Rice Cultivation Season Research Articles

Evaluating river basin plans’ effects on water stress in Thailand’s economic development area

ABSTRACT Surging water demand necessitates strategic water management to maintain efficiency and accessibility. In Thailand’s Eastern Economic Corridor Project, water demand escalated from 2005 to 2018 by 54%, prompting water management plans using pipe diversion. However, this plan merely shifts scarcity issues due to limitations and climate uncertainties. The Water Stress Index assessed the impact using distributed hydrological modelling, revealing the 3Rs scenario, and a dry season rice cultivation lowered by 26%. Specific basins still face extreme stress. Integrating scenarios can refine and alleviate stress, suggesting a combined scenario approach, improving Water Stress Index and efficiently identifying vital water reduction strategies.

Influence of various organic nutrient management technologies on microbial abundance, growth, and yield of rice (Oryza sativa L.) under field conditions

A field study (three years) was carried out to evaluate the outcome of various organic nutrient management technologies including farmyard manure (FYM) and poultry manure (PM) integrated with chemical fertilizers for microbial dynamics and growth and yield of rice at Experimental Farm of Nuclear Institute of Agriculture (NIA), Tandojam, Sindh, Pakistan. The most broadly grown rice variety, NIA-Shandar was selected for this study. The experiment involved integrating organic technologies, specifically Farm Yard Manure (FYM) and Poultry Manure (PM), each applied at 10 tons per hectare. These organic technologies were combined with varying levels of inorganic fertilizers: half (60 kg N ha-1 and 45 kg P2O5 ha-1) and full (120 kg N ha-1 and 90 kg P2O5 ha-1) recommended doses. Additionally, zinc was applied at 10 kg ha-1. The study employed a randomized complete block design (RCBD) with three replications to assess treatment effects. Both organic technologies perform better for microbial dynamics and rice growth and yield enhancement either alone technology or combined with chemical fertilizers during three rice seasons. The maximum general microbial abundance (9.70 log10 CFU g soil-1), N2 fixing (7.37 log10 CFU g soil-1), P solubilizing (7.97 log10 CFU g soil-1) and Zn solubilizing(6.75 log10 CFU g soil-1) population was recorded in FYM alone or with half N and P2O5 fertilizer application. The highest plant height (106 cm), tiller numbers(17.10), panicle numbers (26.53), panicle length (26.32 cm), one thousand grainweight (26.53 g) and rice grain yield (7.92 t ha-1) were perceived in FYM with full rate N and P2O5 fertilizer application. Both technologies along with chemical fertilizer induced soil properties and soil nutrients which reflected to increase soil microbial abundance and growth and yield of rice however, FYM showed higher potential than poultry manure during the three years rice cultivation seasons. Hence, it was indicated that a significant contribution to the development of sustainable agricultural technologies that prioritize soil health,environmental stewardship, and food security.

Fingerprinting of emerging contaminants in L'Albufera natural park (Valencia, Spain): Implications for wetland ecosystem health

Wetlands are crucial ecosystems that are increasingly threatened by anthropogenic activities. L'Albufera Natural Park, the second-largest coastal wetland in Spain, faces significant pressures from surrounding agricultural lands, industrial activities, human settlements, and associated infrastructures, including treated wastewater inputs. This study aimed at (i) establishing pathways of emerging pollutants entering the natural wetland using both target and non-target screening (NTS) for management purposes, (ii) distinguishing specific contamination hotspots through Geographic Information System (GIS) and (iii) performing basic ecological risk assessment to evaluate ecosystem health. Two sampling campaigns were conducted in the spring and summer of 2019, coinciding with the start and end of the rice cultivation season, the region's primary agricultural activity. Each campaign involved the collection of 51 samples. High-resolution mass spectrometry (HRMS) was employed, using a simultaneous NTS approach with optimized gradients for pesticides and moderately polar compounds, along with complementary NTS methods for polar compounds, to identify additional contaminants of emerging concern (CECs). Quantitative analysis revealed that fungicides comprised a substantial portion of detected CECs, constituting approximately 50% of the total quantified pesticides. Tebuconazole emerged as the predominant fungicide, with the highest mean concentration (>16.9 μg L−1), followed by azoxystrobin and tricyclazole. NTS tentatively identified 16 pesticides, 43 pharmaceuticals and personal care products (PPCPs), 24 industrial compounds, and 12 other CECs with high confidence levels. Spatial distribution analysis demonstrated significant contamination predominantly in the southwestern region of the park, gradually diminishing towards the north-eastern outlet. The composition of contaminants varied between water and sediment samples, with pharmaceuticals predominating in water and industrial compounds in sediments. Risk assessment, evaluated through risk quotient calculations based on parent compound concentrations, revealed a decreasing trend towards the outlet, suggesting wetland degradation capacity. However, significant risk levels persist throughout much of the Natural Park, highlighting the urgent need for mitigation measures to safeguard the integrity of this vital ecosystem.

