Rice Straw Removal Research Articles

Effect of Different Tillage and Residue Management Options on Soil Water Transmission and Mechanical Behavior

Understanding the variability in the mechanical and hydrological soil characteristics resulting from diverse tillage and residue management practices is essential for evaluating the adoption of conservation strategies to preserve soil’s physical well-being. Zero-tillage techniques combined with residue retention or incorporation have gained widespread recognition for their capacity to conserve soil and water resources, reduce energy consumption, and enhance soil quality and environmental sustainability. Nevertheless, the choice of tillage and residue management options may vary depending on the geographical locations and specific soil conditions. To assess the impacts of four distinct tillage and residue management approaches, a two-year experiment (2020–2021 and 2021–2022) was conducted: T1: conventional tillage followed by wheat sowing after the removal of rice straw (CT-RS); T2: zero tillage with wheat sowing using a Happy Seeder while retaining rice straw (ZT+RS); T3: conventional tillage followed by wheat sowing after rice straw incorporation using a reversible mouldboard plough (CT+RS); T4: minimum tillage with wheat sowing using a Super Seeder with rice straw incorporation (MT+RS); the effects were recorded on the physical soil properties. Our findings indicate that zero tillage combined with residue retention (T2) had a positive influence on various physical soil attributes. Notably, significant differences were observed among the tillage and residue management options, particularly in terms of the bulk density with T1 exhibiting the highest values and the lowest being in T2, whereas the soil penetration resistance was lowest in T3 compared to T1. In the case of T3, sandy loam and clay loam soils had the highest measured saturated hydraulic conductivity values, measuring 5.08 and 4.57 cm h−1 and 4.07 and 3.73 cm h−1, respectively. Furthermore, T2 (zero tillage with residue retention) demonstrated the highest mean weight diameter (MWD) and maximum water stable aggregate. These results collectively underscore the positive effects of adopting zero tillage and retaining residue (T2) on soil structure and quality, particularly concerning the mechanical and hydrological soil properties.

Improved soil structural stability under no-tillage is related to increased soil carbon in rice paddies: Evidence from literature review and field experiment

Improving soil structural stability (SSS) and soil organic carbon (SOC) are critical for soil health and environmental pollution mitigation. No-tillage alters many soil properties (e.g., SOC), however, its effects on SSS in rice paddies are unclear. Therefore, we used field experiment and meta-analysis to determine the effects of no-tillage on wet stability of aggregates (WSA), clay dispersibility (ClayDis), mean weight diameter (MWD), and aggregate SOC distribution and mineralization in rice paddies. The field experiment included four tillage practices: no-tillage, rotary tillage and moldboard plow tillage with rice straw retention (NTS, RTS and CTS respectively), and moldboard plow tillage with rice straw removal (CT). The WSA at 0–5 cm soil depth was significantly higher under NTS compared with CTS. The ClayDis at 5–10 cm soil depth under NTS was 36% lower ( P < 0.05) than CTS. The relationship between SOC and WSA fits a broken stick model, with an inflection point of clay/SOC ratio at 12.5. Higher SOC under no-tillage might result from the protection of >2 mm aggregates (macroaggregates) and lower SOC mineralization of < 2 mm aggregates. Additionally, the meta-analysis showed that no-tillage increased ( P < 0.05) the macroaggregate content, WSA and MWD. However, the current research regarding tillage effects on paddy ClayDis is insufficient. In rice paddies, the increased macroaggregate content may contribute to increasing SOC, which improves SSS under no-tillage. • No-tillage in rice cropping increased soil structural stability. • Aggregate stability increases with SOC content and its mineralization. • SOC mineralizability of <2 mm aggregates was low under no-tillage. • No-tillage increased SOC storage in >2 mm aggregates. • Carbon mineralization did not differ among aggregate size classes.

