprocessing addition to the current technology.

Comparative study of ethanol production from sodium hydroxide pretreated rice straw residue using Saccharomyces cerevisiae and Zymomonas mobilis.

Rice straw is a suitable alternative to a cheaper carbohydrate source for the production of ethanol. For pretreatment efficiency, different sodium hydroxide concentrations (0.5-2.5% w/v) were tested. When compared to other concentrations, rice straw processed with 2% NaOH (w/v) yielded more sugar (8.17 ± 0.01mg/ml). An alkali treatment induces effective delignification and swelling of biomass. The pretreatment of rice straw with 2% sodium hydroxide (w/v) is able to achieve 55.34% delignification with 53.30% cellulose enrichment. The current study shows the effectiveness of crude cellulolytic preparation from Aspergillus niger resulting in 80.51 ± 0.4% cellulose hydrolysis. Rice straw hydrolysate was fermented using ethanologenic Saccharomyces cerevisiae (yeast) and Zymomonas mobilis (bacteria). Overall, superior efficiency of sugar conversion to ethanol 70.34 ± 0.3% was obtained with the yeast compared to bacterial strain 39.18 ± 0.5%. The current study showed that pretreatment with sodium hydroxide is an effective method for producing ethanol from rice straw and yeast strain S. cerevisiae having greater fermentative potential for bioethanol production than bacterial strain Z. mobilis.

Anaerobic digestion of lignocellulosic waste for enhanced methane production and biogas-digestate utilization

Lignocellulosic biomass is an important source for nutrient management in agricultural systems and has a largely unexploited potential for biogas production. The digestates from the anaerobic digestion (AD) process are widely used in agriculture systems due to their nutrient composition and organic matter, making them a valuable source for plants. As a result, methane (CH4) production from AD of lignocellulosic biomass waste, such as rice straw, corn stalk, and grape stalk, was determined in this study, and their anaerobic digester residues were studied at various concentrations to investigate their potential on tomato plant growth and fruit yield. The biogas and CH4 yields of the pretreated rice straw, corn stalk, and grape stalk were determined through the AD process for 72 days, and the results revealed a gradual increase in the cumulative biogas and CH4 production until the end of the AD process (72 days). The cumulative biogas from rice straw, corn stalk, and grape stalk was 359.3, 309.9, and 215.1 L/kg VS, respectively. However, the biogas production of rice straw was higher than that of corn stalk, and grape stalk by 15.6% and 67%, respectively. The cumulative CH4 yield of rice straw was higher than that of corn stalk, and grape stalk by 21.1% and 76.3%, respectively. The results also showed that tomato growth significantly increased under grape stem residue (GSR) more than under rice straw residue (RSR) and corn stalk residue (CSR), as well as under untreated control and control infected with Fusarium oxysporum f. sp. lycopersici (FOL). The increase in bioreactor residue concentration resulted in a significant increase in tomato growth parameters, crop yield, and tomato quality. The results confirmed that 20% of GSR increased the tomato's physical and chemical properties compared with control, RSR, and CSR. The soil content of total nitrogen, phosphorus, and potassium gradually increased with the increase in residue concentrations before and after AD, and the maximum concentration was obtained at 25% of GSR. Therefore, anaerobic digestate could be economically viable, which can be a good solution for sustainable lignocellulosic biomass waste management and plant growth.

Comparative Analysis of Compost Quality Produced from Fungal Consortia and Rice Straw by Varying C/N Ratio and its Effect on Germination of Vigna radiata

Composting is considered to be one of the best methods for handling organic waste. It is a natural process and takes months to give quality mature compost. Characteristics of initial wastes and process conditions are the compost maturity deciding factors. Some biological inoculants, e.g., bacteria and fungi, can reduce the compost time and improve its quality. This research is based on the hypothesis that using fungus consortia on rice straw will boost the activities of microbes and, as a result, the rate of composting. The hypothesis was tested by preparing compost using rice straw residue with and without the applications of fungal consortia. Fungal consortia of Aspergillus flavus, Aspergillus fumigatus, and Aspergillus terreus cellulose-degrading strains along with Pusa-1121 rice variety were used for the study. Different C/N ratios were achieved by varying rice straw, green leaves, poultry droppings, and fungal inoculant proportions. During various stages of composting, changes in total nitrogen, organic carbon, C/N ratios, and other parameters were calculated. The germination index of Mung beans (Vigna radiata) was used to measure the quality of the completed compost extract. Statistical analysis with the help of a two-tailed independent t-test at the confidence level of 95% was applied to determine the statistical difference between the treatments and control. It has been found that the Seed Germination index of treatment C/N 30 was 91.5% and that of C/N 26 was 79.1% which were significantly (p<0.01) different from the 54% GI of control.

