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Nitrogen (N) is an essential but generally limiting nutrient for biological systems. Development of the Haber-Bosch industrial process for ammonia synthesis helped to relieve N limitation of agricultural production, fueling the Green Revolution and reducing hunger. However, the massive use of industrial N fertilizer has doubled the N moving through the global N cycle with dramatic environmental consequences that threaten planetary health. Thus, there is an urgent need to reduce losses of reactive N from agriculture, while ensuring sufficient N inputs for food security. Here we review current knowledge related to N use efficiency (NUE) in agriculture and identify research opportunities in the areas of agronomy, plant breeding, biological N fixation (BNF), soil N cycling, and modeling to achieve responsible, sustainable use of N in agriculture. Amongst these opportunities, improved agricultural practices that synchronize crop N demand with soil N availability are low-hanging fruit. Crop breeding that targets root and shoot physiological processes will likely increase N uptake and utilization of soil N, while breeding for BNF effectiveness in legumes will enhance overall system NUE. Likewise, engineering of novel N-fixing symbioses in non-legumes could reduce the need for chemical fertilizers in agroecosystems but is a much longer-term goal. The use of simulation modeling to conceptualize the complex, interwoven processes that affect agroecosystem NUE, along with multi-objective optimization, will also accelerate NUE gains.

Sierra Mixe maize is a landrace variety from Oaxaca, Mexico, that utilizes nitrogen derived from the atmosphere via an undefined nitrogen fixation mechanism. The diazotrophic microbiota associated with the plant's mucilaginous aerial root exudate composed of complex carbohydrates was previously identified and characterized by our group where we found 23 lactococci capable of biological nitrogen fixation (BNF) without containing any of the proposed essential genes for this trait (nifHDKENB). To determine the genes in Lactococcus associated with this phenotype, we selected 70 lactococci from the dairy industry that are not known to be diazotrophic to conduct a comparative population genomic analysis. This showed that the diazotrophic lactococcal genomes were distinctly different from the dairy isolates. Examining the pangenome followed by genome-wide association study and machine learning identified genes with the functions needed for BNF in the maize isolates that were absent from the dairy isolates. Many of the putative genes received an 'unknown' annotation, which led to the domain analysis of the 135 homologs. This revealed genes with molecular functions needed for BNF, including mucilage carbohydrate catabolism, glycan-mediated host adhesion, iron/siderophore utilization, and oxidation/reduction control. This is the first report of this pathway in this organism to underpin BNF. Consequently, we proposed a model needed for BNF in lactococci that plausibly accounts for BNF in the absence of the nif operon in this organism.

Inoculation with Bacillus subtilis is a promising approach to increase plant yield and nutrient acquisition. In this context, this study aimed to estimate the B. subtilis concentration that increases yield, gas exchange, and nutrition of lettuce plants in a hydroponic system. The research was carried out in a greenhouse in Ilha Solteira, Brazil. A randomized block design with five replications was adopted. The treatments consisted of B. subtilis concentrations in nutrient solution [0 mL “non-inoculated”, 7.8 × 103, 15.6 × 103, 31.2 × 103, and 62.4 × 103 colony forming units (CFU) mL−1 of nutrient solution]. There was an increase of 20% and 19% in number of leaves and 22% and 25% in shoot fresh mass with B. subtilis concentrations of 15.6 × 103 and 31.2 × 103 CFU mL−1 as compared to the non-inoculated plants, respectively. Also, B. subtilis concentration at 31.2 × 103 CFU mL−1 increased net photosynthesis rate by 95%, intercellular CO2 concentration by 30%, and water use efficiency by 67% as compared to the non-inoculated treatments. The concentration of 7.8 × 103 CFU mL−1 improved shoot accumulation of Ca, Mg, and S by 109%, 74%, and 69%, when compared with non-inoculated plants, respectively. Inoculation with B. subtilis at 15.6 × 103 CFU mL−1 provided the highest fresh leaves yield while inoculation at 15.6 × 103 and 31.2 × 103 CFU mL−1 increased shoot fresh mass and number of leaves. Concentrations of 7.8 × 103 and 15.6 × 103 increased shoot K accumulation. The concentrations of 7.8 × 103, 15.6 × 103, and 31.2 × 103 CFU mL−1 increased shoot N accumulation in hydroponic lettuce plants.

Sustainable corn production requires a dramatic shift toward natural soil fertility rather than relying solely on synthetic fertilizers. Cover crops play an important role in improving the productivity of subsequent row crops through improving soil properties. The main goal of this study was to investigate if increasing cover crop biomass through applying a higher density can enhance soil characteristics in the short term and contribute more nitrogen to succeeding corn silage. In a two-year field study (2018–2019), the influence of faba bean (Vicia faba L.) as a cover crop on soil characteristics and corn silage (Zea mays L.) production was evaluated. Treatments consisted of five levels of faba bean density (0, 25, 35, 40, and 80 plants m−2) and four application rates of urea-based nitrogen fertilizer (0, 100, 200, and 300 kg ha−1) in a no-till system. The measured soil characteristics were not significantly affected through increasing cover crop density to 80 plants m−2. The faba bean roots comprised 33% of total biomass in densities ranging from 25–40 plants m−2. The highest total N yield (root + shoot) was 133 kg N ha−1, obtained from 40 faba bean plants m−2. The faba bean root decomposed faster than the shoot, and the addition of N to the corn accelerated 50% N release from the roots but had no significant effect on shoot decomposition. Corn planted after 40 plants m−2 faba bean yielded 28% more than the corn with no faba bean. Corn yielded less in no-cover-crop fields even when it received the highest synthetic N rate (300 kg N ha−1), indicating the value of including faba bean in rotation with corn. [ABSTRACT FROM AUTHOR]

Legumes grow in temperate and warm climates, being susceptible to unpredictable episodes of water deficit. This study aimed to evaluate (i) morphology and N‐compound contents in roots and nodules, (ii) N and C contents in shoots and (iii) crop yield in two peanut cultivars with contrasting drought tolerance, inoculated with a reference N‐fixing strain and challenged by water deficit conditions. For that, seeds of two peanut cultivars, Granoleico (sensitive, S) and EC‐98 (tolerant, T) were inoculated with Bradyrhizobium sp. SEMIA6144 and 30 days after sowing, plants were separated into the experimental groups: control, drought stress and drought stress and subsequent rehydration. Although the results obtained on root anatomy and histology revealed differential responses between cultivars, they were not associated with tolerance traits in EC‐98 (T). In contrast, nodules of EC‐98 (T) showed invariable diameter and infection zone upon the exposition to drought stress and rehydration compared to nodules of Granoleico (S) plants exposed to the same treatments. EC‐98 (T) showed invariable contents of C in shoots and of nitrates and ureides in roots and nodules of stressed and rehydrated plants, an increase in total amino acids only in nodules of stressed plants and a small reduction in N‐content (compared with the sensitive cultivar). The status of these variables related to C‐ and N‐metabolism could be associated with an efficient biological nitrogen fixation. Besides, EC‐98 (T) yielded better both in a crop cycle with adequate water supply and in a dry year and the inoculation improved yield in both cultivars. Thus, the inoculation with N‐fixing bacteria is recommended for EC‐98 (T) in seasons with expected drought stress cycles in crops. [ABSTRACT FROM AUTHOR]

