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Arbuscular mycorrhizal fungi (AMF), particularly the Glomerales group, play a paramount role in plant nutrient uptake, and abiotic and biotic stress management in rice, but recent evidence revealed that elevated CO2 concentration considerably reduces the Glomerales group in soil. In view of this, the present study was initiated to understand the interaction effect of native Glomerales species application in rice plants (cv. Naveen) under elevated CO2 concentrations (400 ± 10, 550 ± 20, and 700 ± 20 ppm) in open‐top chambers. Three different modes of application of the AMF inoculum were evaluated, of which, combined application of AMF at the seedling production and transplanting stages showed increased AMF colonization, which significantly improved grain yield by 25.08% and also increased uptake of phosphorus by 18.2% and nitrogen by 49.5%, as observed at 700‐ppm CO2 concentration. Organic acids secretion in rice root increased in AMF‐inoculated plants exposed to 700‐ppm CO2 concentration. To understand the overall effect of CO2 elevation on AMF interaction with the rice plant, principal component and partial least square regression analysis were performed, which found both positive and negative responses under elevated CO2 concentration. [ABSTRACT FROM AUTHOR]

Oxidative stress generates reactive oxygen species which causes cell damage of living organisms and are normally detoxified by antioxidants. Indirect reports signify the damages caused by reactive oxygen species and neutralized by antioxidant, but the direct evidence to confirm this hypothesis is still unclear. To validate our hypothesis, an attempt was made in a diazotrophic bacterium (Azotobacter chroococcum Avi2) as a biological system, and hydrogen peroxide (H 2 O 2) and ascorbic acid were used as oxidative stress and antioxidant supplement, respectively. Additionally, rice plant-growth attributes by Avi2 was also assessed under H 2 O 2 and ascorbic acid. Results indicated that higher concentration of H 2 O 2 (2.5 mM-4.5 mM) showed the complete mortality of Avi2, whereas one ppm ascorbic acid neutralized the effect of H 2 O 2. Turbidity, colony forming unit, DNA quantity, nifH gene abundance, indole acetic acid and ammonia productions were significantly (p < 0.5) increased by 11.93%, 17.29%, 19.80%, 74.77%, 71.89%, and 42.53%, respectively in Avi2-treated with 1.5 mM H 2 O 2 plus ascorbic acid compared to 1.5 mM H 2 O 2 alone. Superoxide dismutase was significantly (p < 0.5) increased by 60.85%, whereas catalase and ascorbate peroxidase activities were significantly (p < 0.05) decreased by 64.28% and 68.88% in Avi2-treated with 1.5 mM H 2 O 2 plus ascorbic acid compared to 1.5 mM H 2 O 2 alone. Germination percentage of three rice cultivars (FR13a, Naveen and Sahbhagi dhan) were significantly (p < 0.5) increased by 20%, 13.33%, and 4%, respectively in Avi2-treated with 0.6 mM H 2 O 2 plus ascorbic acid compared with uninoculated control. Overall, this study indicated that ascorbic acid formulation neutralizes the H 2 O 2 -oxidative stress and enhances the survivability and plant growth-promoting efficacy of A. chroococcum Avi2 and therefore, it may be used as an effective formulation of bio-inoculants in rice under oxidative stress. • Efficacy of Azotobacter chroococcum Avi2 was studied under H 2 O 2 stress and ascorbic acid. • Higher concentration of H 2 O 2 (2.5 mM–4.5 mM) showed a complete mortality of Avi2. • One ppm ascorbic acid neutralized the effect of H 2 O 2 (∼4.5 mM) and retrieved Avi2 growth. • Ascorbic acid increased the diazotrophic efficacy of Avi2 by 74.77% in 1.5 mM H 2 O 2. • Ascorbic acid enhanced the rice plant-growth attributes in Avi2-treated with 0.6 mM H 2 O 2. [ABSTRACT FROM AUTHOR]