Diverse biological communities promote SOM molecular diversity and compositional transformations during natural fallow stage in paddy fields

Monoculture cultivation patterns in agro-ecosystems only provide less varied soil organic matter (SOM) molecules of plant origin. Whether and how the natural fallow stage between cultivation seasons facilitates the restoration of SOM molecular diversity and mitigates the adverse impacts of constant cropping pattern is elusive. Here, we utilized FT-ICR-MS, UHPLC-MS/MS, and high-throughput sequencing to investigate the biological change processes in SOM molecular composition under cultivation and fallow status in a long-farmed paddy field. Our study showed that SOM molecular diversity increased by 45.70%–85.36% in fallow stage compared to rice cultivation season. SOM molecular diversity was positively correlated with bacterial diversity and root exudate molecular diversity, and negatively correlated with fungal diversity. Notably, root exudate molecular diversity accounted for 48.48% of the variation in SOM molecular diversity. The increased SOM molecular diversity in fallow stage was attributed more to the diverse plant-produced molecules than the microbe-consumed molecules. Plant species turnover resulted in the conversion of root exudate components to Organoheterocyclic compounds and Organic acids/derivatives from rice planting stage to fallow stage. Recruited microbes were dominated by Basidiomycita, Ascomycota, Acidobacteria, Chloroflexi and Proteobacteria, resulting in the transformation from carbohydrates, lipid-like SOM molecules to lipid-like and lignin-like SOM molecules. Both field and microcosm experiments confirmed that root exudates are the main source of SOM molecules, and are influenced by the soil microbial community. This study provides solid evidence that fallow status in agro-ecosystems provides explosion of biodiversity and counteracts the negative effects of long-term monoculture cultivation on SOM diversity.Graphical

Energy Utilization and Greenhouse Gas (GHG) Emissions of Tillage Operation in Wetland Rice Cultivation

In Malaysia, wetland rice is cultivated over two cropping seasons: the main season, from June to November, and the off-season, from January to June. The aim of this study was to investigate tillage operations in rice production in relation to actual field operations and under real field conditions for two rice cultivation seasons. The results showed that 80.7%, 17%, and 2.3% of the total time was spent on the actual operation, turning time, and reversing time, respectively. The results also showed that the mean effective field capacity, field efficiency, and fuel consumption were 1.2 ha/h, 80%, and 7.6 L/ha, respectively. The distribution of energy used in the first, second, and third tillage passes amounted to 37%, 33%, and 30% of the total energy, respectively. Fuel, machinery, and total GHG emissions were 62.4, 7.6, and 70 kg CO2eq/ha, respectively. Fuel represented the highest contributor of energy expenditure and GHG emissions. The distributions of GHG emissions in the first, second, and third tillage passes were 37%, 32%, and 31% of the total GHG emissions. The results reveal that carrying out minimum-tillage operations led to a reduction in environmental impacts.