Carbon pathways in aggregates and density fractions in Mollisols under water and straw management: Evidence from 13C natural abundance

Mollisols have a high potential to mitigate climate change and play an important role in the global carbon (C) cycle due to their inherently high soil organic matter (SOM). However, little is known about the mechanism of C stabilization in Mollisols, especially subjected to different management effects. To trace C stabilization between aggregates and SOM density fractions in Mollisols, soil samples were collected from different experimental plots: controlled irrigation + rice (Oryza sativa L.) straw removal (CI), flooded irrigation + rice straw removal (FI), controlled irrigation + rice straw return (CI-SR), and flooded irrigation + rice straw return (FI-SR). Each soil sample was separated into three aggregate size classes (>250 μm, 53–250 μm, and <53 μm), then each class individually subjected to density fractionation to obtain free and occluded light fractions (fLF and oLF), as well as dense and mineral-heavy fractions (DF and MF). The overall C content and 13C abundance of fractions were measured to interpret C transfer and accumulation among aggregate and density fractions. The highest increase in the soil organic C (9.27–24.88%) was observed in CI-SR compared with the other treatments. Irrigation and straw return primarily affected C accumulation within macroaggregates and the MF, which were the dominant forms in the aggregates and density fractions, respectively. An enrichment in δ13C was found from macroaggregates to silt + clay, and from light to heavy fractions, indicating that Mollisols macroaggregates and light fractions acted as the source or initial store of plant residues, and that the C in the silt + clay class and heaviest fraction contained more microbially-transformed C than did the macroaggregates and light fractions. A detailed scheme of C transfer within aggregates and SOM fractions based on the δ13C natural abundance revealed the following general sequence: free light → occluded light → dense → mineral fractions, concurring with results reported at upland sites. There is a greater probability of C transfer between SOM density fractions under CI. This contrasted with the results that CI decreases the possibility of C exchange between aggregates than FI, which indicates differences in the C stabilization processes between no-flooded and flooded conditions of Mollisols. In addition, straw returning can reduce the possibility of C exchange both between and within aggregates, which plays a significant role in maintaining the stability of the Mollisols carbon cycle. The present study provides further detailed insights into the C stabilizing mechanisms in Mollisols which depend on management (straw, water status). This finding is conducive to the sustainable use and management of Mollisols toward maintaining or increasing C stock and in realizing the objective of C-neutral agriculture.

Long-term impacts of nitrogen fertilization and straw incorporation on rice production and nitrogen recovery efficiency under plastic film mulching cultivation

The application of nitrogen (N) fertilizer as base fertilizer in plastic film mulching cultivation (PFMC) system easily leads to soil N deficiency in the late growth period of rice. The combination of N fertilization and straw incorporation was put forward and their impacts on rice yield and grain N recovery efficiency (NRE) based on a long-term experiment in a PFMC system were evaluated. Five N application levels included 0, 45, 90, 135, and 180 kg ha−1 and two subplots were rice straw removal (RSR) and rice straw incorporation (RSI). Moreover, RSR and RSI in a conventional flooding cultivation (CFC) system with 135 kg ha−1 N application rate were also included. The results showed that the optimum N application rate was 135 kg ha−1. At this N application level, the promotion effect on yield and grain N uptake over years in PFMC system was more obvious than that in CFC system. Continuous PFMC might accelerate the mineralization of soil organic matter and the increase of soil N availability. However, RSI had no obvious promotion effect on the increment of yield, grain NRE, and soil available N with years compared with RSR in PFMC system. In conclusion, film mulching with the N fertilizer application rate of 135 kg ha−1 improved soil thermal condition in early growth stage of rice, and thus enhanced the availability of soil N, grain N uptake, and yield. This provides a reference for PFMC application in water-saving rice production system.

Effects of different tillage practices on the distribution of soil total nitrogen and carbon/nitrogen ratio at different soil depths in a double rice cropping system

ABSTRACT Soil total nitrogen (STN) and the carbon/nitrogen ratio (C/N) influence both crop production and microbial activity, but their distributions under different tillage practices are not clearly understood. This study investigated the effects of tillage practices on the vertical and temporal distributions of STN and the C/N ratio as well as on the distributions of STN fractions in a double rice cropping system from 2012 to 2017. Four tillage practices were established in 2005 in Southern China, i.e. no-till with rice straw mulch (NTS), rotary tillage with rice straw retention (RTS), plough tillage with rice straw retention (CTS), and with rice straw removal (CT). Even at 20–30 cm soil depth, long-term rice straw retention significantly increased STN and its fractions compared to those for CT. Noticeably, at 0–5 cm soil depth, the C/N ratio under NTS was 1.6–6.5% lower than those of other treatments, with a larger amount of rice straw input. In addition, long-term rice straw retention (NTS, RTS, and CTS) increased rice yield by 6.2–14.2% compared to that for CT. Therefore, long-term rice straw retention is recommended in this region due to its ability to increase N accumulation (even at deeper soil depths), which might improve the rice production.