Soil bacterial communities are considered as an essential member of the microbial community, contributing to soil health. Continuous application of chemical fertilizers alters the bacterial community structure (BCS) thereby disturbing the soil biogeochemical cycling. The present study highlights the 16S rRNA amplicon sequencing-based variation of BCS through Illumina-MiSeq ® in a 47 years old long-term fertilized paddy soil and its relation with grain yield (GY), straw biomass (SB) and various soil properties. The experiment comprising six treatments: control (no fertilizers), nitrogen (N), nitrogen + phosphorus (P) + potassium (K), farmyard manure (FYM), FYM + N and FYM + NPK. Data on rice crop performance indicated that GY and SB significantly ( p  ≤ 0.05) enhanced by 45.1%–49.3% and 36.9–39.4% in FYM + NPK compared to control. Relative abundance of bacterial phyla varied across inorganic and organic fertilizer treatments. Dominant phyla across all treatments were Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, and Firmicutes, accounting for about 80–85% of total operational taxonomic units (OTUs). N application alone over 47 years encouraged certain bacterial phyla (Firmicutes, Actinobacteria, and Nitrospira) while major (Proteobacteria, Acidobacteria and Cyanobacteria) and minor (Fibrobacteres, Spirochaetes, TM7 and GNO4) bacterial phyla were found to be suppressed compared to other treatments. Moreover, continuous use of chemical N in paddy soil, considerably suppressed some diazotrophs taxa Burkholderiales, Enterobacteriaceae, and other taxa Kaistobacter, Anaeromyxobacter, Bdellovibrio, and MND1. Redundancy analysis coupled with principal component analysis revealed that BCS was significantly influenced by soil pH and presence of higher nitrogen content. Interestingly, the highest proportion of bacterial OTUs was recorded in balanced fertilizer (NPK) (without FYM) and therefore, this result suggested for the first time that continuous application of NPK encouraged the beneficial bacterial community without compromising of GY and SB. Overall, the present study indicated that continuous application of N and NPK with or without FYM for more than four decades in paddy soil, encouraged certain BCS whereas, N application alone suppressed certain beneficial bacterial phyla, resulting in the alteration of soil biodiversity and rice productivity. [ABSTRACT FROM AUTHOR]

Diazotrophs are one of the most important microbial communities which play a key role in rhizosphere to enhance plant growth-promotion by supplying fixed nitrogen to the plants. The aim of present study was to analyze the frequency and diversity of diazotrophs in the rhizospheres of five genotypes of aromatic rice ( Oryza sativa cultivars Nua Kalajeera, Ketekijoha, Nua Desheri, Nua Chandan and Kala Namak) grown in ten years old long-term aromatic rice-rice (LARR) cropping system under sub-humid tropical condition. In this study, it was observed that very less frequency of active diazotrophs (0–14.28%) in the rhizosphere of aromatic rice genotypes based on polymerase chain reaction (PCR)-based nifH gene amplification, dot blot hybridization and acetylene reduction assay (ARA). The following five isolates (B10, B12, B29, BK16, NKR16) from rhizosphere of aromatic rice and the reference strain Azospirillum brasilence showed nifH amplification and positive signal for dot blot. None of these isolates showed positive in ARA test except A. brasilence . Basic local alighnment search tool (BLAST) homology of nifH sequences of B10, B12, B29, BK16 and NKR16 matched with Gluconoacetobacter diazotrophicus , Pseudomonas stutzeri , Klebsiella sp., Klebsiella pneumoniae and Sinorhizobium meliloti, respectively. Whereas, isolates B10, B12 and BK16 were identified as Bacillus cereus, Enterobacter sp., and Lysinibacillus sp., respectively based on 16S-rDNA sequencing. As per nifH sequences, these diazotrophs (B10, B12, B29, BK16, NKR16) fall under α and γ-proteobacter, whereas 16S-rDNA sequences revealed that they belonged to firmicutes and γ-proteobacter. Multiple sequence alignment of nifH gene sequences showed wider variation among diazotrophs, however 3D structure of NifH protein revealed the less diversity among isolates. Moreover, restriction digestion of 16S-rDNA using tetracutters ( MspI, MboI and HaeIII ) deciphered a unique pattern among small population of diazotrophs.The results of this finding provided an interesting data and novel information of diazotroph diversity in LARR cropping system. Finally, the present study indicated that the continuous application of high dose of inorganic nitrogenous fertilizers (nitrogen at the rate of 60 & 80 kg N ha −1 year −1 in wet and dry seasons, respectively) limit the frequency and diversity of rhizospheric diazotrophs in the LARR cropping system. [ABSTRACT FROM AUTHOR]