A potential of iron slag-based soil amendment as a suppressor of greenhouse gas (CH4 and N2O) emissions in rice paddy

Iron slag-based silicate fertilizer (SF) has been utilized as a soil amendment in rice paddy fields for over 50 years. SF, which contains electron acceptors such as oxidized iron (Fe3+) compounds, is known to reduce methane (CH4) emissions, which have a global warming potential (GWP) of 23, higher than that of carbon dioxide (CO2). However, the dynamics of nitrous oxide (N2O), which has a GWP of 265, were questionable. Since the reduced Fe (Fe2+) can react as an electron donor, SF application might suppress N2O emissions by progressing N2O into nitrogen gas (N2) during the denitrification process. To verify the influence of SF application on two major greenhouse gas (GHG) dynamics during rice cultivation, three different kinds of SF were prepared by mixing iron rust (>99%, Fe2O3) as an electron acceptor with different ratios (0, 2.5, and 5%) and applied at the recommended level (1.5 Mg ha−1) for rice cultivation. SF application was effective in decreasing CH4 emissions in the earlier rice cropping season, and seasonal CH4 flux was more highly decreased with increasing the mixing ratio of iron rust from an average of 19% to 38%. Different from CH4 emissions, approximately 70% of seasonal N2O flux was released after drainage for rice harvesting. However, SF incorporation was very effective in decreasing N2O emissions by approximately 40% over the control. Reduced Fe2+ can be simultaneously oxidized into Fe3+ by releasing free electrons. The increased electron availability might develop more denitrification processes into N2 gas rather than NO and N2O and then decrease N2O emissions in the late rice cultivation season. We could find evidence of a more suppressed N2O flux by applying the electron acceptor-added SFs (SF2.5 and SF5.0) to a 49%–56% decrease over the control. The SF application was effective in increasing rice productivity, which showed a negative-quadratic response to the available silicate (SiO2) concentration in the soil at the harvesting stage. Grain yield was maximized at approximately 183 mg kg−1 of the available SiO2 concentration in the Korean rice paddy, with a 16% increase over no-SF application. Consequently, SF has an attractive potential as a soil amendment in rice paddy to decrease GHG emission impacts and increase rice productivity.

Temporal mercury dynamics throughout the rice cultivation season in the Ebro Delta (NE Spain): An integrative approach

During the last few decades, inputs of mercury (Hg) to the environment from anthropogenic sources have increased. The Ebro Delta is an important area of rice production in the Iberian Peninsula. Given the industrial activity and its legacy pollution along the Ebro river, residues containing Hg have been transported throughout the Ebro Delta ecosystems. Rice paddies are regarded as propitious environments for Hg methylation and its subsequent incorporation to plants and rice paddies' food webs. We have analyzed how Hg dynamics change throughout the rice cultivation season in different compartments from the paddies' ecosystems: soil, water, rice plants and fauna. Furthermore, we assessed the effect of different agricultural practices (ecological vs. conventional) associated to various flooding patterns (wet vs. mild alternating wet and dry) to the Hg levels in rice fields. Finally, we have estimated the proportion of methylmercury (MeHg) to total mercury in a subset of samples, as MeHg is the most bioaccumulable toxic form for humans and wildlife. Overall, we observed varying degrees of mercury concentration over the rice cultivation season in the different compartments. We found that different agricultural practices and flooding patterns did not influence the THg levels observed in water, soil or plants. However, Hg concentrations in fauna samples seemed to be affected by hydroperiod and we also observed evidence of Hg biomagnification along the rice fields’ aquatic food webs.

