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Plants grown under salinity are subject to many morphological and physiological disorders. In this context, practices that can enable the use of saline water are essential. The deleterious effects of salinity can be mitigated by using beneficial microorganisms, especially diazotrophic bacteria. In this context, this study aimed to evaluate the effect of bacterial inoculation and co-inoculation using Bradyrhizobium spp. and Azospirillum brasilense on the growth, nodulation and production of cowpea under salt stress. The experiment was conducted using a randomized block design, in a 4 × 5 factorial arrangement, corresponding to four nitrogen sources (N1 - without nitrogen and without inoculant; N2 - fertilization with mineral nitrogen and without inoculant; N3 - inoculation of Bradyrhizobium spp.; and N4 - co-inoculation of Bradyrhizobium spp. and Azospirillum brasilense) and five values of electrical conductivity of irrigation water - ECw (0.4, 1.9, 3.4, 4.9 and 6.4 dS m-1), with five replicates. Co-inoculation with Azospirillum brasilense and Bradyrhizobium spp. favors the growth, production and nodulation of cowpea plants up to ECw of 0.4 dS m-1. Increase in the electrical conductivity of irrigation water negatively affects the growth, production and nodulation of cowpea plants in Corujinha variety, regardless of the nitrogen source used.

Deadwood is an extremely nitrogen (N) poor plant litter whose decomposition may rely on external N sources. Biological N2 fixation (BNF) by free-living diazotrophs, encoded with the nifH gene, is a potential pathway of N acquisition in deadwood. Still, the control of this process by tree species specific traits is hardly known. Here, we examined (1) BNF rates and nifH gene abundances in deadwood of 13 tree species after 12 years of decomposition and (2) how BNF was related to nutrient concentrations and non-structural carbohydrates (NSC). Comparing our BNF rates with the literature revealed no difference for angiosperms but gymnosperms. Large variability prevented any significant difference in BNF and nifH gene abundance between tree species identities of deadwood. Still, higher BNF and nifH gene abundances occurred in the group of diffuse-porous angiosperms compared to ring-porous angiosperms and gymnosperms. Positive relationships between BNF rates and molybdenum, phosphor, sulfur, and N suggested co-limitation of BNF by several nutrients in deadwood. Relatively high NSC concentrations indicated no carbon limitation of diazotrophs. Furthermore, structural equation modeling highlighted the importance of water content for BNF and nifH gene abundance, although the overall explanatory power was low. In conclusion, BNF is a ubiquitous microbial process in deadwood of all tree species, contributing to N enrichment during the long-term decay process and possibly reducing N limitation for deadwood degrading fungi.

The objective of this work was to verify the contribution of seed inoculation with the bacterium Azospirillum brasilense to promote growth on yield components in wheat crop. For this, experiments were carried out in different locations (Santa Maria and Cruz Alta, RS, Brazil), sowing times (June and July) and years of cultivation (2013 and 2014). A randomized block design with three replications was used. The treatments were composed by the combination of ten cultivars, three nitrogen managements and two types of inoculation (10 x 3 x 2). Inoculation was carried out with liquid inoculant in the seeds. The components of grain yield were evaluated. The average number of tillers per plant was influenced by seed inoculation (1.63 and 1.72) when uninoculated and inoculated, respectively. On the other hand, the hectoliter mass responded inversely, reducing to 75.7 kg hL-1. Inoculation with A. brasilense increased the grain mass (1%) and had no positive influence on the variables number of ears and spikelets per ear, grain yield and hectoliter weight. RESUMO O objetivo deste trabalho foi verificar a contribuição da inoculação de sementes com a bactéria Azospirillum brasilense para a promoção de crescimento sobre os componentes de rendimento na cultura do trigo. Para isso, foram conduzidos experimentos em distintos locais (Santa Maria e Cruz Alta, RS, Brasil), épocas de semeadura (junho e julho) e anos de cultivo (2013 e 2014). Foi utilizado o delineamento de blocos casualisados com três repetições. Os tratamentos foram compostos pela combinação de dez cultivares, três manejos nitrogenados e dois tipos de inoculação (10 x 3 x 2). A inoculação foi realizada com inoculante líquido nas sementes. Foram avaliados os componentes da produtividade de grãos. O número médio de afilhos por planta foi influenciado pela inoculação das sementes (1,63 e 1,72) quando não inoculadas e inoculadas, respectivamente. Já a massa do hectolitro respondeu inversamente reduzindo para 75,7 kg hL-1. A inoculação com A. brasilense aumenta a massa grãos (1%) e não tem influência positiva nas variáveis número de espigas e de espiguetas por espiga, produtividade de grãos e massa hectolítrica.

Improving biological nitrogen fixation (BNF) in cereal crops is a long-sought objective; however, no successful modification of cereal crops showing increased BNF has been reported. Here, we described a novel approach in which rice plants were modified to increase the production of compounds that stimulated biofilm formation in soil diazotrophic bacteria, promoted bacterial colonization of plant tissues and improved BNF with increased grain yield at limiting soil nitrogen contents. We first used a chemical screening to identify plant-produced compounds that induced biofilm formation in nitrogen-fixing bacteria and demonstrated that apigenin and other flavones induced BNF. We then used CRISPR-based gene editing targeting apigenin breakdown in rice, increasing plant apigenin contents and apigenin root exudation. When grown at limiting soil nitrogen conditions, modified rice plants displayed increased grain yield. Biofilm production also modified the root microbiome structure, favouring the enrichment of diazotrophic bacteria recruitment. Our results support the manipulation of the flavone biosynthetic pathway as a feasible strategy for the induction of biological nitrogen fixation in cereals and a reduction in the use of inorganic nitrogen fertilizers.

Sorghum is a crop of great interest in animal feed in semiarid regions. The environment and nitrogen fertilization can influence its productive potential and nutritional quality. This study aimed to evaluate sorghum biomass genotypes associated or not with Azospirillum brasilense managed at different sowing sites on the yield and nutritional value of silage. We evaluated 3 sorghum genotypes combined with 3 fertilization strategies using urea, Azospirillum brasilense and the urea/A brasilense combination in two planting sites (Janaúba, MG, and Montes Claros, MG). A randomized block design was carried out in a 3 x 3 x 2 factorial arrangement of 3 genotypes, 3 fertilization strategies and 2 sowing sites. Azospirillum brasilense foliar spraying was carried out using a costal (Backpack) atomizer and for silage production, PVC silos with weight and length of 50 cm and 10 cm in diameter were used. There was no triple interaction between the studied variables. There were differences between genotypes and between sites for agronomic traits.Statistical differences were detected between genotypes and sites for chemical composition, and sorghum forage on digestibility evaluations. The region of Montes Claros has greater forage production and the region of Janaúba has better quality of silage. Biomass sorghum genotypes have higher forage production and the Volumax genotype has better silage quality. RESUMO - O sorgo é uma cultura de grande interesse na alimentação animal em regiões semiáridas. O ambiente e a adubação nitrogenada podem influenciar seu potencial produtivo e qualidade nutricional. Este trabalho teve como objetivo avaliar genótipos de biomassa de sorgo associados ou não ao Azospirillum brasilense manejados em diferentes locais de semeadura sobre a produtividade e valor nutricional da silagem. Foram avaliados três genótipos de sorgo associados e três estratégias de adubação utilizando ureia, Azospirillum brasilense e a associação ureia/A. brasilense em dois locais de plantio (Janaúba, MG e Montes Claros, MG). O delineamento foi em blocos casualizados em esquema fatorial 3 x 3 x 2, com 3 genótipos, 3 estratégias de adubação e 2 locais de semeadura. A pulverização foliar de Azospirillum brasilense foi feita com o auxílio de um atomizador costal e para a produção de silagem foram utilizados silos de PVC com peso conhecido e comprimento de 50 cm e 10 cm de diâmetro. Não houve interação tripla entre as variáveis estudadas. Houve diferenças entre genótipos e entre locais para características agronômicas. Também foram observadas diferenças estatísticas entre os genótipos e locais estudados para a composição química e forrageira de sorgo nas avaliações de digestibilidade. A região de Montes Claros possui maior produção de forragem e a região de Janaúba possui melhor qualidade de silagem. Os genótipos de sorgo biomassa apresentam maior produção de forragem e o genótipo Volumax apresenta melhor qualidade de silagem. Made available in DSpace on 2022-06-09T11:19:21Z (GMT). No. of bitstreams: 1 Yield-and-nutritional-value-of-sorghum.pdf: 365529 bytes, checksum: bdb8c33e2072bcb9e2a8f260ac8abc2f (MD5) Previous issue date: 2022

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: We collated estimates of the percentage of legume N derived from atmospheric N2 (%Ndfa) for 14 major grain legumes and then analysed and aggregated the data to derive average values for different crops and regions/countries. The effects of cultivation year and whether data collected from experimental plots were relevant to crops growing in farmers’ fields were examined. Scope: A total of 5374 %Ndfa estimates (observations) were sourced, 4205 from field experiments and 1169 on-farm measurements collected from farmer-grown crops. The largest number of reports (82) and %Ndfa estimates (1391) were for soybean. Conclusions: The %Ndfa estimates for each legume species were consistent across years, except for soybean in North America. For some species estimates were also similar across geographic regions. There were no significant differences (P > 0.05) between estimates of %Ndfa derived from experimental plots and farmer-grown legume crops for nine of the 10 crops evaluated. Three distinct groups were identified with statistically-similar average %Ndfa values with associated standard deviations, namely: pigeonpea, faba bean and lupin – 74±11.8 %; groundnut, green and black gram, cowpea, chickpea, field pea, lentil, vetches and Bambara groundnut – 62±13.4 %; common bean – 38±11.1 %. There were three distinct different regional groupings for soybean: Brazil – 78±6.3 %; North America, Argentina, Asia, Africa and Oceania – 61±14.0 %; Europe – 44±13.8 %. Our findings provide more certainty and simplify the challenge of using field-scale measures of legume %Ndfa to estimate country-to-global inputs of fixed N from grain legumes.

