Better estimation of evapotranspiration and transpiration using an improved modified Priestly-Taylor model based on a new parameter of leaf senescence in a rice field

Evapotranspiration (ET) is at the heart of the global water, energy, and carbon cycles. As ET is difficult and expensive to measure, it is crucial to develop estimation models that can be widely applied. Currently, an improved Priestley-Taylor (PT) model considers soil moisture stress, temperature constraints, and leaf senescence; however, its parameter (fs) for simulating crop senescence is based on empirical values, making it difficult to apply to different varieties and complex external conditions and thus challenging to generalize. We improved the parameters fs in the original model based on the chlorophyll decomposition that accompanies crop senescence through easily observable SPAD values (Soil-Plant Analysis Development readings) in the field. We validated the improved model by obtaining ET of different rice varieties in 2022 and 2023 using the energy balance residual method at the Free Air Concentration Enrichment Experimental (FACE) Facility located in Yangzhou City, China. The results showed that the simulation of leaf senescence using SPAD values was feasible and could be extended to different varieties. The new model using improved leaf senescence parameter for estimating ET and transpiration (T) in three plots (2022 and 2023) exhibited slightly enhanced accuracy, particularly at the later stages of crop growth. Moreover, the higher the T/ET ratio of the cropland, the more significant the improvement. This new development enhances the ability of PT models to estimate ET and T using readily available field observations and provides some suggestions for wider application in the field for other crop species.

Different microbial communities in paddy soils under organic and nonorganic farming

Organic agriculture is a farming method that provides healthy food and is friendly to the environment, and it is developing rapidly worldwide. This study compared microbial communities in organic farming (Or) paddy fields to those in nonorganic farming (Nr) paddy fields based on 16S rDNA sequencing and analysis. The predominant microorganisms in both soils were Proteobacteria, Chloroflexi, Acidobacteria, Actinobacteria, and Nitrospirota. The alpha diversity of the paddy soil microbial communities was not different between the nonorganic and organic farming systems. The beta diversity of nonmetric multidimensional scaling (NMDS) revealed that the two groups were significantly separated. Distance-based redundancy analysis (db-RDA) suggested that soil pH and electrical conductivity (EC) had a positive relationship with the microbes in organic paddy soils. There were 23 amplicon sequence variants (ASVs) that showed differential abundance. Among them, g_B1-7BS (Proteobacteria), s_Sulfuricaulis limicola (Proteobacteria), g_GAL15 (p_GAL15), c_Thermodesulfovibrionia (Nitrospirota), two of f_Anaerolineaceae (Chloroflexi), and two of g_S085 (Chloroflexi) showed that they were more abundant in organic soils, whereas g_11-24 (Acidobacteriota), g__Subgroup_7 (Acidobacteriota), and g_Bacillus (Firmicutes) showed differential abundance in nonorganic paddy soils. Functional prediction of microbial communities in paddy soils showed that functions related to carbohydrate metabolism could be the major metabolic activities. Our work indicates that organic farming differs from nonorganic farming in terms of microbial composition in paddy soils and provides specific microbes that might be helpful for understanding soil fertility.

Blood parameters of adult marsh frogs Pelophylax ridibundus (Amphibia: Ranidae) in rice paddies subjected to intense agrochemical use

We present the results of an in situ study of a set of blood parameters in adult marsh frogs (Pelophylax ridibundus (Pallas 1771) from populations inhabiting the largest system of rice fields in Bulgaria, the Tsalapitsa rice fields (TRF), under chronic stress conditions. This study was conducted in spring 2022 to assess the health status of TRF frogs compared to that of frogs occupying a reference site (RS). Furthermore, this study also compared the results obtained for the TRF population with those obtained in a study conducted at the exact same location with P. ridibundus individuals in 2013 (Zhelev et al. 2018). This comparison highlights the potential effects of persistent use of agrochemicals (pesticides and fertilizers) on the marsh frogs of later generations. Our results suggest that the general health of marsh frogs in the polluted site (PS) in southern Bulgaria has severely deteriorated. Frogs of both sexes were anemic with weakened immune systems compared to those living in the RS. The long-term use of agrochemicals in the PS affected males to a greater extent than it did females. Statistically significant hypochromia was observed in males, combined with general leukopenia, neutrophilia, lymphopenia, monocytosis, eosinophilia, and higher neutrophil/lymphocyte (N/L) ratios.

