Influences of the Integrated Rice-Crayfish Farming System with Different Stocking Densities on the Paddy Soil Microbiomes

Integrated rice-fish farming has emerged as a novel agricultural production pattern to address global food security challenges. Aiming to determine the optimal, scientifically sound, and sustainable stocking density of red claw crayfish (Cherax quadricarinatus) in an integrated rice-crayfish farming system, we employed Illumina high-throughput 16S rRNA gene sequencing to evaluate the impact of different stocking densities of red claw crayfish on the composition, diversity, function, and co-occurrence network patterns of soil bacterial communities. The high stocking density of red claw crayfish reduced the diversity and evenness of the soil bacterial community during the mid-culture stage. Proteobacteria, Actinobacteria, and Chloroflexi emerged as the most prevalent phyla throughout the experimental period. Low stocking densities initially boosted the relative abundance of Actinobacteria in the paddy soil, while high densities did so during the middle and final stages. There were 90 distinct functional groups identified across all the paddy soil samples, with chemoheterotrophy and aerobic chemoheterotrophy being the most abundant. Low stocking densities initially favored these functional groups, whereas high densities enhanced their relative abundances in the later stages of cultivation. Medium stocking density of red claw crayfish led to a more complex bacterial community during the mid- and final culture stages. The experimental period showed significant correlations with soil bacterial communities, with total nitrogen (TN) and total phosphorus (TP) concentrations emerging as primary factors contributing to the alterations in soil bacterial communities. In summary, our findings demonstrated that integrated rice-crayfish farming significantly impacted the soil microbiomes and environmental factors at varying stocking densities. Our study contributed to theoretical insights into the profound impact of integrated rice-crayfish farming with various stocking densities on bacterial communities in paddy soils.

[Provincial-scale Soil As Migration and Transformation and Rice Safe Planting Zoning: A Case Study of Guizhou Province]

To explore the distribution characteristics of paddy soil and rice AS content, as well as the health risks of rice consumption, and to evaluate the safe planting ability of rice, 209 paddy soil samples and 1 567 groups of paddy soil-rice samples were collected, their As content and basic soil physical and chemical properties were determined, and the single-factor pollution index method was used to evaluate the pollution degree of the samples. The results showed that:① the soil of paddy fields in Guizhou Province was mainly neutral, and its fertilizer retention capacity and organic matter content were above the medium level, and the soil was relatively fertile. The range of ω(As) in paddy soil was 0.042-91.75 mg·kg-1, the geometric mean was 10.03 mg·kg-1, and the cumulative effect of paddy soil As was lower than that of natural soil As (P<0.05) by independent sample T. Compared with the screening value (0.2 mg·kg-1) of the Soil Pollution Risk Management and Control Standard for Agricultural Land (GB 15618-2018), the excess rate of soil samples was 15.37%. ② The ω (As) range of rice grain samples was 0.001-0.937 mg·kg-1, the geometric average value was 0.108 mg·kg-1, 10.21% of the rice grain samples exceeded the limit value of "Limit of Contaminants in Food (trial)" (GB 2762-2022), and the locations where the exceedances are mainly found are in the central and northern parts of Qiannan Prefecture, as well as around industrial and mining activity zones in the southern counties and districts of Zunyi. ③ As ingested through rice posed non-carcinogenic risk and carcinogenic risk for adults and children, and the impact on children was greater than that of adults. There is no strict control area for safe rice planting in Guizhou Province, and rice can be safely planted.

[Research Advances in Barrier Technology of Paddy Soil Co-contaminated with As and Cd]

Arsenic (As) and cadmium (Cd) are the most common toxic and harmful heavy metal elements in paddy soils and are easily transferred from the soil to grains. At present, As and Cd and their co-contamination in paddy soils in China are widespread, posing a serious threat to food security and human health. As and Cd have opposite environmental behaviors in soil, and the simultaneous remediation of co-contamination with As and Cd is a current technical difficulty for safe rice production. This review focuses on several practical techniques for simultaneous mitigation of As and Cd uptake and transport in rice in recent years, including water management, passivation, drenching techniques, electrokinetic remediation, phytoremediation, selection of low-accumulation rice varieties, and foliar spraying application. The treatment effects, mechanisms of action, and constraints of various technologies are summarized and analyzed; the development direction of the main barrier control technologies is proposed and the importance of constructing a comprehensive technology model with high regional adaptability is emphasized to provide a reference for the remediation of co-contamination with As and Cd in paddy and safe rice production.

[Effects of Fertilizer Application Strategy Adjustments on Nitrogen and Phosphorus Loss from Typical Crop Systems in Taihu Lake Region]

The intensity of crop farming fertilizer input is generally high in the Taihu Lake Region, with chemical fertilizer as the main form. Due to inappropriate fertilizer application, nitrogen and phosphorus loss have occurred, causing serious agricultural non-point source pollution. The Ministry of Agriculture and Rural Affairs of China has launched the "zero-growth action for chemical fertilizer use" and "replacement action with organic fertilizer" ("two actions" for short) campaigns since 2015. Local agricultural sectors adjusted fertilizer application strategies of crop farming to respond to the call of two actions. However, the current research is still focusing on reducing the total amount of fertilizer application and increasing the area of organic fertilizer application, which is mainly based on grain crops. The study of agricultural environment problems is still lacking, especially in vegetable, orchard, and tea systems. Therefore, a study was carried out in the typical agricultural area of Suzhou City Wuzhong District from 2019 to 2021. Based on the data of the amount of nitrogen and phosphorus removal by harvest crops and soil nitrogen and phosphorus residual in paddy, vegetable, orchard, and tea systems, the loss was estimated. The responses of nitrogen and phosphorus loss from typical crop systems to fertilizer application strategy adjustments were studied through analysis of different factors. The results showed that fertilizer application rate was the key to control nitrogen and phosphorus loss. Additionally, the suitable replacement ratio of organic fertilizer could further reduce the loss risk. It should be noted that the urgent demand for nutrients in crop growth should be considered to determine the timing of organic fertilizer application, and agricultural machinery should be used to assist organic fertilizer application to reduce labor output if possible. Fertilizer efficiency was the core of environmental friendliness and economic benefits of crop farming. Hence, improving fertilizer efficiency should be the guidance of fertilizer application strategy adjustment. Our suggestions on the adjustment of fertilizer application strategy in different crop systems in the study area are as follows:attention should be paid to the nitrogen, phosphorus, and potassium input ratio in paddy systems to further reduce nitrogen and phosphorus loss. Planting structure adjustment should be emphasized in vegetable systems to promote fertilizer efficiency. The strategy to satisfy both tea and orchard growth from a composite system perspective would help to build crop systems that meet the needs of green agricultural development.

nov., isolated from paddy field soil

Bacterial strains were collected from the soil of a paddy field around Dongguk University in Goyang, Republic of Korea. Two Gram-stain-negative, rod-shaped, aerobic or facultatively anaerobic bacterial strains were designated S5^T and Sa^T. The results of analysis of phylogenetic trees based on 16S rRNA and whole-genome sequences indicated that these two strains represented a member of the genus Runella and a member of the genus Dyella, respectively. S5^T exhibited 99.22, 98.10 and 97.68 % similarity to Runella rosea HYN0085^T, Runella aurantiaca YX9^T and Runella slithyformis DSM 19594^T, respectively. S5^T grew at 15-40 °C (optimum, 25 °C), at pH 6.5-12.0 (optimum, pH 9.5) and in the presence of 0-0.5 % (w/v) NaCl (optimum, 0 %). Sa^T exhibited 99.18 %, 98.36 %, 97.82 % and 97.68 % similarity to Dyella thiooxydans ATSB10^T, Frateruia defendens DHo^T, Fulvimonas yonginensis 5HGs31-2^T and Dyella ginsengisoli Gsoil 3046^T, respectively, and grew at 20-40 °C (optimum, 30 °C), at pH 5.5-11.0 (optimum, pH 8) and in the presence of 0-4.5 % (w/v) NaCl (optimum, 2.5 %). The average nucleotide identity difference values of S5^T, Sa^T and the species reference strains were 92.16-93.62 % and 92.71-93.43%, which confirms that the S5^T and Sa^T represent two novel species of the genera Runella and Dyella, respectively. The draft genome of S5^T consisted of 7 048 502 bp, with a DNA G+C content of 44.9 % and that of Sa^T of 4 398 720 bp with a DNA G+C content of 67.9 %. The phylogenetic, phenotypic and physiological characteristics permitted the distinction of the two strains from their families, and we thus propose the names Runella salmonicolor sp. nov. (type strain S5^T = KACC 22689^T = TBRC 16343^T) and Dyella lutea sp. nov. (type strain Sa^T=KACC 22690^T = TBRC 16344^T).

Residue Distribution and Daily Exposure of Per- and Polyfluoroalkyl Substances in Indica and Japonica Rice

Per- and polyfluoroalkyl substances (PFAS) have excellent chemical stability but have adverse environmental impacts of concern. Furthermore, bioaccumulation of PFAS in rice varieties─which is the essential staple food crop in Asia─has not been verified. Therefore, we cultivated Indica (Kasalath) and Japonica rice (Koshihikari) in the same Andosol (volcanic ash soil) paddy field and analyzed the air, rainwater, irrigated water, soil, and rice plants for 32 PFAS residues, throughout the cultivation to human consumption. During the rice cultivation period, the cultivation environment in atmospheric particulate matter (PM) constituted perfluoroalkyl carboxylic acids (PFCAs), with minimal perfluorinated sulfonic acids (PFSAs). Furthermore, perfluorooctanesulfonic acid (PFOS) migrates at a PM > 10 to drop in a cultivation field and was conducive to leakage and accumulation of PFCAs in air particles in the field environment. Moreover, precipitation was a sources of irrigation water contamination, and cultivated soil with a high carbon content could capture PFSAs and PFCAs (over C₁₀). There were no major differences in residual PFAS trends in the rice varieties, but the distribution of PFAS in the growing soil, air, and rainwater differed. The edible white rice part was mainly affected by irrigation water in both varieties. Monte Carlo simulations of daily exposure assessments of PFOS, PFOA, and perfluorononanic acid showed similar results for Indians consuming Indica rice and Japanese consuming Japonica rice. The results indicate that the ultratrace PFAS residue concentrations and their daily exposure were not cultivar-specific.