In the northeastern of Pará, cowpea is one of the main protein sources of the population. This study aimed to evaluate the effects of liming, the P and K mineral fertilization, and the combination of seed inoculation with Rhizobium associated with mineral N supplementation in the growth and production of cowpea cultivars. Two experiments were carried out in two consecutive years at the Federal Rural University of Amazonia (Capitão Poço-PA). A randomized block experimental design with subdivided plots was used with four replications, two cowpea cultivars (BRS Tapaihum and BRS Marataoã) and six fertilization and liming treatments: i) without fertilization and without liming; ii) P and K mineral fertilization, liming and seed inoculation with Rhizobium; iii) P and K mineral fertilization and seed inoculation with Rhizobium; iv) N, P and K mineral fertilization and liming; v) P and K mineral fertilization and liming; and vi) N, P and K mineral fertilization, liming and seed inoculation with Rhizobium. Cowpea responded to liming and P and K mineral fertilization, but not N fertilization. There was no difference between the supply of N through seed inoculation or mineral fertilization. Thus, it is suggested to inoculate seeds with Rhizobium in order to maintain the soil N reserve.

Summary Legume–rhizobia symbiosis enables biological nitrogen fixation to improve crop production for sustainable agriculture. Small heat shock proteins (sHSPs) are involved in multiple environmental stresses and plant development processes. However, the role of sHSPs in nodule development in soybean remains largely unknown. In the present study, we identified a nodule‐localized sHSP, called GmHSP17.9, in soybean, which was markedly up‐regulated during nodule development. GmHSP17.9 was specifically expressed in the infected regions of the nodules. GmHSP17.9 overexpression and RNAi in transgenic composite plants and loss of function in CRISPR‐Cas9 gene‐editing mutant plants in soybean resulted in remarkable alterations in nodule number, nodule fresh weight, nitrogenase activity, contents of poly β‐hydroxybutyrate bodies (PHBs), ureide and total nitrogen content, which caused significant changes in plant growth and seed yield. GmHSP17.9 was also found to act as a chaperone for its interacting partner, GmNOD100, a sucrose synthase in soybean nodules which was also preferentially expressed in the infected zone of nodules, similar to GmHSP17.9. Functional analysis of GmNOD100 in composite transgenic plants revealed that GmNOD100 played an essential role in soybean nodulation. The hsp17.9 lines showed markedly more reduced sucrose synthase activity, lower contents of UDP‐glucose and acetyl coenzyme A (acetyl‐CoA), and decreased activity of succinic dehydrogenase (SDH) in the tricarboxylic acid (TCA) cycle in nodules due to the missing interaction with GmNOD100. Our findings reveal an important role and an unprecedented molecular mechanism of sHSPs in nodule development and nitrogen fixation in soybean.

Strawberry (Fragaria x ananassa, Duch.) is an important crop worldwide. However, since it is a highly demanding crop in terms of the chemical conditions of the substrate, a large part of strawberry production implies the application of large amounts of fertilizers in the production fields. This practice can cause environmental problems, in addition to increases in the fruit’s production costs. In this context, applying plant growth-promoting bacteria in production fields can be an essential strategy, especially thanks to their ability to stimulate plant growth via different mechanisms. Therefore, this study aimed to test in vitro and in vivo the potential of bacteria isolated from strawberry leaves and roots to directly promote plant growth. The isolates were tested in vitro for their ability to produce auxins, solubilize phosphate and fix nitrogen. Isolates selected in vitro were tested on strawberry plants to promote plant growth and increase the accumulation of nitrogen and phosphorus in the leaves. The tested isolates showed an effect on plant growth according to biometric parameters. Among the tested isolates, more expressive results for the studied variables were observed with the inoculation of the isolate MET12M2, belonging to the species Brevibacillus fluminis. In general, bacterial inoculation induced strain-dependent effects on strawberry growth. In vitro and in vivo assays showed the potential use of the B. fluminis MET12M2 isolate as a growth promoter for strawberries.

For sustainable agriculture nitrogen must be adequately supplied because it is the most limiting major nutrient required by all living plants. This experiment was conducted at the two ecological zones, Sudan savannah in Kano State and Guinea savannah in Bauchi state of Nigeria during the 2016 cropping season. The design of the experiment was Randomized Complete Block Design (RCBD) with seven treatments and four replications in each site. The treatments were; legume fix, alosca, 50 kg N ha-1, cattle manure, legume fix + cattle manure, alosca + cattle manure and control. The result showed that Legume fix had the highest grain N uptake (90.51 kg N ha-1) which differed significantly (P≤0.001) from the rest of the treatments. At Guinea savannah legume fix gave the highest N uptake value (95.53 kg N ha-1) which was significantly different from all treatments except legume fix + cattle manure. However, 50 kg N ha-1 gave the least (48.64 kg N ha-1) even lower than the control and differs significantly with the rest of treatments (P≤0.001). Legume fix gave the highest P uptake value (9.66 kg P ha-1) which significantly differed from all other treatments. At Sudan savannah, significant differences (P ≤ 0.001) occurred between some of the treatments. Alosca + cattle manure recorded the highest K uptake (49.99 kg K ha-1). Result for the fixed N in the Sudan and Guinea savannahs soybean field revealed a significant difference between the treatments and the control.

Made available in DSpace on 2022-04-28T19:40:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Purpose: A field experiment was carried out to evaluate the effect of foliar Si application associated with inoculation of seeds and nitrogen management on the physiological quality and grain yield of common beans. Methods: The experiment was laid out in randomized blocks with a 5 × 2 × 2 factorial design (four replicates on common bean cultivar Pérola). The first factor was foliar Si application at the concentrations: 0, 1.0, 2.0, 3.0, and 4.0 g L-1 of silicon. The second factor was the effect of the presence or absence of seed inoculation, while the third factor was the splitting of nitrogen topdressing (120 kg N ha-1). Parameters evaluated were relative chlorophyll index (RCI), foliar N and Si contents, gas exchanges, grain yield, and economic viability. Results: Split fertilization of 60 + 60 kg N ha-1 at 20 and 40 days after emergence (DAE) showed better results of grain yield, approximately 41 % higher than splitting of 80 + 40 kg N ha-1 at 20 and 40 DAE, regardless of fertilization containing Si. Foliar Si application increased grain yield in the order of 10 % (uninoculated seeds) and 25 % (inoculated seeds), regardless of splitting of nitrogen fertilization, using the highest Si concentration (4.0 g L-1). Regardless of seed inoculation, the splitting of 60 + 60 kg N ha-1, associated with the application of 3.0 g Si L-1, resulted in the maximum grain yield, approximately 20 % higher than the control. Conclusion: Application of 2.0 g Si L-1 promoted differential profits of up to US$ 236.72 regardless of seed inoculation and splitting of N fertilization. School of Agronomy Federal University of Goiás (UFG), Esperance Avenue, Campus Samambaia Brazilian Agricultural Research Company National Rice and Bean Research Center São Paulo State University (UNESP) São Paulo State University (UNESP)

Biological nitrogen fixation (BNF) represents the natural pathway by which mosses meet their demands for bioavailable/reactive nitrogen (Nr) in peatlands. However, following intensification of nitrogen fertilizer and fossil fuel use, atmospheric Nr deposition has increased exposing peatlands to Nr loading often above the ecological threshold. As BNF is energy intensive, therefore, it is unclear whether BNF shuts down when Nr availability is no longer a rarity. We studied the response of BNF under a gradient of Nr deposition extending over decades in three peatlands in the U.K., and at a background deposition peatland in Sweden. Experimental nitrogen fertilization plots in the Swedish site were also evaluated for BNF activity. In situ BNF activity of peatlands receiving Nr deposition of 6, 17, and similar to 2 kg N ha(-1) yr(-1) was not shut down but rather suppressed by 54, 69, and 74%, respectively, compared to the rates under background Nr deposition of kg N ha(-1) yr(-1). These findings were corroborated by similar BNF suppression at the fertilization plots in Sweden. Therefore, contribution of BNF in peatlands exposed to chronic Nr deposition needs accounting when modeling peatland's nitrogen pools, given that nitrogen availability exerts a key control on the carbon capture of peatlands, globally.

Biological nitrogen fixation efficiency can be increased by co-inoculation with Bradyrhizobium spp. and Azospirillum brasilense, allowing even greater uptake of water and nutrients, leading to higher yields and enabling the insertion of unusual crops, such as cowpea (Vigna unguiculata L. Walp.), in the agricultural production system in the Cerrado region of Brazil. Thus, this study aimed to evaluate the technical and economic viability of cowpea in the Cerrado region, as a function of N doses and co-inoculation of seeds with Azospirillum brasilense and Bradyrhizobium. The study was carried out in a no-tillage system in Selvíria, MS, Brazil. The experimental design was a randomized block design, with four repetitions, arranged in a 3 x 5 factorial scheme, corresponding to three types of inoculation (without inoculation - control, with two strains of Bradyrhizobium spp. SEMIA 6462 and SEMIA 6463 - the conventional inoculation of cowpea, and these two strains of Bradyrhizobium spp. plus A. brasilense strains Ab-V5 and Ab-V6); and five N doses (0, 20, 40, 80 and 160 kg ha-1), as urea, applied as topdressing. The following evaluations were performed: grain yield, total operating cost, effective operating cost, gross revenue, operating profit, profitability index, equilibrium price and equilibrium yield. Co-inoculation with A. brasilense increases cowpea grain yield, which makes cowpea production in the Cerrado region of Brazil technically and economically viable, without the need to apply N fertilizers in topdressing. RESUMO A eficiência da fixação biológica de nitrogênio pode ser aumentada pela coinoculação com Azospirillum brasilense e Bradyrhizobium, propiciando maior absorção de água e nutrientes, refletindo em maiores produtividades e permitindo a inserção de culturas não usuais nos sistemas agrícolas na região de Cerrado, como o feijão-caupi (Vigna unguiculata L. Walp.). Desta forma, o objetivo com este estudo foi avaliar a viabilidade técnica e econômica da produção de feijão-caupi em região de Cerrado, em função de doses de N e da coinoculação nas sementes com Azospirillum brasilense e Bradyrhizobium. O estudo foi desenvolvido em sistema plantio direto em Selvíria, MS. O delineamento experimental foi em blocos casualizados com quarto repetições, dispostos em esquema factorial 3 x 5, correspondendo a três tipos de inoculação (sem inoculação - testemunha, com duas estirpes de Bradyrhizobium spp., SEMIA 6462 e SEMIA 6463 - a inoculação convencional de feijão-caupi, e estas duas estirpes de Bradyrhizobium sp mais A. brasilense estirpes Ab-V5 e Ab-V6 - a coinoculação); e cinco doses de N (0, 20, 40, 80 e 160 kg ha-1, na forma de ureia, aplicada em cobertura. As seguintes avaliações foram realizadas: produtividade de grãos, custo operational total, custo operacional efetivo, receita bruta, lucro operacional, índice de lucratividade, preço de equilíbrio e produtividade de equilíbrio. A coinoculação com A. brasilense aumentou a produtividade de grãos do feijão-caupi, sendo uma tecnologia tecnicamente e economicamente viável, sem a necessidade de aplicação de fertilizante nitrogenado em cobertura.