Valuation of rice straw residues: Production of silylated methylcellulose containing propylamine and propylethylenediamine for use as anticorrosion and antibacterial

Green technology is a scientific movement seeking to eliminate industrial chemicals and replace them with natural products by valorizing natural resources or biological waste. In this work, we present the extraction of cellulose from rice straw and chemically modified water-dispersible cellulose (methylcellulose) by performing a methylation process. The methylcellulose is chemically bonded to N-[3-(trimethoxysilyl)propyl]ethylenediamine, and (3-aminopropyl)triethoxysilane compounds to produce a cellulose–organosilane hybrid. The prepared compounds were studied with appropriate techniques such as 1H NMR, XRD, FTIR, TGA, Raman spectroscopy, FE-SEM, and AFM. The prepared materials were used as corrosion inhibitors of steel in 1 N H2SO4 for studies of potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The materials were also studied as antibacterial agents. The results indicate the successful use of a modified extracted cellulose hybrid in the corrosion field and as an antibacterial agent. Quantum chemical assessments based on density functional theory (DFT) of the trimethoxysilyl propylamine and dimethoxymethylsilyl propylethylenediamine grafted methylcellulose were calculated. The results obtained showed the agreement of the theoretical data with the experimental data.

Cultivation of Navicula sp. on rice straw hydrolysate for the production of biogenic silica

Rice straw hydrolysate (RSH) prepared at room temperature was found to be rich in silica (140 ± 4.1 mg L-1) and other nutrients (nitrate-N: 160 ± 4.3 mg L−1, total dissolve phosphate: 164 ± 6.7 mg L−1, ammoniacal-N: 439.8 ± 17 mg L−1). The aim of this work was to study four RSH dilutions (10, 30, 50, 70% v/v) to cultivate Navicula sp. with modified ASN-III as a control. The best result was achieved in 30% RSH in terms ofdoubling time (d = 1.49 days) and growth rate (µmax = 0.46 day−1). Compared to control, specific growth rate and biomass productivity were increased by 2.93 folds and 1.85 folds, respectively. Cultivation in 5 L reactor with optimized 30% RSH yielded frustule (54.2 ± 1.9%), carbohydrate (12.4 ± 1.2%), lipid (18.9 ± 1.4%), and protein (8.2 ± 0.6%). The residual solid fraction showed 18.99% increased theoretical methane yield than raw rice straw. Overall, the present process offers a sustainable solution to manage rice straw residue and recover nanoporous silica.

Effects of long-term organic matter application on soil carbon accumulation and nitrogen use efficiency in a double-cropping rice field

Increasing soil carbon (C) sequestration in paddy field and improving rice nitrogen use efficiency (NUE) are vital for sustainable agriculture and environmental protection. It was a benefit practice for achieving these goals by taken rice straw and organic manure managements. However, there is still need to further investigate the effects of different long-term fertilizer managements on soil C sequestration and NUE under the double-cropping rice system in southern of China. Therefore, the effects of different long-term (36-years) fertilizer practices on soil C sequestration and NUE under the double-cropping rice system in southern of China were investigated in the present paper. The field experiment was included four different fertilizer treatments: chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and without fertilizer input as a control (CK). This result indicated that soil C content at plough layer in paddy field with RF and OM treatments were increased, compared with MF and CK treatments. Besides input C directly into paddy field, soil original organic C accumulation with RF and OM treatments were increased by 1.54% and 3.01%, compared with MF treatment. This result indicated that soil TOC content increase rate and annual topsoil organic C sequestration rate in paddy field with RF and OM treatments increased by 55.56%, 88.89% and 48.05%, 76.62%, compared with MF treatment, respectively. Compared with MF treatment, NUE with RF and OM treatments increased by 10.43% and 22.61%, respectively, mainly due to increasing soil organic C. Grain yield of double-cropping rice with RF and OM treatments increased by 1009.5 and 1166.5 kg ha−1, compared with MF treatment, respectively. This result indicated that there was significantly correlation between NUE/NUENPK and TOC content with RF and OM treatments, at early rice and late rice growth seasons. Therefore, it was benefit practice for increasing soil carbon sequestration and improving rice NUE in the double-cropping rice system with long-term application of rice straw and organic manure managements.