Optimizing Rice Yield and Nutrient Uptake: Investigating the Interaction Between Nitrogen and Potassium in Wet Season Rice Cultivation

Optimizing Rice Yield and Nutrient Uptake: Investigating the Interaction Between Nitrogen and Potassium in Wet Season Rice Cultivation

Assessment of greenhouse gas mitigation from rice cultivation using alternate wetting and drying and rice straw biochar in Thailand

The mitigation of greenhouse gas (GHG) emissions and water usage optimization in rice cultivation is challenging for many agricultural countries, including Thailand, who have set goals of reaching net zero emissions and coping with droughts caused by climate change. Alternate wetting and drying (AWD) and biochar application are possible practices for achieving cleaner rice production through reduction of GHG emissions and water consumption. However, these methods’ potential varies by site, especially in areas with limited control of water levels. This study assessed the effects of AWD at different drying levels (10, 15, and 20 cm below the soil surface) and rice straw biochar on GHG emissions, yield production, water use, soil characteristics, and economic aspects. This study was conducted over two rice cultivation seasons: a major season in 2022 and a second season in 2023 at a field in Kalasin Province, northeastern Thailand. Using AWD and biochar reduced annual GHG emissions by 48.2% and 8.01%, respectively. Deeper drying levels of AWD showed greater mitigation potential than shallow levels. The combination of AWD and biochar had additional potential for GHG mitigation, however, this impact did not show statistical change as compared to their separate potentials. The adoption of AWD and biochar could also maintain the amount of rice yield compared to traditional practice. All levels of AWD saved irrigation water consumption by an average of 16.8% per season; the highest potential was observed in AWD at 10 cm below the soil surface. Biochar improved soil health after two seasons by enhancing soil pH and organic carbon sequestration. The combination of AWD and biochar did not additionally augment the capacity in water saving of AWD or soil improvement of biochar. The AWD water regime also did not increase net profits, while biochar decreased net profits due to the required investment in biochar production. Using AWD is a feasible way to mitigate GHG emissions and save water without affecting rice productivity and net profits in northeastern Thailand.

Rice planting reduced N2O emissions from rice-growing seasons due to increased nosZ gene abundance under a rice-wheat rotation system

Paddy fields experience more frequent events because of redox-induced changes during their growth period, which further govern the processes that influence soil N2O emissions. However, studies on the effects of rice planting on soil N2O emissions and the relevant mechanisms are scarce. Thus, a field employing rice-wheat rotation (RW) in central China, including treatments with rice planting (RW-CC) and without rice planting (RW-NC), was selected to investigate the effects of rice planting on N2O emissions. Several key soil variables and functional genes (nirS, nirK, and nosZ) related to N2O-production and consumption were selected to determine the mechanisms underlying the effects of rice planting on N2O emissions. The results showed that seasonal N2O emissions from RW-NC treatment were 0.88 ± 0.08 and 1.69 ± 0.24 kg N ha−1 for the first and subsequent rice cultivation seasons, respectively, and were significantly higher than those from RW-CC treatment (0.51 ± 0.10 and 1.04 ± 0.18 kg N ha−1, respectively). This indicated the mitigation effect of rice planting on field N2O emissions. For both the RW-CC and RW-NC treatments, N2O fluxes were positively correlated with soil ammonium (NH4+), microbial biomass carbon (MBC), and nirK genes, and negatively correlated with the nosZ gene, indicating that the production- and consumption-related functional genes of soil available C, N, and N2O are the key factors controlling N2O emissions. Compared to RW-NC treatment, a higher abundance of the nosZ gene and lower (nirS+nirK)/nosZ ratios for RW-CC treatment may contribute to a greater reduction of N2O to N2, thus resulting in decreased N2O emissions. Structural equation model (SEM) analysis showed that soil moisture (flood depth), NH4+, MBC, and functional genes together accounted for more than 85 % of the explanatory effects on N2O emissions for both treatments. In general, our research indicates that promoting rice planting could reduce soil N2O emissions during the rice-growing season, thereby reducing the exposure of soil to N fertilization when adopting field agronomic practices; our results also suggest that crop rotation and intercropping should be encouraged.