Deciphering insights into rhizospheric microbial community and soil parameters under the influence of herbicides in zero-tillage tropical rice-agroecosystem

Extensive use of chemicals like herbicides in rice and other fields to manage weeds is expected to have a lasting influence on the soil environment. Considering this rationale, we aimed to decipher the effects of herbicides, Pendimethalin and Pretilachlor, applied at 0.5 and 0.6 kg ha-1, respectively on the rhizosphere microbial community and soil characteristics in the tropical rice field, managed under zero tillage cultivation. The quantity of herbicide residues declined gradually since application up to 60 days thereafter it reached the non-detectable level. Most of the soil variables viz., microbial biomass, soil enzymes etc., exhibited slight reduction in the treated soils compared to the control. A gradual decline was observed in Mineral-N, MBC, MBN and enzyme activities. Quantitative polymerase chain reaction results showed maximal microbial abundance of bacteria, fungi and archaea at mid-flowering stage of rice crop. The 16 rRNA and ITS region targeted amplicons high throughput sequencing microbial metagenomic approach revealed total of 94, 1353, and 510 species for archaea, bacteria and fungi, respectively. The metabarcoding of core microbiota revealed that the archaea comprised of Nitrososphaera, Nitrosocosmicus, and Methanosarcina. In the bacterial core microbiome, Neobacillus, Nitrospira, Thaurea, and Microvigra were found as the predominant taxa. Fusarium, Clonostachys, Nigrospora, Mortierella, Chaetomium, etc., were found in core fungal microbiome. Overall, the study exhibited that the recommended dose of herbicides found to be detrimental to the microbial dynamics, though a negative relation between residues and soil variables was observed that might alter the microbial diversity. The outcomes offer a comprehensive understanding of how herbicides affect the microbial community in zero tillage rice soil, thus has a critical imputation for eco-friendly and sustainable rice agriculture. Further, the long-term studies will be helpful in elucidating the role of identified microbial groups in sustaining the soil fertility and crop productivity.

A combination of organic fertilizers partially substitution with alternate wet and dry irrigation could further reduce greenhouse gases emission in rice field

Alternate wet and dry (AWD) irrigation and organic fertilizers substitution (OFS) have contrasting effects on CH4 and N2O emissions in rice cultivation. Combining these two practices may be feasible for simultaneous reduction of CH4 and N2O emission from paddy. Hence, we conducted a two-year field experiment to explore the reduction of greenhouse gases under the combination of AWD and OFS. The field experiment which was designed with two irrigation methods (continuous flooding (CF) irrigation and AWD irrigation), and five nitrogen regimes (N0, N135, and N180 represent 0, 135, and 180 kg N ha-1, respectively, ON25 and ON50 represent 25% and 50% OFS for inorganic fertilizer, respectively). The results showed a single-peak emission for CH4 fluxes during the whole rice growing season in all water and nitrogen treatments while the N2O fluxes peak only observed during tillering period with AWD irrigation. AWD irrigation and OFS showed a limited reduction in global warming potential (GWP). These were owing to that AWD irrigation reduced 38.3% CH4 emissions while increase 145.9% N2O emissions when compared to CF irrigation, and the low rate (25%) OFS only reduced CH4 emission by 29.4% while high rate (50%) only reduce N2O emission by 38.8% when compared to conventional inorganic nitrogen fertilizer (N180). Combined AWD and ON25 could maximize the reduction in GWP and yield-scaled GWP, which were reduce 58.0% and 52.5%, respectively, compare to the conventional water and nitrogen management (CF and N180). Furthermore, the structural equation modelling (SEM) indicated that the soil dissolved organic carbon (DOC) and rice aboveground biomass showed a significant positive effect on CH4 fluxes while soil NH4+ with a negative effect, and the soil NH4+, nitrification potential, denitrification potential significant affected N2O fluxes with a positive effect while DOC with a negative effect. These results investigated that 25% OFS rate for inorganic fertilizer could further reduce warming potential in AWD irrigation rice field.

Preciseness, rather than simplicity, is required to assess pesticide reduction strategies: Findings from rice production in Japan

Pesticide reduction is given high priority in the worldwide sustainability agenda. The reduction of pesticide impacts, rather than the reduction of application rates, has become a common criterion for monitoring policy progress. However, simplicity-an essential requirement in improving the applicability of pesticide impact assessment-may distort the accuracy of the evaluation and therefore prevent effective pesticide reduction. Here, we present contrasting results that underscore how the selection of evaluation methods that differ in simplicity affects the assessment results of pesticide reduction strategies. Briefly, we analysed the impact of conversion from conventional to low-input management adopting both a simplified linear-based method and a precise method that includes newly calculated nonlinear approach-based characterization factors for 109 active ingredients (AIs). The two methods were then used to estimate the freshwater ecotoxicity impact of eight rice farms in Japan where both conventional pesticide application and pesticide reduction strategies are practiced. The results show that the simplified method generated anomalies at the farm level through overestimation and underestimation of the individual AI impacts. Patterns that contributed to extreme changes of impact at the farm level were also identified. These findings suggest a strong need for a precise evaluation method for effectively monitoring policy progress at the farm level.