Reprogramming the genetic regulation of nitrogen fixation and assimilation in a root-associated diazotroph to produce novel strains can restore ammonium production in the presence of exogenous nitrogen inputs., Plants depend upon beneficial interactions between roots and root-associated microorganisms for growth promotion, disease suppression, and nutrient availability. This includes the ability of free-living diazotrophic bacteria to supply nitrogen, an ecological role that has been long underappreciated in modern agriculture for efficient crop production systems. Long-term ecological studies in legume–rhizobia interactions have shown that elevated nitrogen inputs can lead to the evolution of less cooperative nitrogen-fixing mutualists. Here we describe how reprogramming the genetic regulation of nitrogen fixation and assimilation in a novel root-associated diazotroph can restore ammonium production in the presence of exogenous nitrogen inputs. We isolated a strain of the plant-associated proteobacterium Kosakonia sacchari from corn roots, characterized its nitrogen regulatory network, and targeted key nodes for gene editing to optimize nitrogen fixation in corn. While the wild-type strain exhibits repression of nitrogen fixation in conditions replete with bioavailable nitrogen, such as fertilized greenhouse and field experiments, remodeled strains show elevated levels in the rhizosphere of corn in the greenhouse and field even in the presence of exogenous nitrogen. Such strains could be used in commercial applications to supply fixed nitrogen to cereal crops.

Biological nitrogen fixation (BNF) is an important nitrogen source for both N2-fixers and their neighboring plants in natural and managed ecosystems. Biological N fixation can vary considerably depending on soil conditions, yet there is a lack of knowledge on the impact of varying soils on the contribution of N from N2-fixers in mixed swards. In this study, the amount and proportion of BNF from red clover were assessed using three grassland soils. Three soil samples, Hallsworth (HH), Crediton (CN), and Halstow (HW) series, were collected from three grassland sites in Devon, UK. A pot experiment with 15N natural abundance was conducted to estimate BNF from red clover, and the proportion of N transferred from red clover to the non-N2 fixing grass in a grass-clover system. The results showed that BNF in red clover sourced from atmosphere in the HH soil was 2.92 mg N plant−1, which was significantly lower than that of the CN (6.18 mg N plant−1) and HW (8.01 mg N plant−1) soils. Nitrogen in grass sourced from BNF via belowground was 0.46 mg N plant−1 in the HH soil, which was significantly greater than that in CN and HW soils. However, proportionally there were no significant differences in the percentage N content of both red clover and grass sourced from BNF via belowground among soils, at 65%, 67%, 65% and 35%, 27%, 31% in HH, CN, and HW, respectively. Our observations indicate that the amount of BNF by red clover varies among grassland soils, as does the amount of N sourced from BNF that is transferred to neighboring plants, which is linked to biomass production. Proportionally there was no difference among soils in N sourced from BNF in both the red clover plants and transferred to neighboring plants.

The application of plant growth promoting bacteria (PGPB) represents a friendly alternative to the environment, in contrast to the use of chemical fertilizers. Endophytic bacteria can develop inside the plant tissues and directly benefit the plant. Gluconacetobacter diazotrophicus is a versatile bacterium that has been isolated from different plants and possesses different physiological properties that would serve to improve plant development. In this research, five cultures of G. diazotrophicus were isolated from sugarcane samples from the northern coast of Peru. The isolates showed the ability to solubilize phosphates and zinc, produce IAA, and resist salt stress (NaCl 1%). Antagonism evaluations showed that they can inhibit up to 75%, 57%, 40%, 49% and 17% of the development of Fusarium sp., Alternaria sp., Roselinia sp., Lasiodiplodia sp., and Sclerotinia sp., respectively. Inoculation plant experiments were developed by inoculating individual and bacteria mixture. All treatments showed plant growth promotion in sugarcane, but mixture of G. diazotrophicus LASFB 1573, Klebsiella sp. LASFBP 086 and Enterobacter sp. LASFB 009 increased up to 84% and 89% in fresh and dry plant weight, respectively. The results show that the isolates have a high potential as PGPB and could be used later to improve the development of different crops.

I evaluate nitrogen (N) cycling across a rainfall gradient in leeward Kohala on the island of Hawaiʻi, focusing on a large set of vegetation samples collected between 2015 and 2017. Vegetation was sampled at a series of points where soils had been previously characterized across the climate gradient. An array of isotopic and elemental abundance analyses, combined with biomass data from July 2015, reveal relationships between climate, biological N fixation (BNF), and the soil N supply: δ15N of non-leguminous plants predictably mirrors soil δ15N, while legume δ15N values are closer to that of the atmosphere (indicative of BNF), especially towards the wet end of the gradient. Herbaceous legumes have elevated δ15N in the fertile region previously occupied by the Leeward Kohala Field System, indicating a lesser reliance on BNF at moderate rainfall levels. Herbaceous legume biomass also peaks in this region, suggesting the relative decrease in the fraction of N from BNF is not hindering plant growth, but that plants are instead able to derive greater amounts of N from the soil system. As leaf C:N ratios sharply increase in non-leguminous plants below 1,000 mm of annual rainfall while legumes show very consistent C:N across the gradient, BNF appears especially important for legumes in the arid zone while non-legumes face N deficiencies across many rainfall levels.Interestingly, a sharp soil δ15N drop-off in the very arid sites of the leeward Kohala gradient is accompanied by a peak in leguminous tree δ15N (more positive values closer to those of soil), which indicates increased BNF is not responsible for the soil δ15N signal. Leaf nutrient data reveal trends in calcium and phosphorus uptake by woody legumes, suggesting dryland BNF may be limited by the abundance of these elements, although these trends differ distinctly by species and are likely influenced by other nutrients and environmental factors. Herbaceous legumes and non-leguminous grasses all show similar trends in foliar phosphorus, potassium, and iron levels, but legumes show elevated manganese, magnesium, and calcium concentrations versus the grasses. Foliar phosphorus concentrations suggest that the element is plentiful in the soils of leeward Kohala’s fertile zone—formerly the center of the field system—perhaps accounting for high total amounts of BNF that led to the high N levels in the soil there. Potassium concentrations across all plant species also peak in the middle of leeward Kohala’s fertile zone, indicating it could possibly constrain plant growth at the extremes of the gradient.While this study demonstrates the impressive ability of ancient Hawaiians to locate and exploit the most fertile soils of leeward Kohala, the results could also have important implications for the future of the region. For instance, the post-contact replacement of native dryland forests and Hawaiian croplands with exotic pasture plants (including legumes) could have resulted in increased N inputs from BNF and altered micronutrient regimes throughout the soil system that persist to this day. These drastic ecological changes will almost certainly influence ongoing efforts to restore agricultural productivity and connectedness to Kohala’s slopes, as the revitalization of traditional Hawaiian agriculture today will face different challenges than those met by the ancient agriculturalists of the Leeward Kohala Field System.

Exploring natural diversity for biological nitrogen fixation in maize and its progenitors is a promising approach to reducing our dependence on synthetic fertilizer and enhancing the sustainability of our cropping systems. We have shown previously that maize accessions from the Sierra Mixe can support a nitrogen-fixing community in the mucilage produced by their abundant aerial roots and obtain a significant fraction of their nitrogen from the air through these associations. In this study, we demonstrate that mucilage production depends on root cap and border cells sensing water, as observed in underground roots. The diameter of aerial roots correlates with the volume of mucilage produced and the nitrogenase activity supported by each root. Young aerial roots produce more mucilage than older ones, probably due to their root cap's integrity and their ability to produce border cells. Transcriptome analysis on aerial roots at two different growth stages before and after mucilage production confirmed the expression of genes involved in polysaccharide synthesis and degradation. Genes related to nitrogen uptake and assimilation were up-regulated upon water exposure. Altogether, our findings suggest that in addition to the number of nodes with aerial roots reported previously, the diameter of aerial roots and abundance of border cells, polysaccharide synthesis and degradation, and nitrogen uptake are critical factors to ensure efficient nitrogen fixation in maize aerial roots.

A total of 102 bacterial strains isolated from nodules of three Bambara groundnut and one soybean cultivars grown in nineteen soil samples collected from northern Ghana were characterized using multilocus gene sequence analysis. Based on a concatenated sequence analysis (glnII-rpoB-recA-gyrB-atpD-dnaK), 54 representative strains were distributed in 12 distinct lineages, many of which were placed mainly in the Bradyrhizobium japonicum and Bradyrhizobium elkanii supergroups. Twenty-four of the 54 representative strains belonged to seven putative novel species, while 30 were conspecific with four recognized Bradyrhizobium species. The nodA phylogeny placed all the representative strains in the cosmopolitan nodA clade III. The strains were further separated in seven nodA subclusters with reference strains mainly of African origin. The nifH phylogeny was somewhat congruent with the nodA phylogeny, but both symbiotic genes were mostly incongruent with the core housekeeping gene phylogeny indicating that the strains acquired their symbiotic genes horizontally from distantly related Bradyrhizobium species. Using redundancy analysis, the distribution of genospecies was found to be influenced by the edaphic factors of the respective sampling sites. In general, these results mainly underscore the high genetic diversity of Bambara groundnut-nodulating bradyrhizobia in Ghanaian soils and suggest a possible vast resource of adapted inoculant strains. In the northern savanna zones of Ghana, Bambara groundnut-nodulating Bradyrhizobium species are taxonomically diverse.