Site-specific nutrient management: impact on productivity, nutrient uptake and economics of rice-wheat system

A field experiment was conducted on Typic Ustochrept soil at the Crop Research Centre of Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut, for two years (2014–15 to 2015–16) to evaluate site specific nutrient management (SSNM) against state recommendation (SR), integration of SSNM and SR with crop residue and farm yard manure. In terms of crop growth yield, nutrient uptake and economics, SSNM had significantly higher growth parameters, viz. number of tillers/m2 and dry matter accumulation as compared to SR in both rice and wheat crops. Different yield attributes, viz. number of grains/panicle or spike, test weight of rice and wheat were also higher with SSNM. SSNM out yielded for rice, wheat and rice-wheat system (RWS) productivity by 10.3%, 14.1% and 11.9%. System N, P and K uptake under SSNM was also higher by 24.36, 9.55 and 36.01 kg/ha, respectively, compared to SR. An additional income of `12953/ha over SR and maximum return/rupee invested (`2.50) was also recorded with SSNM. Recycling of 5 t/ha rice and wheat straw residue along with SSNM had added advantage.

Performance evaluation of AquaCrop model for rice (Oryza sativa) crop in Trans-Gangetic plains

A field experiment was conducted on Typic Ustochrept soil at the Crop Research Centre of Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut, for two years (2014–15 to 2015–16) to evaluate site specific nutrient management (SSNM) against state recommendation (SR), integration of SSNM and SR with crop residue and farm yard manure. In terms of crop growth yield, nutrient uptake and economics, SSNM had significantly higher growth parameters, viz. number of tillers/m2 and dry matter accumulation as compared to SR in both rice and wheat crops. Different yield attributes, viz. number of grains/panicle or spike, test weight of rice and wheat were also higher with SSNM. SSNM out yielded for rice, wheat and rice-wheat system (RWS) productivity by 10.3%, 14.1% and 11.9%. System N, P and K uptake under SSNM was also higher by 24.36, 9.55 and 36.01 kg/ha, respectively, compared to SR. An additional income of `12953/ha over SR and maximum return/rupee invested (`2.50) was also recorded with SSNM. Recycling of 5 t/ha rice and wheat straw residue along with SSNM had added advantage.

Decomposition of rice straw residues and the emission of CO<sub>2</sub>, CH<sub>4</sub> under paddy rice and crop rotation in the Vietnamese Mekong Delta region - A microcosm study

This study investigated the influence of soil undergoing different crop rotations on the CH<sub>4</sub>, CO<sub>2</sub> emissions, and decomposition of rice straw. The studied soil undergoing crop rotation systems were rice-rice-rice (SR) and baby corn-rice-mungbean (SB). Two main microcosm set-ups: anaerobic (SR-AN, SB-AN) and aerobic (SR-AE, SB-AE) conditions. Litter bags containing rice stems were inserted into the soil and recollected at different time points for chemical analysing and the gas sampling was collected to measure the CO<sub>2</sub> and CH<sub>4</sub> emissions. The results indicated that the total carbon (TC) decreased around 30%, and the TC removal in anaerobic was significantly higher than in aerobic conditions. The residue cellulose content varied in a range from 68.2% to 78.6%, while the hemicellulose content varied from 57.4% to 69.3% at day 50 after incorporation. There were no significant differences in the total nitrogen removal, cellulose, hemicellulose, and lignin contents among the microcosm set-ups. CO<sub>2</sub> emission increased in all the microcosm set-ups with the treatments without rice straw (CTSR, CTSB) in both aerobic and anaerobic conditions. CH<sub>4</sub> release in the SR-AN treatments did not differ significantly compared with the SB-AN treatments. This study confirmed that the decomposition of rice straw residues is faster in the anaerobic paddy soil condition compared to the aerobic crop rotation condition.

