Fallow Paddy Fields Research Articles

Winter forage crops influence soil properties through establishing different arbuscular mycorrhizal fungi communities in paddy field

Winter planting is promising for improving the utilization rate of fallow paddy fields in southern China by establishing arbuscular mycorrhizal fungi (AMF) communities. However, the effects of different winter forage crops on AMF community construction remain unknown. The AMF community establishment of different winter planting forage crops were conducted in oat, rye, Chinese milk vetch, and ryegrass, with winter fallow as a control. The AMF colonization rate, soil AMF spore density, community structure and diversity, and soil physicochemical properties were determined. The results showed that the total nitrogen and available nitrogen in winter Chinese milk vetch were 11.11% and 16.92% higher than those in winter fallow (P < 0.05). After planting winter forage crops, the AMF spore density in winter oat, rye, Chinese milk vetch, and ryegrass soil were 127.90%, 64.37%, 59.91%, and 73.62% higher than that before planting, respectively (P < 0.05). Claroideoglomus was the dominant AMF genus in the soil of winter planting oat, rye, and ryegrass. The average membership function value of winter Chinese milk vetch was the highest, indicating that it had the best comprehensive effect on soil physicochemical properties, AMF community structure and diversity, and fresh forage yield. Winter forage crops could increase the spore pool of soil AMF and improve the soil AMF community structure and diversity. Winter Chinese milk vetch in paddy field had the best comprehensive effect on soil physicochemical properties and soil AMF community according to the comprehensive evaluation. These findings provide a theoretical basis for sustainable development and utilization of the southern rice paddy ecosystem.

Morchella esculenta cultivation in fallow paddy fields and drylands affects the diversity of soil bacteria and soil chemical properties.

The properties of paddy field (DT) and dry land (HD) soil and food production can be enhanced by the cultivation of Morchella esculenta (ME) during the fallow period. However, whether ME cultivation affects the soil health and microbial diversity of paddy fields and drylands during the cultivation period remains unclear, and this has greatly limited the wider use of this cultivation model. Here, we analyzed the soil chemical properties and bacterial diversity (via metabarcoding sequencing) of DT and HD soils following ME cultivation. Our findings indicated that ME cultivation could enhance soil health. The content of soil phosphorus and potassium (K) was increased in DT soil under ME cultivation, and the K content was significantly higher in HD soil than in DT soil under ME cultivation. ME cultivation had a weak effect on alpha diversity, and ME cultivation affected the abundance of some genera of soil bacteria. The cultivation of ME might reduce the methane production capacity of DT soil and enhance the nitrogen cycling process of HD soil based on the results of functional annotation analysis. Network analysis and correlation analysis showed that Gemmatimonas, Bryobacter, and Anaeromyxobacter were the key bacterial genera regulating soil chemical properties in DT soil under ME cultivation, and Bryobacter, Bacillus, Streptomyces, and Paenarthrobacter were the key taxa associated with the accumulation of K in HD soil. The results of our study will aid future efforts to further improve this cultivation model.

Influences of no‐tillage on the yield and silage fermentation quality of Italian ryegrass

AbstractIt is common in southern China that rice (Oryza sativa L.) fields are sown with a cover crop like Italian ryegrass (Lolium multiflorum L.) following autumn harvest. The objective of the present research was to compare the effects of different no‐tillage methods on the yield, nutritive composition and silage fermentation quality of Italian ryegrass. Italian ryegrass was planted in winter fallow paddy fields on 9 days (NT9) and 5 days (NT5) prior to rice harvest and on 1 day after rice harvest for 2 years. Sowing prior to harvest was no‐tillage, and sowing after rice harvest was either no‐tillage (NT1) or conventional tillage (CK). The grass was harvested and ensiled two times each year. The growing year had no significant effects on the yield and most nutrition components, while it had significant effects on pH value, butyric acid and NH3‐N contents of silage. There were no differences in the yield, nutritional composition and silage fermentation quality among sowing methods. The neutral detergent fiber and acid detergent fiber of NT1 decreased slightly compared with NT9, NT5 and CK (p &gt; .05). There was no difference in silage fermentation quality among the four treatments. The best sowing method for Italian ryegrass with second cut in winter fallow paddy was no‐tillage sowing after rice harvest.

