Soil organic carbon dynamics shift by incorporating wheat straw in paddy soil in China.

The objective of this study was to explore the effects of unfertilized control (CK), mineral NPK fertilizer (NPK), NPK plus medium-rate wheat straw (MSNPK), and NPK plus high-rate wheat straw (HSNPK) on soil organic carbon (SOC) fractions and C-cycle enzymes at distinct depths (0-5, 5-10, 10-20, 20-30, and 30-50 cm) in paddy soil. The SOC content at 0-50 cm depth ranged from 8.50 to 21.15 g kg-1 , following the trend HSNPK > MSNPK > NPK > CK. Correspondingly, the content of water-soluble organic carbon (WSOC), microbial biomass carbon (MBC), particulate organic carbon (POC), and easily oxidizable carbon (EOC) ranged from 0.08 to 0.27 g kg-1 , 0.11 to 0.53 g kg-1 , 1.48 to 8.29 g kg-1 , and 3.25 to 7.33 g kg-1 , respectively, and HSNPK exhibited the highest values for these parameters among all treatments and soil depths, with significant differences observed compared to NPK and CK (p < 0.05). The cellulase activity of HSNPK was significantly (p < 0.05) higher by 6.12%-13.30% compared to the CK at 0-30 cm depth; while the activity of invertase and ß-glucosidase of HSNPK were significantly (p < 0.05) higher by 34.09%-433.43% and 26.61%-130.50%, respectively, compared to the CK at 0-50 cm depth. Enzyme activities were significantly (p < 0.05) correlated with SOC fractions and the dominant factors driving changes in enzyme activities were WSOC, POC, and EOC. HSNPK was associated with the highest SOC fractions and enzyme activities, indicating that it was the most favorable management practice for promoting soil quality in rice paddy fields.

A non-chemical weed control strategy, introducing duckweed into the paddy field.

BACKGROUND: Herbicide resistance in weeds and environmental pollution resulting from excessive application of chemical herbicides keeps increasing. Development of environment-friendly and effective weed management strategies are required for sustainable agricultural production. In this study we investigated the effects of duckweeds (Landoltia punctata (G. Meyer) Les & D. J. Crawford and Spirodela polyrhiza (Linnaeus) Schle iden) introduction on the weed community and rice growth in paddy fields. RESULTS: The study was conducted in the two rice-growing seasons (2018 and 2019) with three treatments: rice grown without duckweed introduction (CK), with L. punctata introduction (LP), and with S. polyrhiza introduction (SP). On average, LP and SP significantly reduced total weed density by more than 90% and 97%, respectively. Early in the rice-growing season, both duckweed species completely prevented weed growth. Further, both species significantly promoted rice plant growth in the advanced stages. SP significantly improved grain yield of rice by 23%. Light transmittance, temperature of the floodwater and soil, floodwater pH, and dissolved oxygen content significantly decreased following introduction of the duckweeds, indicating that the duckweeds introduction might inhibit weeds growth by altering environmental factors. CONCLUSION: This study provides a possible environment-friendly way to inhibit weed biomass in the paddy field by introducing duckweeds and interpreted the possible reasons of the impacts of duckweed on environmental variables. Weed control is beneficial for rice growth. Duckweed coverage might be limited in open fields and the associated practice requires additional investigation. © 2022 Society of Chemical Industry.

Straw return promoted the simultaneous elimination of sulfamethoxazole and related antibiotic resistance genes in the paddy soil.