Current status of carbon neutrality in Chinese rice fields (2002-2017) and strategies for its achievement

China has pledged to achieve carbon neutrality by 2060 to address global climate change, and achieving carbon neutrality in rice fields is a vital component of this commitment. However, the current status of carbon neutrality in rice fields in China is unclear, and there are few feasible strategies to achieve its successful implementation. Therefore, this study calculated the net carbon sequestration rate (NCSR, i.e., carbon sequestration minus carbon emissions) of rice fields in China from 2002 to 2017 to clarify the carbon neutrality status of Chinese rice fields. Furthermore, the effects of field management measures, rice sown area, and rice yield on NCSR were analyzed to identify suitable carbon neutralization pathways in Chinese rice fields. Our findings indicated that the annual carbon sequestration rate in rice fields was lower than the carbon emissions, resulting in continuous net emissions of 195.49 Tg CO₂-eq yr^-1. The NCSR of paddy fields increased first and then decreased with increases in rice sown area and yield. Meta-analysis indicated that management measures such as water conservation and biochar significantly increased NCSR by ~5766.50 kg CO₂-eq ha^-1 yr^-1 and 22,296.62 kg CO₂-eq ha^-1 yr^-1, respectively. Our findings suggests that proper control of rice sown area and the adoption of reasonable field management measures (water conservation and biochar) can promote carbon neutrality in Chinese rice fields.

Foraging Strategy of Black-faced Spoonbill During Breeding Period in Rice Fields of Korea

Rice fields are important habitats for a variety of water birds, and their importance is increasing with the destruction of natural wetlands. This study was conducted to understand the foraging strategy of the black-faced spoonbill, an internationally endangered species, in rice fields. To achieve this objective, the feeding success rate of black-faced spoonbills in rice fields was analyzed considering the species' feeding behavior, environmental factors, and external factors. The number of sweeps per minute and number of steps per minute were evaluated as features of feeding behavior; rice field type, water level, and rice height as environmental factors; and the size of a flock and number of other species in the fields when black-faced spoonbills were feeding as external factors. The feeding success rate of the black-faced spoonbills increased as they were feeding while moving at a fast pace in a rice field with a water level of 10 cm or below, rice height of 15 cm, and without herons (competitor species). These factors may be an effective strategy to increase the probability of food acquisition by black-faced spoonbills in rice fields. Therefore, to allow black-faced spoonbills during breeding season to use the rice fields for feeding, it is necessary to maintain a water level of 15 cm or less before transplanting rice. Moreover, the use of pesticides must be minimized to increase abundance of the food resources in rice fields.

Indigenous farmers' perceptions of problems in the rice field agroecosystems in the upper Baram, Malaysia

BACKGROUND

Rice field agroecosystems produce food for more than half of the world's population and deliver important services supporting farmers' livelihoods. However, traditional rice field agroecosystems are facing a variety of problems, including pests or markets that are hard to access. This research explored indigenous farmers' perceptions of the problems, their causes and consequences, and the solutions applied to address them in the rice field agroecosystem. Furthermore, the study investigated how indigenous farmers related these problems to the surrounding landscape elements and to microzones in the fields.

METHODS

Data were collected in two villages in the upper Baram, Sarawak using a qualitative approach that included sketch drawings and face-to-face interviews. Forty-three indigenous farmers of the Kenyah, Penan and Sa'ban ethnic groups were interviewed in their rice fields. The sketch drawings were used to identify the perceived landscape elements, while the oral interviews were employed to identify perceived microzones. Furthermore, the interviews elicited the perceived problems in the rice field agroecosystem and their relations to landscape elements and microzones.

RESULTS

The findings identified a total of nine environmental problems, e.g. animal disturbance, six social problems, e.g. difficult to access farm inputs, and eight agricultural technology system problems, e.g. poor soil quality, with some found to be rooted in complex causes and affecting agricultural productivity. While some problems were perceived at field level, microzones were frequently used as sub-field indicators of the problems. The surrounding landscape elements were perceived as both a source of the problems and as a means of avoiding them. To solve the problems, farmers applied preventive and reactive strategies based on traditional knowledge and scientific knowledge, resulting in a hybridisation of knowledge systems.

CONCLUSIONS

By including environmental, social, agricultural technology system problems and different spatial scales, this research contributes to addressing issues that can be overlooked when focusing on only one dimension of the problems. These results contribute to a better understanding of how indigenous farmers perceive, cope with and adapt to problems in rice field agroecosystems, which is important for landscape management.