Crop residue retention increases greenhouse gas emissions but reduces chemical fertilizer requirement in a vegetable-rice rotation

Retaining crop residues on site after harvesting can maintain soil fertility, reduce fertilizer requirements and restore soil organic carbon on intensively cultivated land. However, how crop residue retention and reduced chemical fertilizer application affect greenhouse gas emissions and crop yield in vegetable-rice rotations is poorly understood. We studied the effect of chemical fertilizer application alone (control, without straw retention), straw retention with 100 % nitrogen fertilizer application (STF) or with three levels of reduced chemical fertilizer application (SFR1, SFR2 and SFR3) in a vegetable-rice rotation in a mesocosm system. In the vegetable season, crop yield was maintained but the agronomic efficiency (AE) was higher in SFR1, SFR2 and SFR3 as compared to STF and the control. In the rice season under flooded condition, the methanogens were higher in SFR1, SFR2 and SFR3 compared to the control, but not different between STF and SFR1. The STF showed higher methane and nitrous oxide emissions, but carbon dioxide emissions and AE remained unaffected compared to the control in the vegetable-rice rotation. The SFR2 and SFR3 treatments maintained crop yields, increased AE, and decreased N2O emissions as compared with STF, but the CH4 emissions were 29.8 % lower in SFR2 than SFR3 in the vegetable-rice rotation. We concluded that straw retention with reduced chemical fertilizer application can maintain crop yield in a vegetable-rice rotation but has the potential to increase CH4 emissions in the rice cultivation season.

Different composites inhibit Cd accumulation in grains under the rice-oilseed rape rotation mode of karst area: A field study

Ensuring the safe production of food and oil crops in soils with elevated cadmium (Cd) content in karst regions is crucial. We tested a field experiment to examine the long-term remediation effects of compound microorganisms (CM), strong anion exchange adsorbent (SAX), processed oyster shell (POS), and composite humic acids (CHA) on Cd contamination in paddy fields under a rice-oilseed rape rotation system. In comparison to the control group (CK), the application of amendments significantly increased soil pH, cation exchange capacity (CEC), and soil organic matter (SOM) content while markedly decreasing the content of available Cd (ACd). During the rice cultivation season, Cd was predominantly concentrated in the roots. Relative to the control (CK), the Cd content in each organ was significantly reduced. The Cd content in brown rice decreased by 19.18–85.45%. The Cd content in brown rice following different treatments exhibited the order of CM > POS > CHA > SAX, which was lower than the Chinese Food Safety Standard (GB 2762–2017) (0.20 mg/kg). Intriguingly, during the oilseed rape cultivation season, we discovered that oilseed rape possesses potential phytoremediation capabilities, with Cd mainly accumulating in roots and stems. Notably, CHA treatment alone significantly decreased the Cd content in oilseed rape grains to 0.156 mg/kg. CHA treatment also maintained soil pH and SOM content, consistently reduced soil ACd content, and stabilized Cd content in RSF within the rice-oilseed rape rotation system. Importantly, CHA treatment not only enhances crop production but also has a low total cost (1255.230 US$/hm2). Our research demonstrated that CHA provides a consistent and stable remediation effect on Cd-contaminated rice fields within the crop rotation system, as evidenced by the analysis of Cd reduction efficiency, crop yield, soil environmental change, and total cost. These findings offer valuable guidance for sustainable soil utilization and safe production of grain and oil crops in the context of high Cd concentrations in karst mountainous regions.

Greenhouse Gases Emission from Rice Paddy under Different Tillage Intensity during Fallow Season

Reduced tillage is a useful practice to increase soil organic carbon (SOC) stock and decrease methane (CH4) emission in a rice paddy. However, the impacts of reduced tillage on the global warming potential (GWP) are generally analyzed for CH4 fluxes only during rice cultivation season. This study was conducted to investigate the effects of tillage on greenhouse gas (GHG) emission including both CH4 and nitrous oxide (N2O) and SOC stock changes were evaluated during the fallow season under two different tillage systems (conventional tillage and reduced tillage practice). The emission rate of GHG emissions was monitored using the closed chamber method. The SOC stock changes were estimated by the net ecosystem C budget (NECB), which is defined as the difference between total organic C input and output. Finally, the net global warming potential (net GWP), which was calculated as CO2 equivalents was compared between the different tillage system in rice paddy during fallow season. The net GWP of tillage and reduced tillage treatment were 4.09 and 4.96 Mg CO2 eq. ha-1, respectively during fallow season. However, the net GWP was not significantly different tillage systems. The decrease of SOC stock as CO2 emission was the most influential part on increasing the net GWP. Our study suggest that regardless of tillage conditions, it is necessary to establish a greenhouse gas reduction strategy focusing on increasing SOC accumulation during the fallow season. However, as this study was conducted for only single fallow season, long-term study is required to estimate the cumulative effects of tillage treatment on GHG emissions during fallow seasons in paddy.Net global warming potential (net GWP) under different tillage systems during fallow season in rice paddy (CT, conventional tillage; RT, reduced tillage).