Effect of growth stage on Italian ryegrass (Lolium multiflorum Lam.) silage fermentation from microbiological perspective

BackgroundItalian ryegrass is a temperate climate crop, which is widely cultivated in the winter fallow paddy fields of subtropical China. The utilization efficiency of Italian ryegrass depends greatly on its growth stage at harvest. Previous studies have reported the optimum stage for harvesting various forage to balance their quality and quantity. However, when considering the practice condition, such as rainy or unavailability of harvest equipment, the harvest stage of forage cannot always be implemented according to the production schedules. Thus, to characterize the effect of growth stage on the silage fermentation profile, bacterial community construction and metabolisms of carbohydrates and amino acids, Italian ryegrass were naturally ensiled at the filling stage (FSN) and the dough stage (DSN), respectively. After ensiling for 1, 3, 7, 15, 30, and 60 days, triplicate silos were opened for sampling.ResultsThe growth of Italian ryegrass increased the pH, dry matter, neutral, and acid detergent fiber contents, but decreased buffering capacity, crude protein and water-soluble carbohydrates contents, and the epiphytic microbiota of Italian ryegrass harvested at the filling stage was simpler than that harvested at the dough stage. During ensiling, FSN had lower pH and higher organic acid content than DSN. The bacterial succession rate in FSN was also faster than DSN, which showed that Lactobacillus becomes the dominant genus in the early stage of ensiling. The predicted metabolisms revealed that carbohydrate and amino acid metabolisms were the two main metabolisms in silage fermentation. When compared with epiphytic microbiota, ensiling enhanced carbohydrate metabolism and diminished amino acid metabolism. The difference of these two metabolisms between FSN and DSN was obvious at the early stage of ensiling.ConclusionsGrowth stage affected the chemical and microbial composition of Italian ryegrass, so as to the fermentation profile, bacterial community and its metabolisms intensity. Italian ryegrass harvested at the filling stage was prone to ferment. The complexity of epiphytic microbiota made Italian ryegrass harvested at the dough stage more difficult to ferment.Graphical

Changes in Soil Chemical Properties Due to Long-Term Compost Fertilization Regulate Methane Turnover Related Gene Abundances in Rice Paddy

Maintaining rice yield, soil function, and fertility are essential components of long-term compost fertilization. However, paddy fields are major sources of anthropogenic methane emissions. The aim of the study is to evaluate the changes in soil chemical properties and their concurrent impact on the abundance of methanogenesis (mcrA) and methane oxidation (pmoA) related genes among compost (Com), NPK+Compost (NPKCom), and unfertilized (NF) fallow paddy fields under long-term compost fertilization. Results showed that compost and NPK+Compost fertilization altered the soil chemical properties of paddy fields with a significant increase in the functional gene abundance potentially associated with Methanobacteriaceae for mcrA (1.23 × 106 to 3.84 × 106 copy number g−1 dry soil) and methane oxidizing bacteria such as Methylomonas and Methylobacter for pmoA (1.65 × 106 to 4.3 × 106 copy number g−1 dry soil). Ordination plots visualized these changes, where treatments clustered distinctly indicating that Com and NPKCom treatments were characterized by paddy soils with elevated OM, TN, K and P content and higher abundances of methanogenesis and methane oxidation related genes. The study showed that long-term compost fertilization resulted in paddy fields with high nutrient content and high gene abundance, attributed to methanogens and methane oxidizing bacteria that responded well with compost fertilization. These results indicated the potential of these fallow paddy fields for methane emission and methane oxidation and that they are ‘primed’, potentially influencing subsequent paddy field responses to long-term compost application.