Thermal Stress Induces Metabolic Responses in Juvenile Qingtian Paddy Field Carp Cyprinus carpio var qingtianensis

Extreme fluctuations in water temperature lead to significant economic losses for the aquaculture industry. Cyprinus carpio var qingtianensis (locally called Qingtian paddy field carp), is a local variety commonly found in Zhejiang province, China. Unlike traditional aquaculture environments, the water temperature range between day and night in the rice field environment is much larger, and the high temperature in summer may exceed the growth threshold of fish because there is no manual intervention; therefore, the study of how the Qingtian paddy field carp (PF carp) adapts to high-temperature conditions can shed light how the species adapt to the rice field environment. To investigate the molecular mechanisms of this fish under thermal stress, the liver metabolomics of Qiangtian paddy field carp (PF carp) were analyzed. In this study, metabolomics was used to examine the metabolic reaction of PF carp (102 days old, 104.69 ± 3.08 g in weight, 14.65 ± 0.46 cm in length) at water temperatures of 28 °C (control group, CG), 34 °C (experimental group (EG) 34), and 38 °C (EG38). The results show that 175 expression profile metabolites (DEMs), including 115 upregulated and 60 downregulated metabolites, were found in the CG vs. EG34. A total of 354 DEMs were inspected in CG vs. EG38, with 85 metabolites downregulated and 269 metabolites upregulated. According to the pathway enrichment study, various pathways were altered by thermal stress, including those of lipid, amino-acid, and carbohydrate metabolism. Our study presents a potential metabolic profile for PF carp under thermal stress. It also demonstrates how the host responds to thermal stress on a metabolic and molecular level.

Effects of Long-Term Fertilizer Practices on Rhizosphere Soil Autotrophic CO2-Fixing Bacteria under Double Rice Ecosystem in Southern China

Soil autotrophic bacterial communities play a significant role in the soil carbon (C) cycle in paddy fields, but little is known about how rhizosphere soil microorganisms respond to different long-term (35 years) fertilization practices under double rice cropping ecosystems in southern China. Here, we investigated the variation characteristics of rhizosphere soil RubisCO gene cbbL in the double rice ecosystems of in southern China where such fertilization practices are used. For this experiment we set up the following fertilizer regime: without any fertilizer input as a control (CK), inorganic fertilizer (MF), straw returning (RF), and organic and inorganic fertilizer (OM). We found that abundances of cbbL, 16S rRNA genes and RubisCO activity in rhizosphere soil with OM, RF and MF treatments were significantly higher than that of CK treatment. The abundances of cbbL and 16S rRNA genes in rhizosphere soil with OM treatment were 5.46 and 3.64 times higher than that of CK treatment, respectively. Rhizosphere soil RubisCO activity with OM and RF treatments increased by 50.56 and 45.22%, compared to CK treatment. Shannon and Chao1 indices for rhizosphere soil cbbL libraries with RF and OM treatments increased by 44.28, 28.56, 29.60, and 23.13% compared to CK treatment. Rhizosphere soil cbbL sequences with MF, RF and OM treatments mainly belonged to Variovorax paradoxus, uncultured proteobacterium, Ralstonia pickettii, Thermononospora curvata, and Azoarcus sp.KH33C. Meanwhile, cbbL-carrying bacterial composition was obviously influenced by soil bulk density, rhizosphere soil dissolved organic C, soil organic C, and microbial biomass C contents. Fertilizer practices were the principal factor influencing rhizosphere soil cbbL-carrying bacterial communities. These results showed that rhizosphere soil autotrophic bacterial communities were significantly changed under conditions of different long-term fertilization practices Therefore, increasing rhizosphere soil autotrophic bacteria community with crop residue and organic manure practices was found to be beneficial for management of double rice ecosystems in southern China.

Optimization and validation of blade parameters for inter-row weeding wheel in paddy fields

The performance of existing rice-paddy weeding machines is not optimal. In this study, the influence of the installation angle of the weeding-wheel blade on cutting resistance and soil-slippage ability was analyzed. The optimal blade angle of the weeding wheel (i.e., the angle at which the resistance to the weeding wheel is minimal and the disturbance speed of the soil maximal) was shown to be< 20°; numerical simulation showed the actual optimal value to be 0°. Different weeding depths (30, 40, and 50 mm), rotation speed of weeding wheel (120, 180, and 240 r/min), and weeder forward speeds (0.3, 0.6, and 0.9 m/s) were used as test factors, and the rates of seedling injury and weeding were used as performance-evaluation criteria to optimize the machine in a secondary orthogonal-rotation combination test. Field experiments showed that the weeding wheel can exhibit optimal working performance under the operating conditions of weeding depth of 39 mm, rotation speed of 175 r/min, and forward speed of 0.6 m/s. The seedling injury and weeding rates were 4.4% and 88.2%, respectively, which were consistent with the numerically predicted results and met the agronomic requirements. This study provides a technical reference for the improvement of paddy-field weeding components.

[Effects of Chemical Fertilizer Reduction Combined with Straw Application on Diazotrophic Communities in a Double Rice Cropping System]

Based on a three-year field experiment, the effects of reduced chemical fertilizer combined with straw application on paddy yield, soil fertility properties, and community structure of diazotrophs in a double-rice cropping field three years after straw application were examined. Three treatments were applied:conventional fertilizer application (CF), chemical fertilizer reduction combined with a low straw application rate (CFLS, 3 t·hm^-2), and a high straw application rate (CFHS, 6 t·hm^-2). The results showed that CFLS and CFHS did not significantly reduce rice grain yield (P>0.05); significantly neutralized soil acidification; increased soil microbial biomass carbon and nitrogen, dissolved organic carbon, and organic carbon content (P<0.05); and significantly reduced soil redox potential, ammonium nitrogen, and nitrate nitrogen contents (P<0.05). This was more conducive to improve soil nitrogen use efficiency. Compared with those under the CF treatment, the natural nitrogen fixation functional communities of CFLS and CFHS increased the Shannon, PD, and Evenness indexes (P<0.05) due to the improvement of conditions such as the increase in soil carbon storage and the decrease in acidification degree. The relative abundance of microbial communities with nitrogen fixation, carbon fixation, and plant growth promotion functions such as Ferrigenium, Sulfurivermis, Methylomonas, Methylovulum, Ectothiorhodospira, and Nostoc increased significantly (P<0.05). In conclusion, the reduction in chemical fertilizer combined with 3 t·hm^-2 and 6 t·hm^-2 straw application was an effective measure to improve the community structure of soil diazotrophs and the potential of soil nitrogen fixation.

[Effect of gradual increase of atmospheric CO2 concentration on nitrate-dependent anaerobic methane oxidation in paddy soils]

Nitrate-dependent anaerobic oxidation of methane (AOM) is a new pathway to reduce methane emissions from paddy ecosystems. The elevated atmospheric CO₂ concentration can affect methane emissions from paddy ecosystems, but its impact on the process of nitrate-dependent AOM is poorly known. Based on the automatic CO₂ control platform with open top chambers and the ¹³CH₄ stable isotope experiments, the responses of the activity of nitrate-dependent AOM, abundance and community composition of Candidatus Methanoperedens nitroreducens (M. nitroreducens)-like archaea to the gradual increase of CO₂ concentration were investigated in paddy fields. We set up two CO₂ concentration treatments, including an ambient CO₂ and a gradual increase of CO₂(increase of 40 μL·L^-1 per year above ambient CO₂ concentration until 160 μL·L^-1). The results showed the nitrate-dependent AOM rate of 0.7-11.3 nmol CO₂·g^-1·d^-1 in the studied paddy fields, and quantitative PCR showed the abundance of M. nitroreducens-like archaeal mcrA genes of 2.2×10⁶-8.5×10⁶ copies·g^-1. Compared to the ambient CO₂ treatment, the slow elevated CO₂ treatment enhanced the nitrate-dependent AOM rate and stimulated the abundance of M. nitroreducens-like archaea, particularly in 5-10 cm soil layer. The gradual increased CO₂ concentration treatment did not change the community composition of M. nitroreducens-like archaea, but significantly decreased their diversity. The soil organic carbon content was an important factor influencing the nitrate-dependent AOM process. Overall, our results showed that the gradual increase of CO₂ concentration could promote the nitrate-dependent AOM, suggesting its positive role in mitigating methane emissions from paddy ecosystems under future climate change.

Impacts of Rotation-Fallow Practices on Bacterial Community Structure in Paddy Fields

Soil nutrients and microbial community play a central role in determining crop productivity in agroecosystems. However, the relationship between microbial community structure and soil nutrients in various crop rotation-fallow systems remains unclear. Thus, we designed a 3-year crop rotation-fallow field with five cropping systems (one continuous cropping, three rotational cropping, and one fallow system). We conducted a comprehensive analysis by evaluating crop yield, soil physicochemical properties, and overall bacteria composition. Our results showed that rotation-fallow treatments markedly influenced the crop yield and soil physicochemical properties. Proteobacteria, Acidobacteriota, and Chloroflexi were the dominant phyla in all rotation-fallow treatments. pH, available-phosphorus, total nitrogen, and soil organic matter had considerable effects on the soil bacterial community structure in 2019; however, only available-phosphorus had an impact on soil bacterial community in each treatment in 2020. In summary, with the increase of tillage years, different rotational fallow systems can increase paddy yield by promoting soil nutrient uptake and increasing the relative abundances of bacteria in paddy fields. IMPORTANCE Soil nutrients and microbial community play a central role in determining crop productivity. Therefore, elucidating the microbial mechanisms associated with different cropping systems is indispensable for understanding the sustainability of agroecosystem. In the present study, we designed a 3-year field rotation experiment using five cropping systems, including one continuous cropping, three rotational cropping, and one fallow system, to indagate the outcomes of soil microbial community structures in the different tillage systems. Our results showed that the different rotational fallow systems had positive impacts on crop yield, soil physicochemical properties, and bacterial community structure and that available phosphorus might be a key determinant for the limited bacterial community structure in various rotation-fallow systems following a 3-year field experiment. This study suggests that crop rotation-fallow systems play critical roles in improving bacterial community structure.

