Different Growth Stages Of Rice Research Articles

Vertical and temporal variations in activity, abundance, and composition of nitrite-driven anaerobic methanotrophs in a paddy field

Paddy soil is an important source of methane (CH4) emissions, and the nitrite-driven anaerobic oxidation of methane (AOM) mediated by Candidatus Methylomirabilis bacteria is a crucial process for CH4 mitigation. However, the vertical and temporal fluctuations in nitrite-driven AOM activity, as well as the abundance and composition of Methylomirabilis bacteria in paddy soil, remain poorly understood. We investigated the potential rate of nitrite-driven AOM and the composition of Methylomirabilis bacteria at varying depths (0–40 cm, at 10 cm intervals) within a paddy soil during different growth stages of rice, including tillering, jointing, flowering, and milky. The potential rate of nitrite-driven AOM ranged from 0.24 to 20.6 nmol CO2 g−1 (dry soil) d−1, and the abundance of Methylomirabilis bacterial 16S rRNA genes varied from 5.8 × 106 to 4.4 × 107 copies g−1 dry soil. The 10–20 cm soil depth showed higher potential activity and bacterial abundance compared to other depths, and the tillering and jointing stages exhibited greater activity and abundance. The composition of Methylomirabilis bacteria showed significant variation across different soil depths but remained stable throughout the growth stages of rice. Soil organic carbon content was positively correlated with potential nitrite-driven AOM rate, and nitrite content was negatively correlated with the abundance of Methylomirabilis bacteria. Soil organic carbon and ammonium content had a significant impact on the composition of Methylomirabilis bacteria. The results underscore the substantial influence of soil depth and the growth stage of rice on nitrite-driven AOM in paddy ecosystems.

Effects of Equal Amounts Silicon Fertilizer Application on Soil Bioavailability of Cadmium and Cadmium Uptake by Rice

Cadmium (Cd) contamination of paddy fields is a global concern, as it can cause the accumulation of Cd in food. To explore the effects of equal application of silicon fertilizers on the bioavailability of cadmium and soil Cd uptake at different growth stages of rice, a field experiment was conducted with five silicon fertilizers under the same silicon dose (225 kg·hm-2). The results revealed that the Cd contents in roots, stems, and leaves increased with the extension of the rice growth stage. The application of silicon fertilizers reduced the Cd contents in roots, stems, and leaves in brown rice by 14.9%, 28.2%, and 12.2%, respectively. Compared with that in the control, the Cd content of brown rice in the SiCaMgFe and SiW treatments was decreased by 21.1% (P<0.05) and 21.2% (P<0.05), respectively. Similarly, Cd content in iron plaque (DCB-Cd) increased with the extension of the rice growth period, which accounted for 15.8%-42.8% of the total Cd content in roots, and the DCB-Cd content was different in each stage of rice. The content of exchangeable Cd (Exc-Cd) in soil at the mature stage of rice decreased by 36.4%, and the other fractions increased by 12.5%-48.2%. The results showed significant negative correlations between the Cd contents and Si in roots, DCB-Cd and soil available Cd and available Si, Exc-Cd and Car-Cd, and soil available Cd and pH value. Cd content in roots was positively correlated with DCB-Cd. With the equal dose of silicon fertilizer, the treatments of SiCaMgFe and SiW could effectively reduce the Cd content in rice. The application of silicon fertilizer promoted the transfer of Exc-Cd to Carb-Cd by increasing the soil pH value and the soil available Si content, meanwhile reducing the soil available Cd, Exc-Cd contents, the adsorption of Cd by the iron film on the root surface, and the adsorption capacity of iron plaque and root, thereby reducing the absorption of Cd by rice.

Design and experimental assessment of a field-spraying system with nozzles employing reciprocating up-and-down movements.