Ultisol is a type of soil with low organic matter, pH, and nutrient content, including molybdenum, leading to low productivity. This study aimed to investigate the use of dry land using molybdenum and lime (CaCO3) inoculated with Rhizobium strain Nod+Fix+ to increase the soybean production of Willis and Baluran cultivars. This research was conducted from May to September 2021 in Pallangga Subdistrict, Gowa Regency, South Sulawesi, Indonesia. The study used a split-plot design with three replications for each treatment. The first factor was soybean varieties, consisting of Baluran and Willis cultivars. The second factor was the composition of the bacterial strain Nod+ Fix+, lime CaCO3 and NH4-molybdate, which consisted of without (Rhizobium strain Nod+ Fix+ + CaCO3 + NH4-molybdate); Rhizobium strain Nod+ Fix+ + CaCO3 1.0 ton/ha + NH4-molybdate 250 g/h); Rhizobium strain Nod+ Fix+ + CaCO3 1.5 tons/ha + NH4-molybdate 500 g/h); and Rhizobium strain Nod+ Fix+ + CaCO3 2.0 tons/ha + NH4-molybdate 750 g/h). The results showed that treating the bacterial strain Nod+ Fix+ + MoCo (1.0:0.6) kg/ha achieved the best results on growth, nutrient uptake (Nitrogen, Phosphorus and Potassium), and soybean yields, both for Willis and Baluran varieties on ultisol soils. [ABSTRACT FROM AUTHOR]

The search for sustainable agriculture has increased interest in using endophytic bacteria to reduce fertilizer use and increase stress resilience. Stress-adapted plants are a potential source of these bacteria. Some species of these plants have not yet been evaluated for this, such as pangolão grass, from which we considered endophytic bacteria as potential plant growth promoters. Bacteria from the root, colm, leaves, and rhizospheric soil were isolated, and 132 strains were evaluated for their in vitro biological nitrogen fixation, IAA and siderophores production, and phosphate solubilization. Each mechanism was also assessed under low N availability, water stress, and low-solubility Fe and P sources in maize greenhouse experiments. All strains synthesized IAA; 63 grew on N-free media, 114 synthesized siderophores, and 46 solubilized P, while 19 presented all four mechanisms. Overall, these strains had better performance than commercial inoculant in all experiments. Still, in vitro responses were not good predictors of in vivo effects, which indicates that the former should not be used for strain selection, since this could lead to not testing strains with good plant growth promotion potential. Their heterologous growth promotion in maize reinforces the potential of stress-adapted plant species as potential sources of strains for inoculants. [ABSTRACT FROM AUTHOR]

Background and Aims: Nitrospirillum amazonense strain CBAmC is a nitrogen-fixing bacterium that has been used for sugarcane inoculation. Despite its beneficial effects, however, little is known about the establishment and colonization of this microorganism in its inoculated host plant. Furthermore, alternative inoculation methods need to be tested in the sugarcane crop. The objective of the present work was to quantify and visualize CBAmC in sugarcane cultivar RB867515 after using three inoculation methods. Methods: Utilizing one node as propagation material, three bacterial inoculation methods were tested under greenhouse conditions. For up to 60 days after inoculation (DAI), qPCR was used to quantify the bacterial loads in the plant or substrate while FISH-CLSM was used to confirm the establishment and colonization profile of CBAmC in different plant tissues. Results: FISH-CLSM indicated that the CBAmC strain could establish itself on different tissues of sugarcane, especially roots. qPCR revealed variable bacterial loads in the plants inoculated according to the three methods tested. In addition, little or no bacterial loads were detected in the substrate a few days after inoculation, regardless of the method used. Conclusions: N. amazonense CBAmC proves to be a bacterium that preferentially associates with the surface of the root tissues of sugarcane propagated by one node, instead of colonizing internal plant tissues or remaining in the soil. The inoculation method consisting of immersion of the mini-setts in bacterial suspension proved to be more efficient than the inoculation methods of applying the suspension onto the post-sprouting substrate or to the lowest leaf. [ABSTRACT FROM AUTHOR]

Common bean (Phaseolus vulgaris L.) yield is limited by prolonged drought conditions and nutrients scarcity in the soil. The Colombian Agricultural Research Corporation (AGROSAVIA) selected five common bean genotypes for presenting biofortification characteristics, good grain size and water deficit tolerance, however, sustainable techniques are required that contribute to the adaptation of these genotypes, and mitigate the impact of drought and nutrient scarcity on the crop production. Plant growth promoting rhizobacteria is an alternative to improve nutrients absorption and plants adaptation to adverse conditions. In this work, the efficiency of rhizobia in biological nitrogen fixation (BNF) in selected common bean genotypes was evaluated. Soil samples were taken in the rhizosphere and roots of the five bean genotypes at the Motilonia Research Center, as well as two alternative samplings in other areas of the Cesar department. Bean seeds were used as a trap to obtain nodules in the laboratory. The nodulation and biological nitrogen fixation of 11 strains from the AGROSAVIA bank in five bean genotypes were evaluated and the symbiotic efficiency of 7 of the strains in four of the genotypes was measured. Three isolates with rhizobia characteristics, symbionts of the 77-SMG22 genotype, were obtained. The most efficient strains in BNF were P17 and P22 in genotype 45-HTA10-2, strains C229 and P37 in 48-HTA14-1, in genotype 56-DAB295 all symbiont strains were efficient (C229, P03, P22 and P37), and in the 77-SMG22 genotype the most efficient treatment was the commercial inoculant Rhizobiol®. Therefore, the strains from the AGROSAVIA bank promote the development of some common bean genotypes reflected in the growth of the plants. [ABSTRACT FROM AUTHOR]