Soil microbial communities play an essential role in maintaining soil fertility and considered as ecological indicators to evaluate soil health. In the present study, long-term effects of organic and inorganic fertilizers on functional diversity of soil microbial communities, and their correlation with soil organic carbon, microbial biomass and activities, were observed under sub-humid tropical rice-rice cropping system. This experiment comprises six treatments viz . control (plots without application of chemical fertilizers and farm yard manure), nitrogen (N at the rate of 60 & 80 kg ha −1 in wet and dry seasons, respectively), nitrogen + phosphorus + potassium (NPK), farm yard manure (FYM), FYM + N and FYM + NPK. The results indicated that pH of the soil under the treatments decreased from its initial value, whereas total organic carbon increased in FYM-treated plots. Microbial biomass carbon and nitrogen in FYM + NPK were increased by 50.0 and 46.4%, respectively as compared to control treatment. Carbon and nitrogen mineralization; and soil enzyme activities were significantly ( p ≤ 0.05) higher in FYM + NPK over control. The average well color development (AWCD) values derived from Biolog ® eco-plates followed the order of FYM + N > FYM > FYM + NPK > NPK > N > Control. Shannon index was greater (p ≤ 0.05) in FYM-treated soil as compared to control and chemical treated soil. Principal component analysis (PCA) indicates a clear separation of the cluster of treatments with FYM application (FYM and FYM + NPK) and treatments without FYM (N and NPK). Shannon index was significantly correlated with available phosphorus ( p ≤ 0.002) and carbon mineralization ( p ≤ 0.015). Biplot analysis suggested that polymer and amino acid utilizing microbes were dominant, irrespective of all treatments. These results revealed that continuous application of nitrogen fertilizer alone has responded a shift in soil microbial community in the long run and decreased the functional diversity of microbes. However, application of FYM either alone, or in combination with chemical fertilizers, could restore soil fertility. Moreover, the information generated from this experiment though Biolog ® may be the first particularly with reference to the dominance of polymer and amino acid utilizing microbes, irrespective of treatments under long-term fertilized paddy soil. [ABSTRACT FROM AUTHOR]

Growing interest in sustainable agriculture has prompted this study aiming to evaluate nutritional content of rice grain produced from an organic production system. Here, we grew nine quality rice cultivars under organic methods in the wet and dry seasons, and the nutritional values, grain quality, and physiological parameters were compared with respective cultivars grown under the standard cultivation method (SCM). Obtained results revealed that the yield and plant height were lower, but tillering capacity was higher, in the organic field compared with the standard one. The organic crop showed significantly lower contents of protein and phytate compared with reference values under the SCM. Antioxidative capacity and its responsible phytochemicals such as phenolics, flavonoids, and γ-oryzanol were also significantly higher under organic cultivation than under the SCM. Among physicochemical characteristics, apparent amylose content, gel consistency, and area and perimeter of grain were also higher in the organic crops, but hulling quality, milling quality, head rice recovery, and all other cooking qualities were at par. Higher crude oil and lower total protein content of rice bran were observed in the organic crop, but ash, fiber, and moisture contents did not vary significantly in these two cultivation systems. [ABSTRACT FROM AUTHOR]