Proper dense planting pattern can improve rice yield. For an ordinary boom sprayer, it is still difficult for the droplets to penetrate the dense rice canopy even if an auxiliary airflow is used, especially in the middle and late growth stages. The deposits of droplets at the bottom of the rice plants are typically small. In this study, a spraying system was designed with nozzles creating reciprocating movements into the middle and bottom of the rice canopy. An air pump provided power to push the nozzles up and down. A time relay and a solenoid valve were used to control the cycle and stroke of the reciprocating movement. At different growth stages of rice, comparative tests were conducted between the air-assisted spraying pattern (without reciprocating movement of nozzles) and the reciprocating movement spraying pattern (without auxiliary airflow). The results showed that for the reciprocating movement spraying pattern, the droplet number densities in the middle and bottom of the rice in the late growth stages increased from 78 to 124/cm2 and from 19 to 121/cm2 , respectively, and the coverage rates increased from 13.34% to 24.26% and from 3.61% to 21.21%, respectively. The droplet depositions increased from 0.603 to 1.139 mg cm-2 and from 0.095 to 1.001 mg cm-2 , respectively. This spraying pattern can increase droplet deposits at the middle and bottom of the crop and improve uniformity. © 2023 Society of Chemical Industry.

Ecophysiological Responses of Rice (Oryza sativa L.) to Drought and High Temperature

Global rice crop production is being threatened by a frequent rise in high temperatures and drought. Drought and heat stresses adversely affect the morphological, physiological, and biochemical characteristics of rice, resulting in reduced crop productivity. Heat and drought stresses entail physiological changes in rice plants, such as stomata closure, reduced photosynthesis, loss of turgor adjustment, and reduction in crop productivity. These stresses also cause metabolic changes by increasing the activities of antioxidative enzymes, phytohormones, abscisic acid, reactive oxygen species, and reactive stress metabolites. Among the different growth stages of rice, the reproductive stage is the most sensitive stage to high temperature and drought, resulting in low seed setting and grain yield. Genetic improvement and development of drought and heat-stress-tolerant rice varieties increase seed setting and enhance yield production even under stress conditions. Because of the multigenic nature of traits, the development of drought and high-temperature-tolerant varieties through genetic improvement is the best approach. Here, we summarized the effects of heat and drought stresses on the physiological traits of rice. We focused on different approaches to managing high-temperature and drought stresses, such as an adjustment in cultural practices, genetic improvement through molecular breeding, and the development of transgenics and chemical spray from an agricultural practice perspective.

Comparison of Soil Properties in Different Fertilizer Input Systems in Lowland Rice at the Third Year in Transition

Synthetic inorganic fertilizers (SIF) have the potential to impose detrimental environmental effects and are frequently utilized in Sri Lankan conventional rice farming. To maximize rice yield while maintaining soil health, soil nutrient management is vital. In this study, the soil properties of rice fields maintained using conventional (as recommended by the Department of Agriculture (DOA), 2013), reduced (50% DOA + 50% organic), and organic Input Management Systems (IMSs) were studied. The Rajarata University of Sri Lanka's Faculty of Agriculture established this experiment during the Maha season of 2020–2021 utilizing a Randomized Complete Block Design. At the initial, 50% flowering, and harvesting stages, soil samples were obtained from three distinct IMSs with three replicates at surface (0 - 15 cm) and subsurface (15 - 30 cm) soil depths. The data were analyzed using linear mixed effect models followed by Tukey's mean comparison. Three IMSs and three different stages of rice growth exhibited substantially varying soil pH, EC, available P, and exchangeable K values in this third transition year (p&lt;0.05). Despite being highly varying across IMSs, soil CEC was not significantly different (p&gt;0.05) among the stages of rice growth. Three IMSs' soil available N did not change significantly (p&gt;0.05) yet differed across growth stages (p&lt;0.05). In comparison to those obtained with conventional IMS, rice grain yield with organic IMS produced levels that were noticeably similar. The highest grain yield was produced with reduced IMS (p&lt;0.05). This illustrates the possibility of boosting yields and sustaining soil fertility by substituting organic manure for 50% of SIF.