Straw return could provide a natural available carbon source for the soil microorganisms, which might affect the environmental behaviours of organic pollutants. In this study, microcosm system was constructed to investigate the effect of rice straw return on the fate of sulfamethoxazole (SMX) and related antibiotic resistance genes (ARGs). The results showed that straw return (1% of soil dry mass) could accelerate the degradation of SMX via co-metabolism. In the treatment group with rice straw, SMX was rapidly decomposed into small molecular compounds (e.g., (Z)-1-amino-3-oxobut-1-en-1-aminium and benzenesulfinic acid) within the first six days, and SMX was undetectable after 60 days; while for the SMX group without rice straw, 1.3 mg kg-1 of SMX still remained at the 60th day. Straw return could enhance the relative abundances of Proteobacteria involved in SMX degradation, including Microvirga and Ramlibacter, which co-metabolized SMX via the degradation pathways of mineralizable components and aromatic compound. Furthermore, straw return significantly eliminated the ARGs. After 60 days, the int1 and sul1 abundances of the treatment group with rice straw were less than one-tenth of the SMX group without rice straw. The redundancy and network analysis of bacterial community and environmental factors showed that dissolved organic carbon and bacteria belonged to Proteobacteria and Actinobacteria might play positive roles in eliminating ARGs. Our results demonstrate that straw return could promote the simultaneous elimination of SMX and corresponding ARGs, which provides a promising approach to effectively treat antibiotics and ARGs in the farmland.

The effect of integrated rice-frog ecosystem on rice morphological traits and methane emission from paddy fields.

Integrated Rice-frog Ecosystem (IRFE) has the potential to reduce methane (CH4) emission and maintain yields from paddy fields. However, the quantitative relationship between rice morphological traits and CH4 emission remains to be explored. In this study, a 2-year field experiment was conducted to evaluate the effect of IRFE on rice morphological traits and CH4 emission from paddy fields and the ecological mechanisms. This study was conducted to analyze twelve aboveground and eight underground rice morphological traits, rice yields, and CH4 flux and emission from the paddy fields with six frog densities (0, 3750, 7500, 15,000, 30,000, and 60,000 frogs ha-1). The results showed that IRFE reduced CH4 emission by 24.70%-41.75% and 21.68%-51.21% in the 2018 and 2019 rice growth seasons, respectively. Moreover, CH4 emission decreased with the increase of frogs. Frogs also increased the diameter, biomass, and volume of rice roots, thus promoting rice growth. Root biomass, thousand-grain weight, and harvest index were also closely related to the yield. Root porosity and oxygen secretion capacity were negatively correlated with CH4 flux. Frogs increased root porosity and oxygen secretion, thereby reducing CH4 emission. The present study demonstrated that reducing CH4 emission and improving rice yields could be simultaneously achieved by altering rice morphological traits in IRFE.

Effects of long-term integrated agri-aquaculture on the soil fungal community structure and function in vegetable fields.

The diversity and community structure of soil fungi play an important role in crop production and ecosystem balance, especially in paddy-upland vegetable field systems. High-throughput sequencing was used to study changes in the soil fungal community structure and function in paddy-upland vegetable field systems. The results showed that compared with traditional planting, the diversity and community structure of soil fungi were changed by the combination of flooding and drought, the Shannon index increased by 11.07%, and the proportion of the dominant species, Mortierella, decreased by 22.74%. Soil available nitrogen, total phosphorus, available phosphorus, total nitrogen and organic matter played a leading role in the initial stage of the experiment, while the dominant factor changed to total potassium 3 years later and then to soil pH and water content 6 years later. FUNGuild analysis showed that the proportion of three independent trophic modes of soil fungi were increased by the combined flooded-drought model, and there were multiple interaction factors, For example, nutrient supply, pH and planting pattern. This study showed that soil fertility, crop yield and economic benefits were better than the traditional model after three years of planting and breeding. The longer the time, the better the effect.

The changes of antioxidant system and intestinal bacteria in earthworms (Metaphire guillelmi) on the enhanced degradation of tetracycline.