[Comparison of Bacterial Community Structure in Soil Aggregates Between Natural Karst Wetland and Paddy Field]

Studying the impact of land-use changes in wetland systems on the community structure of bacteria in soil aggregates can provide a theoretical basis for elucidating the impact mechanisms of the stability of wetland soil aggregates. The soil samples (0-20 cm) were collected from a natural wetland and paddy field in the Huixian karst wetland. The bacterial community structure in soil aggregates (macroaggregates 0.25-2 mm, microaggregates 0.053-0.25 mm, and silt-clay<0.053 mm) were analyzed using high-throughput sequencing and ecological network analysis. The results showed that ① the proportion of microaggregates in the paddy field was 29.64%, which was significantly higher than that in the natural wetland (22.20%), and ② there were differences in the relative abundance of bacteria between the natural wetland and paddy field. The relative abundance of Chloroflexi in macroaggregates, microaggregates, and silt-clay in the paddy field were 7.97%, 8.56%, and 7.40%, respectively, which were significantly higher than those in the natural wetland (4.93%, 4.81%, and 3.76%). The relative abundance of Anaerolineales in macroaggregates, microaggregates, and silt-clay in the paddy field were 2.35%, 3.03%, and 2.65%, respectively, which were significantly higher than those in the natural wetland (0.92%, 0.91%, and 0.43%).③ Ecological network analysis showed that the number of nodes, edges, and the average numbers of neighbors in microaggregates and the silt-clay network in the paddy field were higher than those in the natural wetland, the average connectivity of the network was greater in the two components, and the characteristic path length was shorter. There was a longer characteristic path length, higher modularity, and lower average connectivity in the macroaggregate network of the paddy field. The above results indicated that the bacterial community structure in soil aggregates was altered after a natural wetland was used as a paddy field. The material circulation and information transmission efficiency of bacterial communities was higher in both microaggregates and silt-clay of the paddy field, whereas the bacterial community structure with low network tightness and high modularity in macroaggregates was more stable.

Change of Rice Paddy and Its Impact on Human Well-Being from the Perspective of Land Surface Temperature in the Northeastern Sanjiang Plain of China

Large-scale and high-speed paddy land expansion has appeared in Northeast China since the 21st century, causing the change in land surface temperature. The lack of continuous investigation limits the exploration of discoveries in this region. To address this limitation, a collaborative approach that combined human-computer interaction technology, gravity center model and spatial analysis was established. It provided some new findings in spatiotemporal evolution, migration trajectory and surface cooling effect of the paddy field in Northeastern Sanjiang Plain, a center of paddy field planting in China. The results show that: (1) A sustained paddy expansion was monitored, with a total area ranging from 2564.58 km² to 11430.94 km², along with a rate of growth of 345.72% from 2000 to 2020. Correspondingly, its reclamation rate changed to 47.53% from 10.66%, showing the improved planting level of the paddy field. (2) Gravity center of paddy field continued to be revealed northward with a 5-year interval from 2000 to 2020. Migration distance of the straight line reached 23.94 km², with the direction offset of 27.20° from east to north. (3) Throughout the growing season of crops, the land surface temperature of paddy field was 27.73°, 29.38°, 27.01°, 25.62° and 22.97° from May to October; and the cooling temperature effect of paddy field was investigated, with the reduced values of 0.61°, 0.79° and 1.10° in the low-, medium- and high-paddy field density regions from 2000 to 2020, respectively. Overall, these new findings in the cold temperate zone, high latitude region of the Northern Hemisphere, provided the reference for the investigation of paddy field monitoring and its environmental effects in China and other regions.

[Comparison of Bacterial Community Structure and Functional Groups of Paddy Soil Aggregates Between Karst and Non-karst Areas]

Studying the similarities and differences in microbial community structure and functional groups in soil aggregates between karst areas (KA) and non-karst areas (NKA) can provide a theoretical basis for revealing the interaction mechanism between soil organic microorganisms and soil aggregate structure stability in KA. The surface soils (0-20 mm) were collected from paddy fields both in KA and NKA. The aggregates were divided into macro-aggregates (Mac, 0.25-2 mm), micro-aggregates (Mic, 0.053-0.25 mm), and silt-clay fractions (SC,<0.053 mm) using the wet sieving method. The microbial community structure of soil aggregates was analyzed using high-throughput sequencing. The keystone taxa were analyzed by the co-occurrence network, and their functions were predicted by FAPROTAX. The results showed that:① the proportion of Mac, mean weight diameter, and geometric mean diameter of aggregates in KA were 30.94%, 0.41 mm, and 0.15 mm, respectively. These three factors in KA were significantly higher than those in NKA, indicating that the environment in the KA was conducive to the formation of aggregates. ② The relative abundances of Acidobacteria, Proteobacteria, Acidobacteria(Gp3, Gp4, and Gp6), and Sphingomonas in three particle size aggregates in KA were higher than those in NKA. The relative abundance of Chloroflexi (6.13%) in Mic in KA was significantly higher than that in SC (2.79%). ③ Co-occurrence network analysis showed that Proteobacteria and Acidobacteria were keystone taxa in three particle size aggregates. The positive correlation edge (65.5%) of bacteria in KA was the highest, and most of the correlation was synergistic. ④ Chemoheterotrophy (15.52%, 15.30%, and 16.89%) and aerobic chemoheterotrophy (14.62%, 14.38%, and 15.97%) were the most dominant functional groups in the three particle size aggregates in KA, and their relative abundance was significantly higher than those in NKA. The relative abundance of chitinolysis in Mac in KA (0.46%) was significantly higher than that in SC (0.39%). The results showed that the soil environment in KA can improve the stability of the aggregates, and the bacterial community structure, key groups, and functional groups in the three particle size aggregates in KA were significantly different from those in NKA.

Effects of Water and Fertilizer Management Practices on Methane Emissions from Paddy Soils: Synthesis and Perspective

Water and fertilizer management practices are considered to have great influence on soil methane (CH₄) emissions from paddy fields. However, few studies have conducted a quantitative analysis of the effects of these management practices. Here, we selected 156 observations of water management from 34 articles and 288 observations of fertilizer management from 37 articles and conducted a global meta-analysis of the effects of water and fertilizer management practices on soil CH₄ emissions in paddy fields. In general, compared with traditional irrigation (long-term flooding irrigation), water-saving irrigation significantly decreased soil CH₄ emissions but increased rice yield. Among the different practices, intermittent irrigation had the fewest reductions in CH₄ emissions but the greatest increase in rice yield. In addition, fertilization management practices such as manure, mixed fertilizer (mixture), and straw significantly enhanced CH₄ emissions. Rice yields were increased under fertilization with a mixture, traditional fertilizer, and controlled release fertilizer. Our results highlight that suitable agricultural water and fertilizer management practices are needed to effectively reduce CH₄ emissions while maintaining rice yields. We also put forward some prospects for mitigating soil CH₄ emissions from paddy fields in the context of global warming in the future.

Partial Substation of Organic Fertilizer With Chemical Fertilizer Improves Soil Biochemical Attributes, Rice Yields, and Restores Bacterial Community Diversity in a Paddy Field

Conventional farming systems are highly reliant on chemical fertilizers (CFs), which adversely affect soil quality, crop production and the environment. One of the major current challenges of current agriculture is finding ways to increase soil health and crop yield sustainably. Manure application as a substitute for CF is an alternative fertilization strategy for maintaining soil health and biodiversity. However, little is known about the complex response of soil bacterial communities and soil nutrients to manure and CFs application. This study reports the response of soil nutrients, rice yield, and soil microbial community structure to 2 years of continuous manure and CFs application. The study consisted of six treatments: no N fertilizer control (Neg-Con); 100% CF (Pos-Con); 60% cattle manure (CM) + 40% CF (High-CM); 30% CM + 70% CF (Low-CM); 60% poultry manure (PM) + 40% CF (High-PM), and 30% PM + 70% CF (Low-PM). We used high-throughput sequencing of 16S ribosomal RNA gene amplicons to characterize the soil bacterial communities. Results revealed that the addition of manure significantly altered the soil bacterial community composition and structure; and enhanced the relative abundance of phyla Proteobacteria, Chloroflexi, Firmicutes, Acidobacteria, and Planctomycetes. Organic fertilizer treatments, particularly high CM and PM had the highest measured soil bacterial diversity of all treatments. Similarly, integrated application of manure and CFs increased the soil biochemical traits [i.e., pH, total N (TN), soil organic C (SOC), microbial biomass N (MBN), and microbial biomass C (MBC)] and rice grain yield. Average increases in SOC, TN, MBN, and MBC were 43.66, 31.57, 24.34, and 49.45%, respectively, over the years in the High-PM compared with Pos-Con. Redundancy analysis showed that the dominant bacteria phyla were correlated with soil pH, SOC, TN, and microbial biomass, but the relative abundance of Proteobacteria was strongly correlated with environmental factors such as soil pH, SOC, TN, and MBC. We employed a structural equation model to examine the relationship between microbial biomass, soil nutrients and grain yield among treatments. This analysis supported the hypothesis that soil nutrient content and availability directly affect rice grain yield while soil bacteria indirectly affect grain yield through microbial biomass production and nutrient levels. Overall, the findings of this research suggest that the integrated application of CF and manure is a better approach for improving soil health and rice yield.

[Changing Characteristics of Carbon-Based Greenhouse Gas Fluxes in Paddy Field in the Middle-Lower Yangtze Plain in China]

In recent years, carbon emission research has been receiving increasing attention. China has put forward the strategic goal of achieving a carbon emission peak by 2030. Hence this research is very important for the measurement of greenhouse gas emissions in China. CO₂ and CH₄ fluxes from a paddy field in the middle-lower Yangtze Plain in China were analyzed based on the eddy covariance technique. The CO₂ flux showed an "U" curve during the observation period, with an average flux of -3.33 μmol·(m²·s)^-1, which was a sink. Negative values appeared at the tillering stage, and the minimum was shown at the heading period. The CH₄ flux trend was roughly opposite to the that of the CO₂ flux, which first increased and then decreased. It raised rapidly during the tillering and jointing stages and then dropped rapidly from the peak to the trough during the booting stage, and only a slight increase was found in the blooming stage. The maximum flux[0.40 μmol·(m²·s)^-1] appeared at the beginning of the booting stage and the end of the jointing stage, and the average flux was 0.11 μmol·(m²·s)^-1. The CO₂ flux was positive at night and negative during the day. It decreased from 07:00 and reached a minimum around 13:00 at -16.01 μmol·(m²·s)^-1. The CH₄ flux was low at night and high during the daytime. It increased at 06:00 and reached a peak around 14:00, at approximately 0.16 μmol·(m²·s)^-1. An exponential correlation was found between air temperature and CH₄ flux. The vapor pressure deficit showed a linear correlation with CH₄ flux. The response of environmental factors on CO₂ fluxes and CH₄ fluxes on a diurnal scale was greater than that on a seasonal scale, and the daytime response was greater than that at night. CH₄ flux decreased significantly with the increase in CO₂ flux on the diurnal scale, but the correlation was not obvious on the seasonal scale. The increased CH₄ flux slowed down after fertilizing.