• Individual and combined applications of Ascorbic acid (AA) and Azotobacter chroococcum Avi2 were assessed in DT and DS-rice cultivars for photosynthetic efficacy, antioxidants and PGP under moisture deficit stress (MS). • Avi2 + AA enhanced RWC and chlorophyll contents in rice leaves, while reduced EL and proline under MS. • SOD, CAT and nifH gene were increased in Avi2 + AA under MS in both DT and DS rice cultivars. • Avi2 + AA also increased the ChlF- coefficients under MS, indicating a sign of plant wellness. • Overall, Avi2 + AA could serve as an effective formulation to alleviate MS vis à vis enhance PGP traits in rice. This group has previously reported the role of ascorbic acid (AA) as an antioxidant for survivability and ability to enhancing diazotrophic efficacy in Azotobacter chroococcum Avi2 under hydrogen peroxide (H 2 O 2) stress. However, the present study showed the combined application of AA and Avi2 in drought-susceptible (IR64 and Naveen) and drought-tolerant (Ankit and Satyabhama) rice cultivars to determine their photosynthetic efficacy (chlorophyll fluorescence-imaging), antioxidants, and plant growth-promotion (PGP) under moisture deficit stress (MS, −60 kPa). The results indicated that combined application of AA and Avi2 significantly (p < 0.05) increased the total chlorophyll, relative water content, electrolytic leakage, super oxide dismutase, and catalase activities in all rice cultivars as compared to other MS treatments, whereas stress indicators like proline and H 2 O 2 contents were proportionally increased under MS and their concentration were normalized under combined application of AA and Avi2. Photochemical quenching, non-photochemical quenching, photosynthetic electron transport rate, and the effective quantum efficiency were found to be increased significantly (p < 0.05) in Avi2 + AA as compared to other MS treatments. Moreover, rice roots harbored significantly (p < 0.05) higher copy number of nifH gene in Avi2 + AA treatment followed by Avi2 compared to flooded control and other MS treatments. Combined application of AA and Avi2 also increased the grain yield significantly (p < 0.05) by 7.09 % and 3.92 % in drought-tolerant (Ankit and Satyabhama, respectively) and 31.70 % and 34.19 % in drought-susceptible (IR64 and Naveen, respectively) rice cultivars compared to MS treatment. Overall, the present study indicated that AA along with Avi2 could be an effective formulation to alleviate MS vis à vis enhances PGP traits in rice. [ABSTRACT FROM AUTHOR]

Elevated carbon dioxide (eCO 2), higher dose of recommended nitrogen (HDN), and water deficit stress (WDS) are three important factors which influence individually on diazotrophic community in paddy soil, thereby affecting crop yield and its nitrogen use efficiency. However, the combined effects of eCO 2 , HDN, and WDS on soil diazotrophic community remains inadequate particularly in rice. Hence, the present study was conducted in CO 2 -maintained open-top chamber to assess the diazotrophic community under combined influence of eCO 2 (550 ± 20 μmol mol−1 as compared to ambient CO 2 i.e. 400 ± 10 μmol mol−1) and HDN (120 kg N ha−1, 50% higher than recommended dose of N for rice i.e. 80 kg N ha−1, in sub-humid tropical region of eastern India) with and without WDS (−60 kPa) at two growth stages of rice (tillering, TI and panicle initiation, PI) and correlated with soil carbon (C) pools and enzyme activities. The results indicated that soil organic C, readily mineralizable C, microbial biomass C, acid and alkaline phosphatase activities were significantly (p < 0.05) increased under combined influence of eCO 2 and HDN at both TI and PI stages of rice without WDS. The results also showed that abundance of nifH varied from ambient CO 2 (aCO 2) to eCO 2 and found higher in aCO 2 under recommended dose of nitrogen (RDN) without WDS, whereas under eCO 2 , nifH copy number was found higher under HDN at both TI and PI stages of rice without WDS. Biplot analysis revealed that abundance of nifH and nitrifiers were highly correlated under aCO 2 coupled with RDN without WDS. Illumina MiSeq®-based targeted nifH metagenome showed that eCO 2 encouraged the relative abundance of Proteobacteria and Cyanobacteria, whereas suppressed the other diazotrophic phyla like Actinobacteria, Firmicutes, and Chlorobi, but the reverse trend was observed in HDN treatments. Heatmap analysis revealed a unique differentiation of Rhizobiales and