Simple Summary Nitrogen acquisition strategies mediated by insect symbionts through biological nitrogen fixation (BNF) and nitrogenous waste recycling (NWR) were reviewed and compared in our paper, and a model for nitrogen provisioning in insects was then constructed. In our model, (1) insects acquired nitrogen nutrition from food stuffs directly, and the subprime channels (e.g., BNF or NWR) for nitrogen provisioning were accelerated when the available nitrogen in diets could not fully support the normal growth and development of insects; (2) the NWR strategy was more accessible to more insects due to its energy conservation and mild reaction conditions; (3) ammonia produced by different channels was used for essential nitrogenous metabolites synthesis via the glutamine synthetase and glutamate synthase pathways. Abstract Nitrogen is usually a restrictive nutrient that affects the growth and development of insects, especially of those living in low nitrogen nutrient niches. In response to the low nitrogen stress, insects have gradually developed symbiont-based stress response strategies—biological nitrogen fixation and nitrogenous waste recycling—to optimize dietary nitrogen intake. Based on the above two patterns, atmospheric nitrogen or nitrogenous waste (e.g., uric acid, urea) is converted into ammonia, which in turn is incorporated into the organism via the glutamine synthetase and glutamate synthase pathways. This review summarized the reaction mechanisms, conventional research methods and the various applications of biological nitrogen fixation and nitrogenous waste recycling strategies. Further, we compared the bio-reaction characteristics and conditions of two strategies, then proposed a model for nitrogen provisioning based on different strategies.

This study aims to explore the possibility of a reduced application of inorganic nitrogen (N) fertiliser on the yield, yield qualities, and biological nitrogen fixation (BNF) of the hydroponic common bean (Phaseolus vulgaris L.), without compromising plant performance, by utilizing the inherent ability of this plant to symbiotically fix N2. Until the flowering stage, plants were supplied with a nutrient solution containing N-concentrations of either a, 100%, conventional standard-practice, 13.8 mM; b, 75% of the standard, 10.35 mM; or c, 50% of the standard, 6.9 mM. During the subsequent reproductive stage, inorganic-N treatments b and c were decreased to 25% of the standard, and the standard (100% level) N-application was not altered. The three different inorganic-N supply treatments were combined with two different rhizobia strains, and a control (no-inoculation) treatment, in a two-factorial experiment. The rhizobia strains applied were either the indigenous strain Rhizobium sophoriradicis PVTN21 or the commercially supplied Rhizobium tropici CIAT 899. Results showed that the 50–25% mineral-N application regime led to significant increases in nodulation, BNF, and fresh-pod yield, compared to the other treatment, with a reduced inorganic-N supply. On the other hand, the 75–25% mineral-N regime applied during the vegetative stage restricted nodulation and BNF, thus incurring significant yield losses. Both rhizobia strains stimulated nodulation and BNF. However, the BNF capacity they facilitated was suppressed as the inorganic-N input increased. In addition, strain PVTN21 was superior to CIAT 899—as 50–25% N-treated plants inoculated with the former showed a yield loss of 11%, compared to the 100%-N-treated plants. In conclusion, N-use efficiency optimises BNF, reduces mineral-N-input dependency, and therefore may reduce any consequential negative environmental consequences of mineral-N over-application.

Nitrogen (N) and phosphorus (P) nutrient enrichment is important for grasslands. This study aimed to determine how soils enriched with N and P influenced soil concentration correlations and affected the growth kinetics, mineral nutrition, and nitrogen-use efficiencies of Vachellia sieberiana grown in a greenhouse experiment. The soils used as the growth substrate were analysed and showed extreme acidity (low soil pH, 3.9). Nitrogen-enriched soils were more acidic than P-enriched soils. Exchangeable acidity was strongly negatively correlated with an increase in soil pH, with soil pH between 3.9 and 4.1 units showing the strongest decline. Plant saplings showed increased root biomass, shoot biomass, total biomass, and plant N and P concentrations when grown in soils with high soil P concentrations. Extreme soil acidification in N-enriched soil was one of the main factors causing P unavailability, decreasing sapling growth. Extreme soil acidification increased concentrations of toxic heavy metals, such as Al which may be alleviated by adding lime to the extremely acidic soils. Research implications suggest that soil pH is an important chemical property of the soil and plays a significant role in legume plant growth. Legume species that are unable to tolerate acidic soils may acquire different strategies for growth and functioning.

Legumes improve soil fertility through the symbiotic association with microorganisms, such as rhizobia, which fix the atmospheric nitrogen and make nitrogen available to the host and other crops by a process known as biological nitrogen fixation (BNF). Legumes included in the cropping system improve the fertility of the soil and the yield of crops. The advantages of legumes in the cropping system are explained in terms of direct nitrogen transfer, residual fixed nitrogen, nutrient availability and uptake, effect on soil properties, breaking of pests' cycles, and enhancement of other soil microbial activity. The best benefits from the legumes and BNF system can be utilized by integrating them into cropping systems. The most common practices to integrate legumes and their associated BNF into agricultural systems are crop rotation, simultaneous intercropping, improved fallows, green manuring, and alley cropping. However, the level of utilizing nitrogen fixation requires improvement of the systems, such as selecting appropriate legume genotypes, inoculation with effective rhizobia, and the use of appropriate agronomic practices and cropping systems. Therefore, using legumes at their maximum genetic potential, inoculation of legumes with compatible rhizobia, and using appropriate agronomic practices and cropping systems are very important for increasing food production. Importantly, the utilization of legumes as an integral component of agricultural practice in promoting agricultural productivity has gained more traction in meeting the demand of food production of the world populace. Priority should, thus, be given to value the process of BNF through more sustainable technologies and expansion of knowledge to the system.

The main aim of this study was to assess genetic diversity within the natural populations of field pea rhizobia on different field sites in Northwestern Croatia and to evaluate their symbiotic efficiency. Identification of related bacterial strains was carried out using RAPD and rep-PCR methods and on the basis of differences in the nodulation nodD gene region by PCR-RFLP method. Indigenous strains have been shown to differ significantly from each other as well as from the reference strains Rhizobium leguminosarum bv. viciae used in these study. Based on the nodulation genes, it was found that most isolates have the same or very similar nodulation nodD region except the isolates K22 and K23. A greenhouse studie was performed for evaluation of symbiotic efficiency of strains. The highest nodule dry weight was determined by inoculation with strains K23, K22, K17 and K20, indicating their high infectivity and nodulation ability. Significantly higher green mass and dry matter yield in abouveground plant parts were determined by inoculation with two indigenous strains K26 and K16 that showed potentially high symbiotic efficiency compared to other tested strains.

Multiple factors influence rice yield. Developing management practices that increase crop yield and an efficient use of resources are challenging to modern agriculture. Consequently, the aim of this study was to evaluate biological nitrogen fixation and bacterial phosphorous solubilization (biofertilization) practices with the selection of the sowing date. Three sowing dates (May, July and August) were evaluated when interacting with two mineral nutrition treatments using a randomized complete block design in a split-plot arrangement. Leaf carbon balance, leaf area index, interception and radiation use efficiency, harvest index, dry matter accumulation, nutritional status, and yield were quantified. Results showed that the maximum yield was obtained in the sowing date of August. Additionally, yield increased by 18.92% with the biofertilization treatment, reaching 35.18% of profitability compared to the local production practice. High yields were related to a higher carbon balance during flowering, which was 11.56% and 54.04% higher in August than in July and May, respectively, due to a lower night temperature. In addition, a high efficient use of radiation, which in August was 17.56% and 41.23% higher than in July and May, respectively, contributed to obtain higher yields and this behavior is related to the selection of the sowing date. Likewise, a rapid development of the leaf area index and an optimum foliar nitrogen concentration (>3%) were observed. This allowed for greater efficient use of radiation and is attributed to the activity of nitrogen-fixing and phosphate solubilizing bacteria that also act as plant growth promoters. RESUMEN El rendimiento del arroz está influenciado por múltiples factores. Desarrollar prácticas de manejo que aumenten el rendimiento y sean más eficientes en el uso de los recursos es un reto de la agricultura. En consecuencia, el objetivo de este estudio fue evaluar las prácticas fijación biológica de nitrógeno y solubilización de fosforo por bacterias (biofertilización) con la selección de fecha de siembra. Se evaluaron tres fechas de siembra (mayo, julio y agosto) en interacción con dos tratamientos de nutrición mineral empleando un diseño en bloques completos al azar en arreglo de franjas divididas. Se cuantificó el balance de carbono, índice de área foliar, intercepción y uso eficiente de radiación, índice de cosecha, acumulación de masa seca, estado nutricional y rendimiento. Los resultados mostraron que el máximo rendimiento se obtuvo en la fecha de siembra de agosto; adicionalmente, con la biofertilización el rendimiento se incrementó en 18.92%, alcanzando una rentabilidad del 35.18% en comparación con la práctica local de producción. El alto rendimiento se relacionó con un mayor balance de carbono durante la floración, que fue un 11.56 y 54.04% mayor en agosto, comparado con julio y mayo respectivamente, debido a una menor temperatura nocturna. Asimismo, un alto uso eficiente de la radiación que en agosto fue un 17.56 and 41.23% mayor que julio y mayo respectivamente, contribuyó a mayores rendimientos y este comportamiento se relacionó con la selección de la fecha de siembra. Además, se observó un rápido desarrollo del índice de área foliar y de la concentración optima del nitrógeno foliar (>3%). Esto permitió alcanzar un mayor uso eficiente de la radiación y se atribuye a la actividad de las bacterias fijadoras de nitrógeno y solubilizadoras de fosforo que también son promotoras del crecimiento.