[Changing Characteristics of Carbon-Based Greenhouse Gas Fluxes in Paddy Field in the Middle-Lower Yangtze Plain in China]

In recent years, carbon emission research has been receiving increasing attention. China has put forward the strategic goal of achieving a carbon emission peak by 2030. Hence this research is very important for the measurement of greenhouse gas emissions in China. CO₂ and CH₄ fluxes from a paddy field in the middle-lower Yangtze Plain in China were analyzed based on the eddy covariance technique. The CO₂ flux showed an "U" curve during the observation period, with an average flux of -3.33 μmol·(m²·s)^-1, which was a sink. Negative values appeared at the tillering stage, and the minimum was shown at the heading period. The CH₄ flux trend was roughly opposite to the that of the CO₂ flux, which first increased and then decreased. It raised rapidly during the tillering and jointing stages and then dropped rapidly from the peak to the trough during the booting stage, and only a slight increase was found in the blooming stage. The maximum flux[0.40 μmol·(m²·s)^-1] appeared at the beginning of the booting stage and the end of the jointing stage, and the average flux was 0.11 μmol·(m²·s)^-1. The CO₂ flux was positive at night and negative during the day. It decreased from 07:00 and reached a minimum around 13:00 at -16.01 μmol·(m²·s)^-1. The CH₄ flux was low at night and high during the daytime. It increased at 06:00 and reached a peak around 14:00, at approximately 0.16 μmol·(m²·s)^-1. An exponential correlation was found between air temperature and CH₄ flux. The vapor pressure deficit showed a linear correlation with CH₄ flux. The response of environmental factors on CO₂ fluxes and CH₄ fluxes on a diurnal scale was greater than that on a seasonal scale, and the daytime response was greater than that at night. CH₄ flux decreased significantly with the increase in CO₂ flux on the diurnal scale, but the correlation was not obvious on the seasonal scale. The increased CH₄ flux slowed down after fertilizing.

Population dynamics and diversity of trematode infections in Bithynia siamensis goniomphalos in an irrigated area in northeast Thailand

Several trematodes including Opisthorchis viverrini utilize Bithynia siamensis goniomphalos as a snail intermediate host in their life cycles. In order to capture a comprehensive range of host–parasite interactions and their transmission dynamic patterns, B. s. goniomphalos were sampled monthly over 4 consecutive years in an irrigated paddy-field habitat in northeast Thailand. Using a standard cercarial shedding method, a high diversity of trematodes (17 types) was recovered. Virgulate xiphidiocercariae were the most prevalent (7.84%) followed by O. viverrini (0.71%). In addition to seasonal and environmental factors, the quantity of irrigation water for rice cultivation correlated with transmission dynamics of trematodes in B. s. goniomphalos. The peak prevalence of all trematode infections combined in the snails shifted from the cool-dry season in 2010–2012 to the hot-dry season in 2013 associated with an increasing quantity of water irrigation. A low frequency of mixed trematode infections was found, indicating that the emergence of virgulate cercariae, but not of O. viverrini, was negatively impacted by the presence of other trematodes in the same snail. Taken together, the observed results suggest that interactions between host and parasite, and hence transmission dynamics, depend on specific characteristics of the parasite and environmental factors including irrigated water for rice cultivation.

Control of the Invasive Agricultural Pest Pomacea canaliculata with a Novel Molluscicide: Efficacy and Safety to Nontarget Species

The golden apple snail Pomacea canaliculata is an invasive pest that causes extensive damage to agricultural production. P. canaliculata is also an intermediate host of Angiostrongylus cantonensis, which causes human eosinophilic meningitis. In this study, the molluscicidal activity and safety profile of a novel molluscicide PBQ [1-(4-chlorophenyl)-3-(pyridin-3-yl)urea] were evaluated. PBQ exhibited strong molluscicidal potency against adult and juvenile snails (LC₅₀ values of 0.39 and 0.07 mg/L, respectively). In field trials, PBQ killed 99.42% of the snails at 0.25 g a.i./m². An acute toxicity test in rats demonstrated that PBQ is a generally nonhazardous chemical. PBQ is also generally safe for nontarget organisms including Brachydanio rerio, Daphnia magna, and Apis mellifera L. Transcriptomics analysis revealed that PBQ had a significant impact on the carbohydrate and lipid metabolism pathways, which provided insights into its molluscicidal mechanism. These results suggest that PBQ could be developed as an effective and safe molluscicide for P. canaliculata control.

Google Earth Engine-Based Identification of Flood Extent and Flood-Affected Paddy Rice Fields Using Sentinel-2 MSI and Sentinel-1 SAR Data in Bihar State, India

Flood is the major cause of fatalities associated with natural disasters in the world. In India especially in the state of Bihar, where about half of the area (North Bihar) gets flooded every year due to the overflow of major rivers during the rainy season. Which severely affects human lives, properties, agricultural production, farmers and their livelihood. Usually, the basins of the Kosi and Gandak rivers are known for their worst affects in Bihar. Synthetic aperture radar (SAR) is widely used for robust monitoring of flood events due to its ability to image the surface of the earth in all weather conditions. However, limited studies are available on flood patterns of Bihar and their impact on agriculture. Here, we investigated the flood extents and affected paddy rice fields for Bihar during the months of June–October (2020) using all accessible Sentinel-1 SAR and Sentinel-2 MSI images with additional supporting datasets available on the Google Earth Engine. The study showed that a large portion of Bihar (7019 km2) was submerged during monsoon season. The floodwater remains in the agricultural fields for 50 to 65 days causing severe damage to the Kharif crops, mainly rice. The extreme effect of flood was seen in agricultural lands (11.23% of the total area) and populations (15.56% of the total population) in Bihar. Satellite-based identification of flood progression and affected rice fields can be helpful for decision-makers at the time of disaster to prioritize relief and rescue operations.

Mitigation of Paddy Field Soil Methane Emissions by Betaproteobacterium Azoarcus Inoculation of Rice Seeds

Paddy fields are a major source of atmospheric methane, a greenhouse gas produced by methanogens and consumed by methanotrophs in flooded soil. The inoculation of rice seeds with the bacterium Azoarcus sp. KH32C alters the rice root-associated soil bacterial community composition. The present study investigated the effects of KH32C-inoculated rice cultivation on soil methanogens and methanotrophs involved in methane emissions from a rice paddy field. KH32C-inoculated and non-inoculated rice (cv. Nipponbare) were cultivated in a Japanese rice paddy with and without nitrogen fertilizer. Measurements of methane emissions and soil solution chemical properties revealed increases in methane flux over the waterlogged period with elevations in the concentrations of dissolved methane, dissolved organic carbon, and ferrous iron, which is an indicator of soil reduction levels. Reverse transcription quantitative PCR and amplicon sequencing were used to assess the transcription of the methyl-coenzyme M reductase gene (mcrA) from methanogens and the particulate methane monooxygenase gene (pmoA) from methanotrophs in paddy soil. The results obtained showed not only the transcript copy numbers, but also the compositions of mcrA and pmoA transcripts were related to methane flux. KH32C-inoculated rice cultivation recruited soil methanogens and methanotrophs that suppressed high methane synthesis, increased methane consumption, and decreased methane emissions by 23.5 and 17.2% under non-fertilized and nitrogen-fertilized conditions, respectively, while maintaining rice grain yield. The present study demonstrated the mitigation of paddy field methane emissions arising from the use of KH32C in rice cultivation due to its influence on the compositions of soil methanogen and methanotroph populations.

Devosia rhizoryzae sp. nov., and Devosia oryziradicis sp. nov., novel plant growth promoting members of the genus Devosia, isolated from the rhizosphere of rice plants

Two novel Gram-negative, aerobic, asporogenous, motile, rod-shaped, orange and white pigmented, designated as LEGU1^T and G19^T, were isolated from the roots of rice plants, collected from Goyang, South Korea. Phylogenetic analysis based on their 16S rRNA gene sequences revealed that they belonged to the genus Devosia and formed a different lineage and clusters with different members of the genus Devosia. These strains shared common chemotaxonomic features. In particular, they had Q-10 as the sole quinone, phosphatidylglycerol, diphosphatidylglycerol as the principal polar lipids and C_16:0, C_18:1ω7c 11-methyl and summed feature 8 (comprising C_18:1ω7c/C_18:1ω6c) as the main fatty acids. The draft genome sequences of strains LEGU1^T and G19^T were 3,524,978 and 3,495,520 bp in size, respectively. Their average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values were 72.8-81.9% and 18.7-25.1%, respectively, with each other and type strains of related species belonging to the genus Devosia, suggesting that these two strains represent novel species. The G + C content of strains LEGU1^T and G19^T were 62.1 and 63.8%, respectively. Of the two strains, only LEGU1^T produced carotenoid and flexirubin-type pigment. Both strains produced siderophore and indole acetic acid (IAA) in the presence of L-tryptophan. Siderophore biosynthesis genes, auxin responsive genes and tryptophan biosynthesis genes were present in their genomes. The present study aimed to determine the detailed taxonomic positions of the strains using the modern polyphasic approach. Based on the results of polyphasic analysis, these strains are suggested to be two novel bacterial species within the genus Devosia. The proposed names are D. rhizoryzae sp. nov., and Devosia oryziradicis sp. nov., respectively. The plant growth promoting effects of these strains suggest that they can be exploited to improve rice crop productivity. The type strain of D. rhizoryzae is LEGU1^T (KCTC 82712^T = NBRC 114485^T) and D. oryziradicis is G19^T (KCTC 82688^T = NBRC 114842^T).