APPLICATION OF LAPAN A3 SATELLITE DATA FOR THE IDENTIFICATION OF PADDY FIELDS USING OBJECT BASED IMAGE ANALYSIS (OBIA)

The role of agriculture is directly related to SDG No.2, which is running a programme until 2030 to reduce national poverty, eradicate hunger by increasing food security and improving nutrition and support sustainable agriculture. Problems faced include the reduction in agricultural land, which results in lower rice production, and the limited information on the monitoring of paddy fields using spatial data. The purpose of this study is to identify paddy fields using LAPAN A3 satellite imagery based on OBIA classification. The data used were from LAPAN A3 multispectral imagery dated 19 June 2017, Landsat 8 imagery dated 17 June 2017, DEM SRTM (BIG), and the Administrative Boundary Map (BIG). The analysis method was segmentation by grouping image pixels, and supervised classification by taking several sample areas based on Random Stratified Sampling. The results will be carried using a confusion matrix. The classification results produced four classes; watery paddy fields, vegetation paddy fields, fallow paddy fields, and non-paddy fields, using of the green, red, and NIR bands for the LAPAN A3 data. From the results of the segmentation process, there remain some oversegmented features in the appearance of the same object. Oversegmentation is due to an inaccurate value assignment to each algorithm parameter when the segmentation process is performed. For example, watery paddy fields appear almost the same as open land (fallow paddy fields), the water object is darker purple. The visual classification results (Landsat 8 data) are considered as the reference for the digital classification results (LAPAN A3). Forty-eight samples were taken and divided into four classes, with each class consisting of 12 samples. The results of the accuracy test show that the total accuracy of the object-based digital classification for visual classification is 62.5% with a Kappa accuracy value of 0.5. The conclusion is that LAPAN A3 data can be used to identify paddy fields based on spectral resolution and to complement Landsat 8 data. To improve the accuracy of the classification results, more samples and the correct RGB composition are needed.

Cover crops can produce livestock forage in Chinese subtropical regions

AbstractIt is common in South China that rice (Oryza sativa L.) fields are seeded with a cover crop following autumn harvest. The objective was to compare the effects of different no‐tillage methods on cover crop yield, nutritive composition, and silage fermentation quality of forage wheat (Triticum aestivum L. cv. Shimai‐1) and Italian ryegrass (Lolium multiflorum L.). Cover crops were planted in winter fallow paddy fields 9 (NT9) and 5 (NT5) d prior to rice harvest and 1 d after rice harvest. Cover crops seeded prior to harvest were no‐tillage planted and cover crops seeded after rice harvest were either no‐tillage (NT1) or seeded using conventional techniques (CT1; plow followed by seeding). The cover crop biomass was determined before rice sowing in spring. Compared to NT9 and NT5, the dry matter (DM) and crude protein (CP) yields of NT1 and CT1 were slightly higher. Compared to Italian ryegrass, forage wheat had high relative feed value and DM yield. The neutral detergent fiber concentration of NT9 and NT5 was higher than NT1 and CT1 (P &lt; .05), whereas the water‐soluble carbohydrates (WSC) concentration was lower than NT1 and CT1 (P &lt; .05). The CP, crude fiber, and WSC concentrations of forage wheat were lower than Italian ryegrass (P &lt; .05). Interaction between years and cover crop type were observed in silage fermentation quality (P &lt; .05). The best sowing method for forage wheat and Italian ryegrass on winter fallow paddy fields was no‐tillage sowing after rice harvest, based upon the present study.

Effects of no-tillage sowing on soil properties and forage wheat and Italian ryegrass yields in winter fallow paddy fields.

In South China, it is common practice for the late rice (Oryza sativa) that is planted during the summer in the paddy fields after harvest to be used for fallowing or to plant winter forage crops. The land is ploughed before early rice planting. Both forage wheat (Triticum aestivum) and Italian ryegrass (Lolium multiflorum) have relatively high nutritional value, and planting them in winter fallow paddy fields could potentially address food shortages and provide quality forage for livestock. In this study, we examined the effects of no-tillage sowing 5 days before rice harvest (NB5), no-tillage sowing 1 day after rice harvest (NA1), and conventional tillage sowing (CK) 1 day after rice harvest on forage wheat and Italian ryegrass soil properties, dry matter (DM), and crude protein (CP) yields. Soil and plant samples were collected after three months of crop growth. The results showed that the NB5 and NA1 soil bulk density (0-20 cm soil layer) tended to increase when compared to that of the CK field. The NA1 treatment increased the total soil nitrogen and organic matter content. The enzyme activities and total soil porosity in the no-tillage forage wheat and Italian ryegrass fields tended to decrease, while the no-tillage water content and soil capillary porosity tended to increase when compared to that of the CK field. Overall, planting year significantly influenced soil chemical properties (except for total nitrogen) and enzyme activity, but crop type had no significant effect on soil physical-chemical properties (except for capillary moisture capacity) and enzyme activity. Sowing methods had no significant effects on the crop DM and CP yields. The DM yield was affected by the interaction between planting year and sowing methods, or between sowing methods and crop type. No-tillage also increased the number of species and aboveground weed biomass. We concluded that the best sowing method for forage wheat and Italian ryegrass in winter fallow paddy fields was no-tillage sowing following rice harvest.