Field Validation on Incorporation of Rice Husk Biochar and Paddy Straw Compost on Crop Attributes and Soil Properties in Rice Ecosystem

Aim: To study the effect of rice husk biochar and rice straw compost on Rabi season rice cultivation.
 Study Design: The randomized block design was used. The treatments of different doses of soil amendments like rice husk biochar, rice straw compost and recommended fertilizer doses are applied.
 Place and Duration of Study: The experimental trial was conducted during the Rabi season (January - April) of 2022 at Tamil Nadu Rice Research Institute, Aduthurai, Tamil Nadu, India.
 Methodology: The study consisted of 11 sets of RBD design treatments replicated thrice. The rice variety of ADT57 Short duration variety was used for this study. The observation has been recorded during the crop growing period at regular intervals.
 Results: The study results revealed that application of PSB @ 2kg/ha + RSC @ 5 t/ha + 75% RDF (T10) treatment showed the highest plant growth parameters like plant height (27.88, 74.22 and 108.89 cm), number of tillers m-2 (122, 620 and 642), leaf area index (2.62, 6.53 and 8.47), SPAD reading (47.22, 43.64 and 40.46), root length (18.86, 37.45 and 56.31 cm) and root volume (17.85, 26.01 and 37.77 ml) at 30, 60 and 90 DAT respectively and yield parameters like grain yield (5133 kg/ha), straw yield (7090 kg/ha), panicle length (25.28cm) and number of productive tillers m-2 (571.6) and was significantly on par with application of PSB @ 2kg/ha + Rice Husk Biochar (RHB) @ 5 t/ha + 75% RDF (T6) and superior over the other all treatments. Plant growth parameters of application of PSB @ 2kg/ha + Rice Husk Biochar (RHB) @ 5 t/ha + 75% RDF (T6) recorded the plant height (27.41, 73.76 and 108.29 cm), number of tillers m-2 (118, 613 and 630), leaf area index (2.54, 6.42 and 8.38), SPAD reading (46.26, 43.10 and 40.20), root length (18.35, 37.05 and 55.40 cm) and root volume (17.42, 25.44 and 37.33 ml) at 30, 60 and 90 DAT respectively and yield parameters like grain yield (4953 kg/ha), straw yield (7077 kg/ha), panicle length (25.07 cm) and number of productive tillers m-2 (555). So, the application of PSB @ 2 kg/ha + RSC @ 5 t/ha + 75% RDF has recorded the best results than all other treatments. With respect to soil properties, application of Rice husk Biochar (RHB) @ 5t/ha + 75% RDF (T4) has reduced the soil bulk density (from 1.52 to 1.47) and application of rice straw compost @ 5t/ha has increased the soil pH (from 6.58 to 7.14) as compared to other treatments whereas the nutrient status (nitrogen (from 212 to 266 kg ha-1); phosphorus (from 45.41 to 61.59 kg ha-1) and potassium (from 192 to 218.4 kg ha-1) has increased by application of PSB @ 2kg/ha + RSC @ 5t/ha + 100% RDF (T11) than other treatments.