Validating algorithms designed for fertilization control in rice farming system

Rice yields in Rwanda seldom reach values expected for irrigated production, in part due to poor fertilization management. To adapt well-known best practices to local conditions, two fuzzy fertilization algorithms were designed for conditions of rice production in Rwanda. Fuzzy algorithms have a linguistic rule base of 183 IF THEN statements linking measurable field conditions to crop yield. Interviews with government agricultural experts and published knowledge of site conditions were used to create the rule base which incorporates the known nutrient requirements of the different growth stages of rice. Fuzzy algorithms are intended for use in an Internet of Things (IoT) system. To validate the algorithms, historical weather and field data are used to drive yield simulations for different plots during the first growing season of 2020 at sites in northeast Rwanda. Predicted yields are compared to measured yields for scenarios with different irrigation levels and fertilization amounts and with and without full Internet connectivity. Insights are provided on the potential of these fuzzy methods to improve rice nutrient management for increased yields in low-income countries are discussed.

Rice yield penalty and quality deterioration is associated with failure of nitrogen uptake from regreening to panicle initiation stage under salinity.

In recent years, the development and utilization of saline land for rice cultivation have effectively expanded grain productivity. Rice is a salt-sensitive crop, and the increasing salinity problem threatens rice yield and quality. Therefore, we conducted open field experiments to study the effect of salinity on different growth stages of rice. Irrigating saline treatment was conducted at three different growth stages: irrigating saline from the regreening stage to the panicle initiation stage (S1), irrigating saline from the panicle initiation stage to the flowering stage (S2), and irrigating saline from the flowering stage to the maturity stage (S3). Each treatment period lasted for about 30 days. At the same time, irrigating saline water from the regreening stage to the maturity stage (S4) treatment was added in 2022 to explore the performance of salt stress during the whole growth period of rice. Based on the treatment of these different saline irrigation growth periods, three saline concentrations were incorporated, including salinity 0‰ (T1), 3‰ (T2), and 6‰ (T3) concentrations. No irrigating saline during the whole growth period was also used as a control (CK). The results indicated that rice grain yield and quality were most sensitive to saline treatment during S1 among the three stress periods. At the S1 stage, salinity mainly reduced the nitrogen uptake, resulting in stunted plant growth, reducing tillering, yield, and yield components, and deteriorating the rice quality. Compared to the control, IEN (grain yield over the total amount of N uptake in plants at maturity) was more sensitive at the S1 stage than S2 and S3 stages under salinity. Furthermore, the findings of our study suggest that under salinity, rice growth is not only directly affected by the higher sodium (Na+) content in plants, but the higher concentration of Na+ reduced the ability of plants to uptake nitrogen. Thus, more attention should be paid to the field management of the S1 stage, the most sensitive stage during rice cultivation in salinized areas. It is necessary to avoid salt damage to rice during this period and ensure irrigation with precious freshwater resources.

Responses of Rice and Related Cadmium Transporter Genes to the Passivating Microbial Agent MBLHAP.

Alkali-producing microorganisms and hydroxyapatite (HAP), a chemical passivation agent, have a certain remediation effect on cadmium (Cd) -contaminated soil. They can decrease the available Cd content in the soil to a certain extent and reduce the overall Cd content of rice planted in the soil. The Cd-contaminated soil was treated with the passivating bacterial agent that had been developed. Changes in the Cd concentration of rice leaves and soil were observed. Real-time PCR was used to analyse the expression levels of Cd transport protein genes in rice. Then, we determined the activities of super-oxide dismutase (SOD), catalase (CAT) and peroxidase (POD) at different stages of rice growth. The results showed that after HAP, alkali-producing microorganisms and passivating microbial agents were applied to the Cd treated soil. The total Cd content in rice leaves was reduced by 66.80%, 80.32% and 81.35%. The expression differences of genes related to Cd transporter proteins were measured, and the results showed that the changes in gene regulation were consistent with the changes in Cd content of rice leaves. The changes in SOD activity, CAT activity and POD activity further indicated that the three enzymes could alleviate the adverse effects of Cd stress by regulating the related enzyme activities in rice. In conclusion, alkali-producing microorganisms, HAP and passivating bacterial agents can effectively reduce the toxicity of Cd to rice, and reduce the absorption and accumulation of Cd in rice leaves.