[Effects of Different Fertilization Patterns on Nitrogen Leaching Loss from Paddy Fields Under Reduced Nitrogen]

Nitrogen leaching loss in paddy fields is one of the main ways of farmland non-point source pollution. To explore the suitable fertilization of rice fields in the Erhai Lake Basin and reduce the nitrogen loss from paddy fields, a field experiment was conducted by setting single applications of chemical or organic fertilizer, combined organic and inorganic application, and single application of controlled release fertilizer under reduced nitrogen conditions. The results showed that, compared with the conventional fertilization treatment(CF), there was no significant difference in rice grain and straw yield between the single chemical fertilizer treatment(T1) and the organic-inorganic combined treatment(T3); the single organic fertilizer treatment(T2) decreased the rice grain yield by 13.0%, and decreased straw yield by 17.1%; single application of controlled-release fertilizer(T4) increased rice grain and straw yield by 15.7% and 21.0%, respectively. Further, compared with CF, the single application of chemical fertilizer(T1), organic fertilizer(T2), and organic-inorganic combined application(T3) reduced the total nitrogen leaching loss at 30 cm depths by 26.9%, 18.0%, and 33.9%, respectively. The loss of ammonia nitrogen leaching with T1, T2, and T3 decreased by 24.4%, 36.9%, and 36.6%, respectively, and the loss of nitrate nitrogen leaching decreased by 40.2%, 4.8% and 46.4%. The total nitrogen leaching at 60 cm soil depths was reduced by 34.2%, 26.3%, and 42.1%, the loss of ammonia nitrogen leaching was reduced by 31.4%, 35.7%, and 46.6%, and the loss of nitrate nitrogen leaching was reduced by 8.0%, 10.1%, and 23.9% for T1, T2, and T3, respectively. The total nitrogen loss at 30 and 60 cm depths increased by 41.6% and 14.0% in the single application of controlled release fertilizer(T4) treatment. Considering factors such as agronomic and environmental benefits of different fertilization modes, T1 and T3 are suitable environmentally friendly alternative fertilization modes.

The Road to Practical Application of Cadmium Phytoremediation Using Rice

Cadmium (Cd) is a toxic heavy metal that causes severe health issues in humans. Cd accumulates in the human body when foods produced in Cd-contaminated fields are eaten. Therefore, soil remediation of contaminated fields is necessary to provide safe foods. Rice is one of the primary candidates for phytoremediation. There is a genotypic variation of Cd concentration in the shoots and grains of rice. Using the world rice core collection, ‘Jarjan’, ‘Anjana Dhan’, and ‘Cho-ko-koku’ were observed with a significantly higher level of Cd accumulation in the shoots and grains. Moreover, OsHMA3, a heavy metal transporter, was identified as a responsive gene of quantitative trait locus (QTL) for high Cd concentration in the shoots of these three varieties likewise. However, it is difficult to apply practical phytoremediation to these varieties because of their unfavorable agricultural traits, such as shatter and easily lodged. New rice varieties and lines were bred for Cd phytoremediation using OsHMA3 as a DNA marker selection. All of them accumulated Cd in the shoots equal to or higher than ‘Cho-ko-koku’ with improved cultivation traits. Therefore, they can be used for practical Cd phytoremediation.

Controlled Irrigation and Drainage Reduce Rainfall Runoff and Nitrogen Loss in Paddy Fields

In southern China, the growing period of rice is synchronized with the rainy period, and the loss of nutrients (such as nitrogen) due to unreasonable irrigation and drainage, along with rainfall and runoff, has become the main source of agricultural nonpoint source pollution. The laws of runoff and nitrogen loss in paddy fields under different irrigation and drainage modes are not clear. In this study, field experiments were adopted to observe the runoff and nitrogen loss under typical rainfall and throughout the whole growth period. The results showed that, compared with the traditional irrigation and drainage mode, the controlled irrigation and drainage mode reduced the drainage of two typical rainfall processes by 47.5% and 31.3% and the peak drainage by 38.9% and 14.4%. Compared with those under the traditional irrigation and drainage mode, the average concentrations of total nitrogen, nitrate nitrogen, and ammonium nitrogen under the controlled irrigation and drainage mode were reduced by 22.2%, 22.7%, and 27.8%, respectively, during the whole rainfall process on July 21 and were decreased by 27.1%, 11.4%, and 25.6%, respectively, on August 25. In irrigated rice areas, under the controlled irrigation and drainage mode, drainage was reduced after two intercepts through paddy fields and drainage ditches. The nitrogen concentration in the drainage ditch decreased due to the increase in retention time and the effect of the ditch and field wetland. Compared with the traditional irrigation and drainage mode, the total nitrogen, nitrate nitrogen, and ammonium nitrogen loads of the controlled irrigation and drainage mode were reduced by 69.8%, 65.3%, and 69.7%, respectively.

Impacts of Agricultural Capitalization on Regional Paddy Field Change: A Production-Factor Substitution Perspective

Paddy fields are significant in ensuring food security and improving the agricultural ecological environment. In economic terms, paddy field use is affected by input costs and crop market price. There is insufficient understanding of factor input costs caused by agricultural production-factor substitution, driving paddy field change. This study uses a panel regression model to analyze the influence of agricultural production-factor substitution on paddy field use from 1990 to 2016. The case area is Hubei province, China. The results show that the overall growth trend in paddy fields is unequivocal in China's grain production areas. The improvement in agricultural production conditions, including irrigation and land quality, has a positive effect on the area proportion of paddy fields. With socioeconomic developments, the relationship between the substitution of nitrogen fertilizer for farmland and the area proportion of paddy field is inverted-U shaped, while the effect of the substitution of machinery for labor is U-shaped. The main conclusion is that the process of agricultural production-factor substitution, intended to maximize labor and land productivity, will increase the area proportion of paddy field. Public policies should focus on improving the level of agricultural mechanization and crop diversity to protect food security and sustainable agricultural intensification.

Effect of different short-term tillage management on nitrogen-fixing bacteria community in a double-cropping paddy field of southern China

Soil nitrogen (N)-fixing bacteria community plays an important role in the N cycling process in soil, but there is still limited information about how the soil microbes that drive this process to respond to combined application of tillage and crop residue management under the double-cropping rice (Oryza sativa L.) paddy field in southern of China. Therefore, the effects of 6-years short-term tillage treatment on soil N-fixing bacteria community under the double-cropping rice paddy field in southern China were studied by using the polymerase chain reaction-denaturing gradient gel electrophoresis method. The field experiment included four tillage treatments: conventional tillage with crop residue incorporation (CT), rotary tillage with crop residue incorporation (RT), no-tillage with crop residue retention (NT), rotary tillage with crop residue removed as control (RTO). The results showed that the diversity index and richness index of cbbLR and nifH genes with CT, RT, and NT treatments were increased, compared with RTO treatment. Compared with RTO treatment, the abundance of cbbLR gene with CT, RT, and NT treatments were increased by 6.54, 4.73, and 2.78 times, respectively. Meanwhile, the abundance of nifH gene with CT, RT, and NT treatments were 5.32, 3.71, and 2.45 times higher than that of RTO treatment. The results also indicated that soil autotrophic Azotobacter and nitrogenase activity with CT and RT treatments were significantly higher (p < .05) than that of RTO treatment. There was an obvious difference in characteristic of soil N-fixing bacteria community between the application of crop residue and without crop residue input treatments. In summary, the results indicated that the abundance of N-fixing bacteria community in the double-cropping rice paddy field increased with conventional tillage and rotary tillage practice.

Effects of Short-Term Soil Tillage Management on Activity and Community Structure of Denitrifiers under Double- Cropping Rice Field

Soil physical and chemical characteristics, soil potential denitrification rates (PDR), community composition and nirK-, nirS- and nosZ-encoding denitrifiers were studied by using MiSeq sequencing, quantitative polymerase chain reaction (qPCR), and terminal restriction fragment polymorphism (T-RFLP) technologies base on short-term (5-year) tillage field experiment. The experiment included four tillage treatments: conventional tillage with crop residue incorporation (CT), rotary tillage with crop residue incorporation (RT), no-tillage with crop residue retention (NT), and rotary tillage with crop residue removed as control (RTO). The results indicated that soil organic carbon, total nitrogen and NH₄⁺-N contents were increased with CT, RT and NT treatments. Compared with RTO treatment, the copies number of nirK, nirS and nosZ in paddy soil with CT, RT and NT treatments were significantly increased. The principal coordinate analysis indicated that tillage management and crop residue returning management were the most and the second important factors for the change of denitrifying bacteria community, respectively. Meanwhile, this study indicated that activity and community composition of denitrifiers with CT, RT and NT treatments were increased, compared with RTO treatment. This result showed that nirK, nirS and nosZ-type denitrifiers communities in crop residue applied soil had higher species diversity compared with crop residue removed soil, and denitrifying bacteria community composition were dominated by Gammaproteobacteria, Deltaproteobacteria, and Betaproteobacteria. Therefore, it is a beneficial practice to increase soil PDR level, abundance and community composition of nitrogen-functional soil microorganism by combined application of tillage with crop residue management.

[Effects of Different Rotation Patterns of Oil-Rice on Methane and Nitrous Oxide Emissions in Rice Fields]

A field experiment was carried out to investigate the effects of different rice-rape rotation systems on methane and nitrous oxide emissions, which were measured using the static chamber/gas chromatography method, prediction of their global warming potentials (GWP), and greenhouse gas intensity (GHGI) in paddy fields. The results showed that the average cumulative emissions of CH₄from a double cropping paddy field, single season rice field (including middle or late), rape field, and leisure land were 135.25, 55.64, 5.05, and 1.89 kg ·hm^-2, respectively. The CH₄ emission during the rice season accounted for 91.8%-98.5% of the annual CH₄ emission in different rotation years, and the contents of dissolved organic carbon in paddy soil exhibited a significantly positive correlation with CH₄ emission. The CH₄ emission in conventional late rice paddy was 18.7% higher than that of hybrid late rice paddy (P<0.05). The average cumulative emissions of N₂O from double cropping paddy field, single season rice field (including middle or late), rape field, and leisure land were 0.94, 0.64, 1.38, and 0.24 kg ·hm^-2, respectively. Out of the total annual N₂O emission, 57.2% to 70.2% was from the rape field; 17.8% and 30.6% was due to the winter fallow treatments with previous crop type of double corpping rice and single season rice, respectively. There was no significant difference in N₂O emission between hybrid rice and conventional rice paddy fields. The GWP of double cropping rice-winter fallow and double cropping rice-rape was higher than that of rice-rape and rice-winter fallow, and the GWP of CH₄ in rice season accounted for 71.2% to 90.9% of the annual GWP of rotation. The highest treatment of GHGI was rice-rice-rape, and the treatment of rice-oil and rice-winter slack was lower. According to the comprehensive environmental and economic benefits, the late hybrid rice-rape patterns should be selected to reduce greenhouse gases in multiple cropping rice fields of South China.