Do Fallow Season Cover Crops Increase N2O or CH4 Emission from Paddy Soils in the Mono-Rice Cropping System?

Cover crop management during the fallow season may play a relevant role in improving crop productivity and soil quality, by increasing nitrogen (N) and soil organic carbon (SOC) accumulation, but has the possibility of increasing greenhouse gas (GHG) emissions from the soil. A year-long consistency experiment was conducted to examine the effects of various winter covering crops on annual nitrous oxide (N2O) together with methane (CH4) emissions in the mono-rice planting system, including direct emissions in the cover crop period and the effects of incorporating these crops on gaseous emissions during the forthcoming rice (Oryza Sativa L.) growing period, to improve the development of winter fallow paddy field with covering crops and to assess rice cultivation patterns. The experiment included three treatments: Chinese milk vetch-rice (Astragalus sinicus L.) with cover crop residue returned (T1), ryegrass (Lolium multiflorum L.)-rice with cover crop residue returned (T2), and rice with winter fallow (CK). Compared with CK, the two winter cover crop treatments significantly increased rice yield, soil organic carbon (SOC) and total nitrogen (TN) by 6.9–14.5%, 0.8–2.1% and 3.4–5.4%, respectively. In all cases, the fluxes of CH4 and N2O could increase with the incorporation of N fertilizer application and cover crop residues. Short-term peaks of these two gas fluxes were monitored after all crop residues were incorporated in the soil preparation period, the early vegetative growth period and the midseason drainage period. The winter cover crop residue application greatly enhanced CH4 and N2O cumulative emissions compared with CK (by 193.6–226.5% and 37.5–43.7%, respectively) during rice growing season and intercropping period. Meanwhile, the mean values of global warming potentials (GWPs) from paddy fields with different cropping crops were T2 &gt; T1 &gt; CK. Considering the advantages of crop productivity together with environmental safety and soil quality, Chinese milk vetch-rice with cover crop residue returned would be the most practicable and sustainable cultivation pattern for the mono-rice cropping systems.

Molecular quantification of spider preying on springtails in winter-spring fallow waterlogged paddy fields

Fallow waterlogged paddy field (FWPF) is a subtropical type of winter-spring fallow rice fields. Arthropod predation is crucial for their survival during the long-duration FWPF seasons. No research has been conducted in the trophic link of arthropod predators and their prey in FWPFs. Here, we used a quantitative real-time PCR approach, both in lab and field, to detect the trophic link. DNA-based identification confirmed the results of a morphological classification in two dominant species of springtail, Homidia socia Denis and H. tiantaiensis Chen and Lin (Collembola: Entomobryidae). The fastest degradation in H. socia DNA copy numbers in spider Pirata subpiraticus (Bosenberg and Strand) (Araneida: Lycosidae) guts occurred within 8 h under lab conditions. Quantitative comparisons of preying on H. socia by H. socia DNA copy numbers indicated that Oedothorax insecticeps (Bosenberg and Strand), Erigonidium graminicolum (Sundevall) (Araneida: Linyphiidae) and P. subpiraticus were more active springtail predators than others under field conditions. There were significant differences in the DNA copy numbers of springtails in gut of P. subpiraticus among different overwintering periods that was significantly positive related to the springtail densities. This study highlights springtail importance at species level as the prey of spiders in FWPFs and illustrates the utility of our approach to quantify their trophic linkages among different spider species or postharvest seasons.