(Odonata: Libellulidae) from rice fields

BACKGROUND

Microplastic (MP) contamination has been discovered in aquatic systems throughout the world. They are well known as contaminants in aquatic species, but there is a gap in understanding about pathways of MP contamination into humans (i.e., through aquatic animals). The goal of this study is to assess MP contamination in an edible aquatic insect (Pantala sp.) living in rice fields.

METHODS

A dragonfly larva, Pantala sp. (Odonata: Libellulidae), was tested for MPs. The study concentrated on three distinct anatomical compartments (whole body, gastrointestinal tract, and body without gastrointestinal tract), each of which was examined separately. For the physical identification and chemical analysis of MPs, a stereomicroscope and a Fourier transformed infrared spectroscope (FT-IR) were used, respectively.

RESULTS AND DISCUSSION

The microplastics content was 121 in the whole body, 95 in the gastrointestinal tract, and 66 in the body without the gastrointestinal tract, with an average of 1.34 ± 1.11, 1.06 ± 0.77, and 0.73 ± 0.51 abundance/ individual, respectively. The most common MPs discovered during this study were fragments, followed by fibers and rods. The chemical analysis by FT-IR confirmed three different polymers, including polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polypropylene (PP). There was no significant difference in MP abundances among the sample types (Kruskal-Wallis chi-squared = 2.774, df = 2, p = 0.250). The findings suggest that eating an edible aquatic insect (Odonata: Pantala sp.) could be one way for humans to ingest MPs.

A high abundance of Firmicutes in the intestine of chinese mitten crabs (Eriocheir sinensis) cultured in an alkaline region

The Chinese mitten crab (Eriocheir sinensis) is a popular aquaculture product in East Asia, especially in China. In the last decade, rice-crab co-culture has rapidly expanded in China. Under this model, crabs are raised in rice fields instead of in traditional aquaculture ponds. In this study, we cultured two varieties of Chinese mitten crabs (Changjiang and Liaohe) in an alkaline region in northwest China and used Illumina MiSeq sequencing to compare the intestinal bacterial alpha diversity and community structure between traditional and co-culture aquaculture models, between two crab varieties, and between female and male crabs. Significant variations in intestinal bacterial communities were found between crab varieties and between female and male crabs but not between aquaculture models. These results show that rice-crab co-culture operations did not obviously impact the crab intestinal bacterial community compared with traditional pond aquaculture. Firmicutes was the most abundant bacterial phylum in the crab intestines (78%, relative abundance). Three dominant operational taxonomic units (OTUs) represented 73.2% of Firmicutes sequences and 56.8% of all sequences. A dominant OTU assigned as Firmicutes that was negatively correlated with crab body length, width, and weight was found in the source water for the experimental area. The results of this study suggest that the aquaculture of Chinese mitten crabs in alkaline regions requires more study to improve cultivation techniques.

Evaluation of thiobencarb runoff from rice farming practices in a California watershed using an integrated RiceWQ-AnnAGNPS system

The development of modeling technology to adequately simulate water and pesticide movement within the rice paddy environment faces several challenges. These include: (1) adequately representing ponded conditions; (2) the collection/implementation of temporal/spatial pesticide application data at field scales; (3) the integration of various mixed-landuses simulation schemes. Currently available models do not fully consider these challenges and results may not be sufficiently accurate to represent fate and transport of rice pesticides at watershed scales. Therefore, in this study, an integrated simulation system, "RiceWQ-AnnAGNPS", was developed to fully address these challenges and is illustrated in a California watershed with rice farming practices. The integrated system successfully extends field level simulations to watershed scales while considering the impact of mixed landuses on downstream loadings. Moreover, the system maintains the application information at fine spatial scales and handles varying treated paddy areas via the "split and adjust" approach. The new system was evaluated by investigating the fate and transport of thiobencarb residues in the Colusa Basin, California as a case study. Thiobencarb concentrations in both water and sediment phases were accurately captured by the calibrated RiceWQ model at the edge of field. After spatial upscaling, the integrated system successfully reflected both the seasonal pattern of surface runoff and the timing of monthly thiobencarb loadings. Incorporating future enhancements can further improve model performance by including more detailed water drainage schedules and management practices, improving the accuracy of summer runoff estimations, and incorporating a more sophisticated in-stream process module. This integrated system provides a framework for evaluating rice pesticide impacts as part of a basin level management approach to improve water quality, which can be extended to other rice agrochemicals, or other areas with fine-scale spatial information of pesticide applications.