A set of 165 Recombinant inbred lines (RILs) derived from an interspecific cross of chickpea was used to identify QTLs for key biological nitrogen fixation (BNF) traits. The phenotyping of BNF and related traits was done at two different agroclimatic zones viz., Central plain zone (Ludhiana) and Sub-Mountainous undulating zone (Gurdaspur) for 2 consecutive rabi seasons (2018–2020). Wild parent C. reticulatum ILWC292 showed significantly high performance in terms of biological nitrogen fixation (BNF) traits over the cultivated C. arietinum GPF-2. The triple interaction of genotypes × locations × years was significant (p 0.05) for all BNF traits in parental lines. Highly significant positive correlation was obtained between grain yield and key growth and symbiotic parameters at both the sites. Phenotypic analysis revealed nodule dry weight and leghaemoglobin content as key traits for BNF efficiency and contrasting DNA bulks were constituted on the basis of these traits. Out of 535 SSR markers, 139 exhibited polymorphism between the parental lines on polyacrylamide gel electrophoresis. A total of 30 SSR markers showed polymorphism between the higher and lower bulks for nodule dry weight and leghaemoglobin content. Out of these, 20 SSRs did not show any segregation distortion in RIL population as determined by chi square analysis (p < 0.05) and were used for quantitative trait loci (QTL) analysis. Using QTL cartographer, markers- CAGM02697, CAGM09835, CAGM09777, CAGM09227, CAGM09021, CAGM08679 were found linked with QTLs for BNF. These markers can be validated further for identification of genes for BNF traits and marker assisted selection in chickpea. To the best of our knowledge this is the first report on identification of genomic regions associated with key BNF traits in chickpea across different agro-climatic zones. [ABSTRACT FROM AUTHOR]

As the use of microbial inoculants in agriculture rises, it becomes important to understand how the environment may influence microbial ability to promote plant growth. This work examines whether there are light dependencies in the biological functions of Azospirillum brasilense, a commercialized prolific grass-root colonizer. Though classically defined as non-phototrophic, A. brasilense possesses photoreceptors that could perceive light conducted through its host's roots. Here, we examined the light dependency of atmospheric biological nitrogen fixation (BNF) and auxin biosynthesis along with supporting processes including ATP biosynthesis, and iron and manganese uptake. Functional mutants of A. brasilense were studied in light and dark environments: HM053 (high BNF and auxin production), ipdC (capable of BNF, deficient in auxin production), and FP10 (capable of auxin production, deficient in BNF). HM053 exhibited the highest rate of nitrogenase activity with the greatest light dependency comparing iterations in light and dark environments. The ipdC mutant showed similar behavior with relatively lower nitrogenase activity observed, while FP10 did not show a light dependency. Auxin biosynthesis showed strong light dependencies in HM053 and FP10 strains, but not for ipdC. Ferrous iron is involved in BNF, and a light dependency was observed for microbial 59Fe2+ uptake in HM053 and ipdC, but not FP10. Surprisingly, a light dependency for 52Mn2+ uptake was only observed in ipdC. Finally, ATP biosynthesis was sensitive to light across all three mutants favoring blue light over red light compared to darkness with observed ATP levels in descending order for HM053 > ipdC > FP10. [ABSTRACT FROM AUTHOR]

Globally, optimized doses of exogenously applied growth regulators hold the potential to sustainably boost the growth and productivity of leguminous crops, including green gram. A field investigation was undertaken at the Agronomy Farm of the University of Agriculture Faisalabad, Pakistan in 2021–2022 to determine the highest-performing doses of foliar-applied salicylic acid (S1 = 0 and S2 = 75 ppm) and gibberellic acid (G1 = 0, G2 = 30, G3 = 60, G4 = 90 and G5 = 120 ppm) for green gram (cv. NIAB-MUNG 2011) sown under irrigated conditions in a semiarid climate. The response variables included physiological growth traits (CGR and net assimilation rate (NAR)), yield attributes (plant height (PH), PBs and the number of pods per plant−1 (NP), pod length (PL) and SW, grain (GY) and biological yields (BY), the biosynthesis of pigments (chlorophyll a, chlorophyll b and total chlorophyll along with carotenoids) and protein (P) contents. The results revealed that S2G5 remained unmatched in that it exhibited the highest crop growth rate, while it remained on par with S2G4 and S2G3 in terms of its net assimilation rate. Additionally, S2G5 maximized plant height, the number of pod-bearing branches and pods per plant, pod length, seed number per pod−1 and 1000-seed weight, which led to the highest grain yield and biological yield (104% and 69% greater than those of the control, respectively). Moreover, the same treatment combination also surpassed the rest of the treatments because it recorded the largest amounts of chlorophyll and carotenoid contents, and the P content was increased to 24% greater than that observed for the control treatment. Thus, the exogenous application of salicylic acid (75 ppm) and gibberellic acid (120 ppm) might be recommended to green gram growers to sustainably increase the plant's yield and nutritional value, and these findings may serve as a baseline for conducting more studies to test higher doses of these growth regulators. [ABSTRACT FROM AUTHOR]

Bryophytes maintain symbiosis with bacteria influencing the local nutrient budget. Moss bacterial communities are composed of a core microbiome and bacteria recruited from environmental sources. Notably, symbiotic N2-fixing bacteria contribute to the N budget in northern ecosystems through biological nitrogen fixation. This process may be affected by the abundance of diazotrophs and moss nutrient content. We used the abundant moss Racomitrium lanuginosum in a forest tundra and shrub tundra in Northern Quebec, Canada, to investigate the bacterial and diazotrophic communities associated with habitat type using amplicon sequencing of the bacterial 16S rRNA and nifH genes and test whether the moss core microbiome has recruitment from the soil bacteria community. The nifH amplicons and element analysis were used to test the effect of diazotrophic abundance and moss nutrient content on N2-fixation activity estimated by acetylene reduction assays. Moss microbial communities between tundra types hosted similar bacterial diversity but differentially abundant groups and characteristic microbial interaction patterns. The core microbiome of R. lanuginosum is composed of bacteria strongly associated with northern mosses with no significant recruitment from the soil. The relative abundances of dominant diazotrophs are significantly correlated with acetylene reduction rates. In contrast, the moss nutrient content did not significantly drive N2-fixation. The proteobacterial genera Azorhizobium and Rhodomicrobium represent newly reported bacteria associated with N2-fixation rates in the tundra. We identified critical bacterial groups related to moss-bacterial symbiosis and N2-fixation in the forest-tundra transition zone, a changing environment susceptible to climate warming. [ABSTRACT FROM AUTHOR]

Brazil is an important peanut producer, but despite its high production, there still needs to be an inoculant for the peanut crop. In addition, the use of microorganisms that promote plant growth (PGPM) is not common, and this crop is highly dependent on chemical fertilizers. An excellent alternative to reduce the use of fertilizers and chemical inputs in peanut crops while reducing the production cost and environmental impact is the use of PGPM. The objective of this study was to evaluate the effects of Azospirillum brasilense, Bacillus subtilis, Bradyrhizobium japonicum, and Trichoderma harzianum as single inoculants and co-inoculants on the growth promotion and productivity of peanuts in greenhouse and field conditions. In the greenhouse, the experiment was conducted with 12 treatments with six repetitions. In the field conditions, the experiment was conducted with five treatments with four repetitions. Both experiments were conducted in randomized blocks. In general, all the microorganisms evaluated in the present study promoted increases in root dry mass, shoot dry mass, phosphorus concentrations, and plant height in the greenhouse and under field conditions compared with the control. Interestingly, the mixtures of microorganisms inoculated in peanut plants did not promote greater plant growth and development compared with inoculations of the microorganisms separately. Specifically, in the field, the highest productivity was found for the inoculation of B. japonicum alone. The PGPM evaluated in the present study for peanut crops generally promoted some increases in productivity in greenhouse and field conditions.