The Impacts of Phosphorus-Containing Compounds on Soil Microorganisms of Rice Rhizosphere Contaminated by Lead

The cost effectiveness of using exogenous phosphorus to remediate heavy metals in soil, which would alter the structure of the soil microbial community, had been widely acknowledged. In the present study, phospholipid fatty acid (PLFA) technology was taken as the breakthrough point, and rhizosphere soil microorganisms in different growth stages (jointing stage and maturity stage) of Minghui 86 (MH) and Yangdao No.6 (YD) rice were taken as the research objects. As revealed by the results, the rhizosphere soil microorganisms of MH and YD had distinct sensitivities to exogenous phosphorus and had a certain inhibitory effect on MH and YD enhancement. The sensitivity of rice root soil microorganisms to exogenous phosphorus also varied in different growth stages of rice. Bacteria were the dominant microorganism in the soil microbial community of rice roots, and the gain of exogenous phosphorus had a certain impact on the structure of the two soil microbial communities. Through analysis of the microbial community characteristics of MH rice and YD soil after adding exogenous phosphorus, further understanding was attained with respect to the effect of exogenous phosphorus on the microbial community characteristics of rice rhizosphere soil and the impact thereof on ecological functions.

Effects of chilling at different growth stages on rice photosynthesis, plant growth, and yield

Chilling is the main limiting factor for rice production in high-altitude and high-latitude regions. Many studies have reported the impacts of chilling on leaf photosynthesis and biomass accumulation, but few of them explored the response of photosynthesis to chilling at different growth stages of rice and whether the decrease of photosynthesis at each stage is caused by stomatal or non-stomatal limiting factor. In order to achieve high grain yield for rice, it is critical to understand how chilling affects leaf photosynthesis and plant growth. In this study, we conducted a two-year field experiment (in 2018 and 2019) to investigate the effects of chilling at booting, flowering, and grain filling stages on leaf photosynthesis, plant growth, and grain yield for a japonica rice cultivar (Songjing6). At each target growth stage, the treatment included four chilling temperatures (12, 15, 18, and 21 ℃, respectively) and four chilling durations (2, 4, 6, and 8 days, respectively). The results showed that rice photosynthesis gradually decreased as the chilling temperature was decreasing and the chilling duration was increasing. The net photosynthetic rate decreased the most at the booting stage, followed by the flowering stage, and the grain filling stage. Compared with the chilling treatment at 2 days, the chilling treatment at 12, 15, and 18 ℃ for 4, 6, and 8 days reduced net photosynthetic rate by 15.1–36.1 %, 18.7–27.2 %, and 15.2–17.2 % at the booting, flowering, and grain filling stages, respectively. The chilling-induced decrease in net photosynthetic rate was mainly attributed to stomatal limiting factor at the booting and flowering stages but non-stomatal limiting factor at the grain filling stage. During the chilling treatment, the available light for rice plants was reduced and the rice plants were impaired in their ability to use weak light. The decrease in photosynthesis lead to reduced leaf source capacity and crop growth rate, hence the reduced aboveground biomass and increased source and sink increment ratio, and ultimately decreased the grain yield for rice. Our results indicate that maintaining efficient photosynthetic functioning at the booting and flowering stages is the key to combat chilling stress for rice. • Chilling decreased the net photosynthetic rate of rice most at the booting stage, followed by the flowering stage and the grain filling stage. • Chilling-induced decrease in the net photosynthetic rate was mainly attributed to stomatal limiting factor at the booting and flowering stages, but non-stomatal limiting factor at the grain filling stage. • The simulation of light response curve showed chilling at the booting and flowering stages decreased photosynthetic capacity and photosynthetic effective time，while chilling mainly affects the ability of using strong light at the grain filling stage.