Tetracycline (TC) in soil severely imperils food security and ecosystem function. Metaphire guillelmi is a common species in farmland. It could impact the degradation of antibiotics. However, how it affects is rarely unknown. Hence, the present study aimed to investigate the effects of M. guillelmi on the TC degradation in soil and the changes of the antioxidant system and intestinal bacteria in M. guillelmi. The treatments that M. guillelmi was inoculated on soil contaminated with different TC concentrations were contrasted with those without M. guillelmi. After 21 days, the degradation rate of TC significantly increased by 13.70%, 18.14% and 29.01% at 10, 50 and 100 mg kg -1 TC dose, respectively, due to the inoculation of M. guillelmi. The half-life of TC was also shortened nearly by 1/3 to 2/3. Superoxide dismutase (SOD) increased in a dose-dependent manner with the increase of TC concentration on the 7th and 14th day. Catalase (CAT) and glutathione S-transferase (GST) presented an inverted U-shaped dose response on the 7th day, and the peak of enzyme activities occurred at TC concentration of 0.1, 1 mg kg -1 (CAT) and 0.1 mg kg -1 (GST). Malondialdehyde (MDA) contents did not change significantly. At the phylum level, only Verrucomicrobia significantly decreased under 1 mg kg -1 and 100 mg kg -1 TC dose. Genus Paracoccus, Singulisphaera, Acinetobacter and Bacillus significantly increased and became the dominant bacterium during the TC degradation. Overall, the antioxidant system and intestinal bacteria of M. guillelmi were affected by the different concentrations of TC pollution, which provided new ideas for the research of mechanism of TC degradation by earthworms in the future.

Minerals loaded with oxygen nanobubbles mitigate arsenic translocation from paddy soils to rice.

Inhibiting reductive transformation of arsenic (As) in flooded paddy soils is fundamentally important for mitigating As transfer into the food chain. In this study, oxygen-nanobubble-loaded-zeolites (ZON) and -vermiculites (VON) were tested as a novel approach for supplying oxygen to paddy soils to inhibit As influx into rice. The dynamic physio- and bio-chemical variations in the rhizosphere and bulk soil were profiled in a rhizobox experiment. Upon adding ZON and VON, the redox potential and dissolved oxygen consistently increased throughout the cultivation period. The improved redox environment inhibited As(III) release into porewater and increased As(V) adsorbed on crystalline Fe (hydr)oxides, following the reduction of arsC and arrA gene abundances and enhancement of the aioA gene. Moreover, adding ZON and VON promoted root iron plaque formation, which increased As retention on iron plaque. Both ZON and VON treatments mitigated As translocation from soil to rice, meanwhile increasing root and shoot biomass. ZON was superior to VON in repressing As transfer and promoting rice growth due to its higher oxygen loading capacity. This study provides a novel and environment-friendly material to both mitigate the As translocation from paddy soil to rice and improve rice growth.

Rice-duck co-culture integrated different fertilizers reduce P losses and Pb accumulation in subtropical China.

Double pollution with phosphorus (P) losses and potential lead (Pb) accumulation in rice fields could lead to eutrophication and crop toxicity, respectively, and affect people's health. To promote the sustainable and environmentally friendly development of agriculture, we conducted field experiments using a randomized block design to explore P losses, Pb accumulation and any potential association between P and Pb forms in rice-duck (RD) co-culture system and rice monoculture (RM) system combined with different fertilizers applied: the no fertilizer (RD and RM), chemical fertilizer (RDF and RMF), organic fertilizer (RDO and RMO), and a mixture of 70% chemical and 30% organic fertilizers (RDFO and RMFO) treatments with consistent P inputs. The results showed that RDFO had the best advantages in reducing the losses of TP (total phosphorous) (by 6.67%) and DRP (dissolved reactive phosphate) (32.72%) as well as the contents of available Pb (by 7.57%) and the accumulation of Pb in grains (26.32%) compared with RMF. RDFO also achieved the highest grain yield, reaching 10.97 t ha-1, and exhibited a lower soil weak-acid-extracted Pb (readily be taken up by plants) concentration than RDF and RMF. RDO resulted in greater TP leaching (increase by 10.62%) and lower DRP leaching (decrease by 36.57%) than RMF. It also exhibited the lowest concentration of weak-acid-extracted Pb and higher the concentration of grain Pb than that in other treatments. RDF reduced TP (by 5.33%) and DRP (by 16.36%) losses to a greater extent and the concentration of available and grain Pb were respectively 6.58% and 25.57% lower than RMF. Therefore, RDFO was the most recommended agricultural system for the studied region. Furthermore, different soil Pb forms were correlated with different P forms of soil and leakage and runoff water, which depended mainly on the fertilizer type and specific soil redox environment in the rice fields. The ratio of organic to inorganic fertilizer, the choice of organic fertilizer type, the assessment and timing of the detection of potential farmland pollution risks and association between different forms of P and Pb are worthy of further discussion.