Legumes in Conservation Agriculture (CA) have the potential to increase crop productivity and sustainability of the rice-based system. However, there is limited information available on the importance of legume crops in CA in the rice-based system of the Eastern Indo-Gangetic Plain (EIGP). Rice-based cropping is the mainstay of the people in Bangladesh, on the EIGP. These systems are the major food supplier to the region. In addition, they provide income and employment opportunities to the majority of people in the region. However, the system is facing unprecedented challenges and increased risk due to water, energy, labour and capital scarcity, which are exaggerated due to the effects of climate change. This could be further aggravated by deteriorating soil health, depleting underground water, and reduced land and water productivity which ultimately threaten sustainable food production and food security of the EIGP. Hence, sustainable crop intensification is essential, but increasing cropping intensity has reduced the yield of single crops by degrading soil properties. To address these constraints, Conservation Agriculture (CA), with a minimum tillage system, residue retention and crop diversification with legumes, could be an effective approach for improving crop productivity while sustaining the natural resources in intensive rice-based systems of EIGP. The addition of legumes in crop rotation is a suitable technique for crop diversification due to its multiple benefits related to soil health and natural resources. Diverse legume crops involving rice-based cropping exist at different agro-ecological zones in Bangladesh, and their rotation definitely could act a major role in promoting the CA in rice-based systems. Legume-based rotation offers multiple benefits, such as biological nitrogen fixation, improves soil pores through the deep root system, P-availability, soil fertility and enhanced nutrient cycling, and reducing the use of external input and thereby minimizing greenhouse gas emission and groundwater pollution, improving water productivity, and minimizes diseases and pest incidence. As a result, crop rotation with legumes has a high potential for CA and sustainable rice-based cropping systems in Bangladesh. The gaps between legume and non-legume crops in CA for each parameter suggest a noteworthy possibility for the improvement of rice-based systems in EIGP. This review suggests further sustainability improvements can be achieved through future field research focused on the inclusion of legume crops in the diverse rice-based systems under CA.

Sulfate reducing bacteria (SRB) comprise one of the few prokaryotic groups in which biological nitrogen fixation (BNF) is common. Recent studies have highlighted SRB roles in N cycling, particularly in oligotrophic coastal and benthic environments where they could contribute significantly to N input. Most studies of SRB have focused on sulfur cycling and SRB growth models have primarily aimed at understanding the effects of electron sources, with N usually provided as fixed-N (nitrate, ammonium). Mechanistic links between SRB nitrogen-fixing metabolism and growth are not well understood, particularly in environments where fixed-N fluctuates. Here, we investigate diazotrophic growth of the model sulfate reducer Desulfovibrio vulgaris var. Hildenborough under anaerobic heterotrophic conditions and contrasting N availabilities using a simple cellular model with dual ammoniotrophic and diazotrophic modes. The model was calibrated using batch culture experiments with varying initial ammonium concentrations (0–3000 µM) and acetylene reduction assays of BNF activity. The model confirmed the preferential usage of ammonium over BNF for growth and successfully reproduces experimental data, with notably clear bi-phasic growth curves showing an initial ammoniotrophic phase followed by onset of BNF. Our model enables quantification of the energetic cost of each N acquisition strategy and indicates the existence of a BNF-specific limiting phenomenon, not directly linked to micronutrient (Mo, Fe, Ni) concentrations, by-products (hydrogen, hydrogen sulfide), or fundamental model metabolic parameters (death rate, electron acceptor stoichiometry). By providing quantitative predictions of environment and metabolism, this study contributes to a better understanding of anaerobic heterotrophic diazotrophs in environments with fluctuating N conditions.

Abstract Background Nitrogen is considered the most limiting nutrient element for herbivorous insects. To alleviate nitrogen limitation, insects have evolved various symbiotically mediated strategies that enable them to colonize nitrogen-poor habitats or exploit nitrogen-poor diets. In frugivorous tephritid larvae developing in fruit pulp under nitrogen stress, it remains largely unknown how nitrogen is obtained and larval development is completed. Results In this study, we used metagenomics and metatranscriptomics sequencing technologies as well as in vitro verification tests to uncover the mechanism underlying the nitrogen exploitation in the larvae of Bactrocera dorsalis. Our results showed that nitrogenous waste recycling (NWR) could be successfully driven by symbiotic bacteria, including Enterobacterales, Lactobacillales, Orbales, Pseudomonadales, Flavobacteriales, and Bacteroidales. In this process, urea hydrolysis in the larval gut was mainly mediated by Morganella morganii and Klebsiella oxytoca. In addition, core bacteria mediated essential amino acid (arginine excluded) biosynthesis by ammonium assimilation and transamination. Conclusions Symbiotic bacteria contribute to nitrogen transformation in the larvae of B. dorsalis in fruit pulp. Our findings suggest that the pattern of NWR is more likely to be applied by B. dorsalis, and M. morganii, K. oxytoca, and other urease-positive strains play vital roles in hydrolysing nitrogenous waste and providing metabolizable nitrogen for B. dorsalis.

The usage of plant growth-promoting bacteria (PGPB) in mitigation of harmful effects of lead (Pb) toxicity in plants and bioremediation of it from soils is a sustainable, effective and low-cost strategy. The experiment was laid out to investigate the role of PGPB on morphological and physiological growth, root system architecture and nodulation of lentil under Pb stress. The experiment was conducted according to completely randomized factorial design with four replications at the laboratory of the Field Crops Department, Siirt University, Siirt in 2022. The four Pb levels and three bacterial inoculations were used in the experiment. Plant height, seedling fresh weight, root fresh weight, seedling dry weight, root dry weight, total chlorophyll content, taproot length, number of lateral roots, total root length and number of nodule varied between 15.7-25.9 cm, 0.123-0.235 g, 0.019-0.092 g, 0.0104-0.0326 g, 0.0076-0.0146 g, 27.9-47.2%, 8.9-19.2 cm, 4.00-14.67, 17.6-44.8 cm and 1.37-10.63, respectively. Bio-priming with PGPB containing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity increased dry matter accumulation up to 56.1% and 22.9% in shoots and roots, respectively. Chlorophyll content enhanced up to 17.9% compared with control application. Besides, root system architecture and nodule formation were improved by bio-priming both under stress and non-stress conditions. Bio-priming with PGPB may be a sustainable solution to mitigate oxidative stress and promote plant growth and yield in lentil under Pb-contaminated soils.