The objective of this study was to evaluate the effect of the isolated and joint use of Azospirillum brasilense inoculation and the application of thiamine, on seed or leaf, on the development of millet in two cycles. A randomized complete block design was used in five replicates. The treatments were composed of the isolated or combined inoculation with Azospirillum brasilense and the application of thiamine, on seed (10 ml kg-1) or leaf spray (10 ppm). The relative levels of chlorophyll a, b and total, plant height, number of shoots, fresh and dry mass production and dry matter index of plants were evaluated. In the first cycle, treatments were only effective for the relative chlorophyll contents, and in general, the treatment with isolated inoculation of A. brasilense stood out, differing significantly from the treatment with thiamin applied on seed. In the second cycle, there was significant effect of the treatments on the variables of plant height and number of shoots, in which a maximum height of 165 cm and production of 140 shoots m-2 with application of thiamin on seed and with the use of A. brasilense and thiamine applied on the leaf, respectively. Thus, it was concluded that inoculation with A. brasilense increases the relative chlorophyll content in millet during the first cycle. The joint use of inoculation with A. brasilense and the application of thiamine can be used as a strategy to increase the number of shoots.

Significance Biological nitrogen fixation (BNF) is responsible for large new N inputs to terrestrial ecosystems, particularly in pristine, high-latitude areas undergoing rapid global change. The most common form of nitrogenase requires molybdenum (Mo) and Mo limitation of BNF is ubiquitous. Mo-free alternative forms of nitrogenase exist, but their roles in environmental BNF have remained uncertain. This study on N2-fixing cyanolichens provides extensive field evidence, at an ecosystem scale, that vanadium (V)-based nitrogenase greatly contributes to BNF when Mo availability is limited. Mo exposure data in circumboreal forests further suggest that V-based BNF is widespread. The results showcase the resilience of BNF to micronutrient limitation and reveal strong links between the biogeochemical cycle of macronutrients and micronutrients in terrestrial ecosystems., Biological nitrogen fixation (BNF) by microorganisms associated with cryptogamic covers, such as cyanolichens and bryophytes, is a primary source of fixed nitrogen in pristine, high-latitude ecosystems. On land, low molybdenum (Mo) availability has been shown to limit BNF by the most common form of nitrogenase (Nase), which requires Mo in its active site. Vanadium (V) and iron-only Nases have been suggested as viable alternatives to countering Mo limitation of BNF; however, field data supporting this long-standing hypothesis have been lacking. Here, we elucidate the contribution of vanadium nitrogenase (V-Nase) to BNF by cyanolichens across a 600-km latitudinal transect in eastern boreal forests of North America. Widespread V-Nase activity was detected (∼15–50% of total BNF rates), with most of the activity found in the northern part of the transect. We observed a 3-fold increase of V-Nase contribution during the 20-wk growing season. By including the contribution of V-Nase to BNF, estimates of new N input by cyanolichens increase by up to 30%. We find that variability in V-based BNF is strongly related to Mo availability, and we identify a Mo threshold of ∼250 ng·glichen−1 for the onset of V-based BNF. Our results provide compelling ecosystem-scale evidence for the use of the V-Nase as a surrogate enzyme that contributes to BNF when Mo is limiting. Given widespread findings of terrestrial Mo limitation, including the carbon-rich circumboreal belt where global change is most rapid, additional consideration of V-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry.

Diazotroph mutants designed using metabolic engineering to excrete surplus ammonium were used to enhance nitrogen fixation and plant growth, as the levels of nitrogen fixation attained with diazotrophs are insufficient for the plant’s needs. In this study, wild-type (A1501) and engineered ammonium-excreting (1568/pVA3) strains of nitrogen-fixing Pseudomonas stutzeri strains were tested in vitro based on plant growth-promoting traits, such as phosphate solubilization ability, indole acetic acid (IAA) production and nitrogenase activities, as well as ammonium excretion as affected by mannitol-mediated osmotic stress. The maize plant growth-promoting effect of the A1501 and 1568/pVA3 strains was evaluated in pots and in the field, and the 15N-dilution technique was employed to assess the proportion of plant nitrogen derived from nitrogen fixation. The results demonstrate that the 1568/pVA3 strain displayed higher IAA production and nitrogenase activity than A1501 and released significant quantities of ammonium. After 50 days, in all of the conditions assayed, maize inoculated with 1568/pVA3 accumulated more plant biomass (3.3% on average) and fixed N (39.4% on average) than plants inoculated with A1501. In the field experiment, the grain yield of maize was enhanced by 5.6% or 5.9% due to the inoculation of seeds with 1568/pVA3 in the absence or presence of exogenous N fertilizer, respectively. Therefore, the engineered P. stutzeri strain tested in the greenhouse and field was shown to perform better than the wild-type strain with respect to maize growth parameters and biologically fixed nitrogen.

Biological nitrogen fixation (BNF) as a result of mutual symbiosis between the rhizobia and the cultivated legume have a vital role to balance the nutrient paucity in the soil. Modern researches shows that the BNF can be the important factors regulating and maintaining the defendable agriculture and ensuring food security especially in the developing countries. The use of artificial nitrogen fertilizers to rise crop yield is an internment farming practice, despite its unfavorable effects and hazards to the environment and human population which can be substituted by rhizobial inoculants as a bio-fertilizers. The present study was aimed to isolate and characterize the Rhizobium from the nine different selected legumes. The Rhizobium bacterium was isolated from the nodules of the nine legume plants on YEMA medium which was found to show white translucent, circular convex colonies and characterized by the non-absorption of Congo red dye. The strains were found to be fast growing except for the rhizobial strains isolated from the Soybean and cowpeas (Bradyrhizobium) which were slow growing. The various biochemical tests of the isolated strains like catalase, bromothymol blue, Urea hydrolysis were favorable while Glucose-Peptone Agar (GPA), starch hydrolysis, Citrate utilization were found to be negative. For the ability to utilize the 2% NaCl, the strains TFR showed positive growth, the strains PSR, PhVR, VUR showed the poor tolerance while the rest of the strains showed no tolerance to the 2% NaCl. DOI: http://dx.doi.org/10.5281/zenodo.4906255

Identification of elite nitrogen-fixing rhizobia strains is a continuous and never ending effort, since new legume species can be cultivated in different agro systems or are introduced into new areas. This current study reports on the taxonomic affiliation and symbiotic proficiency of nine strains of Trifolium-nodulating rhizobia isolated from different pasture areas in Spain, as well as three Rhizobium leguminosarum bv. trifolii reference strains, on eleven Trifolium species. Based on 16S rRNA gene sequences the strains belonged to the R. leguminosarum species complex. Additional phylogenetic analyses of the housekeeping genes recA, atpD and rpoB showed the strains were closely related to the species R. leguminosarum, R. laguerreae, R. indicum, R. ruizarguesonis or R. acidisoli. In addition, three strains had no clear affiliation and could represent putative new species, although two of the reference strains were positioned close to R. ruizarguesonis. nodC gene phylogeny allowed the discrimination between strains isolated from annual or perennial Trifolium species and placed all of them in the symbiovar trifolii. Neither geographic origin nor host-plant species could be correlated with the taxonomic affiliation of the strains and a high degree of phenotypic diversity was found among this set of strains. The strong interaction of plant species with the rhizobial strains found for biological nitrogen fixation (BNF) was noteworthy, and allowed the identification of rhizobial strains with a maximum proficiency for certain trefoil species. Several strains showed high BNF potential with a wide range of clover species, which made them valuable strains for inoculant manufacturers and they would be particularly useful for inoculation of seed mixtures in natural or cultivated pastures., This work was partially supported by the National Institute of Agriculture Research Project RM 2010-00014-00-00 (INIA-MAPA).

Rhizobia inoculation with effective strains is an environmentally friendly approach for enhancing nodulation and yield of legumes. To obtain an ideal strain for inoculant production, the strain's performance must be matched to the environmental conditions. A 2 × 9 cross-factorial experiment laid in a randomized complete block design with three replications on farmers' fields in the northern part of Ghana was set up to evaluate the rhizobia's performance. The factors were groundnut varieties (Chinese and Samnut 22) and nine strains consisting of five native rhizobia (KNUST 1001, 1002, 1003, 1032, and 1031), two commercial strains (Biofix and BR3267), and a positive (N+) and absolute control (N–). In addition, the population of the strains was assessed after a cropping season. The strains' performance on groundnut was location and variety dependent. At Cheshegu, KNUST 1031 and 1002 significantly increased seed yield of the Chinese variety compared to other strains; however, KNUST 1031 elicited a 24% yield increase while KNUST 1002 caused a 16% yield increase over the control. Strain KNUST 1031 increased the seed yield of the Chinese variety by 24% while KNUST 1002 increased the seed yield of Samnut by 16%. Only KNUST 1002 elicited a significant seed yield increase in Samnut 22 at Cheshegu. At Binduri, strain KNUST 1003 significantly increased the seed yield of the Chinese variety by 35% relative to the control. Samnut 22 did not show a clear preference for any of the strains. The Chinese variety did not show a clear response to the strains at Tanina. However, Samnut 22 responded to KNUST 1002 as it increased seed yield by 45% relative to the control. On average, the seed yield at Tanina (846.15 kg ha−1) was less than the seed yield recorded at Binduri (1,077.66 kg ha−1) and Cheshegu (1,502.78 kg ha−1). Inoculation with strains KNUST 1002, 1003, and 1031 was all profitable under the current experimental conditions as they recorded value cost ratios (VCRs) above the threshold of 3–4. The study has shown that strains KNUST 1002, 1003, and 1031 have the potential to be used in inoculant formulation to increase groundnut production and enhance the income of smallholder groundnut farmers in northern Ghana.