Prior nitrogen fertilization stimulated N2O emission from rice cultivation season under a rapeseed-rice production system

Prior nitrogen fertilization stimulated N2O emission from rice cultivation season under a rapeseed-rice production system

Water salinity variability mapping for flooded paddy plots at Kuala Kedah, Malaysia

Salinity is an essential parameter in rice cultivation activity. It has a significant impact on paddy growth and also the yield of paddy. However, the level of salinity concentration in paddy plots depends on the surrounding conditions. The distance of the paddy area from the coastline, the temperature and intensity of rainfall should be considered in studies involving water quality. Additionally, the tide of events is also included in this study because of the position of the study area near the coastline. Therefore, this study was conducted to assess the level of salinity in two different rice cultivation seasons and describe the level of salinity concentration using a salinity variability map using the Inverse Distance Weighted (IDW) interpolation method. The data collection activities involved water sampling at 44 water inlets for each paddy plot in 30 hectares of the study area by referring to the Day After Sowing (DAS) as the paddy’s growth stage. These water samples were collected on 10 DAS, 40 DAS, and 60 DAS and subsequently tested using a portable conductivity meter namely EC500 Exstick II pH/Conductivity/Temperature Meter. Parallelly, georeference data which is latitude, longitude and elevation were gathered using Garmin GPSMAP 64s. Then, these data were analyzed using the IDW interpolation method in ArcGIS software and comes with salinity variability maps. The produced maps give an overview of the salinity concentration distribution by color scale range. Based on these salinity variability maps, the highest salinity concentration was recorded on 10 DAS and 60 DAS during Season 1 2019 and Season 2 2019, respectively for both tidal events. This result shows that the salinity concentration trend for both seasons is different due to the amount of rainfall received and the position of the paddy plot compared to the mean temperature factor. Keywords: GIS, interpolation, oryza sativa , rice, saline water, seawater encroachment

Effect of different rice farming practices on the bioavailability of mercury: A mesocosm experiment with common goldfish (Carassius auratus)

Wetlands such as rice paddies are important ecosystems that provide habitat for a numerous range of species but are considered as a major source of mercury in the most toxic form of methylmercury. An in situ mesocosm experiment was conducted during the rice cultivation season of 2018 in rice paddies from the Ebro Delta (NE Spain) to investigate the bioaccumulation of mercury in fish. Common goldfish (Carassius auratus) were exposed to three types of rice-fields subject to different agricultural management (conventional or ecological agriculture) and different hydric practices (wet, dry) and were sampled monthly. Total mercury concentration in fish increased over time for almost all the fields under study, but the mercury increase was particularly higher for fish exposed to ecological fields. We conducted δ15N and δ13C measurements to follow up fish diet changes within or among fields. The results have shown there were no variations in the diet of the fish over time within fields, although differences among management practices were observed, which could explain to some extent the THg variation in fish exposed to each of the agricultural practices. Results indicate that wetting and drying rice fields might be a greater source of mercury for fish and a potential hotspot for MeHg production enhanced by physicochemical parameters. Thus, mercury bioaccumulation in fish inhabiting rice paddies depend on several factors what, in turn, could lead to biomagnification across the food webs.

Salinity-affected threshold yield loss: A signal of adaptation tipping points for salinity management of dry season rice cultivation in the coastal areas of Bangladesh

The potential existence of threshold yield loss in dry season rice growing systems under coastal saline environment remains unexplored, a scenario that could have policy relevance in government planning of rice intensification in the coastal areas of Bangladesh. This study applied the adaptation tipping points (ATPs) approach to investigate threshold yield loss from multiple perspectives of farmers affected by salinity. Data were generated from 280 randomly-selected farmers (rice farmers, n = 109; shrimp farmers, n = 107; salt farmers, n = 64) from two coastal sub-districts using a semi-structured survey. Key informant interviews and focus group discussions were conducted to complement the survey results. Our study revealed that despite government actions to promote dry season rice cultivation, farmers have been growing less rice in this season, with salinity-affected yield loss being the prime reason. Most of the rice farmers have considered that they would discontinue rice cultivation in this season due to yield loss, while shrimp and salt farmers have already reduced rice cultivation for the same reason and shifted to shrimp and salt farming as they perceived these enterprises as highly profitable and require less labour than rice farming. Rice farmers would tolerate a greater rice yield loss (23%) under saline conditions compared with the shrimp (16%) and salt farmers (14%). The yield loss thresholds indicate the need for government actions to support and encourage integrated land management for rice, shrimp and salt farming, rather than research and extension efforts for dry season rice expansion alone. These actions could strengthen sustainable livelihood options to ensure food security, and contribute to the achievement of sustainable development goals, for instance no poverty (SDG-1), zero hunger (SDG-2), and good health and well-being (SDG-3).