Pseudomonadales under eCO 2 coupled with RDN without WDS. Moreover, three-way interactions of eCO 2 , HDN, and WDS also showed significant (p < 0.05) difference of soil C pools and enzymatic activities at both growth stages of rice. Overall, the present study showed that diazotrophic community in paddy soil was significantly (p < 0.05) altered by the additive effects of eCO 2 , HDN, and WDS. • Diazotrophs were analyzed under combined influence of eCO 2 , HDN, and water deficit paddy soil. • Abundance of nifH was significantly increased under combined effects of eCO 2 and HDN. • nifH- Illumina MiSeq® revealed that 35.6 to 66.2% of OTUs belonged to Bradyrhizobiaceae. • Rhizobiales and Pseudomonadales were predominant in eCO 2 and RDN without WDS. • eCO 2 and HDN significantly increased the soil carbon pools and enzyme activities in paddy soil. [ABSTRACT FROM AUTHOR]

Over years of intensive cultivation and imbalanced fertilizer use, the soils of the Indian subcontinent have become deficient in several nutrients and are impoverished in organic matter. Recently, this region has started emphasizing a shift from inorganic to organic farming to manage soil health. However, owing to the steadily increasing demands for food by the overgrowing populations of this region, a complete shift to an organic farming system is not possible. The rice–wheat cropping system (RWCS) is in crisis because of falling or static yields. The nations of this region have already recognized this problem and have modified farming systems toward integrated nutrient management (INM) practices. The INM concept aims to design farming systems to ensure sustainability by improving soil health, while securing food for the population by improving crop productivity. Therefore, this paper was synthesized to quantify the impact and role of INM in improving crop productivity and sustainability of the RWCS in the context of the Indian subcontinent through meta-analysis using 338 paired data during the period of 1989–2016. The meta-analysis of the whole data for rice and wheat showed a positive increase in the grain yield of both crops with the use of INM over inorganic fertilizers only (IORA), organic fertilizers only (ORA), and control (no fertilizers; CO) treatments. The increase in grain yield was significant at p < 0.05 for rice in INM over ORA and CO treatments. For wheat, the increase in grain yield was significant at p < 0.05 in INM over IORA, ORA, and CO treatments. The yield differences in the INM treatment over IORA were 0.05 and 0.13 Mg ha−1, respectively, in rice and wheat crops. The percent yield increases in INM treatment over IORA, ORA, and CO treatments were 2.52, 29.2, and 90.9, respectively, in loamy soil and 0.60, 24.9, and 93.7, respectively, in clayey soil. The net returns increased by 121% (INM vs. CO) in rice, and 9.34% (INM vs. IORA) and 127% (INM vs. CO) in wheat crop. Use of integrated nutrient management had a positive effect on soil properties as compared to other nutrient management options. Overall, the yield gain and maintenance of soil health due to INM practices over other nutrient management practices in RWCS can be a viable nutrient management option in the Indian subcontinent. [ABSTRACT FROM AUTHOR]

Abstract Rice is the foremost staple food in the world, safeguarding the global food and nutritional security. Rise in atmospheric carbon dioxide (CO 2) and water deficits are threatening global rice productivity and sustainability. Under real field conditions these climatic factors often interact with each other resulting in impacts that are remarkably different compared to individual factor exposure. Rice soils exposed to drought and elevated CO 2 (eCO 2) alters the biomass, diversity and activity of soil microorganisms affecting greenhouse gas (GHG) emission dynamics. In this review we have discussed the impacts of eCO 2 and water deficit on agronomic, biochemical and physiological responses of rice and GHGs emissions from rice soils. Drought usually results in oxidative stress due to stomatal closure, dry weight reduction, formation of reactive oxygen species, decrease in relative water content and increase in electrolyte leakage at almost all growth and