Effects of Salinity on Earthworms and the Product During Vermicomposting of Kitchen Wastes.

Population growth and social changes have recently contributed to an exaggerated increase in kitchen wastes in China. Vermicomposting has recently been recognized as an effective and eco-friendly method of organic waste treatment through the combination of earthworms and microbes. However, the influence of salt in kitchen wastes on vermicomposting have been unknown. The goal of this study was to analyze the influence of different salinities on earthworms (Eisenia fetida) and the products during the vermicomposting of kitchen wastes. In our research, kitchen wastes were divided into four different salinities: 0% (A), 0.1% (B), 0.2% (C) and 0.3% (D). The chemical characters of substrates and earthworm growth were measured on the 14th day and the 28th day of composting. Our results show that the high salinity (measured >0.2%) prevented earthworms from properly growing and had negative effects on quality of products in composting. T2 (measured salinity = 0.2%) had the highest average body weight, nitrate nitrogen, and available phosphorus. Thus, the salinity of kitchen wastes should be pretreated to less than 0.2% before vermicomposting.

Microbial Community Structures and Important Associations Between Soil Nutrients and the Responses of Specific Taxa to Rice-Frog Cultivation.

Rice-frog cultivation is a traditional farming system in China and has been reintroduced as an agricultural practice in China in recent years. The microbial community in paddy rhizospheric soils has attracted much attention because many microorganisms participate in functional processes in soils. In this study, Illumina MiSeq sequencing-based techniques were used to investigate soil microbial communities and functional gene patterns across samples obtained by conventional rice cultivation (CR) and rice-frog cultivation (RF). The results showed that RF significantly affected the microbial community composition and richness, which indicated that the rhizospheric microorganisms responded to the introduction of tiger frogs into the paddy fields. Operational taxonomic units (OTUs) from Sandaracinaceae, Anaerolineaceae, Candidatus Nitrososphaera, Candidatus Nitrosotalea, Candidatus Nitrosoarchaeum and some unclassified OTUs from Euryarchaeota and Agaricomycetes were significantly enriched by RF. The abiotic parameters soil organic carbon (SOC), nitrate nitrogen (NO3 --N), and available phosphorus (AP) changed under RF treatment and played essential roles in establishing the soil bacterial, archaeal, and fungal compositions. Correlations between environmental factors and microbial communities were described using network analysis. SOC was strongly correlated with Anaerolineaceae, Methanosaeta, and Scutellinia. NO3 --N showed strong positive correlations with Opitutus, Geobacter, and Methanosaeta. NH4 ++-N was strongly positively associated with Sideroxydans, and TN was strongly positively correlated with Candidatus Nitrotoga. Compared to conventional CR, RF greatly enriched specific microbial taxa. These taxa may be involved in the decomposition of complex organic matter and the transformation of soil nutrients, thus promoting plant growth by improving nutrient cycling. The unique patterns of microbial taxonomic and functional composition in soil profiles suggested functional redundancy in these paddy soils. RF could significantly affect the bacterial, archaeal, and fungal communities though changing SOC and AP levels.