Increases in Genetic Diversity of Weedy Rice Associated with Ambient Temperatures and Limited Gene Flow.

Simple SummaryIncreased genetic diversity in plants is probably associated with greater ambient temperatures. To test this hypothesis, we studied genetic diversity and differentiation of weedy rice populations occurring in the early- and late-season rice cultivation fields in Leizhou of southern China. Data collected from 10-year climatic records showed a higher average temperature in the late rice-cultivation seasons than in the early rice-cultivation seasons. Results obtained based on 27 SSR (simple sequence repeat) loci indicated greater genetic diversity in the late-season weedy rice populations, in addition to the considerable genetic differentiation between the early- and late-season weedy rice populations. We therefore conclude that a higher ambient temperature might be an important factor to promote the formation of genetic diversity in the late-season weedy rice populations.Hypotheses regarding the association of increased species or genetic diversity with gradually warmer regions as a global pattern have been proposed, but no direct and solid experimental data are available to approve the association between plant genetic diversity and ambient temperatures. To test the diversity-temperature hypothesis, we studied genetic diversity and genetic differentiation of weedy rice (Oryza sativa f. spontanea) populations occurring naturally in early- and late-season rice fields that share nearly the same ecological conditions but with slightly different temperatures. Data collected from 10-year historical climatic records indicated a ~2 °C higher average air temperature in the late rice-cultivation seasons than in the early seasons. Results based on molecular fingerprints of 27 SSR (simple sequence repeat) loci showed a higher level of genetic diversity in the late-season weedy rice populations than in the early-season populations. In addition, a positive correlation was detected between the increased proportion of genetic diversity (ΔHe) and genetic differentiation among the weedy rice populations, suggesting limited gene flow. Therefore, we conclude from this study that increased genetic diversity in the late-season weedy rice populations is probably caused by the higher ambient temperatures. This finding provides evidence for the possible association between genetic diversity and ambient temperatures.

Effects of crop rotation on enhanced occurrence of arbuscular mycorrhizal fungi and soil carbon stocks of lowland paddy fields in seasonaly dry tropics

The impacts of crop rotation systems on the arbuscular mycorrhizal fungal (AMF) spore density, mycorrhizal colonization of rice roots, soil C fractions and C stocks in seasonally dry climatic zone of Sri Lanka were examined in Rice–Soybean (RS) and Rice–Onion (RO) crop rotation systems during the subsequent rice cultivation season and, compared these with a rice monoculture, i.e. Rice–Rice (RR). The study also examined the correlations between AMF occurrence and soil carbon stocks. Results revealed that RS crop rotation system significantly enhances the occurrence of AMF spores in soil with a higher fraction of large sized spores, the total organic C (TOC), microbial biomass C (MBC), water soluble C (WSC), labile C and a high AMF colonization in rice roots in the subsequent rice cultivation season. The diversity of AMF morphospecies were also the highest in RS. Reduction in AMF density in the soil in RR crop rotation system may be due to prolonged anaerobic conditions prevailed. The growth of onion has drastically reduced the AMF colonization in rice and soil C contents. Soil carbon stocks showed positive correlations with % root colonization and AMF spore number in soil. Thus, the study confirmed that C stocks in paddy soils can be improved by intercropping with AMF supporting plants like soya bean. This is the first report that shows positive correlations of AMF sporulation and % root colonization in lowland rice with soil carbon stocks.