An assessment of irrigated rice production energy efficiency and environmental footprint with in-field and off-field rice straw management practices

The research provided scientific evidences for improved rice straw management. Rice cultivation with in-field burning of rice straw is the worst option with the lowest energy efficiency and highest air pollution emission. This article comprises a comparative assessment of energy efficiency and the environmental footprint of rice production using four different rice straw management scenarios, namely, straw retained, straw burned, partial straw removal, and complete straw removal. Paddy yield, grain quality, and energy balance were assessed for two seasons while greenhouse gas emissions (GHGE) were measured weekly starting from land preparation through to the cropping and fallow period. Despite the added energy requirements in straw collection and transport, the use of collected rice straw for mushroom production can increase the net energy obtained from rice production systems by 10–15% compared to burning straw in the field. Partial and complete removal of rice straw reduces GHGE by 30% and 40% compared to complete straw retention, respectively.

Effect of the long-term application of organic matter on soil carbon accumulation and GHG emissions from a rice paddy field in a cool-temperate region, Japan. -I. Comparison of rice straw and rice straw compost -

ABSTRACT The influence of the long-term combination of rice straw removal and rice straw compost application on methane (CH4) and nitrous oxide (N2O) emissions and soil carbon accumulation in rice paddy fields was clarified. In each of the initial and continuous application fields (3 and 39−51 years, respectively), three plots with different applications of organic matter were established, namely, rice straw application (RS), rice straw compost application (SC) and no application (NA) plots, and soil carbon storage (0−15 cm), rice grain yield and CH4 and N2O fluxes were measured for three years. The soil carbon sequestration rate by the organic matter application was higher in the SC plot than in the RS plot for both the initial and continuous application fields, and it was lower in the continuous application field than in the initial application field. The rice grain yield in the SC plot was significantly higher than those in the other plots in both the initial and continuous application fields. Cumulative CH4 emissions followed the order of the NA plot < the SC plot < the RS plot for both the initial and continuous application fields. The effect of the organic matter application on the N2O emissions was not clear. In both the initial and continuous application fields, the increase in CH4 emission by the rice straw application exceeded the soil carbon sequestration rate, and the change in the net greenhouse gas (GHG) balance calculated by the difference between them was a positive, indicating a net increase in the GHG emissions. However, the change in the GHG balance by the rice straw compost application showed negative (mitigating GHG emissions) for the initial application field, whereas it showed positive for the continuous application field. Although the mitigation effect on the GHG emissions by the combination of the rice straw removal and rice straw compost application was reduced by 21% after 39 years long-term application, it is suggested that the combination treatment is a sustainable management that can mitigate GHG emissions and improve crop productivity.

Returning the Rice Residue Affects Accumulation and Physicochemical Properties of Wheat Starch

Core Ideas Returning residue increased wheat production per plant, increased total starch, and decreased amylose content. Residue return sped up endosperm cell development, increasing B‐type starch granules at 17 and 27 d after anthesis. Residue return increased the proportion of small B‐type starch granules. Morphology of B‐type starch did not differ between groups of rice straw returned to the field vs. the residue return treatments. Residue return decreased relative crystallinity and increased the ratio of amorphous to ordered carbohydrates. Removing rice (Oryza sativa) straw has the potential to impact nutrient cycling and wheat quality. The objective of this study was to determine the impact of rice straw removal on wheat production and quality. The experiment contained three rice residue rates: none, rice residue mixed into the surface 5‐cm depth, and rice residue mixed into the 15‐cm soil depth. Returning the rice residue increased the wheat production per plant, total starch content, and decreased amylose content. Incorporating rice straw into the surface 5 cm or the 15 cm of soil depth accelerated endosperm development and increased the amounts of B‐type starch granules at 17 and 27 d after anthesis, and the proportion of small B‐type starch granules. Incorporating rice straw into the surface 5 cm or the 15 cm soil depth decreased the relative degree of crystallinity and increased the ratio of amorphous structure to ordered carbohydrate structure in the external region of the granules. Pasting parameters including peak, breakdown, final, and setback viscosities increased, whereas pasting time and temperature decreased in the returning the rice residue group. Returning the rice residue at 5 and 15 cm exhibited similar effects on the granule development and physicochemical properties of wheat starch. The impact of returning the rice residues to the soil on wheat production and wheat kernel quality was attributed to enhanced soil fertility. This study may contribute to knowledge on crop cultivation, crop physiology, and food science.