Background: Legumes can fix atmospheric nitrogen (N) and facilitate N availability to their companion plants in crop mixtures. However, biological nitrogen fixation (BNF) of legumes in intercrops varies largely with the identity of the legume species. The aim of our study was to understand whether BNF and concentration of plant nutrients by common bean is influenced by the identity of the companion plant species in crop mixtures. In this greenhouse pot study, common beans were cultivated with another legume (chickpea) and a cereal (Sorghum). We compared BNF, crop biomass and nutrient assimilation of all plant species grown in monocultures with plants grown in crop mixtures. Results: We found beans to exhibit low levels of BNF, and to potentially compete with other species for available soil N in crop mixtures. The BNF of chickpeas however, was enhanced when grown in mixtures. Furthermore, biomass, phosphorous and potassium values of chickpea and Sorghum plants were higher in monocultures, compared to in mixtures with beans; suggesting competitive effects of beans on these plants. Concentration of calcium, magnesium and zinc in beans was higher when grown with chickpeas than with Sorghum. Conclusions: It is generally assumed that legumes benefit their companion plant species. Our study highlights the contrary and shows that the specific benefits of cereal-legume mixtures are dependent on the growth rate of the species concerned. We further highlight that the potential of legume-legume mixtures is currently undervalued and may play a strong role in increasing N use efficiency of intercrop-based systems. [ABSTRACT FROM AUTHOR]

Despite evidence showing that plant diversity or tree mixtures increase carbon storage in experimental grasslands or mixed forests, the effects of understorey plant communities on changes in soil organic carbon (SOC) storage in planted forests remain unclear, especially for monoculture plantations. Therefore, based on field observations in monoculture plantations on the Loess Plateau in China, we investigated the direct effects of understorey species richness (USR) and plantation age on SOC storage, and identified the indirect effects of understorey legume species richness (ULSR) and soil moisture (SM) mediated by USR. Results indicated that plantation age and USR significantly increased SOC sequestration with almost equal effects. The changes in the relationship between USR and SOC storage varied along the water availability gradient, from significantly positive (in plots with SM ≤11.14%) to insignificant (in plots with SM >11.14%). We observed that ULSR could increase SOC sequestration by promoting USR, while SM had negative and positive effects on ULSR and USR, respectively. Our findings can provide insights into plantation management in semiarid regions: Thinning mature plantations and introducing understorey legumes can increase SOC sequestration and maintain water resource sustainability. [ABSTRACT FROM AUTHOR]

Background: Biological nitrogen fixation converting atmospheric dinitrogen to ammonia is an important way to provide nitrogen for plants. Pseudomonas stutzeri DSM4166 is a diazotrophic Gram-negative bacterium isolated from the rhizosphere of cereal Sorghum nutans. Endogenous constitutive promoters are important for engineering of the nitrogen fixation pathway, however, they have not been systematically characterized in DSM4166. Results: Twenty-six candidate promoters were identified from DSM4166 by RNA-seq analysis. These 26 promoters were cloned and characterized using the firefly luciferase gene. The strengths of nineteen promoters varied from 100 to 959% of the strength of the gentamicin resistance gene promoter. The strongest P12445 promoter was used to overexpress the biological nitrogen fixation pathway-specific positive regulator gene nifA. The transcription level of nitrogen fixation genes in DSM4166 were significantly increased and the nitrogenase activity was enhanced by 4.1 folds determined by the acetylene reduction method. The nifA overexpressed strain produced 359.1 µM of extracellular ammonium which was 25.6 times higher than that produced by the wild-type strain. Conclusions: The endogenous strong constitutive promoters identified in this study will facilitate development of DSM4166 as a microbial cell factory for nitrogen fixation and production of other useful compounds. [ABSTRACT FROM AUTHOR]

Aims: The improvement of biological nitrogen fixation (BNF) is beneficial to improving legume yield and soil fertility. Thus, the potential of a white-rot fungus Ceriporia lacerata HG2011 in promoting soybean BNF and yield along with the mechanisms was investigated. Methods: Fungal metabolites and the effects of C. lacerata HG2011 on rhizobial growth, chemotaxis, and biofilm formation were investigated through pure culture. Soybeans inoculated with this fungus were grown in the climatic cabinet, greenhouse, and field for measuring nodulation parameters, BNF-related enzyme activity, BNF, and yield. Results: Although C. lacerata HG2011 had no significant influence on the growth of the rhizobium Ensifer fredii S2-1, the rhizobial chemotaxis and biofilm formation were improved by this fungus broth in pure culture. C. lacerata HG2011 dwelled on the root surface, increased root tips and surface area, produced the nodulation-associated metabolites (phytohormones, flavonoids, and low-molecular-weight organic acids) and hydrolases (cellulase, pectinase, protease, and phosphatase), mobilized soil P and Fe, and stimulated the activities of plant BNF-related enzymes (nitrogenase, glutamine synthetase, and dehydrogenase). Compared with fungus-free control plants, C. lacerata HG2011 improved nodulation and increased %Ndfa by 3.61–4.64%, BNF by 29.26–40.68%, nutrients uptake (N, P, and K) by 4.38–19.60%, and mean grain yield by 10.55% in the fields. Conclusion: C. lacerata HG2011 promoted rhizobial chemotaxis as well as soybean nodulation and BNF via releasing phytohormones and improving mineral nutrition. Thus, the fungal inoculant significantly increased soybean yield in both greenhouse and fields, showing a promising application in legume cultivation. [ABSTRACT FROM AUTHOR]

The seed treatment with Mo associated with other elements, such as Ni and Co, and with micronutrients, such as Cu, Mn, and Zn, has been highlighted. The use of these associations can affect the adequate dose of Mo and the risk of toxicity. This study aimed to determine whether the optimal and the toxic dose of Mo can be affected by the accompanying elements of the group Co and Ni in relation to Cu, Mn, and Zn for the treatment of soybean seeds. Two experiments were carried out. The treatments in experiment I consisted of five doses of a product containing Mo, Co, and Ni at the concentrations of 0, 30-, 60-, 90-, and 120-mL ha−1. In experiment II, the treatments consisted of five doses of a product containing Mo, Cu, Mn, and Zn at the concentrations of 0, 50-, 100-, 200-, and 400-mL ha−1. The optimal dose of Mo was low (6.7 g ha−1) when applied along with Cu, Mn, and Zn as accompanying elements in relation to Co and Ni (17.5 g ha−1 of Mo). Application of the optimal dose provided an increase in N accumulation and in the chlorophylls, carotenoids, and phenolic compounds, decreasing the extravasation of electrolytes and increasing photosynthetic efficiency, dry matter, and yield. Mo toxicity was more severe with Cu, Mn, and Zn as accompanying elements, already occurring at the low dose of 18.9 g ha−1 Mo, which is much lower when Mo is associated with Co and Ni (32 g ha−1 Mo). [ABSTRACT FROM AUTHOR]