Effect of biochar addition on CO2 exchange in paddy fields under water-saving irrigation in Southeast China

Biochar has been widely applied to paddy fields to improve soil fertility, crop productivity and carbon sequestration, thereby leading to variations in the CO₂ exchange between the paddy fields under flooding irrigation and the atmosphere, as indicated by many previous reports. However, few relevant reports have focused on paddy fields under water-saving irrigation. This study conducted a field experiment to investigate the effects of three biochar addition rates (0, 20 and 40 t ha^-1) on the CO₂ exchange between paddy fields under controlled irrigation (CI, a water-saving irrigation technique) and the atmosphere in the Taihu Lake region of Southeast China. Our results showed that biochar addition increased the paddy field ecosystem respiration (R_eco) and the soil respiration rate (R_s) in the CI paddy fields. And biochar application increased the total CO₂ emissions and the total soil CO₂ emissions, especially at a rate of 40 t ha^-1. In contrast, gross primary productivity (GPP) was decreased and the net ecosystem exchange of CO₂ (NEE) was increased with biochar addition. However, biochar addition at a rate of 20 t ha^-1 significantly increased the total CO₂ absorption and the net CO₂ absorption of the CI paddy fields (p < 0.05), whereas biochar addition at a rate of 40 t ha^-1 had no effect on the total CO₂ absorption and decreased the total net CO₂ absorption. At the same time, biochar addition significantly increased soil catalase, invertase and urease activities and contributed substantially to the increase in soil invertase activity. In addition, the soil bacterial, fungal and actinomycetal abundances were evidently increased with biochar addition, of which the soil fungal abundance showed the greatest increase. A high correlation was observed between soil catalase and invertase activities and soil microbial abundance. R_eco was highly correlated with air and soil temperatures and soil enzyme activity. A significant quadratic polynomial correlation was observed between GPP and leaf area index (p < 0.01). The combination of biochar addition at a rate of 20 t ha^-1 and water-saving irrigation has the potential to increase the size of the carbon sink and promote soil enzyme and microbial activities in paddy field ecosystems.

Minimal tillage and intermittent flooding farming systems show a potential reduction in the proliferation of Anopheles mosquito larvae in a rice field in Malanville, Northern Benin

Background

Irrigation systems have been identified as one of the factors promoting malaria disease around agricultural farms in sub-Saharan Africa. However, if improved water management strategy is adopted during rice cultivation, it may help to reduce malaria cases among human population living around rice fields. This study aimed to assess the impact of the different irrigation practices on malaria transmission, as well as to evaluate the water management system that will best mitigate malaria transmission in Malanville, Benin.

Methods

Knowledge, Attitude and Practice (KAP) study was conducted on 104 households staying on and around the rice fields in Malanville. The study focused on the frequency of mosquito bites and preventive measures against malaria as well as soil preparation and rice planting methods. Mosquito larvae density was assessed in different water management system: continuous flooding (CF) or intermittent flooding (IF), deep tillage (DT) or minimal tillage (MT) and normal levelling (NL) or abnormal levelling (AL) in an experimental hut set-up. Larvae were collected using dipping methods and their density was determined.

Results

Three tillage systems, which include the use of tiller, plow and hoe, were identified on the rice field. Continuous flooding was the only irrigation system used by farmers. Retrospective data from Malanville Health Centre revealed higher malaria cases during rice production season, which was also confirmed by field participants. The density of Anopheles larvae was reduced by 80.8%, 30.8% and 40.7% (P = 0.000) during transplanting, tillering and maturation periods, respectively with intermittent flooding compared to continuous flooding. In addition, a clear reduction of larva density was observed with both intermittent flooding systems applied to minimal tillage (MT + IF + NL) and intermittent flooding applied to deep tillage (DT + IF + AL), showing that intermittent flooding could reduce the abundance of malaria vector in rice fields.

Conclusion

Recommending intermittent flooding technology for rice cultivation may not only be useful for water management but could also be an intentional strategy to control mosquitoes vector-borne diseases around rice farms.

Spiders in rice-paddy ecosystems shift from aquatic to terrestrial prey and use carbon pools of different origin

Spiders are important bio-control agents of rice insect pests such as plant- and leafhoppers. To investigate temporal changes in spider prey and variations in prey due to landscape structure around rice fields, carbon and nitrogen stable isotopes of rice field arthropods were analysed over three consecutive sampling dates during the rice cropping season. Initial isotope composition of gnats and midges emerging from submersed rice fields indicates a larval algae diet, while later values suggest a switch to rice-derived carbon. Initial δ¹³C values of plant- and leafhoppers were higher in fields of rice-heterogeneous landscapes, indicating migration from source populations feeding on C4 grasses into rice fields; later, their δ¹³C values approached those of rice. Isotope values of web-building and cursorial spiders in the earliest samples indicate aquatic gnat and midge prey. The later shift toward terrestrial herbivore prey was more pronounced for small than for larger species and in rice paddies near permanent vegetation, indicating use of prey from the surrounding landscape. The results suggest that rice field spiders are supported by three different carbon pools: (1) aquatic carbon originating from algae and (2) legacy carbon from previous growing cycles, both incorporated via between-season predation on gnats and midges, and (3) carbon from the current rice season incorporated via herbivore prey. In conclusion, fostering aquatic midge and gnat larvae, e.g. via mulching, and integrating rice fields into rice-heterogeneous landscapes likely strengthens biological control of pest species in rice paddies by supporting high populations of spiders between cropping seasons.