Suppression of CH4 Emission by Rice Straw Removal and Application of Bio‐Ethanol Production Residue in a Paddy Field in Akita, Japan

To elucidate the effects of rice straw removal and rice straw‐based bio‐ethanol production residue application on rice growth and methane (CH4) emission from a paddy field, a lysimeter experiment with three treatments (application of rice straw after harvesting (the rice‐straw plot); removal of rice straw and the application of bio‐ethanol production residue (the Et‐residue plot); removal of rice straw (the no‐application plot)) was conducted over three years. Though the grain yields in the Et‐residue and no‐application plots tended to be slightly higher than that in the ricestraw plot, there were no significant differences among the plots (530–546 g∙m−2). Suppression of CH4 emission by the treatments was found clearly in the early part of the growing season. The total CH4 emissions during the rice‐growing season (unit: g∙C∙m−2∙period−1) followed the order of the noapplication plot (11.9) &lt; the Et‐residue plot (14.6) &lt; the rice‐straw plot (25.4), and a significant difference was found between the no‐application and rice‐straw plots. Consequently, bio‐ethanol production from rice straw and a following application of its residue to paddy fields is considered to be a promising technology which can obtain new sustainable energy and suppress CH4 emission without any inhibition on rice growth.

Waterbird response to management practices in rice fields intended to reduce greenhouse gas emissions

There are many benefits of agricultural landscapes for wildlife. In California's Central Valley, post-harvest flooding of rice fields increases the decomposition of rice stubble and provides habitat for over 50 species of waterbirds. These fields are also flooded during planting, providing habitat for spring migrants and locally breeding birds. Because California has lost over 90% of its historic wetlands, flooded rice is critical wildlife habitat, providing 80% of the total flooded habitat in the Sacramento Valley. Flooding rice fields, however, contributes to greenhouse gas (GHG) emissions. Several rice field management practices may reduce methane emissions including reduced flooding in winter, removal of rice straw after harvest (baling), and drill seeding during planting. During the winters of 2011–2012 and 2012–2013, we compared waterbird use in four combinations of post-harvest practices: baled/flooded, baled/non-flooded, non-baled/flooded, and nonbaled/non-flooded. We found significantly higher dabbling duck and shorebird densities in the non-baled/flooded practice compared to the other three practices. During the spring of 2012 and 2013, we compared waterbird use of drill-seeded fields (reduced GHG) with flooded fly-on seeded fields (status quo GHG). We found no significant differences in mean density between the two seeding practices for waterbirds. Our study found evidence that some post-harvest practices (reduced winter flooding, baling) that reduce GHG emissions from rice also reduce use by waterbirds. While reducing GHG is globally necessary to minimizing the impacts of climate change, doing so in an area of hemispheric importance for waterbirds should be done with caution.

Effect of Potassium on Boro-fallow-t. Aman cropping pattern in old Brahmaputra floodplain soil of Bangladesh