[Objective] The present paper aimed to screen leguminous plants suitable for improving the soil of bauxite mine reclaimed soil and provide a reference basis for sustainable agricultural development in mining areas. [Method] Seven legumes, including Sesbania cannabina, Vicia sativa, Astragalus sinicus, V. villosa, Medicago sativa, Stylosanthes guianensis and Coronilla varia, were planted in the reclaimed soil of the Pingguo bauxite mine in Guangxi, and the biomass, presence of root nodules, nutrient content, nitrogen fixation efficiency, biological nitro- gen fixation, soil nutrients, calcium and magnesium ion content, total aluminum and active aluminum content of each legume were determined. The legumes suitable for planting in bauxite mine reclamation soil were screened through principal component analysis, and a partial least squares path model (PLS-PM) was established to explore the factors that affected the biological nitrogen fixation of legumes in bauxite mine reclamation soil. [Result] Among the seven legumes, A. sinicus had the highest below-ground biomass(1.961 g/pot) and above-ground bio-mass (0.344 g/pot), C. varia had the lowest below-ground biomass (0.387 g/pot) and above-ground biomass (0.099 g/pot) while Sesbania had the highest N(7.98% ), P(2.999 g/kg), and K(19.828 g/kg) contents. In terms of nodulation, only Sesbania, A. sinicus, and C. varia had root nodules, while the rest of the legumes did not nodulate. Among the three nodulated legumes, S. cannabina had the highest nitrogen fixation efficiency (80.01%) and biological nitrogen fixation (0.077 g/pot). Principal component analysis of three leguminous plants based on evaluation factors including plant nutrient content, biomass, biological nitrogen fixation, and nitrogen fixation efficiency as evaluation factors showed that comprehensive score of S. cannabina repens was the highest (2.30 points). PLS-PM pathway analysis showed that the biological nitrogen fixation of legumes in bauxite mine reclamation soil was directly influenced by plant nutrient content and soil active aluminum and pH, soil nutrients, and types of plants indirectly influenced the biological nitrogen fixation of legumes by affecting plant nutrient content and soil active aluminum. [Conclusion] S. cannabina, A. sinicus, and C. varia are capable of nodulating and improving the pH, available K, ac- tive aluminum, organic matter content, and biological nitrogen fixation of the reclaimed soil in bauxite mines. Based on the comprehensive e- valuation, S. cannabina is considered as the most suitable legume plant for planting in the reclaimed soil of bauxite mines and can be promo- ted and applied as a legume plant for nitrogen fixation and soil improvement in bauxite mining areas. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agricultural Science & Technology (1008-0864) is the property of Journal of Agricultural Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Glasnik Zastite Bilja is the property of Zadruzna Stampa D.D. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The objective of this work was to assess the effects of A. brasilense inoculation on seeds on the yield performance of maize and black oat as a function of nitrogen rate over a 3-year succession. The experiment was conducted from 2015 to 2018 under field conditions. Maize was grown for three growing seasons in rotation with two seasons of black oat at the same experimental site. A randomized block design with a split-plot arrangement was used. Main plots consisted of A. brasilense inoculation (inoculated and uninoculated plants) and subplots of four nitrogen rates (0, 40, 80, and 120 kg ha-1). Maize plants were evaluated for biometric parameters, yield, and yield components at flowering. Black oat plants were analyzed for dry matter yield at flowering. The inoculation of A. brasilense in maize and black oat seeds in succession does not promote productivity nor does it favor the nitrogen fertilization of these cultures. [ABSTRACT FROM AUTHOR]

This study evaluated the combined effect of foliar spray inoculation with plant growth-promoting bacteria (PGPB) and nitrogen doses on the yield, development, and nutritive value of Megathyrsus maximus cv. BRS Zuri. The experimental design was randomized blocks with four replications, with repeated measures in time. Foliar inoculation of two bacteria (Azospirillum brasilense Ab-V5 (CNPSo 2083) and Ab-V6 (CNPSo 2084) and Pseudomonas fluorescens (CNPSo 2799)) and 40 and 80 kg ha−1 N (urea) rates, in addition to the control (without inoculation and N fertilization), were applied. In the rainy season, at the level of 40 kg ha−1 of N, inoculation of both A. brasilense and P. fluorescens increased, respectively, the tiller number by 33% and 25% (22 February), and the N accumulated in tissues by 42% and 25% (22 January), while in the previous year (21 February) the beneficial effects of both bacteria were observed in the percentage of leaf blade and in the true digestibility in vitro. When the foliar spray was inoculated with A. brasilense Ab-V5 and Ab-V6 and P. fluorescens CNPSo 2799, with 80 kg N ha−1, the root system of Zuri grass increased by 61% and 30%, respectively. [ABSTRACT FROM AUTHOR]

The great challenge of reducing soil nutrient depletion and assuring agricultural system productivity in low-income countries caused by limited synthetic fertilizer use necessitates local and cost-effective nutrient sources. We estimated the changes of the nitrogen budget of agricultural systems in the East African Community from 1961 to 2018 to address the challenges of insufficient nitrogen inputs and serious soil nitrogen depletion in agricultural systems of the East African Community region. Results showed that total nitrogen input increased from 12.5 kg N ha-1yr-1 in the 1960s to 21.8 kg N ha-1yr-1 in the 2000s and 27 kg N ha-1yr-1 in the 2010s. Total nitrogen crop uptake increased from 12.8 kg N ha-1yr-1 in the 1960s to 18.2 kg N ha-1yr-1 in the 2000s and 21.8 kg N ha-1yr-1 in the 2010s. Soil nitrogen stock increased from -2.0 kg N ha-1yr-1 in the 1960s to -0.5 kg N ha-1yr-1 in the 2000s and 0.3 kg N ha-1yr-1 in the 2010s. Our results allow us to substantiate for the first time that soil nitrogen depletion decreases with increasing input of nitrogen in agricultural systems of the East African Community region. This suggests that increases in nitrogen inputs through biological nitrogen fixation and animal manure are the critical nitrogen management practices to curb soil nitrogen depletion and sustain agricultural production systems in the East African Community region in order to meet food demand for a growing population. [ABSTRACT FROM AUTHOR]