Vision-Based Moving Obstacle Detection and Tracking in Paddy Field Using Improved Yolov3 and Deep SORT

Using intelligent agricultural machines in paddy fields has received great attention. An obstacle avoidance system is required with the development of agricultural machines. In order to make the machines more intelligent, detecting and tracking obstacles, especially the moving obstacles in paddy fields, is the basis of obstacle avoidance. To achieve this goal, a red, green and blue (RGB) camera and a computer were used to build a machine vision system, mounted on a transplanter. A method that combined the improved You Only Look Once version 3 (Yolov3) and deep Simple Online and Realtime Tracking (deep SORT) was used to detect and track typical moving obstacles, and figure out the center point positions of the obstacles in paddy fields. The improved Yolov3 has 23 residual blocks and upsamples only once, and has new loss calculation functions. Results showed that the improved Yolov3 obtained mean intersection over union (mIoU) score of 0.779 and was 27.3% faster in processing speed than standard Yolov3 on a self-created test dataset of moving obstacles (human and water buffalo) in paddy fields. An acceptable performance for detecting and tracking could be obtained in a real paddy field test with an average processing speed of 5–7 frames per second (FPS), which satisfies actual work demands. In future research, the proposed system could support the intelligent agriculture machines more flexible in autonomous navigation.

Presence and Health Risks of Obsolete and Emerging Pesticides in Paddy Rice and Soil from Thailand and China

Organochlorine (OCPs) and organophosphorus pesticides (OPPs) have been intensively applied in rice paddy field farming to control pest infestation and increase the yield. In this study, we investigated the presence of organochlorine and organophosphorus pesticides in paddy rice and soil from rice plantations in Thailand and China. According to concentration and distribution of OCPs, the most abundant OCPs residues in rice and soil from Thailand and China were dichlorodiphenyltrichloroethane and hexachlorocyclohexanes. The OPPs of methidathion, carbophenothion, chlorpyrifos, and diazinon were common to Thailand and China in both types of samples. The detection frequency of multiple types of these pesticides was greater than 50% of total samples. The relative concentration of some OPPs residues in rice and soil from Thailand and China were significantly different from each other (p < 0.0083), whereas, no significant difference was observed for the relative concentration of OCPs residues in rice and soil from both countries, except for HCHs (p < 0.05). Bioaccumulation factors of OCPs between rice and soil samples indicated that OCPs and OPPs in soil could accumulate in rice. The carcinogenic and non- carcinogenic risks of OCPs and OPPs seem to be in the safe range as recommended by the European Union.

Control Effects of Chelonus munakatae Against Chilo suppressalis and Impact on Greenhouse Gas Emissions From Paddy Fields

Field and pot experiments were conducted to investigate the control effects of parasitoid wasps (Chelonus munakatae Munakata) on striped rice stem borers and their impacts on N2O and CH4 emissions from paddy fields. Three treatments including no insect (NI), striped stem borer (CS) and parasitoid wasp + striped stem borer (CS+CM) were implemented. The abundance of GHG-related microorganisms in soils was determined by absolute real-time qPCR. Compared with NI, CS and CS+CM significantly increased the ratio of dead tillers, inhibited the growth and vitality of rice roots, and decreased the rice grain yield, while they significantly reduced the seasonal cumulative emissions of N2O and CH4 by 17.7-24.6 and 13.6-35.1%, and decreased the total seasonal global warming potential (GWP) by 13.6-34.7%, respectively. Moreover, compared with CS, CS+CM significantly enhanced the growth and vitality of rice roots, decreased the ratio of dead tillers, improved the rice grain yield, as well as increased the seasonal cumulative CH4 emissions and the total seasonal GWP. Principal component analysis indicated that the morphological features of rice roots play a more important role in regulating GHG emissions than GHG-related microorganisms. The results suggested that C. munakatae can effectively control the outbreak of C. suppressalis and alleviate crop damage with acceptably higher GHG emissions. It is concluded that it can be recommended as an effective, environment-friendly and sustainable approach to prevent and control C. suppressalis.

Effects of Pest Management Practices on Soil Nematode Abundance, Diversity, Metabolic Footprint and Community Composition Under Paddy Rice Fields

The wide-scale adoption of transgenic crops has aroused public concern towards potential impacts to the ecological services of soil fauna, such as soil nematodes. However, few studies has examined whether the cultivation of transgenic rice would pose greater threats to soil nematode community and associated ecological functions than insecticides application. Moreover, what are determinants of soil nematode community in paddy fields remains unclear. During a 3-year field study, rhizosphere soil samples of transgenic-Bt rice, its counterpart non-Bt parental rice and not-Bt rice with insecticides application were taken at four times in the rice developmental cycle using a random block design with three replications for each treatment. We hypothesized that the effects of pest management practice on soil nematode abundance and metabolic footprint change with trophic group and sampling time. We also predicted there were significant differences in structure and composition of soil nematode community across the three treatments examined and sampling times. In agreement with our expectation, the effects of pest management practice on nematode abundance and metabolic footprints depend on trophic group and sampling time. However, pest management practice exerted no apparent effect on nematode diversity and community composition. Soil nutrient availability and C:N molar ratio are the primary regulating factor of soil nematode community in rice paddy fields. In conclusion, our findings implied that changes in abundance, diversity, metabolic footprints associated with the crop growth stage overweighed the application of Bt rice and insecticides. The cultivation of Bt rice Huahui-1 exerted no measurable adverse effect on soil nematode community in rhizosphere soil over 3 years of rice cropping.

[Atmospheric Nitrogen Dioxide, Nitric Acid, Nitrate Nitrogen Concentrations, and Wet and Dry Deposition Rates in a Double Rice Region in Subtropical China]

Nitrogen dioxide (NO₂) and nitric acid (HNO₃) are nitrogen-containing acidic gases in the atmosphere, and they are important precursors of nitrate in aerosol and rainwater. The emission intensity of atmospheric nitrogen oxides is high in the subtropical region of China, but the concentrations and deposition rates of atmospheric nitrogen dioxide, nitric acid, particulate nitrate-nitrogen (NO₃^--N_p), and rainwater nitrate-nitrogen (NO₃^--N_r) in a double rice region in subtropical China are still unclear,. In this study, the atmosphere concentrations of NO₂-N, HNO₃-N, NO₃^--N_p in PM₁₀, and NO₃^--N_r and related meteorological parameters were simultaneously monitored in a typical double rice region within a subtropical hilly region of China, with the aim of determining the characteristics and influencing factors of NO₂-N, HNO₃-N, NO₃^--N_p, and NO₃^--N_r concentrations and quantifying the wet and dry deposition rates. The results showed that the annual mean concentrations of NO₂-N, HNO₃-N, NO₃^--N_p, and NO₃^--N_r were 4.2 μg·m^-3, 0.7 μg·m^-3, 4.0 μg·m^-3, and 1.0 mg·L^-1, respectively, and the deposition rates were 1.5, 3.2, 2.3, and 6.1 kg·hm^-2, respectively. The NO₂-N concentrations were negatively correlated with air temperatures, and the HNO₃-N concentrations were negatively correlated with wind speeds. TheNO₃^--N_p concentrations were negatively correlated with air temperatures, positively correlated with NO₂-N concentrations, but not significantly correlated with HNO₃-N concentrations, thus indicating that NO₂-N concentrations were an important limiting factor forNO₃^--N_p pollution in this study area. The NO₃^--N_r concentrations were negatively correlated with rainfall, as well as the concentrations of HNO₃-N and NO₃^--N_p. The annual total dry and wet depositions of the atmospheric NO₂-N, HNO₃-N, NO₃^--N_p, and NO₃^--N_r were 13.0 kg·hm^-2, which indicates that these compounds are important sources of nitrogen in paddy fields and may have significant impacts on paddy fields and surrounding ecosystems.

[Effects of the Veterinary Antibiotic Sulfamethazine on N2O Emissions and the Associated Microbiological Mechanism in a Rice Field]

Veterinary antibiotics can enter into croplands with animal excrement and can have effects on nitrification and denitrification processes in the agricultural soils. A field experiment was conducted to evaluate the effect of sulfamethazine (SMZ) on N₂O emissions, nitrification, denitrification, and related functional gene abundances within a paddy field. Five treatments were used in the experiment, namely, no fertilizer and no antibiotics applied (CK), and pig manure used as basal fertilizer plus urea applied as topdressing with the addition of 0, 5, 15, and 30 mg·kg^-1 SMZ (SMZ0, SMZ5, SMZ15, and SMZ30, respectively). Soil and gas samples were collected and analyzed periodically throughout the rice growing season. The results showed that the SMZ did not change the seasonal pattern of N₂O emissions. During the entire observation period, there was a significant difference in N₂O fluxes between the SMZ15 and SMZ0 treatment (P<0.05), but there was no significant differences in N₂O fluxes between the SMZ30, SMZ5, and SMZ0 treatment (P>0.05). Medium and high concentrations (SMZ15, SMZ30) increased the cumulative emissions of N₂O at the average level, and these values were 3.47 and 4.67 times higher than that of the SMZ0 treatment, respectively; the soil NO₃^--N content also increased. Medium and high concentrations had a significant activation effect on the gene abundances of total soil bacteria 16S rRNA, ammonia-oxidizing archaea (AOA) amoA, and ammonia-oxidizing bacteria (AOB) amoA during the nitrification process and the gene abundances of nirK, nirS, and nosZ during the denitrification process (P<0.05), while the SMZ treatment with a low concentration had a slight inhibitory effect on the abundance of each gene. The ratios of abundance copies of 16S rRNA, AOA amoA, AOB amoA, and the genes of nirK, nirS, and nosZ treated by SMZ30, SMZ15, and SMZ0 were 1.58, 1.77, 2.15, 1.38, 1.33, 1.42, and 1.24, 1.37, 1.08, 1.65, 1.11, 1.64, respectively, at the average level. The abundance ratios of the six above genes treated by SMZ5 and SMZ0 were less than one and only 0.80, 0.99, 0.92, 0.76, 0.76, and 0.77, respectively. The N₂O fluxes were significantly and positively correlated with the abundances of the nirK gene (P<0.01), thus indicating that SMZ had an effect on N₂O emissions by influencing the activity of denitrifying bacteria. Therefore, the pollution of farmland by veterinary antibiotics should not be ignored, and the use of antibiotics should be controlled reasonably at the source, so as to reduce the environmental and ecological risks.