Vertical distribution and transformation of phosphorus and iron in paddy soils during the whole growth stage of rice

Paddy fields have alternating wet and dry hydrological cycles at different growth stages of rice, driving changes in soil environment and phosphorus (P) transformation and transport. In-situ measurements of dissolved oxygen (DO), iron (Fe), and P concentrations were conducted to determine the vertical distribution of these concentrations together with the hydrological and meteorological data during the whole growth stage. The results demonstrate that soil vertical DO concentrations at different growth stages were greatly influenced by the water level and temperature of the paddy field at the soil-water interface. A strong negative correlation between soil DO and DGT-labile Fe has been observed, whereas a strong positive correlation has been observed between soil Fe concentration and vertical P. In the paddy field, soil DO concentrations were lower during tillering, booting, and heading to flowering than during the other stages. Thus, soluble P fluxes from soil water interfaces (SWIs) to overlying waters were most significant during these three stages. Furthermore, soils in these three stages are capable of sustained release of P and are highly able to buffer P. Consequently, water management in paddy fields should take into account the hydrological environment during these three stages in order to minimize soil P release. The results of our study provide a valuable reference point for controlling soil P and Fe during rice growth.

Identification of microRNAs That Provide a Low Light Stress Tolerance-Mediated Signaling Pathway during Vegetative Growth in Rice.

Low light intensity affects several physiological parameters during the different growth stages in rice. Plants have various regulatory mechanisms to cope with stresses. One of them is the differential and temporal expression of genes, which is governed by post-transcriptional gene expression regulation through endogenous miRNAs. To decipher low light stress-responsive miRNAs in rice, miRNA expression profiling was carried out using next-generation sequencing of low-light-tolerant (Swarnaprabha) and -sensitive (IR8) rice genotypes through Illumina sequencing. Swarnaprabha and IR8 were subjected to 25% low light treatment for one day, three days, and five days at the active tillering stage. More than 43 million raw reads and 9 million clean reads were identified in Swarnaprabha, while more than 41 million raw reads and 8.5 million clean reads were identified in IR8 after NGS. Importantly, 513 new miRNAs in rice were identified, whose targets were mostly regulated by the genes involved in photosynthesis and metabolic pathways. Additionally, 114 known miRNAs were also identified. Five novel (osa-novmiR1, osa-novmiR2, osa-novmiR3, osa-novmiR4, and osa-novmiR5) and three known (osa-miR166c-3p, osa-miR2102-3p, and osa-miR530-3p) miRNAs were selected for their expression validation through miRNA-specific qRT-PCR. The expression analyses of most of the predicted targets of corresponding miRNAs show negative regulation. Hence, miRNAs modulated the expression of genes providing tolerance/susceptibility to low light stress. This information might be useful in the improvement of crop productivity under low light stress.