developmental phases of rice. Elevated atmospheric CO 2 concentration reduces the negative effects of drought by improving plant water relations, reducing stomatal opening, decreasing transpiration, increasing canopy photosynthesis, shortening crop growth period and increasing the antioxidant metabolite activities in rice. Increased scientific understanding of the effects of drought and eCO 2 on rice agronomy, physiology and GHG emission dynamics of rice soil is essential for devising adaptation options. Integration of novel agronomic practices viz., crop establishment methods and alternate cropping systems with improved water and nutrient management are important steps to help rice farmers cope with drought and eCO 2. The review summarizes future research needs for ensuring sustained global food security under future warmer, drier and high CO 2 conditions. Graphical abstract Unlabelled Image Highlights • Agronomic management options are promising for mitigating water deficit stress. • Rice crop behavior under elevated CO 2 condition was discussed. • Opportunities under elevated CO 2 are reviewed to explore the future research needs. [ABSTRACT FROM AUTHOR]

Abstract Use of plant-associated beneficial microbes, especially endophytes are getting popular day by day as they occupy a relatively privileged niche inside different plant tissues with lesser competition for food and shelter than rhizosphere. The effects of different physical factors like temperature, rainfall, and seasonal variation and UV radiation on plant growth promoting endophytic communities are less pronounced than those on the rhizospheric and phylloplane microbes. This present work has been compromised with further utilization of an indigenous rice (Oryza sativa L.) root endophytic Azotobacter sp. strain Avi2 (MCC 3432) (AzA) as a bio-formulation for sustainable rice production based on several physiological parameters (plant height, root length/weight, leaf area, yield, chlorophyll contain), in-vitro comparative plant growth promoting assays, greenhouse and field experiments (dry and wet season). Treatments with AzA exhibited higher yield as well as maximal chlorophyll fluorescence (Fm) of flag leaves in flowering and grain filling stages indicating higher photosynthetic rates. Scanning electron microscopic image of rice roots demonstrated accumulation of bacterial biofilm at the junction of primary and lateral root confirming the root-colonizing ability of the bacterium. The results of the study were quite encouraging as AzA exhibited better vegetative and reproductive growth of rice in pot and field experiment compared to formulated rhizospheric Azotobacter sp. (commercial product). Apart from that plants treated with AzA (supplemented 50% nitrogenous fertilizer of recommended dose) exhibited similar yield parameters when it was compared with the recommended dose of fertilizer (RDF; 120:60:60 mg N:P:K kg−1 soil/ without any bacterial). Therefore, it can be concluded that application of this plant growth promoting endophyte can reduce a substantial amount of N-fertilizer for field application. [ABSTRACT FROM AUTHOR]

Effects of different fertilizers and manure on dynamics of soil organic carbon (SOC) and nitrogen fractions and their stock changes remains unclear under intensively cultivated rice soil profile. Profile soil samples in six treatments viz. control, nitrogen (N), nitrogen-phosphorus-potassium (NPK), farm yard manure (FYM), N + FYM and NPK + FYM were collected from a long term fertilizer experiment continuing since 1969 at ICAR-NRRI, Cuttack, India to study the soil organic carbon and nitrogen fractions (particulate organic carbon, POC; microbial biomass carbon, MBC; particulate organic nitrogen, PON; and microbial biomass nitrogen, MBN) and SOC sequestration. Results from the study revealed that in the control treatment, where no manure or chemical fertilizer was applied,the bulk density was highest. Balanced fertilization and combined use of chemical fertilizers and manure for 41 years increased the SOC in all the plots except the unfertilized control as compared with the initial value (6.6 g/kg). Balanced fertilization (NPK) and integrated fertilization (NPK + FYM) resulted