Soybean physiology, seed yield and composition can vary greatly and are a function of genetics, environment, and management practices. N fertilizer is not often applied to soybeans, but it can affect yield and seed composition, and the outcome of N fertilization has varied widely among studies. To test if certain physiological responses might be linked with positive agronomic responses to N fertilizer, a field study was conducted in varied environments unique to the Southeast United States (US). Five genotypes from maturity groups V-VII were evaluated. Although the environment and genotype had significant effects on most of the physiological characteristics and yield components measured, nitrogen application interacted significantly with environment for seed protein concentration, seed oil concentration, yield, and percent of nitrogen derived from the atmosphere in leaves during the seed fill period. The direction of the nitrogen effect on protein concentration differed among environments, increasing protein concentration in one environment and reducing protein concentration in another environment. Nitrogen application effects did not vary among the genotypes included in this study. Photosynthetic and nitrogen fixation responses to nitrogen application were not clearly linked with seed protein concentration response. A tailored nitrogen recommendation for environment is the best option for improving seed protein in this region with diverse environmental conditions. [ABSTRACT FROM AUTHOR]

Adopting sustainable technologies that optimize biological nitrogen fixation by grain legumes is vital to improve plant growth and ensure high grain yield levels. This study investigated the effectiveness of molybdenum application methods and inoculation with Bradyrhizobium japonicum and Azospirillum brasilense either alone or in combination with nodulation and growth of cowpea and mungbean plants cropping in sandy soil from the Brazilian Cerrado. The experiments were arranged in a randomized block design in a 3 × 5 factorial arrangement with four replicates. The treatments consisted of three Mo application methods (control, seed treatment, and foliar application) and five nitrogen supply methods [control (uninoculated seeds and unfertilized with N), inoculation with Bradyrhizobium japonicum, inoculation with Azospirillum brasilense; co-inoculation with B. japonicum and A. brasilense, and a treatment with mineral N application]. Our results showed that co-inoculation with Bradyrhizobium japonicum and Azospirillum brasilense improves the root nodulation of mungbean plants compared to inoculation of B. japonicum alone or A. brasilense alone. The molybdenum application on seeds or leaves has little effect in enhancing the nodulation and growth of cowpea and mungbean plants grown in agricultural soils from the Brazilian Cerrado. [ABSTRACT FROM AUTHOR]

Brazil is an important peanut producer, but despite its high production, there still needs to be an inoculant for the peanut crop. In addition, the use of microorganisms that promote plant growth (PGPM) is not common, and this crop is highly dependent on chemical fertilizers. An excellent alternative to reduce the use of fertilizers and chemical inputs in peanut crops while reducing the production cost and environmental impact is the use of PGPM. The objective of this study was to evaluate the effects of Azospirillum brasilense, Bacillus subtilis, Bradyrhizobium japonicum, and Trichoderma harzianum as single inoculants and co-inoculants on the growth promotion and productivity of peanuts in greenhouse and field conditions. In the greenhouse, the experiment was conducted with 12 treatments with six repetitions. In the field conditions, the experiment was conducted with five treatments with four repetitions. Both experiments were conducted in randomized blocks. In general, all the microorganisms evaluated in the present study promoted increases in root dry mass, shoot dry mass, phosphorus concentrations, and plant height in the greenhouse and under field conditions compared with the control. Interestingly, the mixtures of microorganisms inoculated in peanut plants did not promote greater plant growth and development compared with inoculations of the microorganisms separately. Specifically, in the field, the highest productivity was found for the inoculation of B. japonicum alone. The PGPM evaluated in the present study for peanut crops generally promoted some increases in productivity in greenhouse and field conditions. [ABSTRACT FROM AUTHOR]

Cover crops can increase agricultural sustainability by protecting soil from erosion, increasing biodiversity, and symbiotically incorporating fixed nitrogen (N) into the soil. Nowadays, however, in Uruguay mostly grasses are planted in autumn to protect the soil from erosion. Another option is to study tropical legumes’ performance as cover crops, which can fix substantial amounts of nitrogen in short growing periods, thereby bridging the knowledge gap in Uruguayan agriculture. The main objective was to evaluate and compare the performance of six tropical legumes (Crotalaria juncea, Crotalaria spectabilis, Crotalaria ochroleuca, Cajanus cajan, Dolichos lablab, Mucuna pruriens) and the temperate legume Glycine max. The evaluation focused on aboveground biomass and the N mass derived from fixation (NmdFix), as well as other attributes; three field experiments were conducted on a southern Uruguay farm during the summers of 2017, 2018, and 2019. The growing cycle lengths for the cover crops in 2017, 2018, and 2019 were 117, 130, and 90 days, respectively. The results showed that when planting was done at late December (2017 and 2018 growing cycles), the species with the highest mean biomass yield were Crotalaria juncea (two year average 12.0 Mg ha-1) and Cajanus cajan (11.0 Mg ha-1), but Cajanus cajan (149 kg ha-1) more than doubled the NmdFix mass of Crotalaria juncea (57 kg ha-1). In 2018 biomass yields were much higher than in 2017, with Glycine max (20.0 Mg ha-1) yielding at a similar level to Crotalaria juncea and Cajanus cajan (20.5 and 18.7 Mg ha-1, respectively). Amounts of NmdFix, however, were much higher in Glycine max and Cajanus cajan (263 and 253 kg N ha-1, respectively), than in Crotalaria juncea (91 kg N ha-1). In 2019 planting had to be delayed until early February and only Glycine max maintained acceptable biomass and NmdFix levels. In conclusion, based on its fixing N potential, for late December sowings Cajanus cajan and Glycine max would be the most promising species for cover crop use, while for late January or early February sowings, only Glycine max would an option because the tropical species seriously impaired their productivity when grew longer into the cooler autumn temperatures.

Due to the increase in food-borne diseases, especially in recent years, consumers' orientation to healthy products and their emphasis on consumption force producers to environmentally friendly products. Nitrogen is the most widely used plant nutrient in the world. Nitrogen, a very expensive input due to its excessive use, pollutes the environment and causes nitrate accumulation in plants. Therefore, vegetable growers strive to replace chemical fertilizers such as nitrogen with environmentally friendly and cost-effective sources. PGPRs stand out in this regard and at the same time, their potential in environmentally and consumer-friendly vegetable production needs to be revealed. In this study, the importance and potential role of N2-fixing PGPR are discussed for the improvement of yield and yield components in environment-friendly vegetable production for healthy human nutrition.