Effect of soil disturbance by agricultural activities on the life history traits of monkey frog (Pithecopus azureus)

We assessed whether soil disturbance by agricultural activity influences the growth, development, and survival of individuals in the larval, metamorphic, and postmetamorphic stages of amphibians. Tadpoles of Pithecopus azureus (Cope, 1862) were reared in microcosms assembled with soil from two sites, a pristine site and a rice field. For 5 weeks, we recorded tadpole growth and development as well as physicochemical variable of the water: temperature, conductivity, dissolved oxygen, and pH. The results show that rice field soil produced a level of acidification in the water that influenced the growth and development rates of tadpoles. Tadpoles reared in rice soil had a significantly lower growth rate and body length, and during a specified period, the development rate of the tadpole was significantly lower than that of tadpoles in pristine soil. Overall, tadpoles in rice soil took 3 days longer to reach metamorphosis and 1 additional day to complete metamorphosis compared with tadpoles exposed to pristine soil. Our study shows that disturbed soils modify the physicochemical conditions of temporary ponds, impacting on the initial life stage of the anurans.

Redox changes in speciation and solubility of arsenic in paddy soils as affected by sulfur concentrations

A substantial amount of sulfate is often supplied in paddy fields with concomitant applications of chemical fertilizers and manure for rice growth. It is unclear how solubility and speciation of arsenic (As) are affected by the levels of soil sulfate and their relationship to soil redox status and sulfur (S) and iron (Fe) speciation in a short cycle of soil reducing (flooding) and oxidizing (drying) periods. The objective of this study was to investigate the solubility of As in relation to chemical speciation of As and S in different levels of soil sulfate through a time series of measurements during a 40-day reduction period (Eh < -130 mV) followed by a 32-day reoxidation period (Eh > 400 mV) using X-ray absorption fine structure (XAFS) spectroscopy. An excess of sulfate decreased extractable and dissolved As in the soil reducing period due to retardation of soil reduction process that decreased soluble As(III) in the soil solid phase. The As species at the end of soil reducing period were 38-41% As(V), 46-51% As(III), and 11-13% As₂S₃-like species, regardless of initial S treatments. In the following soil reoxidation, As₂S₃-like species were sensitive to oxidation and disappeared completely in the first 2 days when the Eh value increased rapidly above 160 mV. The addition of extra sulfate to the soil did not result in the formation of neither reduced S species nor As₂S₃-like species. About 50% of As(III) to the total As persisted over 32 days of soil reoxidation period (Eh > 400 mV), suggesting some mechanisms against oxidation of As(III) such as physical sequestration in soil microsites. This study demonstrates that the extra SO₄ in paddy soils can help mitigate the dissolution of As in reduction and reoxidation periods.

[Nitrous oxide emission, nitrification, denitrification and nitrogen mineralization during rice growing season in 2 soils from Uruguay]

Microbial processes such as mineralization, nitrification and denitrification regulate nitrogen dynamics in the soil. The last two processes may produce nitrous oxide (N₂O). In this work N₂O fluxes were quantified at four moments of the rice cycle, sowing, tillering, panicle initiation and maturity, in two sites that differed mainly in their soil organic matter (OM) content, Salto (higher OM) and Treinta y Tres. Potential net N mineralization, ammonium oxidation and denitrification as well as the most probable numbers (MPN) of ammonia oxidizers and denitrifiers were determined. Potential N mineralization did not vary with the soil type and increased at rice maturity. Neither ammonia oxidation potential nor MPN were different among the soils. However, the soil with higher OM exhibited higher activity and MPN of denitrifiers, irrespective of the rice stage. In turn, at the latest phases of the crop, the MPN of denitrifiers increased coinciding with the highest mineralization potential and mineral N content of the soil. Significant differences in N₂O flux were observed in Salto, where the highest emissions were detected at rice maturity, after the soil was drained (44.2 vs 20.8g N-N₂O/ha d in Treinta y Tres). This work shows the importance of considering the soil type and end-of-season drainage of the rice field to elaborate GHGs (greenhouse gases) inventories.