Field experiment was conducted at the Bangladesh Institute of Nuclear Agriculture (BINA) farm, Mymensingh during 2010-11 to 2011-12 to investigate the effect of different levels of K on Boro-Fallow-T. Aman cropping pattern in Old Brahmaputra Floodplain Soil of Bangladesh. There were four treatments for the first crop (Boro rice): T1 (Control), T2 (50% NPKS), T3 (75%NPKS) and T4 (100% NPKS). The 100% NPKS rates were recommended on the basis of soil test values. T4 treated plot of each block was further split into seven sub-plots to represent seven treatments (T4.1 to T4.7) for the second crop of T. Aman in the sequence. The results reveal that the grain yield of boro rice varied from 2.33 to 6.00 t ha-1 of which the highest yield was recorded with the application of 100% NPKS (T4) and the lowest with T1 (control). The effect of boro rice straw removal or incorporation was clearly visible on the following crop, T. Aman rice. The highest grain and straw yields of T. Aman were obtained with T4.4 treatment, where 75% straw was removed and 25% straw incorporated with soil. The lowest yield was obtained with the control crop without fertilizer or straw residues. The NPKS uptake by T. Aman rice and benefit : cost ratio supported the dominant performances of T4.2 (100% NPS + 50% K + 25% boro rice straw removed). The results suggested that it is possible to reduce K mining from soils as well as to reduce the rate of K fertilizer application, substituting by incorporation of rice straw residues in soil system. DOI: http://dx.doi.org/10.3329/sja.v12i2.21924 SAARC J. Agri., 12(2): 123-133 (2014)

Options for increasing the productivity of the rice–wheat system of north west India while reducing groundwater depletion. Part 2. Is conservation agriculture the answer?

The irrigated rice–wheat system of north west India is not sustainable, as currently practised, due to over-exploitation of groundwater, soil degradation, labour scarcity, high fuel and labour costs, and air pollution from stubble burning. Labour and water scarcity are driving farmers to change from puddling and manual transplanting of rice to mechanised dry seeding. The introduction of dry seeding to the rice–wheat system brings with it the potential to adopt conservation agriculture (CA), with reduced or zero tillage for all crops, and surface residue retention. This would further reduce fuel and labour costs for crop establishment, and air pollution, and also bring benefits for soil structure and nutrient cycling. However, whether conversion to CA rice–wheat systems would help solve the problem of groundwater depletion is less well-understood. In this region, evapotranspiration (ET) must be reduced to reduce groundwater depletion. We used the APSIM cropping system model to examine whether conversion from recommended farmer practice (rFP, comprising puddled transplanted rice, alternate wetting and drying rice water management, rice straw removal, tillage for wheat) to a CA rice–wheat system would reduce ET in Punjab, north west India. We also used the model to identify the optimum system management taking into account effects on total cropping system rice equivalent yield (REY), components of the water balance and water productivity. Maximum REY (mean 14.6tha−1) occurred in systems with 5 June sowing of a popular long duration rice variety, with similar yield for rFP and CA. Irrigation input with CA was much lower (by 390mm) than with rFP, resulting in slightly higher irrigation water productivity (increased from 11.3 to 11.7kgha−1mm−1). However, changing to CA only reduced ET of the highest yielding system by 4% (55mm), and of other current practices (late May and early June sowing of medium and long duration varieties) by less than this. The only way to achieve a substantial reduction in ET was by growing short duration rice varieties in both the rFP and CA systems. However, with current short duration varieties, this came at the cost of both rice and system yields (system yield reduced by an average of about 1.8tha−1). This could be overcome by intensification to 3 crops per year in a CA rice–wheat–mung system (with short duration rice varieties), while still providing a substantial but smaller decrease in ET. This system also had considerable flexibility in rice sowing date, with similar system yields for sowings from 5 June to 15 July. These findings suggest that greater effort to increase the yield potential of short duration rice varieties is warranted. Field experimentation is needed to test the improved systems as suggested by the model simulations, particularly in terms of cropping system yield and ET, and alternatives to rice and wheat should also be evaluated. At the same time, spatial hydrological studies are needed to determine the sustainable level of ET from cropping systems that will allow matching of groundwater depletion and recharge.