Effects of burning rice straw residue on-field on soil organic carbon pools: Environment-friendly approach from a conventional rice paddy in central Viet Nam

Rice straw residue management is still facing many problems worldwide. This study used two environmentally friendly methods to investigate the effects of rice straw burning activity on water-extracted carbohydrate content in long-term paddy soil. Soil samples were collected at a depth within 0–15 cm at the paddy field before and after burning rice straw (pre-burning and post-burning), then extracted by distilled water at the ratio of 1:10 (soil: water) for measuring hot water (at 80 °C) and water extracted carbohydrate (at 25 °C) (HECH and WECH). The results showed that burning rice straw did not alter soil organic carbon (SOC); however, soil pH increased approximately 8.3%. Meanwhile, WECH and HECH ranged from 233 to 630 mg kg−1, with the highest HECH in Pre-burning treatment, while the lowest amount addressed WECH of Post-burning treatment. Extracted carbohydrate decreased after burning rice straw compared to Pre-burning soil. On the other hand, hot water increased 39–58% of carbohydrates compared to water extraction. We conclude that burning rice straw did not affect SOC but tends to reduce their labile carbon pools, and the heating process likely degrade part of SOC when extracted at high temperatures.

Two-stage processing for xylooligosaccharide recovery from rice by-products and evaluation of products: Promotion of lactic acid-producing bacterial growth and food application in a high-pressure process

In this study, we attempted to maximize arabinoxylan conversion into xylooligosaccharide (XOS) from rice husk and rice straw using two saccharification processes and evaluate the promotion of lactic acid-producing bacterial growth, including an investigation of the role of prebiotics in protecting probiotic bacteria in rice drink products in a high-pressure process (HPP). Hydrothermal treatment followed by enzymatic hydrolysis was designed for XOS recovery from rice husk arabinoxylan (RH-AX) and rice straw arabinoxylan (RS-AX). The hydrothermal treatment performed at 170 °C for 20 min and 180 °C for 10 min was the optimal condition to produce XOS liquor from rice husk and rice straw, respectively. Pentopan mono BG successfully recovered XOS from rice husk and rice straw residues at 50 °C, pH 5.5, an enzyme concentration of 50 U and 100 U/g substrate for 24 h. This design converted 92.17 and 88.34% (w/w) of initial RH-AX and RS-AX into saccharides, which comprised 64.01 and 59.52% of the XOS content, respectively. Rice husk xylooligosaccharide (RH-XOS) and rice straw xylooligosaccharide (RS-XOS) had degrees of polymerization ranging from 2 to 6 with some arabino-xylooligosaccharides. RH-XOS and RS-XOS were used to examine the promotion of the growth of lactic acid-producing bacteria strains in the presence of other prebiotics. RH-XOS and RS-XOS strongly promoted the growth of Lactobacillus sakei and Lactobacillus brevis, while other species showed weak to moderate growth. This study represents the first report of the powerful effect of Lactococcus lactis KA-FF1-4 on altering the utilization of XOS but not xylose. Furthermore, for the first time, we reported the capability of XOS to protect probiotics in rice drinks under high-pressure conditions. RH-XOS and RS-XOS resulted in the highest viability of approximately 11 log cfu/mL and exhibited no significant difference compared with the non-HPP treatment. Hence, rice husk and rice straw can be utilized as alternative prebiotic sources that provide biological activity and food applications in the HPP industry.

Evaluation of enzymatic delignification of rice straw residues for bioethanol production

The biomass-based biofuel production from sustainable resources such as lignocellulosics account for the larger alternative energy in the world for achieving zero emissions of greenhouse gas and reduction of global warming. In this study, lignocellulosics, such as rice straw as agricultural residues collected from South 24 Parganas district of West Bengal, have been explored for their potential availability for alternative sources of production of bioethanol. The delignification of rice straw cell wall was performed through alkali pretreatment followed by enzymatic hydrolysis using microorganism Trichoderma reesei, yielded high fermentable sugar for conversion to bioethanol. The efficacy of the delignification process was supported by the structural characteristics of the delignified substrate via scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray fluorescence microscopy and thermogravimetric analysis (TGA). After 240 hours of hydrolysis, the optimum sugar was obtained 135.2 ± 0.45 mg/g from the rice straw. The maximum fermentation efficiency was shown at ~74% in the fed-batch reactor and ~83% in the packed bed reactor using enzyme hydrolysed rice straw at optimal conditions of 33°C and pH = 5.5.