The objective of this study was to evaluate the agronomic efficiency of rhizobia strains already approved or in the selection stage for cowpea, in the Recôncavo da Bahia region, Brazil. Two field experiments were performed in the municipalities of Cruz das Almas and Maragogipe, Bahia, Brazil. A randomized block design was used with seven nitrogen sources and four replicates. Nitrogen sources consisted of the strains UFRB FA51B1, UFRB BA72C2-1, UFLA 03-164T, UFLA 03-84, INPA 03-11B, and two controls without inoculation, one with mineral nitrogen and another without. All the strains nodulated cowpea. The efficiency of the strains was determined by the number of nodules, nodule dry matter, total dry matter, grain yield, nitrogen accumulation in shoots and grain, and relative efficiency. The strain UFLA 03-164T can be recommended for biomass production, green manure, and promotion of grain yields in both soils. In Maragogipe, the UFLA 03-84 and INPA 03-11B strains can be recommended for biomass production, green manure, and promotion of grain yields. The UFLA 03-164T strain showed great potential to promote and grain yield in the two municipalities studied. The strain INPA 03-11B can be recommended for Maragogipe soil. UFLA 03-84 can also be recommended to increase grain yield in Cruz das Almas. Objetivou-se avaliar a eficiência agronômica de estirpes de rizóbio aprovadas ou em fase de seleção para o feijão-caupi no Recôncavo da Bahia. Dois experimentos de campo foram realizados nos municípios de Cruz das Almas e Maragogipe, Bahia. Utilizou-se o delineamento de blocos ao acaso com sete tratamentos e quatro repetições. Os tratamentos consistiram nas linhagens UFRB FA51B1, UFRB BA72C2-1, UFLA 03-164T, UFLA 03-84, INPA 03-11B e dois controles sem inoculação, um com e outro sem nitrogênio mineral. Todas as estirpes foram capazes de nodular o feijão-caupi. A eficiência das linhagens foi determinada pelo número de nódulos, matéria seca dos nódulos, matéria seca, rendimento de grãos, acúmulo de nitrogênio nas brotações e grãos e eficiência relativa. A estirpe UFLA 03-164T pode ser indicada para produção de biomassa, adubação verde e incremento da produção de grãos nos dois solos. Em Maragogipe, as estirpes UFLA 03-84 e INPA 03-11B podem ser indicadas para produção de biomassa, adubação verde e incremento da produção de grãos. A UFLA 03-164T apresentou grande potencial para promoção de massa seca da parte aérea e rendimento de grãos de feijão-caupi nos dois municípios estudados. A INPA 03-11B pode ser recomendada para o solo de Maragogipe. A UFLA 03-84 pode ser recomendada para aumentar a produção de grãos em Cruz das Almas.

This study was designed to investigate the effects of Azospirillum brasilense and Bradyrhizobium sp. co-inoculation coupled with N application on soil N levels and N in plants (total N, nitrate N-NO3− and ammonium N-NH4+), photosynthetic pigments, cowpea plant biomass and grain yield. An isotopic technique was employed to evaluate 15N fertilizer recovery and derivation. Field trials involved two inoculations—(i) single Bradyrhizobium sp. and (ii) Bradyrhizobium sp. + A. brasilense co-inoculation—and four N fertilizer rates (0, 20, 40 and 80 kg ha−1). The co-inoculation of Bradyrhizobium sp. + A. brasilense increased cowpea N uptake (an increase from 10 to 14%) and grain yield (an average increase of 8%) compared to the standard inoculation with Bradyrhizobium sp. specifically derived from soil and other sources without affecting 15N fertilizer recovery. There is no need for the supplementation of N via mineral fertilizers when A. brasilense co-inoculation is performed in a cowpea crop. However, even in the case of an NPK basal fertilization, applied N rates should remain below 20 kg N ha−1 when co-inoculation with Bradyrhizobium sp. and A. brasilense is performed.

In the current study, the impact of the preceding crops on growth, fresh pod yield, nitrogen fixation efficiency, and nitrogen nutrition of faba bean (Vicia faba L.) was investigated for two years in both organic and conventional crops. As preceding crops served cabbage, pea, and faba bean. The pod number per plant (PN) and the total fresh pod yield (TFPY) were significantly lower with cabbage compared to pea and faba bean as preceding crops in both cropping systems and both experimental years. However, in the organic farming system, pea increased significantly in PN and TFPY compared to faba bean as a preceding crop, while in the conventional system, there was no significant difference between the two legumes. The greater yield performance with the two legumes as preceding crops was associated with higher soil NO3-N and total-N concentrations at the beginning of the subsequent faba bean crop. The higher soil N availability when the preceding crop was a legume resulted partly from the higher biomass of crop residues left by these crops on the field after harvest, compared to cabbage. However, it was also associated with a more extensive nodulation of the faba bean roots by rhizobia and a higher percentage of N derived from atmosphere (%Ndfa) in their plant tissues, as determined through the natural abundance of the 15N isotope, when the preceding crop was a legume. The cropping system had no impact on pod yield, but organic farming increased the %Ndfa in both years.

Biological nitrogen fixation (BNF) refers to a microbial mediated process based upon an enzymatic “Nitrogenase” conversion of atmospheric nitrogen (N2) into ammonium readily absorbable by roots. N2-fixing microorganisms collectively termed as “diazotrophs” are able to fix biologically N2in association with plant roots. Specifically, the symbiotic rhizobacteria induce structural and physiological modifications of bacterial cells and plant roots into specialized structures called nodules. Other N2-fixing bacteria are free-living fixers that are highly diverse and globally widespread in cropland. They represent key natural source of nitrogen (N) in natural and agricultural ecosystems lacking symbiotic N fixation (SNF). In this review, the importance ofAzotobacterspecies was highlighted as both important free-living N2-fixing bacteria and potential bacterial biofertilizer with proven efficacy for plant nutrition and biological soil fertility. In addition, we describedAzotobacterbeneficial plant promoting traits (e.g., nutrient use efficiency, protection against phytopathogens, phytohormone biosynthesis, etc.). We shed light also on the agronomic features ofAzotobacterthat are likely an effective component of integrated plant nutrition strategy, which contributes positively to sustainable agricultural production. We pointed outAzotobacterbased-biofertilizers, which possess unique characteristics such as cyst formation conferring resistance to environmental stresses. Such beneficial traits can be explored profoundly for the utmost aim to research and develop specific formulations based on inoculantAzotobactercysts. Furthermore,Azotobacterspecies still need to be wisely exploited in order to address specific agricultural challenges (e.g., nutrient deficiencies, biotic and abiotic constraints) taking into consideration several variables including their biological functions, synergies and multi-trophic interactions, and biogeography and abundance distribution.

The mung bean has a great potential under tropical conditions given its high content of grain protein. Additionally, its ability to benefit from biological nitrogen fixation (BNF) through association with native rhizobia inhabiting nodule microbiome provides most of the nitrogen independence on fertilizers. Soil microbial communities which are influenced by biogeographical factors and soil properties, represent a source of rhizobacteria capable of stimulating plant growth. The objective of this study is to support selection of beneficial bacteria that form positive interactions with mung bean plants cultivated in tropical soils, as part of a seed inoculation program for increasing grain yield based on the BNF and other mechanisms. Two mung bean genotypes (Camaleão and Esmeralda) were cultivated in 10 soil samples. Nodule microbiome was characterized by next-generation sequencing using Illumina MiSeq 16S rRNA. More than 99% of nodule sequences showed similarity with Bradyrhizobium genus, the only rhizobial present in nodules in our study. Higher bacterial diversity of soil samples collected in agribusiness areas (MW_MT-I, II or III) was associated with Esmeralda genotype, while an organic agroecosystem soil sample (SE_RJ-V) showed the highest bacterial diversity independent of genotype. Furthermore, OTUs close to Bradyrhizobium elkanii have dominated in all soil samples, except in the sample from the organic agroecosystem, where just B. japonicum was present. Bacterial community of mung bean nodules is mainly influenced by soil pH, K, Ca, and P. Besides a difference on nodule colonization by OTU sequences close to the Pseudomonas genus regarding the two genotypes was detected too. Although representing a small rate, around 0.1% of the total, Pseudomonas OTUs were only retrieved from nodules of Esmeralda genotype, suggesting a different trait regarding specificity between macro- and micro-symbionts. The microbiome analysis will guide the next steps in the development of an inoculant for mung bean aiming to promote plant growth and grain yield, composed either by an efficient Bradyrhizobium strain on its own or co-inoculated with a Pseudomonas strain. Considering the results achieved, the assessment of microbial ecology parameters is a potent coadjuvant capable to accelerate the inoculant development process and to improve the benefits to the crop by soil microorganisms.

FL was financially supported by PROCISUR and FONTAGRO through the project Uso de leguminosas en sistemas ganaderos sudamericanos. RTI2018-94985-B-100 (to JP). JS was supported by Project BIO2017-83533-P and funded by MCIN/AEI/10.13039/501100011033/FEDER A way to make Europe.