in similar increases in particulate organic carbon, carbon mineralization and microbial biomass carbon, whereas particulate organic nitrogen, nitrogen mineralization and microbial biomass nitrogen were more in integrated fertilization (NPK + FYM) compared with control treatment. Soil organic C and nitrogen stocks changed positively across the fertilizer and manure treatments over the control. In the control plot, at 0–15 cm depth the soil carbon and nitrogen stock was 15.1 and 1.77 Mg ha −1 , respectively which increased to the 19.5 Mg ha −1 in NPK + FYM for carbon and 2.25 Mg ha −1 in N + FYM for nitrogen. As compared to the initial (13.7 Mg ha −1 ), the SOC stock in 0–15 cm depth increased under all the fertilized treatments during 41 year period in the order: NPK + FYM > N + FYM > NPK > FYM > N > control. The rate of increase in SOC (carbon sequestration) due to fertilizer application alone varied between 57 and 89 kg ha −1 yr −1 , while for FYM addition the rate of increase was 61 to 138 kg ha −1 yr −1 , highest being in NPK + FYM. Correlation coefficients between different soil organic C and N fractions indicate differential accumulation pattern of organic C and nitrogen in different depths. Based on crop yield and C storage, integrated fertilization of chemical fertilizers and manure proved to be the best for improving crop productivity and SOC sequestration. [ABSTRACT FROM AUTHOR]

• Labile soil N pools were increased under elevated CO 2 (EC). • Denitrifier population increased,but nitrifier population decreased under EC. • Nitrous oxide emission increased by 43 % under EC. • Partial least square path modelling was employed to distinguish different factors. • N 2 O emission can be accounted by predictive model involving N fractions. Understanding the effect of elevated atmospheric CO 2 on nitrous oxide (N 2 O) emission and plant-microbe interactions in rice soils is of great significance for predicting the long-term response of rice ecosystems to elevated CO 2 concentration. Elevated atmospheric CO 2 concentration has the potential to augment rice production and alter the soil nitrogen (N) dynamics. Because N 2 O emission is controlled by microbial activity, we reasoned that changes in soil N dynamics and activity of soil microbes may affect N 2 O flux from rice soil. In order to examine the influence of elevated CO 2 , different N doses and varying moisture regimes on N 2 O emission from rice soil, we designed a field experiment with 3 CO 2 levels [C 1 = ambient CO 2 (400 ± 10 μmol mol−1), C 2 = elevated CO 2 (550 ± 20 μmol mol−1), C 3 = elevated CO 2 (700 ± 20 μmol mol−1)], 3 N doses [No = No nitrogen, N 1 = 100 kg ha−1, N 2 = 150 kg ha−1] and 2 moisture regimes (M 1 = well watered, M 2 = water deficit stress upto −60 kPa). In this study, path analyses using partial least square path modelling (PLS‐PM) approach was used to distinguish the direct and indirect factors influencing N 2 O emission under ambient and elevated CO 2 conditions. Significant increase was found for labile N fractions such as microbial biomass-N (32 %; p ≤ 0.03) whereas significant decrease was found for NH 4 +-N (40 %; p ≤ 0.0005) and NO 3 --N (32 %; p ≤ 0.001) concentration under elevated over ambient CO 2. Rhizospheric denitrifier population was increased (39 %; p ≤ 0.001) whereas, nitrifier population decreased (41 %; p ≤ 0.001) under elevated as compared to ambient CO 2. Exposure of elevated CO 2 decreased (20 %; p ≤ 0.001) N mineralization whereas it increased N 2 O emission (43 %; p ≤ 0.001). Elevated CO 2 level increased activities of β- glucosidase, urease and fluorescein diacetate showing significant effects on soil N dynamics. Path modelling (PLS-PM) approach indicated a direct effect of nitrifiers and denitrifiers population on N 2 O emission and the effect was more pronounced under elevated CO 2 as compared to ambient CO 2 levels. The developed predictive models for N 2 O emission clarifies that the effect of varying CO 2 levels is more pronounced at rice vegetative stage than reproductive stage. [ABSTRACT FROM AUTHOR]