Effects of hemicellulose pre-extraction and cellulose nanofiber on the properties of rice straw pulp

The aim of this study was to evaluate the influence of mild alkaline pre-extraction on the hemicelluloses removal of rice straw. In addition, the performance of cellulose nanofibers (CNFs) addition on some physico-mechanical properties obtained from extracted and un-extracted (control) samples were investigated. An optimum compromise was found as operating conditions (10% soda, 50°C, and 90min) that provided moderate hemicelluloses removal (48.1%). The residual extracted rice straw particles were subjected to soda–anthraquinone pulping at 160°C for 30–60min with 6 to 18% active alkali charge. Compared with the control samples, the screened yield and Kappa number for extracted pulps decreased slightly. Extracted samples showed better air resistance compared with the un-extracted (control) pulps. However, pre-extraction was found to negatively impact on some mechanical properties such as decrease in burst and tensile indices while addition of CNFs and refining of fibers could improve the strength properties considerably. In general, the addition of CNFs in any concentrations considerably enhanced tensile and burst indices of the sheets in extracted and un-extracted conditions, compared with the unfilled ones. The improvement in mechanical properties was considered one of the key benefits brought by CNFs reinforcement. On the other hand, the stretch properties of the beaten pulps are higher than those of control samples. SEM observations showed that CNFs were deposited on the voids between the rice straw fibers.

Combined Effects of the Continual Application of Composted Rice Straw and Chemical Fertilizer on Rice Yield under a Double Rice Cropping System in the Mekong Delta, Vietnam

We conducted a 12-year field experiment to study the combined effects of rice straw compost and chemical fertilizer application on a double rice cropping system in the Mekong Delta, Vietnam and established 7 treatments using a randomized block design with 3 replications. We calculated the yields of treatments relative to those of conventionally fertilized plots (i.e. with no added rice straw compost), and analyzed their annual trends. In the plots with rice straw compost, we observed a positive trend over 12 continuous wet cropping seasons. In comparison with conventional fertilization, the application of rice straw compost with reduced chemical fertilizer can maintain rice productivity over a longer period. We analyzed the nutrient status of the rice straw at harvest over 4 cropping seasons and observed that the Si concentration of the rice straw in conventionally fertilized plots was significantly lower than that in the plots where rice straw compost was applied. The N, P and Mg concentrations of the rice straw increased with the fertilizer application rate, while the concentrations of K, Ca, Mn, Fe, Zn, and Cu did not differ significantly among treatments. Our results suggest that continuous removal of rice straw may reduce the Si availability in soil, thereby decreasing rice productivity. In addition, we verified that rice straw compost can be an effective source of silicon for paddy rice. Discipline: Soils, fertilizers and plant nutrition Additional key words: nutrient balance, silicon, soil fertility, sustainable land use

Assessing energy efficiencies and greenhouse gas emissions under bioethanol-oriented paddy rice production in northern Japan

To establish energetically and environmentally viable paddy rice-based bioethanol production systems in northern Japan, it is important to implement appropriately selected agronomic practice options during the rice cultivation step. In this context, effects of rice variety (conventional vs. high-yielding) and rice straw management (return to vs. removal from the paddy field) on energy inputs from fuels and consumption of materials, greenhouse gas emissions (fuel and material consumption-derived CO2 emissions as well as paddy soil CH4 and N2O emissions) and ethanol yields were assessed. The estimated ethanol yield from the high-yielding rice variety, “Kita-aoba” was 2.94 kL ha−1, a 32% increase from the conventional rice variety, “Kirara 397”. Under conventional rice production in northern Japan (conventional rice variety and straw returned to the paddy), raising seedlings, mechanical field operations, transportation of harvested unhulled brown rice and consumption of materials (seeds, fertilizers, biocides and agricultural machinery) amounted to 28.5 GJ ha−1 in energy inputs. The total energy input was increased by 14% by using the high-yielding variety and straw removal, owing to increased requirements for fuels in harvesting and transporting harvested rice as well as in collecting, loading and transporting rice straw. In terms of energy efficiency, the variation among rice variety and straw management scenarios regarding rice varieties and rice straw management was small (28.5–32.6 GJ ha−1 or 10.1–14.0 MJ L−1). Meanwhile, CO2-equivalent greenhouse gas emissions varied considerably from scenario to scenario, as straw management had significant impacts on CH4 emissions from paddy soils. When rice straw was incorporated into the soil, total CO2-equivalent greenhouse gas emissions for “Kirara 397” and “Kita-aoba” were 25.5 and 28.2 Mg CO2 ha−1, respectively; however, these emissions were reduced notably for the two varieties when rice straw was removed from the paddy fields in an effort to mitigate CH4 emissions. Thus, rice straw removal avers itself a key practice with respect to lessening the impacts of greenhouse gas emissions in paddy rice-based ethanol production systems in northern Japan. More crucially, the rice straw removed is available for ethanol production and generation of heat energy with a biomass boiler, all elements required for biomass-to-ethanol transformation steps including saccharification, fermentation and distillation. This indicates opportunities for further improvement in energy efficiency and reductions in greenhouse gas emissions under whole rice plant-based bioethanol production systems.