3,4-Dichloroaniline revisited: A study on the fate of the priority pollutant in a sediment-water system derived from a rice growing region in Italy

As ultimate sink for xenobiotics released into the environment, sediments play an important role concerning the evaluation of the fate of foreign compounds. 3,4-Dichloroaniline (3,4-DCA) is a degradation product of herbicide propanil and some urea herbicides. Propanil was extensively used worldwide in rice cultivation. The aim of the study was to examine the fate of ¹⁴C-labeled 3,4-DCA in a sediment-water system; the sediment was derived from a rice field in Northern Italy. After application of ¹⁴C-3,4-DCA, a time-course study was performed using incubation periods from 4h to 56days. Fractions obtained from assays were water phase, sediment phase including methanol and Soxhlet extract as well as non-extractable residues (NER), and mineralized portion (¹⁴CO₂). Soluble fractions were examined by TLC, HPLC and GC-MS. NER found in sediment phases were further fractionated in non-humics, humic acids, fulvic acids and humin. Stability of systems was checked by microbial activity, dissolved oxygen and pH. After 56days of incubation, 23.1% of applied ¹⁴C was mineralized, only 1.30% remained in the water phase, whereas 60.8% was found in the sediment phase, 53.3% of which were NER. Minor metabolites identified were 3,4-dichloroacetanilide (3,4-DCAA) and 3,3',4,4'-tetrachloroazobenzene (TCAB; 2.63% after 56days). According to pH, dissolved oxygen and microbial activity, systems appeared to be stable and not influenced by applied 3,4-DCA. Most striking result was the high mineralization rate as compared to previously published data. This finding suggested an adaptation of the microbial community in the sediment possibly due to decade-long treatment of rice fields with propanil.

Bioaccumulation of organochlorine pesticides and polychlorinated biphenyls by loaches living in rice paddy fields of Northeast China

The concentrations of 21 organochlorine pesticide (OCP) residues and 18 polychlorinated biphenyl (PCB) congeners were measured in two loach species (Misgurnus mohoity and Paramisgurnus dabryanus) and the soils of their inhabiting rice paddies from three typical rice production bases of Northeast China to explore the main factors influencing the bioaccumulation. The concentrations of ∑18PCBs and ∑21OCPs in loaches were determined to be in the ranges of 0.14-0.76 ng g(-1) wet weight (ww) and 1.19-78.53 ng g(-1) ww, respectively. Most of loaches showed the considerably high contamination levels of dichlorodiphenyltrichloroethane (DDT), hexachlorocyclohexane (HCH), hexachlorobenzene (HCB), which accounted for over 97% of the total OCPs. The much lower maximum allowable loach consumption rates (<15 g d(-1)) indicated a high carcinogenic risk that results from the consumption of rice-field loaches. The field biota-soil accumulation factor (BSAF) was calculated as a main measure of bioaccumulation potential. The comparisons of BSAF values and the results of multivariate analysis indicated that habitat-specific environmental conditions, mainly the paddy soil contamination levels and average temperature, decisively affected the bioaccumulation of organochlorine contaminants. When the influence of lipid contents was offset, M. mohoity loaches were found to have a higher potential to accumulation PCBs and OCPs than P. dabryanus loaches, while the bioaccumulation potentials did not exhibit significant differences between juvenile and adult loaches and between male and female loaches. The octanol-water partition coefficient (KOW) was the main chemical factor influencing bioaccumulation potentials. The BSAF values presented an increasing tendency with increasing log KOW values from 6.0 to approximately 7.0, followed by a decreasing tendency with a continuous increase in log KOW values. Moreover, loaches exhibited an isomeric-selective bioaccumulation for p,p'-chlorinated DDTs, α-HCH, β-HCH, δ-HCH and cis-chlordane.

Combination of wet irrigation and nitrification inhibitor reduced nitrous oxide and methane emissions from a rice cropping system