• Integrated nutrient management (INM) results in 11–24 % and 13–27% reduction N 2 O and NH 3 emission. • Increase in methane emission in INM treatments led to overall increase in global warming potential. • Increase in soil labile C pools and enzymatic activities under INM indicated its beneficial impact on soil fertility. Emerging challenges of fertilizer use in intensive rice cultivation system such as nutrient mining, nutrient imbalance and environmental pollution etc. warrant for a rationalized nutrient management strategy combining both organic and inorganic sources. Field trials were conducted with rice cultivar Naveen during wet and dry seasons of 2015-16 to measure greenhouse gas (GHG) emission, nitrogen (N) loss and N use efficiency in low land rice under different integrated nutrient management (INM) options. Six treatments including 0 N, 100 % N from urea, 50 % N from urea + 50 % N from farm yard manure (FYM), 50 % N from urea + 50 % N from poultry manure (PM), 50 % N from urea + 25 % N from rice straw + 25 % N from FYM, and 50 % N from urea + 25 % N from blue green algae (BGA) + 25 % N from FYM were replicated thrice in randomized block design. Results revealed that 11–24% and 13–27 % reduction in nitrous oxide (N 2 O) and ammonia (NH 3) emission respectively, in INM treatments as compared to urea alone. However, increase in methane (CH 4) emission in INM treatments due to inclusion of organics led to overall increase in global warming potential (GWP). Yield reduction to the extent of 9.8–20.0 % in INM treatments as compared to urea alone resulted in higher greenhouse gas intensity (GHGI) in the former. Among different INM treatments, urea + PM and urea + FYM + BGA performed better in terms of yield and GWP than others. Enhancement of labile carbon (C) fractions and enzymatic activities in INM plots indicated the potential of combined application of organics manure and inorganic fertilizer in increasing fertility of soil in long run. Different organic amendments differ among themselves in relation to their effects on soil C and N dynamics and rice yield, which need to be taken into consideration while devising standard INM package for low land rice. [ABSTRACT FROM AUTHOR]

Rice is one of the principal staple foods, essential for safeguarding the global food and nutritional security, but due to different natural and anthropogenic sources, it also acts as one of the biggest reservoirs of potentially toxic metal(loids) like As, Hg, Se, Pb and Cd. This review summarizes mobilization, translocation and speciation mechanism of these metal(loids) in soil-plant continuum as well as available cost-effective remediation measures and future research needs to eliminate the long-term risk to human health. High concentrations of these elements not only cause toxicity problems in plants, but also in animals that consume them and gradual deposition of these elements leads to the risk of bioaccumulation. The extensive occurrence of contaminated rice grains globally poses substantial public health risk and merits immediate action. People living in hotspots of contamination are exposed to higher health risks, however, rice import/export among different countries make the problem of global concern. Accumulation of As, Hg, Se, Pb and Cd in rice grains can be reduced by reducing their bioavailability, and controlling their uptake by rice plants. The contaminated soils can be reclaimed by phytoremediation, bioremediation, chemical amendments and mechanical measures; however these methods are either too expensive and/or too slow. Integration of innovative agronomic practices like crop establishment methods and improved irrigation and nutrient management practices are important steps to help mitigate the accumulation in soil as well as plant parts. Adoption of transgenic techniques for development of rice cultivars with low accumulation in edible plant parts could be a realistic option that would permit rice cultivation in soils with high bioavailability of these metal(loid)s. Unlabelled Image • Mobilization, translocation and speciation mechanism of metal(loids) were discussed. • Mitigation opportunities are reviewed to explore the future research needs. • Genetic approaches are promising for reducing accumulation in grains. • Health risk assessment was done. [ABSTRACT FROM AUTHOR]