Effect of Light-Emitting Diodes on Different Growth Stages of Rice

Effect of red and blue light on seed germination and seedling growth were studied in rice (Oryza sativa L.). Rice seeds were germinated in dark (control) and two types of light emitting-diodes (LED): red and green in the laboratory. The photoperiod of 6 h light and 18 h dark for LEDs treatment and 24h dark treatments with 24/18 ± 2 °C day/night temperature and 78± 2 % relative humidity were maintained in the growth room. Seed germination percentage under red light increased significantly when compared with the control; however, in blue light, germination percent decreased with little difference. First leaf length, first leaf blade length, root length, seedling fresh and dry weight increased under red and blue lights in most of the varieties. Highest germination (98%), longest root (8.18 cm) and high seedling fresh weight (0.527 g) and seedling dry weight (0.061g) in BRRIdhan71 and longest leaf in BRRIdhan75, were recorded under red light. Highest germination (96%), seedling fresh weight (0.414g) and seedling dry weight (0.047g) in BRRIdhan71, longest first leaf (6.50 cm) in BRRIdhan75 and longest root (9.37 cm) in BRRIdhan87 were recorded under blue light. First leaf blade showed only positive correlation with root length (r = 0.489), whereas seedling fresh weight showed complete correlation with seedling dry weight (r =1). Response index was positive in root length, seedling fresh and dry weight under red light. First leaf blade length, seedling fresh and dry weight had the positive response index under blue light. Within the visible spectrum, varying wave lengths of red and blue light alone altered the growth and morphology of rice seedlings, and variable reactions to illumination depended on the rice varieties, necessitating further research.&#x0D; Environ. Sci. &amp; Natural Resources, 13(1&amp;2): 56-62, 2020

Dynamic Mapping of Paddy Rice Using Multi-Temporal Landsat Data Based on a Deep Semantic Segmentation Model

Timely, accurate, and repeatable crop mapping is vital for food security. Rice is one of the important food crops. Efficient and timely rice mapping would provide critical support for rice yield and production prediction as well as food security. The development of remote sensing (RS) satellite monitoring technology provides an opportunity for agricultural modernization applications and has become an important method to extract rice. This paper evaluated how a semantic segmentation model U-net that used time series Landsat images and Cropland Data Layer (CDL) performed when applied to extractions of paddy rice in Arkansas. Classifiers were trained based on time series images from 2017–2019, then were transferred to corresponding images in 2020 to obtain resultant maps. The extraction outputs were compared to those produced by Random Forest (RF). The results showed that U-net outperformed RF in most scenarios. The best scenario was when the time resolution of the data composite was fourteen day. The band combination including red band, near-infrared band, and Swir-1 band showed notably better performance than the six widely used bands for extracting rice. This study found a relatively high overall accuracy of 0.92 for extracting rice with training samples including five years from 2015 to 2019. Finally, we generated dynamic maps of rice in 2020. Rice could be identified in the heading stage (two months before maturing) with an overall accuracy of 0.86 on July 23. Accuracy gradually increased with the date of the mapping date. On September 17, overall accuracy was 0.92. There was a significant linear relationship (slope = 0.9, r2 = 0.75) between the mapped areas on July 23 and those from the statistical reports. Dynamic mapping is not only essential to assist farms and governments for growth monitoring and production assessment in the growing season, but also to support mitigation and disaster response strategies in the different growth stages of rice.

Weed communities in the irrigated rice paddies of northern Iran

Dedicated insights into the diversity, spatial and temporal distribution of rice weed communities, as well as underlying ecological factors, are critical for developing effective ecological weed management strategies in these agroecosystems, leading to the preservation of biodiversity and ecosystem services in a sustainable agriculture framework. To fulfill this aim, 108 vegetation relevés were conducted at 23 sites of rice paddies throughout 9 counties in the north of Iran at various altitudes, during three different phenological stages of rice. Data from vegetation relevés was analyzed using TWINSPAN, resulting in the identification of four main plant community types related to the different stages of rice growth: Echinochloa crus-galli–Paspalum distichum, Spirodela polyrrhiza–Lemna minor, Monochoria vaginalis s.l.–Marsilea quadrifolia, and Cyperus difformis–Ammannia baccifera. Complementary direct (canonical correspondence analysis) and indirect gradient analyses (detrended correspondence analysis) confirmed these communities’ separation and indicated that the most significant environmental factors affecting plant community distribution were soil water content and soil pH. Moreover, out of 72 segetal species of investigated rice paddies, 12 species were alien to Iran, indicating that this agroecosystem provides an important source for the introduction, distribution, and possible spread of alien species into other adjacent ecosystems. Our findings contribute to the knowledge of detecting patterns of weed composition and distribution in rice paddy ecosystems, as well as their interpretation in relation to environmental gradients. They can support the establishment of ecological weed management practices in northern Iran's paddy fields.