To conserve water resources and guarantee food security, a new technology termed as "wet irrigation" is developed and practiced in rice fields; thus, its impact on radiative forcing derived from nitrous oxide (N2O) and methane (CH4) emissions merits serious attention. Dicyandiamide (DCD), a kind of nitrification inhibitor, is proposed as a viable means to mitigate greenhouse gas (GHG) emission while enhancing crop productivity. However, little is known about the response of GHG emission and grain yield to DCD application in a rice system under wet irrigation. In these regard, effects of water regime and DCD application on CH4 and N2O emissions, grain yield, global warming potential (GWP), and greenhouse gas intensity (GHGI) from rice fields were studied. For this study, a field experiment, designed: Treatment II (intermittent irrigation), Treatment WI (wet irrigation), Treatment IID (II plus DCD), and Treatment WID (WI plus DCD), was conducted in Jurong, Jiangsu Province, China, from 2011 to 2012. Relative to Treatment II, Treatment WI decreased CH4 emission significantly by 49-71 % while increasing N2O emission by 33-72 %. By integrating CH4 and N2O emissions and grain yield, Treatment WI was 20-28 and 11-15 % lower than Treatment II in GWP and GHGI, respectively. The use of DCD under wet irrigation reduced N2O emission significantly by 25-38 % (p < 0.05) and CH4 emission by 7-8 %, relative to Treatment WI, resulting in a decline of 18-30 % in GWP. Due to the increase in N use efficiency, maximal grain yield (6-7 %) and minimal GHGI (22-34 %) was observed in Treatment WID. These findings indicate that combined application of N fertilizer and DCD is a win-win strategy in water-saving high-yield rice production with less GHG emission.

Effects of N loading rate on CH4 and N2O emissions during cultivation and fallow periods from forage rice fields fertilized with liquid cattle waste

The use of liquid cattle waste (LCW) as a fertilizer for forage rice is important for material recycling because it can promote biomass production, and reduce the use of chemical fertilizer. Meanwhile, increase in emission of greenhouse gases (GHGs), especially CH4 and N2O would be concerned. We conducted a field study to determine the optimum loading rate of LCW as N to promote forage rice growth with lower GHG emissions. The LCW was applied to forage rice fields, N100, N250, N500, and N750, at four different N loading rates of 107, 258, 522, and 786 kg N ha(-1), respectively, including 50 kg N ha(-1) of basal chemical fertilizer. The above-ground biomass yields increased 14.6-18.5 t ha(-1) with increases in N loading rates. During the cultivation period, both the CH4 and N2O fluxes increased with increases in LCW loading rates. In the treatments of N100, N250, N500, and N750, the cumulative CH4 emissions during the entire period, including cultivation and fallow period were 29.6, 18.1, 54.4, and 67.5 kg C ha(-1), respectively, whereas those of N2O were -0.15, -0.02, 1.49, and 5.82 kg N ha(-1), respectively. Considering the greenhouse gas emissions and above-ground biomass, the yield-scaled CO2-equivalents (CO2-eqs) were 66.3, 35.9, 161, and 272 kg CO2 t(-1) for N100, N250, N500, and N750, respectively. These results suggest that N250 is the most appropriate LCW loading rate for promoting forage rice production with lower GHG emissions.

Biochemical changes in certain enzymes of Lysapsus limellium (Anura: Hylidae) exposed to chlorpyrifos

Different enzyme biomarkers (AChE: acetylcholinesterase, CbE: carboxylesterase, GST: glutathione-S-transferase, CAT: catalase) were measured in digestive tissues of Lysapsus limellum frogs collected from a rice field (RF: chlorpyriphos sprayed by aircraft) and a non-contaminated area (RS: reference site), immediately (24h) and 168 h after aerial spraying with chlorpyrifos (CPF). CPF degradation was also searched in water samples collected from RF and RS, and found that insecticide concentration was reduced to≈6.78% of the original concentration in RF at 168 h. A significant reduction of AChE and CbE activities was detected in L. limellum from RF in stomach and liver at 24 and 168 h, and in intestine only at 24h, with respect to RS individuals. CAT activity decreased in intestine of L. limellum from RF 24h and 168 h after exposure to CPF, whereas GST decreased in that tissue only at 24h. In stomach and liver, a decrease was observed only at 168 h in both CAT and GST. The use of biomarkers (AChE, CbE, GST, and CAT) provides different lines of evidences for ecotoxicological risk assessment of wild frog populations at sites contaminated with pesticides.

Effects of almix herbicide on profile of digestive enzymes of three freshwater teleostean fishes in rice field condition

The present investigation was carried out to compare the alterations of digestive enzymes like amylase, lipase, and protease activities in three teleostean fishes viz., Anabas testudineus, Heteropneustes fossilis and Oreochromis niloticus after application of almix herbicide for 30 days at rice field concentration i.e., 8 g/acre. Highest amylase activity was observed in intestine of A. testudineus (300.76%) and lowest in intestine of H. fossilis (103.89%), while maximum lipase activity was found in stomach of O. niloticus (203.27%) and lowest in stomach of H. fossilis (109.65%). Protease activity was also highest in liver of O. niloticus (270.47%) but lowest in stomach of H. fossilis (114.04%). Changes in the enzymes’ activity were different in respect to fishes and their tissues. According to this analysis, A. testudineus and O. niloticus were more sensitive. So, it can be inferred that long-term exposure of almix even at environment-friendly concentration may cause alterations in the digestive functions.