Soil moisture and activity of nitrite- and nitrous oxide-reducing microbes enhanced nitrous oxide emissions in fallow paddy soils

Although cumulative N2O emissions are greater in the winter fallow season than in the rice-growing period, the mechanisms by which the emissions affect fallow paddy fields remain unclear. We aimed to identify N2O flux characteristics and illustrate how key nirS-, nirK- and nosZ-containing denitrifiers affect N2O emission levels in acidic fallow paddy soil. Five water-filled pore space (WFPS) levels were set at 25%, 50%, 75%, 100% and 125%, respectively. During the 48-h-long, high-flux incubation period, the N2O flux was the highest in soil samples with 75% WFPS, followed by those with 100% WFPS. The size of nirS-containing denitrifier community was more sensitive to the shifts in soil moisture and showed a stronger correlation with N2O flux than that of nirK-containing denitrifiers, whereas higher N2O concentrations induced an increase in the levels of nosZ-containing bacteria. After incubation for 48 h, nirK- and nosZ-denitrifying bacterial composition varied remarkably under 50%, 75%, and 100% WFPS treatments. However, the composition of nirS-containing denitrifying bacterial community gradually varied with an increase in soil moisture from 25% to 100% WFPS. Certain dominant OTUs of nirK- nirS- and nosZ-containing denitrifiers were highly abundant, especially under treatments of 50%, 75% and 100% WFPS, which were closely associated with the N2O flux. Thus, nirK, nirS and nosZ-containing denitrifiers respond to soil moisture differently, and enriched species might mainly be involved in controlling N2O flux in fallow paddy soils via denitrification, while the abundance of nirS-containing denitrifiers might affect N2O emission levels more significantly than that of nirK-containing denitrifiers.

Remarkable N2O emissions by draining fallow paddy soil and close link to the ammonium-oxidizing archaea communities

Fallow paddies experience natural flooding and draining water status due to rainfall and evaporation, which could induce considerable nitrous oxide (N2O) emissions and need to be studied specially. In this study, intact soil columns were collected from a fallow paddy field and the flooding-draining process was simulated in a microcosm experiment. The results showed that both N2O concentrations in the soil and N2O emission rates were negligible during flooding period, which were greatly elevated by draining the fallow paddy soil. The remarkable N2O concentrations in the soil and N2O emission/h during draining both had significant relationships with the Arch-amoA gene (P < 0.01) but not the Bac-amoA, narG, nirK, nirS, and nosZ genes, indicating that the ammonium-oxidizing archaea (AOA) might be the important players in soil N2O net production and emissions after draining. Moreover, we observed that N2O concentrations in the upper soil layers (0–10 cm) were not significantly different from that in the 10–20 cm layer under draining condition (P > 0.05). However, the number of AOA and the nitrification substrate (NH4+-N) in the 0–10 cm layer were significantly higher than in the 10–20 cm layer (P < 0.01), indicating N2O production in the 0–10 cm layer might be higher than the measured concentration and would contribute considerably to N2O emissions as shorter distance of gas diffusion to the soil surface.

Flora, life form characteristics, and plan for the promotion of biodiversity in South Korea’s Globally Important Agricultural Heritage System, the traditional Gudeuljang irrigated rice terraces in Cheongsando

The objectives of this study were to analyze the biodiversity of the Traditional Gudeuljang Irrigated Rice Terraces in Cheongsando, South Korea’s representative GIAHS (Globally Important Agricultural Heritage System) site, with reference to position and land-use features, and to develop a plan to promote agricultural biodiversity in the region. We confirmed approximately 54,000 m2 of Gudeuljang paddy fields by an on-site survey. Of the Traditional Gudeuljang Irrigated Rice Terraces confirmed by onsite inspection, our survey showed that approximately 24,000 m2 are currently being used as paddy fields, approximately 15,000 m2 are being used as dry fields, and approximately 14,000 m2 are fallow. In terms of other non-agricultural land use, there was grassland, including graveyards; artificial arboreal land, such as orchards, rivers and wetlands, and man-made facilities, such as roads and residences. We also confirmed that the Traditional Gudeuljang Irrigated Rice Terraces had higher plant species diversity than conventional terraced rice paddies, and there was a difference in life form characteristics between the two types. Although the superficial topsoil structure is the same for the Traditional Gudeuljang Irrigated Rice Terraces (TGIRTs) and conventional terraced rice paddies, it is thought that the differences in the subsurface structure of the TGIRTs contribute greatly to species and habitat diversity. However, the TGIRTs in Cheongsando are facing degeneration, due to damage and reduction in agricultural activity. The main cause is the reduction in the number of farming households due to an aging population in Cheongsando. In order to address this problem, we proposed a management plan, related to fallow paddy fields in South Korea, to initiate voluntary activities in the TGIRTs.