Cadmium-tolerant facultative endophytic Rhizobium larrymoorei S28 reduces cadmium availability and accumulation in rice in cadmium-polluted soil

In this study, a metal-tolerant facultative endophytic strain S28 isolated from rice seeds was evaluated for the impacts on Cd concentration in medium, rice biomass, and Cd concentration and accumulation in rice in Cd-polluted soil. Inoculation with strain S28 decreased the Cd concentration and increased the pH and putrescine concentrations in solution. Strain S28 increased rice dry weight by 18%–49% at different growth stages of rice compared to the controls. Strain S28 reduced the MgCl 2 -extractable (available) Cd concentration by 11%–25% and increased the carbonate- and organic matter-bound (unavailable) Cd contents by 21%–133% at rice maturation stage in the Cd-polluted soil, respectively, compared to the controls. At the rice maturity stage, strain S28 also increased the relative abundance of Geobacter species related to Cd availability by 28% compared with the control. Inoculation with strain S28 reduced the Cd contents in roots, above-ground parts, and grains of rice plants by 18%–23%, 32%–37%, and 54%, respectively, compared to the controls. Furthermore, the cell counts of strain S28 in the rhizosphere soil and root tissue were 2.5 × 10 5 and 3.1 × 10 4 CFU g −1 , respectively. These findings indicated that the facultative endophytic S28 strain colonized the rice rhizosphere and interior, decreased Cd availability, and increased the Geobacter species abundance, resulting in decreased Cd uptake in rice different tissues. Our results may supply a new understanding on the mechanisms involved in facultative endophytic bacteria-mediated bioremediation and decreased rice Cd accumulation in Cd-contaminated soils. • Arginine decarboxylase-producing endophytic strain S28 was obtained from rice seeds. • S28 immobilized Cd and increased putrescine production in Cd-added solution. • S28 increased the biomass and reduced rice tissue Cd uptake in Cd-polluted soil. • S28 reduced Cd availability by increasing carbonate- and organic matter-bound Cd. • S28 reduced Cd availability by increasing the Geobacter species relative abundance.

Blue, green, and grey water footprints assessment for paddy irrigation-drainage system

Water footprint (WF) quantifies the impact of paddy field evapotranspiration (ET) and non-point source pollution on water resources and is an evaluation index for water sustainability. However, it is difficult to measure accurately using the existing method, which is based on parameter assumption without considering the field water conditions. In this study, a generic and physically based method for blue, green, and grey water accounting in paddy rice cultivation is introduced. We conducted field experiments using the common flood irrigation (CFI) and water-saving irrigation (SWI) modes in Nanjing, East China. By tracing the sources of ET and the migration process of multiple pollutants (TN, TP, NH4+-N, and NO3−-N), the characteristics of blue-green water consumption and the actual amount of water required to dilute pollutants at different growth stages of rice under CFI and SWI were analyzed. The WF of paddy rice was 1000 m3/t (49% WFgreen, 17% WFblue, 34% WFgrey) and 910 m3/t (50% WFgreen, 10% WFblue, 40% WFgrey) for CFI and SWI, respectively. The WF for paddy rice production was reduced by approximately 9% under SWI compared to CFI, with declines of 47% for WFblue and 8% for WFgreen. The SWI mode changed the ratio of blue to green water fluxes in field water by reducing irrigation during non-critical periods, and green water was used preferentially to enhance its utility. This conceptual method is the first to describe the formation mechanism of blue, green, and grey WFs in paddy systems. It can be extended to different scales and agro-ecosystems that show the influence of crop cultivation on water resources.