Effects of Integrated Rice-Frog Farming on Paddy Field Greenhouse Gas Emissions.

Integrated rice-frog farming (IRFF), as a mode of ecological farming, is fundamental in realizing sustainable development in agriculture. Yet its production of greenhouse gas (GHG) emissions remains unclear. Here, a randomized plot field experiment was performed to study the GHG emissions for various farming systems during the rice growing season. The farming systems included: conventional farming (CF), green integrated rice-frog farming (GIRF), and organic integrated rice-frog farming (OIRF). Results indicate that the cumulative methane (CH4) emissions from the whole growth period were divergent for the three farming systems, with OIRF having the highest value and CF having the lowest. For nitrous oxide (N2O) emissions, the order is reversed. IRFF significantly increased the dissolved oxygen (DO), soil redox potential (Eh), total organic carbon (TOC) content, and soil C:N ratio, which is closely related to GHG emissions in rice fields. Additionally, the average emissions of carbon dioxide (CO2) from soils during rice growing seasons ranged from 2312.27 to 2589.62 kg ha-1 and showed no significant difference in the three treatments. Rice yield in the GIRF and OIRF were lower (2.0% and 16.7%) than the control. The CH4 emissions contributed to 83.0-96.8% of global warming potential (GWP). Compared to CF, the treatment of GIRF and OIRF increased the GWP by 41.3% and 98.2% during the whole growing period of rice, respectively. IRFF significantly increased greenhouse gas intensity (GHGI, 0.79 kg CO2-eq ha-1 grain yield), by 91.1% over the control. Compared to the OIRF, GIRF decreased the GHGI by approximately 39.4% (0.59 kg CO2-eq ha-1 grain yield), which was 44.2% higher than that of the control. The results of structural equation model showed that the contribution of fertilization to CH4 emissions in paddy fields was much greater than that of frog activity. Moreover, frog activity could decrease GWP by reducing CH4 emissions from rice fields. And while GIRF showed a slight increase in GHG emissions, it could still be considered as a good strategy for providing an environmentally-friendly option in maintaining crop yield in paddy fields.

Nitrogen leakage in a rice-duck co-culture system with different fertilizer treatments in China.

Nitrogen (N) leakage in paddy fields can cause groundwater pollution. In this study, we conducted a split-plot field experiment over 2 years to compare N leakage in a rice-duck co-culture system and a rice monoculture system with different fertilizer treatments. Four treatments were applied to each field, with consistent N inputs in each fertilizer treatment: no fertilizer (RD and RM, respectively), chemical fertilizer (RDF and RMF, respectively), organic fertilizer (RDO and RMO, respectively), and a mixture of 70% chemical and 30% organic fertilizers (RDFO and RMFO, respectively). In both years, rice-duck co-culture system had lower N leakage than the rice monoculture for the same fertilizer treatment, with average reductions of 14.3 ±â€¯0.1%, 13.5 ±â€¯4.5% and 10.5 ±â€¯3.3% for RDFO, RDF and RDO, respectively. Within the rice-duck co-culture system, the average N leakage across both years was 36.3 ±â€¯6.3% lower in RDO and 16.9 ±â€¯11.5% lower in RDFO than in RMF. RDFO gave the highest grain yield compared with RDF and RDO, average reached 10.35 t ha-1 across both years. In conclusion, our results suggested that rice-duck co-culture reduces environmental risks by controlling N leakage and increasing agricultural productivity. Compared with other treatments in this research, RDFO was the most recommended agricultural production mode in this region because it can reduce the inputs of chemical fertilizer, control nitrogen leakage and increase rice yield.

Three-Source Partitioning of Methane Emissions from Paddy Soil: Linkage to Methanogenic Community Structure.