Efficient degradation of rice straw in the reactors packed by carbon fiber textiles

We have reported for the first time that agricultural and cellulosic waste, i.e., rice straw was directly applied to methanogenic bioreactors containing carbon fiber textiles (CFT) as supporting material. Addition of CFT to the methanogenic bioreactors enhanced the conversion of dichromate chemical oxygen demand of the substrate to methane (41%) to a greater extent than bioreactors without CFT (9%). In addition, removal of rice straw as a suspended solid was increased from 31% (in bioreactors without CFT) to 57% (in those with CFT). Methanogenic 16S rRNA gene analysis showed that the abundance of acetoclastic methanogen, genus Methanosarcina, was about 11 times higher in bioreactors with CFT (suspended fraction plus retained fraction to CFT) than in bioreactors without CFT (suspended fraction), resulting in lower concentration of acetate in bioreactors with CFT (0.4 mM) than in those without CFT (29.7 mM). On the other hand, the abundance of hydrogenotrophic methanogen, genus Methanobacterium, in bioreactors with CFT was similar to those without CFT. Bacterial communities in bioreactors with CFT were different from those in bioreactors without CFT. Our results indicated that specific microbial community and cooperative relationships between microorganisms in reactors containing CFT facilitated efficient decomposition of rice straw and its conversion to methane.

05/02384 Possibility of using waste tire composites reinforced with rice straw as construction materials

To establish energetically and environmentally viable paddy rice-based bioethanol production systems in northern Japan, it is important to implement appropriately selected agronomic practice options during the rice cultivation step. In this context, effects of rice variety (conventional vs. high-yielding) and rice straw management (return to vs. removal from the paddy field) on energy inputs from fuels and consumption of materials, greenhouse gas emissions (fuel and material consumption-derived CO2 emissions as well as paddy soil CH4 and N2O emissions) and ethanol yields were assessed. The estimated ethanol yield from the high-yielding rice variety, “Kita-aoba” was 2.94 kL ha−1, a 32% increase from the conventional rice variety, “Kirara 397”. Under conventional rice production in northern Japan (conventional rice variety and straw returned to the paddy), raising seedlings, mechanical field operations, transportation of harvested unhulled brown rice and consumption of materials (seeds, fertilizers, biocides and agricultural machinery) amounted to 28.5 GJ ha−1 in energy inputs. The total energy input was increased by 14% by using the high-yielding variety and straw removal, owing to increased requirements for fuels in harvesting and transporting harvested rice as well as in collecting, loading and transporting rice straw. In terms of energy efficiency, the variation among rice variety and straw management scenarios regarding rice varieties and rice straw management was small (28.5–32.6 GJ ha−1 or 10.1–14.0 MJ L−1). Meanwhile, CO2-equivalent greenhouse gas emissions varied considerably from scenario to scenario, as straw management had significant impacts on CH4 emissions from paddy soils. When rice straw was incorporated into the soil, total CO2-equivalent greenhouse gas emissions for “Kirara 397” and “Kita-aoba” were 25.5 and 28.2 Mg CO2 ha−1, respectively; however, these emissions were reduced notably for the two varieties when rice straw was removed from the paddy fields in an effort to mitigate CH4 emissions. Thus, rice straw removal avers itself a key practice with respect to lessening the impacts of greenhouse gas emissions in paddy rice-based ethanol production systems in northern Japan. More crucially, the rice straw removed is available for ethanol production and generation of heat energy with a biomass boiler, all elements required for biomass-to-ethanol transformation steps including saccharification, fermentation and distillation. This indicates opportunities for further improvement in energy efficiency and reductions in greenhouse gas emissions under whole rice plant-based bioethanol production systems.