[Research and application progresses on rice water quality (RICEWQ)model.]

Rice production presents a unique environmental condition, with the diseases, insects and weeds being serious during production process. Many kinds of pesticides are used with high frequency. Some pesticides will leach into surrounding water, which shows a high risk for pollution. With the increasing costs of pesticide monitoring and field experiments, mathematical models have become an indispensable part during the process of pesticide registration. As the most reliable and widely used model for pesticide exposure assessment in European paddy fields, rice water quality (RICEWQ) model was mainly used to predict pesticide concentrations in flooded paddy fields and water, and had been preliminarily applied in China. In this review, system structure, the main processes of pesticide fate involved, input and output of RICEWQ model were briefly introduced, and the research progress at home and abroad were summarized. This review would promote the application of RICEWQ model in China and provide reference for related research.

Methylotetracoccus oryzae Strain C50C1 Is a Novel Type Ib Gammaproteobacterial Methanotroph Adapted to Freshwater Environments

Most of the methane produced on our planet gets naturally oxidized by a group of methanotrophic microorganisms before it reaches the atmosphere. These microorganisms are able to oxidize methane, both aerobically and anaerobically, and use it as their sole energy source. Although methanotrophs have been studied for more than a century, there are still many unknown and uncultivated groups prevalent in various ecosystems. This study focused on the diversity and adaptation of aerobic methane-oxidizing bacteria in different environments by comparing their phenotypic and genotypic properties. We used lab-scale microcosms to create a countergradient of oxygen and methane for preenrichment, followed by classical isolation techniques to obtain methane-oxidizing bacteria from a freshwater environment. This resulted in the discovery and isolation of a novel methanotroph with interesting physiological and genomic properties that could possibly make this bacterium able to cope with fluctuating environmental conditions.

Methane-oxidizing microorganisms perform an important role in reducing emissions of the greenhouse gas methane to the atmosphere. To date, known bacterial methanotrophs belong to the Proteobacteria, Verrucomicrobia, and NC10 phyla. Within the Proteobacteria phylum, they can be divided into type Ia, type Ib, and type II methanotrophs. Type Ia and type II are well represented by isolates. Contrastingly, the vast majority of type Ib methanotrophs have not been able to be cultivated so far. Here, we compared the distributions of type Ib lineages in different environments. Whereas the cultivated type Ib methanotrophs (Methylococcus and Methylocaldum) are found in landfill and upland soils, lineages that are not represented by isolates are mostly dominant in freshwater environments, such as paddy fields and lake sediments. Thus, we observed a clear niche differentiation within type Ib methanotrophs. Our subsequent isolation attempts resulted in obtaining a pure culture of a novel type Ib methanotroph, tentatively named “Methylotetracoccus oryzae” C50C1. Strain C50C1 was further characterized to be an obligate methanotroph, containing C_16:1ω9c as the major membrane phospholipid fatty acid, which has not been found in other methanotrophs. Genome analysis of strain C50C1 showed the presence of two pmoCAB operon copies and XoxF5-type methanol dehydrogenase in addition to MxaFI. The genome also contained genes involved in nitrogen and sulfur cycling, but it remains to be demonstrated if and how these help this type Ib methanotroph to adapt to fluctuating environmental conditions in freshwater ecosystems.

IMPORTANCE Most of the methane produced on our planet gets naturally oxidized by a group of methanotrophic microorganisms before it reaches the atmosphere. These microorganisms are able to oxidize methane, both aerobically and anaerobically, and use it as their sole energy source. Although methanotrophs have been studied for more than a century, there are still many unknown and uncultivated groups prevalent in various ecosystems. This study focused on the diversity and adaptation of aerobic methane-oxidizing bacteria in different environments by comparing their phenotypic and genotypic properties. We used lab-scale microcosms to create a countergradient of oxygen and methane for preenrichment, followed by classical isolation techniques to obtain methane-oxidizing bacteria from a freshwater environment. This resulted in the discovery and isolation of a novel methanotroph with interesting physiological and genomic properties that could possibly make this bacterium able to cope with fluctuating environmental conditions.

Inverse analysis to estimate site-specific parameters of a mathematical model for simulating pesticide dissipations in paddy test systems

BACKGROUND

In Japan, while experimental data for the dissipation behavior of paddy pesticides under a standardized test system are available, the application of a mathematical model is limited. This paper proposes a new model calibration procedure for inversely deriving the model parameters from the experimental data. This procedure is tested in the open software R by running an improved Pesticide Concentration in Paddy Field-1 (PCPF-1) model with R packages to analyze the dissipation of simetryn and molinate in flooded lysimeters and paddy fields.

RESULTS

The model fitting was performed by a random minimization routine. Furthermore, the uncertainties of the model parameters envisioned by the global sensitivity analysis were successfully reduced using the Markov chain Monte Carlo technique. The calibrated simulation was validated at each test plot by confirming multiple statistical indices (i.e. Nash-Sutcliffe efficiency 0.88-1.00, percent bias <±5%). The dissipation pathways of two herbicides were quantitatively clarified by the mass balance of calibrated simulations and the effect of the unexpected herbicide runoff was quantified. The case study showed that the adjustment of daily percolation rate in the lysimeter experiment is the key to simulate the actual paddy field condition more accurately, especially in a case where pesticides show higher water solubility and soil mobility.

CONCLUSION

The developed procedure can analyze the experimental data with acceptable accuracy and extract the unobservable information quantitatively. Our approach is applicable to the optimization of not only the model but also future experimental design. © 2018 Society of Chemical Industry.

Part 1: Submerged application of granular pesticides

Three-year comprehensive experiments were conducted to compare the dissipation patterns of a total of 16 pesticides, including 3 metabolites, as granular formulations applied in lysimeters and paddy fields with two soil types. Analytical concentrations of the target pesticides in paddy water were analyzed using a granular kinetic model consisting of the following parameters: release rate, decrease rate, and dissolved concentration. Results of parameter grouping analyses of the kinetic models showed that 56% of data reproducibility (entire grouping) was obtained between replicates for the lysimeters. In comparisons between the lysimeters and paddy fields, 48% of decrease rates and 34% of release rates were grouped, although significant differences were observed with a nearly 90% difference for dissolved concentrations. These differences might be attributed to the hydrological components such as water management and meteorological covariates in paddy fields, the daily percolation in lysimeters and the adsorption-desorption kinetics between paddy water and soil.

[Effects of different paddy-upland multiple cropping rotation systems on soil organic carbon and its fractions in paddy field]

The variations of soil organic carbon and its fractions in different paddy-upland multiple cropping rotation systems were evaluated in field trials in two consecutive years. During paddy-upland multiple cropping rotations conducted over 2 years, the content of soil total organic carbon (TOC) first increased and then decreased. The content of readily oxidized organic carbon (ROC) was highest at the rice tillering stage and lowest at the mature stage. The soil microbial biomass carbon (SMBC) was highest at the tillering stage. The dissolved organic carbon (DOC) content was highest at the mature stage. The maximum and minimum differences were at the booting stage and mature stage for TOC content, at the greening stage and booting stage for ROC content, at the mature stage and the greening stage for DOC content, at the tillering stage and the greening stage for SMBC, respectively. The soil TOC and DOC contents showed the largest variations in the 'winter fallow-early rice-late rice → winter fallow-early rice-late rice' rotation. The soil ROC content showed the largest variation in the 'milk vetch-early rice-late rice → rape-peanut-late rice' rotation. The maximum variation of SMBC was in the 'vegetables-peanut/corn-late rice → milk vetch-early rice-late rice' rotation. The 'potato-maize/soybean-late rice → vegetables-peanut/corn-late rice' rotation resulted in higher soil TOC content at the booting stage. The pattern of 'milk vetch-early rice-late rice → oil rape-peanut-late rice' led to higher soil ROC contents in the early and middle growth stages of late rice. In the 'rape-peanut-late rice → potato-maize/soybean-late rice' rotation, the highest DOC contents were at the greening stage and the mature stage, and the highest SMBC were at the booting stage and the heading stage, respectively. All these diffe-rences were significant. The rank the contents of soil organic carbon fractions from highest to lowest followed the order: TOC>ROC>SMBC>DOC. The results suggested that paddy-upland multiple cropping rotation systems could increase the contents of soil organic carbon and its fractions and improve soil quality and fertility.

Part 2: Nursery-box application and foliar application

Comparative experiments investigating the dissipation of four nursery-box-applied pesticides and three foliar-applied pesticides were conducted using lysimeters and in actual paddy fields. In the lysimeter experiments, there were test plots for submerged application for both application types. Analytical concentrations of the pesticides in paddy water were evaluated using appropriate kinetic models. The detection levels of pesticides in the paddy water for the nursery-box and foliar applications were 10-77% and 42-79% of the submerged application, respectively. The times required for 50% dissipation (DT 50s) in case of the nursery-box and foliar applications were 0.8-10.4 days and 0.5-2.7 days, respectively. Although overall dissipations were affected by the physicochemical properties of the pesticide and the experimental design in the test plots, the initial detection levels in the lysimeters, governed by the runoff at transplanting and the deposition at spraying, were comparable with those in the actual paddy fields.