Identification of the carbon (C) sources of methane (CH4) and methanogenic community structures after organic fertilization may provide a better understanding of the mechanism that regulate CH4 emissions from paddy soils. Based on our previous field study, a pot experiment with isotopic 13C labelling was designed in this study. The objective was to investigate the main C sources for CH4 emissions and the key environmental factor with the application of organic fertilizer in paddies. Results indicated that 28.6%, 64.5%, 0.4%, and 6.5% of 13C was respectively distributed in CO2, the plants, soil, and CH4 at the rice tillering stage. In total, organically fertilized paddy soil emitted 3.51 kg·CH4 ha-1 vs. 2.00 kg·CH4 ha-1 for the no fertilizer treatment. Maximum CH4 fluxes from organically fertilized (0.46 mg·m-2·h-1) and non-fertilized (0.16 mg·m-2·h-1) soils occurred on day 30 (tillering stage). The total percentage of CH4 emissions derived from rice photosynthesis C was 49%, organic fertilizer C < 0.34%, and native soil C > 51%. Therefore, the increased CH4 emissions from paddy soil after organic fertilization were mainly derived from native soil and photosynthesis. The 16S rRNA sequencing showed Methanosarcina (64%) was the dominant methanogen in paddy soil. Organic fertilization increased the relative abundance of Methanosarcina, especially in rhizosphere. Additionally, Methanosarcina sp. 795 and Methanosarcina sp. 1H1 co-occurred with Methanobrevibacter sp. AbM23, Methanoculleus sp. 25XMc2, Methanosaeta sp. HA, and Methanobacterium sp. MB1. The increased CH4 fluxes and labile methanogenic community structure in organically fertilized rice soil were primarily due to the increased soil C, nitrogen, potassium, phosphate, and acetate. These results highlight the contributions of native soil- and photosynthesis-derived C in paddy soil CH4 emissions, and provide basis for more complex investigations of the pathways involved in ecosystem CH4 processes.

Comparison of the Abundance and Community Structure of N-Cycling Bacteria in Paddy Rhizosphere Soil under Different Rice Cultivation Patterns.

Eco-agricultural systems aim to reduce the use of chemical fertilizers in order to improve sustainable production and maintain a healthy ecosystem. The aim of this study was to explore the effects of rice-frog farming on the bacterial community and N-cycling microbes in paddy rhizosphere soil. This experiment involved three rice cultivation patterns: Conventionally cultivated rice (CR), green rice-frog farming (GR), and organic rice-frog farming (OR). The rice yield, paddy soil enzyme activities, physicochemical variables and bacterial and N-cycling bacterial abundances were quantitatively analyzed. Rice-frog cultivations significantly increased soil protease, nitrate and reductase activity. Additionally, the nirS gene copy number and the relative abundance of denitrifying bacteria also increased, however urease activity and the relative abundance of nitrifying bacteria significantly decreased. The bacterial community richness and diversity of OR soil was significantly higher than that of the GR or CR soil. Nitrogen use efficiency (NUE) of GR was highest. The N-cycling bacterial community was positively correlated with the total carbon (TC), total nitrogren (TN) and carbon to nitrogen (C:N) ratio. The present work strengthens our current understanding of the soil bacterial community structure and its functions under rice-frog farming. The present work also provides certain theoretical support for the selection of rational rice cultivation patterns.

The influence of phosphorus on the autotrophic and mixotrophic denitrification.

Autotrophic and mixotrophic denitrification, two approaches of biological denitrification, have drawn more and more attention among the techniques to remove nitrogen from the aquatic environment. This study investigated the influence of phosphorus on the denitrification performance and bacterial community structure in the autotrophic and mixotrophic denitrification reactors. The activity test was applied to evaluate the variation of denitrification activity of autotrophic and mixotrophic sludge before and after phosphorus addition. High-throughput sequencing was used to analyze the change of bacterial community structure. The results showed that NO3--N removal efficiency of autotrophic and mixotrophic denitrification process increased by 40 and 35%, respectively, after phosphorus addition. The sludge denitrification activity of autotrophic and mixotrophic sludge was enhanced significantly. And phosphorus addition could greatly improve the proportion of denitrifying bacteria in both autotrophic (from 11.83 to 64.31%) and mixotrophic denitrifying sludge (from 13.59 to 45.12%). Overall, phosphorus addition could greatly improve the autotrophic and mixotrophic denitrification ability in the phosphorus deficient surface water.