Effect of Dicyandiamide on N2O Emission in Fallow Paddy Field and Rape Cropping

The emissions of greenhouse gas in winter are often neglected, and the latest research results showed that N2O emissions in fallow paddy field and winter oilseed rape are still large, research on mitigating the N2O flux and the mechanism behind them is of significance for mitigating N2O emissions from agricultural soil. By using static chamber techniques and molecular biology techniques, the N2O emission as well as the community composition and abundance of ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) from fallow paddy field, rape cropping with and without DCD treatment in Taoyuan agricultural ecological experiment station of the Chinese Academy of sciences were measured. The results showed that the addition of DCD significantly inhibited N2O emissions in fallow paddy field and rape cropping by 36.7% and 23.6%, respectively. The application of DCD in fallow paddy field inhibited the abundance of AOA and AOB by 59.3% and 73.7%, respectively, but only changed the community structure of AOA. The addition of DCD in rape cropping only changed the community structure and inhibited the abundance of AOB. This research showed that DCD application could effectively mitigate the N2O emissions in fallow paddy field and winter rape cropping under different mitigation mechanisms.

Summary of banding data of migratory wetland birds by using fallow paddy fields in Nanae, Hokkaido, Japan

Summary of banding data of migratory wetland birds by using fallow paddy fields in Nanae, Hokkaido, Japan

Life cycle assessment of bioethanol production from three feedstocks and two fermentation waste reutilization schemes

More than 95% of energy supplies for Taiwan are imported. Conversely, approximately 150,000 ha half-fallow and 50,000 ha fallow paddy fields exist because of increasing labor costs and competition from rice imports. The potential for energy crop production from such underutilized paddy fields merits significant attention. However, selecting crops for optimal environmental performance when producing bioethanol is equally important. The life cycle assessments (LCAs) of rice straw (agricultural waste), Napier grass (energy crop), and Eucalyptus spp. (short rotation coppice) as bioethanol feedstocks in such fallow paddy fields were investigated in this study. The LCAs of two schemes for on-site fermentation waste utilization were also investigated as pellet fuel and molded pulp feedstocks. Experimental and field survey data were used in this study. Due to higher biomass yields, Napier grass and Eucalyptus spp. resulted in 47% and 28%, respectively, less weight-based negative impacts compared to rice. Pursuing high bioethanol production requires consideration of the overall environmental loading. Conversely, the rankings of the three crops based on acreage and bioethanol yield differed due to extensive farming practices and bioethanol conversion yields. On-site production of pellet fuel using fermentation waste was 7% and 31% higher than that of Eucalyptus biomass pellets and imported coal, respectively, for Taiwan. On-site production of molded pulp products using fermentation waste was 5% and 49% higher than that of recycled newspaper and virgin chemical pulp, respectively, for Taiwan. Thus, fermentation waste utilization schemes could provide a broader evaluation for planning alternative crops for bioethanol production.

Improving Rice-Based Cropping Pattern Through Soil Moisture and Integrated Nutrient Management in Mid-Tropical Plain Zone of Tripura, India

An experiment was conducted in three fallow paddy fields situated on the mid-tropical plain zone of a northeastern Indian state (Tripura) to provide rice fallow management options using leftover soil moisture and nutrients. The three experimental fields were managed by growing rice under the system of rice intensification as the rainy season crop and then groundnut, lentil, rapeseed and potato as the post-rainy season crops. Fertilization under the integrated nutrient management system and lifesaving irrigation at critical stages of each post-rainy season crop were provided. Results showed that the field water use efficiency values were 5.93, 2.39, 2.37 and 59.76 kg/(hm2·mm) and that the yield of these crops increased by approximately 20%, 34%, 40% and 20% after applying two lifesaving irrigations in groundnut, lentil, rapeseed and potato, respectively. Therefore, fallow paddy field can provide possible profitable crops during the post-rainy season by utilizing the residual moisture and minimum supplemental irrigation under improved nutrient management practices.