Information on how bacteria in plants and soil, along with extracellular enzymes, affect nutrient cycling in Encephalartos villosus growing in phosphorus deficient and acidic scarp forests is lacking. Bacteria in coralloid roots, rhizosphere, and non-rhizosphere soils were isolated to determine the potential role of soil bacterial communities and their associated enzyme activities in nutrient contributions in rhizosphere and non-rhizosphere soils. The role of soil characteristics and associated bacteria on E. villosus nutrition and nitrogen source reliance was investigated. Encephalartos villosus leaves, coralloid roots, rhizosphere, and non-rhizosphere soils were collected at two scarp forests. Leaf nutrition, nitrogen source reliance, soil nutrition, and extracellular enzyme activities were assayed. A phylogenetic approach was used to determine the evolutionary relationship between identified bacterial nucleotide sequences. The clustering pattern of isolated bacterial strains was primarily dictated by the ecological niches from which they originated (rhizosphere soil, non-rhizosphere soil, and coralloid roots), thus indicating that host-microbe interactions may be a key driver of this pattern, in line with the hologenome theory. There were insignificant differences in the phosphorus and nitrogen cycling enzyme activities in E. villosus rhizosphere and non-rhizosphere soils in both localities. Significantly positive correlations were recorded between nitrogen and phosphorus cycling enzymes and phosphorus and nitrogen concentrations in rhizosphere and non-rhizosphere soils. Additionally, more than 70% of the leaf nitrogen was derived from the atmosphere. This study challenged the conventional expectation that environmental filters alone dictate microbial community composition in similar habitats and revealed that host-microbe interactions, as proposed by the hologenome theory, are significant drivers of microbial community structuring. The isolated bacteria and their plant growth promoting traits play a role in E. villosus nutrition and nitrogen source reliance and secrete nutrient cycling enzymes that promote nutrient availability in rhizosphere and non-rhizosphere soils.

The legume family includes approximately 19,300 species across three large subfamilies, of which Papilionoideae stands out with 13,800 species. Lentils were one of the first crops to be domesticated by humans, approximately 11,000 BP. They are diploid legumes that belong to the Papilionoidea subfamily and are of agricultural importance because of their resistance to drought and the fact that they grow in soil with a pH range of 5.5–9; therefore, they are cultivated in various types of soil, and so they have an important role in sustainable food and feed systems in many countries. In addition to their agricultural importance, lentils are a rich source of protein, carbohydrates, fiber, vitamins, and minerals. They are key to human nutrition since they are an alternative to animal proteins, decreasing meat consumption. Another characteristic of legumes, including lentils, is their ability to form nodules, which gives them a growth advantage in nitrogen-deficient soils because they enable the plant to fix atmospheric nitrogen, thus contributing nitrogen to the soil and facilitating the nutrition of other plants during intercropping. Lentils have also been applied for protection against various human diseases, as well as for phytoremediation, and they also have been applied as environmental bioindicators to identify cytotoxicity. This review addresses the importance of lentils in agriculture and human health.

The application of nitrogen fertilizer is crucial to the growth and biological nitrogen fixation of peanut, especially in the seedling stage where nodules have not yet formed. However, it is still uncertain how much initial nitrogen fertilizer should be applied to promote peanut root growth, nodule formation, and biological nitrogen fixation (BNF). There, a 2-year pot experiment was conducted using Huayu 22 (HY22, large-grain cultivar) and Huayu 39 (HY39, small-grain cultivar) as experimental materials to research the effects of different initial nitrogen fertilizer application rates on peanut root growth (root weight, root length, root mean diameter, root activity) and biological nitrogen fixation capacity (nodule number, nodule weight, biological nitrogen fixation, and nitrogen fixation potential per plant). N0, as control, four initial nitrogen fertilizer application rates were established: 15 kg·hm−2 (N15), 30 kg·hm−2 (N30), 45 kg·hm−2 (N45), and 60 kg·hm−2 (N60). The present results showed that the nodule number, nodule dry weight, nitrogenase activity, and biological nitrogen fixation of the HY22 cultivar under the N15 treatment were higher compared to those under other treatments over the two growing seasons. In addition, the cultivar of HY39 treated with the N15 treatment also increased the nitrogen fixation potential per plant and BNF relative to other treatments. Although the application of 60 kg·hm−2 nitrogen increased the root surface area and root volume, it decreased the nitrogenase activity, nodule dry weight, and nitrogen fixation potential per plant of HY22 and HY39 varieties in both growing seasons. Above all, an initial nitrogen application of 15 kg·hm−2 may be the optimal treatment for promoting peanut nodule formation and biological nitrogen fixation.

Purpose Nitrogen-fixing bacteria (NFB) are essential for biologically fixing nitrogen in natural and soybean crop systems. The use of organomineral fertilizers is a promising crop management tool made from the mixing of an organic source and mineral fertilizers. This study evaluated the efficacy of an organomineral fertilizer (sewage sludge-based) as a carrier for the Azospirillum brasilense inoculation and the influence of A. brasilense plus Bradyrhizobium japonicum on the soybean antioxidant metabolism.Method The experiment was performed under greenhouse conditions. The soybean cultivar (AS 3680 IPRO) was evaluated in a 4×2(+1) factorial scheme, corresponding to four doses of A. brasilense [0, 100, 200, 300 mL ha-1 (2x108 viable cells mL-1) per 50 kg-1 of soybean seeds], with or without B. japonicum [100 mL ha-1 (5x109 viable cells mL-1) per 50 kg-1 of soybean seeds], and a control treatment (without inoculants or fertilizers). Soybean antioxidant metabolism (enzymes, oxidative processes, proline amino acid) was evaluated in different plant stages.Results The seed inoculation with A. brasilense via organomineral fertilizer enhanced the soybean plant protection factors. Plant protection to stresses happened mainly by reductions in the superoxide dismutase activity, lipid peroxidation, and hydrogen peroxide concentration. The co-inoculation of A. brasilense with B. japonicum enhanced the proline activity at the V3 and R5 soybean phenological stage compared to A. brasilense inoculated alone.Conclusion The studied organomineral fertilizer is an efficient inoculant carrier for A. brasilense in soybean plants via seed treatment. The protective results observed for A. brasilense were improved when co-inoculated with B. japonicum.

In Brazil, the common bean is a crop with significant social and economic importance. The prospecting of N2 fixing bacteria is crucial since biological nitrogen fixation (BNF) is an eco-friendly technique. This work aimed to obtain and characterize rhizobium isolates based on morpho-physiological, molecular, and symbiotic efficiency parameters, using the strains SEMIA 4077, SEMIA 4080, and SEMIA 4088 as references. The characteristics of the isolates and colonies, their tolerance to salinity and temperature, as well as their utilization of carbon sources, served as the basis for the morpho-physiological characterization. BOX-PCR, REP-PCR, and ERIC-PCR markers were used for genotypic characterization. Assessment of the symbiotic efficiency was carried out in a greenhouse, determining the number of nodules (NN), nodule dry weight (NDW), shoot dry weight (SDW), and total-N (Total-N) accumulation in the shoot. Among the isolates, those exhibiting: neutral culture medium pH, fast growth, colony diameter