Effects of different fertilizers on methane emissions and methanogenic community structures in paddy rhizosphere soil.

Paddy soil accounts for 10% of global atmospheric methane (CH4) emissions. Many types of fertilizers may enhance CH4 emissions, especially organic fertilizer. The aim of this study was to explore the effects of different fertilizers on CH4 and methanogen patterns in paddy soil. This experiment involved four treatments: chemical fertilizer (CT), organic fertilizer (OT), mixed with chemical and organic fertilizer (MT), and no fertilizer (ctrl). The three fertilization treatments were applied with total nitrogen at the same rate of 300 kg N ha-1. Paddy CH4, soil physicochemical variables and methanogen communities were quantitatively analyzed. Rhizosphere soil mcrA and pmoA gene copy numbers were determined by qPCR. Methanogenic 16S rRNA genes were identified by MiSeq sequencing. The results indicated CH4 emissions were significantly higher in OT (145.31 kg ha-1) than MT (84.62 kg ha-1), CT (77.88 kg ha-1) or ctrl (32.19 kg ha-1). Soil organic acids were also increased by organic fertilization. CH4 effluxes were significantly and negatively related to mcrA and pmoA gene copy numbers, and positively related to mcrA/pmoA. Above all, hydrogenotrophic Methanocella and acetoclastic Methanosaeta were the predominant methanogenic communities; these communities were strictly associated with soil potassium, oxalate, acetate, and succinate. Application of organic fertilizer promoted the dominant acetoclastic methanogens, but suppressed the dominant hydrogenotrophic methanogens. The transformation in methanogenic community structure and enhanced availability of C substrates may explain the increased CH4 production in OT compared to other treatments. Compared to OT, MT may partially mitigate CH4 emissions while guaranteeing a high rice yield. On this basis, we recommend the local fertilization pattern should change from 300 N kg ha-1 of organic manure to the same level of mixed fertilization. Moreover, we suggest multiple combinations of mixed fertilization merit more investigation in the future.

Variations in nutrient and trace element composition of rice in an organic rice-frog coculture system.

Introducing frogs into paddy fields can control pests and diseases, and organic farming can improve soil fertility and rice growth. The aim of this 2-year field study was compare the yield and elemental composition of rice between an organic farming system including frogs (ORF) and a conventional rice culture system (CR). The grain yields were almost the same in the ORF system and the CR system. The ORF significantly increased the contents of phosphorus (P), ion (Fe), zinc (Zn), molybdenum (Mo) and selenium (Se) in rice grain at one or both years. However, the ORF system decreased the calcium (Ca) content in grice grains, and increased the concentration of cadmium, which is potentially toxic. A principal components analysis showed the main impacts of ORF agro-ecosystem on the rice grain ionome was to increase the concentration of P and trace metal(loid)s. The results showed that the ORF system is an ecologically, friendly strategy to avoid excessive use of chemical fertilizers, herbicides and pesticides without decreasing yields, and to improve the nutritional status of rice by increasing the micronutrient contents. The potential risks of increasing Cd contents in rice grain should be addressed if this cultivation pattern is used in the long term.

Modeling the impacts of alternative fertilization methods on nitrogen loading in rice production in Shanghai.