Soil bacterial community as impacted by addition of rice straw and biochar

The application of straw and biochar can effectively improve soil quality, but whether such application impacts paddy soil bacterial community development remains to be clarified. Herein, the impacts of three different field amendment strategies were assessed including control (CK) treatment, rice straw (RS) application (9000 kg ha−1), and biochar (BC) application (3150 kg ha−1). Soil samples were collected at five different stages of rice growth, and the bacterial communities therein were characterized via high-throughput 16S rDNA sequencing. The results of these analyses revealed that soil bacterial communities were dominated by three microbial groups (Chloroflexi, Proteobacteria and Acidobacteria). Compared with the CK samples, Chloroflexi, Actinobacteria, Nitrospirae and Gemmatimonadetes levels were dominated phyla in the RS treatment, and Acidobacteria, Actinobacteria, Nitrospirae and Patescibacteria were dominated phyla in the BC treatment. Compared with the RS samples, Chloroflexi, Acidobacteria, Actinobacteria, and Verrucomicrobia levels were increased, however, Proteobacteria, Gemmatimonadetes, Nitrospirae, and Firmicute levels were decreased in the BC samples. Rhizosphere soil bacterial diversity rose significantly following RS and BC amendment, and principal component analyses confirmed that there were significant differences in soil bacterial community composition among treatment groups when comparing all stages of rice growth other than the ripening stage. Relative to the CK treatment, Gemmatimonadaceae, Sphingomonadaceae, Thiovulaceae, Burkholderiaceae, and Clostridiaceae-1 families were dominant following the RS application, while Thiovulaceae and uncultured-bacterium-o-C0119 were dominant following the BC application. These findings suggest that RS and BC application can improve microbial diversity and richness in paddy rice soil in Northeast China.

Management of Rice Blast (Magnaporthe Oryzae B. Couch) Using Bioagents and Fungicides Under Hill Rice Ecosystem of Uttarakhand State in India

A field study was conducted during Kharif-2015 and 2016 on management of leaf and neck blast disease of rice caused by Magnaporthe oryzae under hill rice ecosystem. Different treatments including biological control agents like Trichoderma sp. and Pseudomonas sp. and chemical fungicides like tricyclozole, azoxystrobin and carbendazim were used at different growth stages of rice. Among the treatments, tricyclozole @ 0.06% was highly effective followed by azoxystrobin @ 0.1% with application immediately after appearance of disease. Trichoderma and Pseudomonas were not effective in reducing the disease pressure. Bangladesh J. Bot. 50(3): 713-716, 2021 (September)

Integrated biomarker responses of rice associated with grain yield in copper-contaminated soil

Copper (Cu) contamination in soil is an environmental issue that affects rice growth and development. This study investigated changes in photosynthetic capacities in combination with integrated biomarker responses at different growth stages of rice (Oryza sativa L. var. Hom Bai Toey) exposed to various concentrations of Cu. A randomized complete block design with four replications was used. Exposure to high copper concentrations of 200 Cu mg kg-1 of soil and more resulted in a marked decline in the photosynthetic efficiency of Photosystem II (Phi2) but increased yield of non-photochemical quenching (PhiNPQ) and yield of non-regulatory energy dissipation (PhiNO) at tillering and flowering stages. In addition, these concentrations induced a delay in the flowering of rice, as a consequence of stress experienced in early growth stage. Significant lipid peroxidation and leaf area reduction were observed with 400 Cu mg kg-1 treatment at flowering stage. Rice grain yield decreased significantly at copper concentrations of 200 and 400 mg kg-1. Overall, excess copper inhibited photosynthetic capacity, growth, and development of rice in the early growth stage, and synergistic effects of yield components contributed to final grain yield reduction at harvesting stage. In addition, calculated integrated biomarker response (IBR) values reflect well the severity of Cu toxicity with a decreasing order from tillering stage to harvesting stage.