Little is known about the interaction between the inoculation of diazotrophic bacteria, the variety, and the substrate used in inoculated sugarcane seedling production. Bearing this in mind, the aim of this study was to evaluate the effects of diazotrophic bacteria inoculation, four sugarcane varieties and four different substrates on the growth and nitrogen accumulation of sugarcane seedlings. Parameters related to sprouting, height, and root growth, as well as nitrogen accumulation, were evaluated. The results indicate that inoculating sugarcane seedlings belonging to the following varieties: RB867515, RB92579, RB966928 and RB975932 with bacteria may increase sprouting speed index, height, root length, fresh and dry matter weight, as well as nitrogen accumulation, which has resulted in a more uniform stem diameter. However, the responses to inoculation differ from variety to variety and are also dependent on the substrate used with better results observed in the commercial substrate and the substrate mixtures containing a higher proportion of organic compost. Understanding the interaction between the variety and the substrate with the bacterial inoculation is essential to the success of the production of inoculated sugarcane seedlings. Made available in DSpace on 2020-04-30T04:39:35Z (GMT). No. of bitstreams: 1 Diazotrophic-bacteria-and-substrates-in-the-growth.pdf: 705788 bytes, checksum: d45a4b406f18a429e32d53dd6c2aa920 (MD5) Previous issue date: 2020 Epub Mar 13, 2020

The increasing global perception of the importance of microbial inoculants to promote productivity and sustainability in agriculture prompts the adoption of bio-inputs by the farmers. The utilization of selected elite strains of nitrogen-fixing and other plant-growth promoting microorganisms in single inoculants creates a promising market for composite inoculants. However, combining microorganisms with different physiological and nutritional needs requires biotechnological development. We report the development of a composite inoculant containing Bradyrhizobium diazoefficiens and Azospirillum brasilense for the soybean crop. Evaluation of use of carbon sources indicates differences between the microbial species, with Bradyrhizobium growing better with mannitol and glycerol, and Azospirillum with malic acid and maleic acid, allowing the design of a formulation for co-culture. Species also differ in their growth rates, and the best performance of both microorganisms occurred when Azospirillum was inoculated on the third day of growth of Bradyrhizobium. The composite inoculant developed was evaluated in five field trials performed in Brazil, including areas without and with naturalized populations of Bradyrhizobium. The composite inoculant resulted in symbiotic performance comparable to the application of the two microorganisms separately. In comparison to the single inoculation with Bradyrhizobium, co-inoculation resulted in average increases of 14.7% in grain yield and 16.4% in total N accumulated in the grains. The performance of the composite inoculant was similar or greater than that of the non-inoculated control receiving a high dose of N-fertilizer, indicating the importance of the development and validation of inoculants carrying multiple beneficial microorganisms.

Funding Information: This modeling study was a joint effort of the Models4Pastures project within the framework of FACCE-JPI. Lutz Merbold and Kathrin Fuchs acknowledge funding received for the Swiss contribution to Models4Pastures (FACCE-JPI project, SNSF funded contract: 40FA40_154245/1) and for the Doc. Mobility fellowship (SNSF funded project: P1EZP2_172121). Lutz Merbold further acknowledges the support received for CGIAR Fund Council, Australia (ACIAR), Irish Aid, the European Union, the Netherlands, New Zealand, Switzerland, UK, USAID, and Thailand for funding to the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) as well as for the CGIAR Research Program on Livestock. The NZ contributors acknowledge funding from the New Zealand Government Ministry of Primary Industries to support the aims of the Livestock Research Group of the Global Research Alliance on Agricultural Greenhouse Gases and from AgResearch's Strategic Science Investment Fund (the Forages for Reduced Nitrate Leaching (FRNL) research program). The UK partners acknowledge funding by DEFRA and the RCUK projects: N-Circle (BB/N013484/1), UGRASS (NE/M016900/1), and GREENHOUSE (NE/K002589/1). R.M. Rees and C.F.E. Topp also received funding from the Scottish Government Strategic Research Programme. Lorenzo Brilli, Camilla Dibari, and Marco Bindi received funding from the Italian Ministry of Agricultural Food and Forestry Policies (MiPAAF). The FR partners acknowledge funding from CN-MIP project funded by the French National Research Agency (ANR-13-JFAC-0001) and from ADEME (no. 12-60-C0023). Open access funding enabled and organized by Projekt DEAL Funding Information: This modeling study was a joint effort of the Models4Pastures project within the framework of FACCE‐JPI. Lutz Merbold and Kathrin Fuchs acknowledge funding received for the Swiss contribution to Models4Pastures (FACCE‐JPI project, SNSF funded contract: 40FA40_154245/1) and for the Doc. Mobility fellowship (SNSF funded project: P1EZP2_172121). Lutz Merbold further acknowledges the support received for CGIAR Fund Council, Australia (ACIAR), Irish Aid, the European Union, the Netherlands, New Zealand, Switzerland, UK, USAID, and Thailand for funding to the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) as well as for the CGIAR Research Program on Livestock. The NZ contributors acknowledge funding from the New Zealand Government Ministry of Primary Industries to support the aims of the Livestock Research Group of the Global Research Alliance on Agricultural Greenhouse Gases and from AgResearch's Strategic Science Investment Fund (the Forages for Reduced Nitrate Leaching (FRNL) research program). The UK partners acknowledge funding by DEFRA and the RCUK projects: N‐Circle (BB/N013484/1), UGRASS (NE/M016900/1), and GREENHOUSE (NE/K002589/1). R.M. Rees and C.F.E. Topp also received funding from the Scottish Government Strategic Research Programme. Lorenzo Brilli, Camilla Dibari, and Marco Bindi received funding from the Italian Ministry of Agricultural Food and Forestry Policies (MiPAAF). The FR partners acknowledge funding from CN‐MIP project funded by the French National Research Agency (ANR‐13‐JFAC‐0001) and from ADEME (no. 12‐60‐C0023). Open access funding enabled and organized by Projekt DEAL Publisher Copyright: ©2020. The Authors. Open access funding enabled and organized by Projekt DEAL

Biological nitrogen fixation (BNF) refers to a microbial mediated process based upon an enzymatic “Nitrogenase” conversion of atmospheric nitrogen (N2) into ammonium readily absorbable by roots. N2-fixing microorganisms collectively termed as “diazotrophs” are able to fix biologically N2 in association with plant roots. Specifically, the symbiotic rhizobacteria induce structural and physiological modifications of bacterial cells and plant roots into specialized structures called nodules. Other N2-fixing bacteria are free-living fixers that are highly diverse and globally widespread in cropland. They represent key natural source of nitrogen (N) in natural and agricultural ecosystems lacking symbiotic N fixation (SNF). In this review, the importance of Azotobacter species was highlighted as both important free-living N2-fixing bacteria and potential bacterial biofertilizer with proven efficacy for plant nutrition and biological soil fertility. In addition, we described Azotobacter beneficial plant promoting traits (e.g., nutrient use efficiency, protection against phytopathogens, phytohormone biosynthesis, etc.). We shed light also on the agronomic features of Azotobacter that are likely an effective component of integrated plant nutrition strategy, which contributes positively to sustainable agricultural production. We pointed out Azotobacter based-biofertilizers, which possess unique characteristics such as cyst formation conferring resistance to environmental stresses. Such beneficial traits can be explored profoundly for the utmost aim to research and develop specific formulations based on inoculant Azotobacter cysts. Furthermore, Azotobacter species still need to be wisely exploited in order to address specific agricultural challenges (e.g., nutrient deficiencies, biotic and abiotic constraints) taking into consideration several variables including their biological functions, synergies and multi-trophic interactions, and biogeography and abundance distribution.

Cereal–legume intercropping increases the nitrogen (N) input from biological nitrogen fixation (BNF) and improves the exploitation of fertilizer and soil N, often leading to higher grain N content and higher productivity per unit land area compared to monocrops. Previous studies have found that these effects are more tangible under low soil and fertilizer N conditions compared to high N availability, and there is a need to assess the N uptake at critical crop development stages in order to time the N application for maximum uptake and use efficiency. The objective of this study was to assess the productivity of pea–barley intercropping compared to monocropping under 0 kg N ha−1 (0 N) and 100 kg N ha−1 (100 N). In 2017, a split plot experimental design was implemented with pea (Pisum sativum) sole crop (SC pea), barley (Hordeum vulgare) sole crop (SC barley), and pea–barley intercrop (IC total) as the main plots and 100 N applications in two 50 kg N ha−1 splits at 30 and 60 days after emergence as subplots within the main plots. The Land Equivalent Ratio (LER), based on grain dry matter (GDM) yields in the pea–barley intercrop (IC total), was higher (1.14 at 0 N and 1.10 at 100 N), indicating 10–14% greater radiation, nutrient, and water use efficiency compared to the sole crops and 4% greater resource use efficiency at 0 N compared to the 100 N; this illustrated greater total intercrop productivity compared to sole crops. The 100 N treatment decreased the SC pea and pea in intercrop (IC pea) GDM and grain dry matter N (GDMN) and increased the GDM and GDMN in SC barley and barley in the intercrop (IC barley). Intercropping increased the grain N content and therefore the protein content of the grains in 0 N and 100 N treatments. The highest fertilizer N yield, % nitrogen derived from fertilizer (%NDFF), and % nitrogen use efficiency (%NUE) were achieved in SC barley followed by IC total, indicating that intercropping improved the soil and fertilizer N use compared to SC pea. The IC pea increased the % nitrogen derived from atmosphere (%NDFA) from 67.9% in SC pea to 70.1% in IC pea. IC total increased the share of %NDFF, %NDFS, and %NDFA compared to the SC pea, which indicated a significant advantage of intercropping due to the complementarity of the component species under limited N supply in the field. Cereal–legume intercropping increases the nitrogen (N) input from biological nitrogen fixation (BNF) and improves the exploitation of fertilizer and soil N, often leading to higher grain N content and higher productivity per unit land area compared to monocrops. Previous studies have found that these effects are more tangible under low soil and fertilizer N conditions compared to high N availability, and there is a need to assess the N uptake at critical crop development stages in order to time the N application for maximum uptake and use efficiency. The objective of this study was to assess the productivity of pea–barley intercropping compared to monocropping under 0 kg N ha−1 (0 N) and 100 kg N ha−1 (100 N). In 2017, a split plot experimental design was implemented with pea (Pisum sativum) sole crop (SC pea), barley (Hordeum vulgare) sole crop (SC barley), and pea–barley intercrop (IC total) as the main plots and 100 N applications in two 50 kg N ha−1 splits at 30 and 60 days after emergence as subplots within the main plots. The Land Equivalent Ratio (LER), based on grain dry matter (GDM) yields in the pea–barley intercrop (IC total), was higher (1.14 at 0 N and 1.10 at 100 N), indicating 10–14% greater radiation, nutrient, and water use efficiency compared to the sole crops and 4% greater resource use efficiency at 0 N compared to the 100 N; this illustrated greater total intercrop productivity compared to sole crops. The 100 N treatment decreased the SC pea and pea in intercrop (IC pea) GDM and grain dry matter N (GDMN) and increased the GDM and GDMN in SC barley and barley in the intercrop (IC barley). Intercropping increased the grain N content and therefore the protein content of the grains in 0 N and 100 N treatments. The highest fertilizer N yield, % nitrogen derived from fertilizer (%NDFF), and % nitrogen use efficiency (%NUE) were achieved in SC barley followed by IC total, indicating that intercropping improved the soil and fertilizer N use compared to SC pea. The IC pea increased the % nitrogen derived from atmosphere (%NDFA) from 67.9% in SC pea to 70.1% in IC pea. IC total increased the share of %NDFF, %NDFS, and %NDFA compared to the SC pea, which indicated a significant advantage of intercropping due to the complementarity of the component species under limited N supply in the field.