Nitrogen (N) loss from paddy fields is an important source of agricultural non-point source pollution that leads to eutrophication of water bodies and degradation of water quality. The impacts of alternative N fertilizer management practices on N loading (N loss through runoff and leaching) from paddy fields in Shanghai were assessed using a process-based biogeochemical model, DNDC. The results indicated that the current fertilization rate in paddy fields of Shanghai (300kgN/ha) exceeds the actual rice demand and has led to substantial N loading of 1142±276kg. The combined application of urea at 150kgN/ha and organic manure at 100kgN/ha was identified as the best fertilization method for rice cultivation in Shanghai; this application maintained optimal rice yields and significantly reduced N loading to 714±151kg in comparison with the current fertilization rate. A sensitivity test was conducted with various input parameters, and the results indicated that fertilization, precipitation and soil properties were the most sensitive factors that regulate N loss from paddy fields. The variability of soil properties, especially SOC led to high uncertainties in the simulated results. Therefore, the local climate conditions and soil properties should be taken into account in the identification of the best management practice (BMP) for rice cultivation, given the high spatially heterogeneous N loading values across all towns used in the simulation. The DNDC model is an effective approach for simulating and predicting N loading in paddy fields under alternative agricultural management practices.

Chemical composition, angiotensin-converting enzyme-inhibitory activity and antioxidant activities of few-flower wild rice (Zizania latifolia Turcz.).

BACKGROUND: The chemical compositions of the stem and leaf sheath of few-flower wild rice were analysed. In addition, their extracts were evaluated for diphenylpicrylhydrazyl (DPPH) free radical-scavenging activity, ferric-reducing antioxidant power and angiotensin-converting enzyme (ACE)-inhibitory activity, since these are important properties of sources of nutraceuticals or functional foods. RESULTS: The stems contained more ascorbic acid (0.06 g kg(-1) fresh weight), protein (28.18 g kg(-1) dry weight (DW)), reducing sugars (308.54 g kg(-1) DW), water-soluble pectin (20.63 g kg(-1) DW), Na(2) CO(3) -soluble pectin (44.14 g kg(-1) DW), K (8 g kg(-1) dry matter (DM), S (6 g kg(-1) DM) and P (5 g kg(-1) DM) but less starch, total dietary fibre, Si, Na and Ca than the leaf sheaths. The DPPH free radical-scavenging IC(50) values of the stem and leaf sheath extracts were 19.28 and 21.22 mg mL(-1) respectively. In addition, the ACE-inhibitory IC(50) value of the stem extracts was 38.54 mg mL(-1). CONCLUSION: Both the stem and leaf sheath extracts exhibited good antioxidant properties, while good ACE-inhibitory activity was detected only in the phosphate buffer solution extracts of the stem. Few-flower wild rice could be processed into formula feeds for fish, poultry, etc. or functional foods for persons with high blood pressure.

Influence of phenanthrene on cadmium toxicity to soil enzymes and microbial growth.

BACKGROUND: Many contaminated sites contain a variety of toxicants. Risk assessment and the development of soil quality criteria therefore require information on the interaction among toxicants. Interactions between heavy metals are relatively well studied, but little is known about those between heavy metals and polycyclic aromatic hydrocarbons (PAHs). METHODS: 0.1 mg/kg dry soil phenanthrene alone or phenanthrene plus 10 mg/kg cadmium (Cd) were added to soil to determine the influence of phenanthrene on Cd toxicity to soil enzymes (invertase, urease, dehydrogenase and phosphatase) and microorganisms (fungi, bacteria and actinomycete) in paddy soil. RESULTS AND DISCUSSION: 0.1 mg/kg phenanthrene did not reduce the number of microorganisms. However, the addition of phenanthrene to soil with Cd enhanced the Cd toxicity to soil enzymes and microorganisms. This deleterious effect was seen to mainly affect the growth of fungi and the activity of invertase, urease and dehydrogenase. The order of combined inhibition of Cd and phenanthrene was fungi>bacteria>actinomycete. CONCLUSION: The presence of phenanthrene might enhance the toxicity of Cd to soil microorganisms. Phenanthrene can easily be used by the soil actinomycetes as a source of carbon and energy and the finding may be supportive to the development of bioremediation techniques.