Evaluation of enzymatic delignification of rice straw residues for bioethanol production

The biomass-based biofuel production from sustainable resources such as lignocellulosics account for the larger alternative energy in the world for achieving zero emissions of greenhouse gas and reduction of global warming. In this study, lignocellulosics, such as rice straw as agricultural residues collected from South 24 Parganas district of West Bengal, have been explored for their potential availability for alternative sources of production of bioethanol. The delignification of rice straw cell wall was performed through alkali pretreatment followed by enzymatic hydrolysis using microorganism Trichoderma reesei, yielded high fermentable sugar for conversion to bioethanol. The efficacy of the delignification process was supported by the structural characteristics of the delignified substrate via scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray fluorescence microscopy and thermogravimetric analysis (TGA). After 240 hours of hydrolysis, the optimum sugar was obtained 135.2 ± 0.45 mg/g from the rice straw. The maximum fermentation efficiency was shown at ~74% in the fed-batch reactor and ~83% in the packed bed reactor using enzyme hydrolysed rice straw at optimal conditions of 33°C and pH = 5.5.

Nitrogen release and re-adsorption dynamics on crop straw residue during straw decomposition in an Alfisol

Returning crop straw to the field not only improves the nitrogen (N) supplying capacity and N retention of soil but also decreases the amount of rural organic waste and prevents air pollution. Therefore, understanding the mechanisms of the N release and re-adsorption dynamics on crop straw residue during straw decomposition in agricultural soil is important, and this understanding can help us strengthen N fertilizer management during the crop growth period. An on-farm incubation experiment was conducted in the Jianghan Plain in Central China under flooded conditions using the nylon mesh bag method. Results showed that the decomposition rate of crop straw was much faster at the beginning of the incubation stage, whereas it was steady during the later stage with no observed differences among the three types of crop straw. After 120 d of incubation, the cumulative decomposition proportion of rice straw, wheat straw and rape straw was 72.9, 56.2, and 66.9%, respectively. The proportion of N that released from the three crop straws was 52.0, 54.4 and 54.9%, respectively. The zeta potentials and Brunauer, Emmett and Teller (BET) surface area of the rice, wheat and rape straw residues increased gradually as the decomposition period progressed. The water adsorption capacity of the rice straw was significantly affected during the decomposition period. The saturated water adsorption capacity of rice straw was the highest at 30 d of decomposition (4.17 g g–1) and then decreased slightly. The saturated water adsorption of wheat and rape straws reached the lowest value at 30 d and then gradually increased and became stable. All the results demonstrated that crop straw and straw residue can re-adsorb NH4+ ions from the surrounding solution. The re-adsorption was affected by the decomposition period and concentration of exogenous NH4+ and was independent of the crop species via the combined efforts of physical and chemical adsorption, ion exchange and water retention on residue surfaces. Future studies will focus on straw returning and N fertilizer application at different levels of moisture content of the soil reduce potential negative effects such as water-logging and excess N caused by the straw substrate.

Functional soil organic matter fractions in response to long-term fertilizer management in a double-cropping paddy field of southern China

AbstractSoil organic matter (SOM) and its fractions play an important role in maintaining or improving soil quality and soil fertility. Therefore, the effects of a 34-year long-term fertilizer regime on six functional SOM fractions under a double-cropping rice paddy field of southern China were studied in the current paper. The field experiment included four different fertilizer treatments: chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM) and without fertilizer input as control (CK). The results showed that coarse unprotected particulate organic matter (cPOM), biochemically, physically–biochemically and chemically protected silt-sized fractions (NH-dSilt, NH-μSilt and H-dSilt) were the main carbon (C) storage fractions under long-term fertilization conditions, accounting for 16.7–26.5, 31.1–35.6, 16.2–17.3 and 7.5–8.2% of the total soil organic carbon (SOC) content in paddy soil, respectively. Compared with control, OM treatment increased the SOC content in the cPOM, fine unprotected POM fraction, pure physically protected fraction and physico-chemically protected fractions by 58.9, 106.7, 117.6 and 28.3%, respectively. The largest proportion of SOC to total SOC in the different fractions was biochemically protected, followed by chemically and unprotected, and physically protected were the smallest. These results suggested that a physical protection mechanism plays an important role in stabilizing C of paddy soil. In summary, the results showed that higher functional SOM fractions and physical protection mechanism play an important role in SOM cycling in terms of C sequestration under the double-cropping rice paddy field.