Purification performance of a shallow free-water-surface constructed wetland receiving secondary effluent for about 5 years

The effluent from combined household wastewater treatment facilities used in unsewered areas of Japan is generally high in nitrogen (N) and phosphorus (P). In Japan, environmental quality standards for zinc (Zn) pollution were enacted recently because of the toxicity of Zn to aquatic ecosystems. In 2004 a fallow paddy field at the Koibuchi College of Agriculture and Nutrition in central Japan was converted into a shallow, 500-m2, free-water-surface constructed wetland to polish the secondary effluent from a dormitory. The wetland was planted with Zizania latifolia. The efficiencies of removal of N, P, and Zn by the wetland were evaluated for about 5 years. The average total N and total P concentrations in the wetland influent were 20.0mg/L and 1.95mg/L, respectively; the corresponding concentrations in the effluent were 10.3mg/L and 0.95mg/L, respectively. The average acid-soluble Zn concentration decreased from 0.048 in the influent to 0.023mg/L after passing through the wetland. Inorganic N, PO4-P, and dissolved Zn were the principal forms of N, P, and Zn removed by the constructed wetland system. Very little particulate Zn, and very little particulate plus organic N or P was removed. The mean first-order rate constants (k) for removal of inorganic-N, PO4-P, and acid-soluble Zn were 10.3m/yr, 18.8m/yr, and 16.5m/yr, respectively. The wetland effectively removed not only nutrient salts but also Zn from the secondary effluent throughout the 5-year study period. The k values for inorganic-N and PO4-P were significantly influenced by temperature, although the k value for acid-soluble Zn was not. These results and mass balance data suggest that N was removed mainly by denitrification and secondarily by adsorption to soil and by plant uptake; P was removed mainly by adsorption to soil and secondarily by plant uptake; and Zn was removed mainly by adsorption to soil. There was little sedimentation of particulates in the shallow constructed wetland.

1P2-D07 入力変動系発電効率検証シミュレータの開発(エコ・グリーンメカトロニクス)

In order to use the stable biomass resources that exist in rural areas, we have developed a bio-methane production cycle system by the technology of GET system, which is a bio-methane production system from renewable energy resources in fallow paddy fields, rice straw. We develop a bio-methane production cycle system simulator in order to clarify performance prediction of this system within a natural environment, the problem of when to build. The authors, considering the system of power generation engine and the heat transfer clarify the environmental factors contribute to the methane fermentation and suggest a fusion system model of engineering and agriculture than ever before.

EFFECT OF FLOODING MANAGEMENT ON CARBON CONTENT OF SOIL AND PLANT AFTER CESSATION OF PADDY RICE CULTIVATION

We measured soil carbon (C) and its stable isotopic composition in paddy fields that had received different fallow treatments for 6 years to investigate how management practices influenced the response of soil C. The experiment compared 4 fallo w treatments in neighboring fields: mowing twice a year and no tillage (MN), mowing twice a year and p uddling once a year (MP), and flooding to 5 or 15 cm and puddling (WP5, WP15) to prevent succession to wasteland and thus permit future cultivation. MN had the potential to increase soil C more than MP5 through larger root and shoot buildup. However, the total soil C content to a depth of 30 cm was signif icantly higher in WP5 (13.7 Mg C ha -1 ) than in MN (11.8 Mg C ha -1 ). The dry-fallow management increased plant growth while reducing soil C. The large root dry weight in MN and MP could have increased soil C through high root turnover, whereas land use change from flooding to dry-land masked the abundant C input. After cultivation stops, flooding plays a significant role in preventing root growth and C se questration in fallow paddy fields.