Effects of Biochar Amendment on CO₂ Emissions from Paddy Fields under Water-Saving Irrigation

The role of carbon pool of biochar as a method of long-term C sequestration in global warming mitigation is unclear. A two-year field study was conducted to investigate the seasonal variations of CO₂ emissions from water-saving irrigation paddy fields in response to biochar amendment and irrigation patterns. Three biochar treatments under water-saving irrigation and one biochar treatment under flooding irrigation were studied, and the application rates were 0, 20, 40, and 40 t ha⁻¹ and labeled as CI + NB (controlled irrigation and none biochar added), CI + MB (controlled irrigation and medium biochar added), CI + HB (controlled irrigation and high biochar added), and FI + HB (flood irrigation and high biochar added), respectively. Results showed that biochar application at medium rates (20 t ha⁻¹) decreased CO₂ emissions by 1.64–8.83% in rice paddy fields under water-saving irrigation, compared with the non-amendment treatment. However, the CO₂ emissions from paddy fields increased by 4.39–5.43% in the CI + HB treatment, compared with CI + NB. Furthermore, the mean CO₂ emissions from paddy fields under water-saving irrigation decreased by 2.22% compared with flood irrigation under the same amount of biochar application (40 t ha⁻¹). Biochar amendment increased rice yield and water use efficiency by 9.35–36.30% and 15.1–42.5%, respectively, when combined with water-saving irrigation. The CO₂ emissions were reduced in the CI + MB treatment, which then increased rice yield. The CO₂ emissions from paddy fields were positively correlated with temperature. The highest value of the temperature sensitivity coefficient (Q₁₀) was derived for the CI + MB treatment. The Q₁₀ was higher under water-saving irrigation compared with flooding irrigation.

[Influence of Spatial Pattern of Paddy Field on the Losses of Nitrogen and Phosphorus in Three Gorges Reservoir Area]

This paper used three plots of paddy field in Wangjiagou small catchment in Fuling District, Chongqing Municipality as a case study. Wangjiagou, located in Three Gorges Reservoir Area, provided a good case in terms of its closeness of surface runoff. The samples of individual rainfall of twelve times and process of two typical individual rainfalls on three plots of sloping paddy field were collected from 2014 to 2015. These samples were used to analyze the influence of spatial pattern of sloping paddy field on the concentration of nitrogen and phosphorus in the surface runoff. The samples of daily runoff in subcatchments in 2010 and 2015 were used to analyze the influence of spatial pattern change of subcatchments' paddy field on the concentration of nitrogen and phosphorus in the surface runoff. The results indicated that the removal rates of TN, NO₃^--N and TP of paddy field at the valley bottom were higher than those in the mid-slopes. The removal rate of TP would be higher if plot size of paddy field at the bottom got bigger. During individual rainfall event, the losses concentration of TN, NO₃^--N and TP in the paddy fields was significantly different among three different spatial patterns during the previous period of heavy rain event, but it became different during the next period of moderate rain event. The two subcatchments' spatial pattern change of paddy field had weakened the intercepting purification ability of nitrogen and phosphorus losses of paddy field in 2015, compared with that in 2010. TN's losses concentration increased significantly during the periods of light and moderate rain event and base flow. TP's losses concentration fluctuated during the event from moderate rain to heavy rain. Hence, increasing the area of paddy field of catchment and optimizing its spatial pattern reasonably were found as effective measures to control agricultural non-point source pollution in the Three Gorges Reservoir Region.

[Effects of the Veterinary Antibiotic Sulfamethazine on Ammonia Volatilization from a Paddy Field Treated with Conventional Synthetic Fertilizer and Manure]

Veterinary antibiotics have been widely detected in croplands due to the application of animal excrements as fertilizer. However, their effects on ammonia (NH₃) volatilization remain unclear. A field experiment was conducted to evaluate the effect of sulfamethazine on NH₃ volatilization from a paddy field when conventional synthetic fertilizer or manure was applied as basal fertilizer. Five different treatments were conducted in this study: without application of fertilizers and antibiotics (CK), compound fertilizer used as basal fertilizer with and without the addition of sulfamethazine (CF+SD and CF respectively), and pig manure used as base fertilizer with and without the addition of sulfamethazine (CM+SD and CM respectively). Urea was used for topdressing in the CF, CF+SD, CM, and CM+SD treatments. The results showed that regardless of the fertilizer type applied, sulfamethazine did not affect the seasonal pattern of NH₃volatilization. However, it promoted the NH₃ volatilization rate in the topdressing stage significantly (P<0.01). During the observation period, the proportions of applied N lost as NH₃-N in the CF+SD and CM+SD treatments were 1.65 and 2.78 times higher than those in the CF and CM treatments, respectively. The promoting effect of sulfamethazine was more obvious in the pig manure treatment than in the compound fertilizer treatment. Sulfamethazine significantly increased the soil urease activity (P<0.05). Furthermore, the NH₃ volatilization rate was positively correlated with urease activity and soil ammonia nitrogen content (P<0.05). This indicates that sulfamethazine can increase the NH₃ volatilization rate by changing the soil urease activity and inorganic nitrogen content. Controlling the misuse of veterinary antibiotics and environmental and ecological risks posed by the antibiotic residues in farmland excrements are urgent problems in China that need to be solved.

[Spatial variability of nutrients and heavy metals in paddy field soils based on GIS and Geostatistics.]

Based on a grid (25 m X 25 m) equidistant sampling, the spatial variability of pH, organic matter, total nitrogen, available phosphorus, CEC and three typical heavy metal elements Cd, As and Pb in soil tillage layer (0-20 cm) were analyzed by using GIS and Geostatistics in the paddy field of 3.56 hm² in Beishan Town, Changsha County, Hunan Province. The results showed that soil pH value and Pb content showed weak variation, and other indexes showed moderate variation. The order of variation was following available phosphorus ＞ Cd ＞ total nitrogen ＞ organic matter ＞ CEC ＞ As ＞ Pb ＞ pH. Results of the semi-variance test showed that the best fitting model of the semi-variance function of organic matter, available phosphorus and As was exponential, and the best semi-variance function of pH, total nitrogen, CEC, Cd, Pb was spherical. All the indicators had a strong spatial correlation except for CEC, which showed moderate spatial correlation. Kriging interpolation analysis showed that pH, total nitrogen, CEC, Pb were plaque distribution, while organic matter, available phosphorus, Cd and As were block and banded distribution. Vegetation, topography and human activities were the main factors driving the variation of soil nutrients and heavy metals in the study area. The correlation between soil nutrients and heavy metals content was significant, among which pH and organic matter, Cd and Pb reached a very significant correlation level.

[Control Effect of Side Deep Fertilization with Slow-release Fertilizer on Ammonia Volatilization from Paddy Fields]

In order to reduce the ammonia volatilization in paddy fields, seven treatments were evaluated. These included three slow-release nitrogen fertilizers[sulfur-coated urea (SCU); resin-coated urea (RCU); release bulk blending fertilizer (RBB)], two fertilization modes[single base fertilization (B) and combined with panicle fertilizer (BF)], and conventional split fertilization (CN). The effects of side deep fertilization for slow-release nitrogen fertilizers on ammonia volatilization and surface water nitrogen dynamics were examined using a rice transplanter with a fertilizer sowing mechanism in the Taihu Lake region. The results showed that total nitrogen and ammonium nitrogen concentration in the surface water of the SCU treatment in the base period were higher, and those for RCU and RBB were lower than in the CN treatment. The cumulative ammonia volatilization during the whole rice season varied among different types of slow-release nitrogen fertilizers from 3.84% to 28.17% of the total N applied. The nitrogen loss from ammonia volatilization using the three slow-release nitrogen fertilizers was decreased when compared with conventional split fertilization. The ammonia volatilization loss exhibited the following relationship for the treatments:CN, B-SCU > BF-SCU, BF-RBB, BF-RCU, B-RBB, and B-RCU. When the slow-release nitrogen fertilizers were applied in single base fertilization, the total ammonia volatilization for the SCU was significantly higher than those for the RCU and RBB, while no significant differences were detected when these three slow-release fertilizers were combined with panicle fertilizer. Moreover, although the ammonia volatilization of BF-SCU was lower than that of B-SCU, those of BF-RCU and BF-RBB were higher than those with the B-RCU and B-RBB treatments, respectively. There are no significant differences for nitrogen volatilization when any of these three different fertilizers are applied as B or BF. The results for the emissions during ammonia volatilization during different stages indicated that the ammonia volatilization of SCU at the basal-tillering fertilization stage (7.54%) and the tillering-panicle fertilization stage (16.04%) were higher than those of the panicle fertilization-mature stage. The N loss from ammonia volatilization for RBB in the base-tillering fertilization stage (2.91%) increased more than in the tillering-panicle fertilization stage and panicle fertilization-mature stage. For RCU treatment, the highest rate for ammonia volatilization was detected at the panicle fertilization-mature stage (2.75%). Compared with the single base fertilization mode, ammonia volatilization during the panicle fertilization-mature stage was increased when combined with panicle fertilizer (BF) for the slow-release fertilizer. There was no obvious correlation between the N loss with ammonia volatilization for the three slow-release nitrogen fertilizers and the concentration of ammonium nitrogen in surface water during the panicle fertilization-mature stage.

Inhibitory Effects of 3,4-Dimethylpyrazole Phosphate on CH4 and N2O Emissions in Paddy Fields of Subtropical China

3,4-Dimethylpyrazole phosphate (DMPP) has been widely employed to reduce nitrogen leaching and greenhouse gas emissions in the soils of dry farmlands. However, the effects of DMPP on the dynamics of nitrogen in paddy fields remain unclear. For this study, treatments with 0%, 0.25%, 0.5%, 1%, or 1.5% DMPP levels of nitrogen fertilization plus urea were designed to determine the effects on greenhouse gas emissions in paddy fields of subtropical China. All DMPP treatments significantly reduced CH4 and N2O emissions, from 54% to 34%, and 94% to 39%, respectively, compared with a urea fertilizer treatment alone. The soil NH4+ content decreased and NO3- increased more slowly with the application of DMPP. The crop yields under the various DMPP treatments showed no significant difference (p < 0.05). We concluded that the application of 0.5% and 1% DMPP may significantly reduce CH4 and N2O emissions in contrast to other treatments. This has important implications for the maintenance of rice yields, while reducing greenhouse gas emissions in paddy fields.