The common bean (Phaseolous vulgarisL.) is a grain legume functionally characterized by its capacity for symbiotic of biological nitrogen fixation. As such, it does not demand the application of synthetic nitrogenous fertilizer and can offer environmental benefits as part of holistic cropping systems. While common bean commodities are highly nutritious, commercial cultivation of this crop is declining in already-industrialized countries. However, recent interest of consumers towards diets that benefit environmental and personal health has rekindled commercial interest in legumes, including the common bean. The aim of this protocol is to identify agronomic practices that are capable of increasing the yield and quality of the common bean for use as food. To address this research question, published literature will be screened for inclusion on the basis of defined eligibility criteria to ensure data sources are selected in an objective and consistent manner. Consistency checks will be carried out for the title, abstract and full texts of the literature collated. The output is expected to be a summary of the knowledge available to maximize the productivity and quality of the common bean as food. This anticipated synthesis will be of utility for a wide range of value-chain stakeholders from farmers and consumers, to research scientists and policy makers.

Soil salinity is one of the major abiotic stresses restricting the use of land for agriculture because it limits the growth and development of most crop plants. Improving productivity under these physiologically stressful conditions is a major scientific challenge because salinity has different effects at different developmental stages in different crops. When supplied exogenously, proline has improved salt stress tolerance in various plant species. Under high-salt conditions, proline application enhances plant growth with increases in seed germination, biomass, photosynthesis, gas exchange, and grain yield. These positive effects are mainly driven by better nutrient acquisition, water uptake, and biological nitrogen fixation. Exogenous proline also alleviates salt stress by improving antioxidant activities and reducing Na+ and Cl− uptake and translocation while enhancing K+ assimilation by plants. However, which of these mechanisms operate at any one time varies according to the proline concentration, how it is applied, the plant species, and the specific stress conditions as well as the developmental stage. To position salt stress tolerance studies in the context of a crop plant growing in the field, here we discuss the beneficial effects of exogenous proline on plants exposed to salt stress through well-known and more recently described examples in more than twenty crop species in order to appreciate both the diversity and commonality of the responses. Proposed mechanisms by which exogenous proline mitigates the detrimental effects of salt stress during crop plant growth are thus highlighted and critically assessed.

International audience; The cultivation of grain legumes (e.g., common bean) in sub-Saharan Africa contributes to the provision of food for a growing population and delivers environmental benefits such as inputs of nitrogen (N) to crops and soil via symbiotic nitrogen fixation (SNF). However, the success of SNF is constrained by several factors such as the poor efficiency of native rhizobial strains to fix N, the low availability of phosphorus (P) and the acidity of soils. Two trials have been conducted in low-fertility tropical soils at the smallholder farm scale in Madagascar to assess the effects of Rhizobium inoculation together with inputs of P and lime on the growth of the common bean. We showed that inoculation with native strains of Rhizobium had significant effects on bean root nodulation, which was increased by up to 15-fold on plant growth, which increased by 78% and on bean yield, which increased by 126%. Moreover, we observed positive and significant relationships between inoculation with Rhizobium and P fertilization on nodulation, plant growth and yield. However, the addition of dolomite lime did not show any effect in our study. The addition of P decreased the mycorrhization rate of roots. Additional research is still needed to improve our understanding of soil fertility conditions (mainly on nutrient availability, including micronutrients) allowing better efficiency of legume symbionts (rhizobium and mycorrhiza) in such low-fertility soils.

Nitrogen (N) deposition and biological N fixation (BNF) are main external N inputs into terrestrial ecosystems. However, few studies have simultaneously quantified the contribution of these two external N inputs to global NPP and consequent C sequestration. Based on literature analysis, we estimated new net primary production (NPP) due to external N inputs from BNF and N deposition and the consequent C sinks in global boreal, temperate and tropical forest biomes via a stoichiometric scaling approach. Nitrogen-induced new NPP is estimated to be 3.48 Pg C yr−1 in global established forests and contributes to a C sink of 1.83 Pg C yr−1. More specifically, the aboveground and belowground new NPP are estimated to be 2.36 and 1.12 Pg C yr−1, while the external N-induced C sinks in wood and soil are estimated to be 1.51 and 0.32 Pg C yr−1, respectively. BNF contributes to a major proportion of N-induced new NPP (3.07 Pg C yr−1) in global forest, and accounts for a C sink of 1.58 Pg C yr−1. Compared with BNF, N deposition only makes a minor contribution to new NPP (0.41 Pg C yr−1) and C sinks (0.25 Pg C yr−1) in global forests. At the biome scale, rates of N-induced new NPP and C sink show an increase from boreal forest towards tropical forest, as mainly driven by an increase of BNF. In contrast, N deposition leads to a larger C sink in temperate forest (0.11 Pg C yr−1) than boreal (0.06 Pg C yr−1) and tropical forest (0.08 Pg C yr−1). Our estimate of total C sink due to N-induced new NPP approximately matches an independent assessment of total C sink in global established forests, suggesting that external N inputs by BNF and atmospheric deposition are key drivers of C sinks in global forests. Based on a stoichiometric scaling approach, we estimated that nitrogen-induced new net primary production is a key driver of C sinks in global forests.

In early soybean cultivars of high productive potential, the use of chemical nitrogen (N) fertilizer may be a critical factor to meet the crop N requirements for obtaining high yields. In order to determine the response of early soybean cultivars to doses and times of nitrogen fertilizer application, associated with the inoculation of Bradyrhizobium japonicum, two field experiments were conducted in a Quartzipsamment soil from the Brazilian tropical Savannah, during the 2016/2017 and 2017/2018 growing seasons. The experimental treatments were arranged in a 2 × 3 × 4 factorial scheme, being two soybean cultivars (BRS 1074 IPRO and ST 797 IPRO), three application times of N fertilizer (sowing, 30 and 50 days after the emergence) and four N doses (0 kg ha-1, 20 kg ha-1, 40 kg ha-1 and 60 kg ha-1). The following variables were evaluated: plant height, shoot dry matter, number of nodules, nodule dry matter, first pod height, number of pods, number of grains per pod, 1,000-grain mass, grain yield and harvest index. The use of N fertilizer did not improve the production components and did not increase the soybean grain yield, regardless of the doses and times of application. Therefore, it was concluded that, if efficient strains of B. japonicum are used in areas of first soybean crop, in a Quartzipsamment soil with medium-high fertility, especially with a relatively high N availability due to the mineralization of the soil organic matter, there is no need to apply starter or late doses of nitrogen fertilizer.

The United States (USA) and Argentina (ARG) account for over 50% of the global soybean [Glycine max (L.) Merr.] production. Soybean N demand is partially met (50–60%) by the biological nitrogen fixation (BNF) process; however, an unanswered scientific knowledge gap exists on the ability of the BNF process to fulfill soybean N demand at varying yield levels. The overall objective of this study is to explore the potential N limitation using different N strategies for historical and modern soybean genotypes. Four field experiments were conducted during 2016 and 2017 growing seasons in Kansas (USA) and Santa Fe (ARG). Twenty-one historical and modern soybean genotypes released from the 1980s to 2010s were tested under three N treatments: (i) control, without N application (Zero-N); (ii) 56 kg N ha–1 applied at R3-R4 growth stages (Late-N); and (iii) 670 kg ha–1 equally split at planting, R1, and R3–R4 growth stages (Full-N). Historical soybean yield gains, from the 1980s to 2010s, were 29% in the USA and 21% in ARG. Following the yield trend, seed N content increased for modern genotypes in parallel to the reduction on seed protein concentration. Regarding N treatments, Full-N produced 12% yield increase in the USA and 4% in ARG. Yield improvement was mainly related to increases in aboveground biomass, seed number (genotype effect), and to a lesser extent, to seed weight (N effect). This study suggests a potential N limitation for soybean, although there are still questions about the way in which N must be provided to the plant. EEA Oliveros Fil: Ortez, O.A. Kansas State University. Department of Agronomy; Estados Unidos Fil: Salvagiotti, Fernando. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Oliveros. Departamento de Agronomía; Argentina Fil: Enrico, Juan Martin. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Oliveros. Departamento de Agronomía; Argentina Fil: Prasad, P.V.V. Kansas State University. Department of Agronomy; Estados Unidos. USDA-ARS. Center for Grain and Animal Health Research; Estados Unidos Fil: Armstrong, P. USDA-ARS. Center for Grain and Animal Health Research; Estados Unidos Fil: Ciampitti, Ignacio A. Kansas State University. Department of Agronomy; Estados Unidos

Soybean biological N2 fixation (BNF) relationships with fertilizer N and yield response have been comprehensively reviewed in the scientific literature. However, the study of the N-gap between N uptake and N supplied by N2 fixation, and the partial N balance (fixed N in aboveground biomass – N seeds) needs further investigation. Therefore, the goals of this synthesis–analysis were to (i) quantify seed production per unit of fixed N under different amounts of N derived from the atmosphere (NDFA, %), (ii) study the N-gap and explore limitations of N2 fixation (kg ha–1) for satisfying plant N demand, and (iii) calculate a partial N balance for soybean and determine its relationship with the N2 fixation process. Data was gathered from 1955 through 2016 using studies reporting BNF, seed yield, and plant N uptake (n = 733 data points). The main outcomes of this review were (i) as NDFA increased, seed production per N2 fixation decreased (from 0.033 to 0.017 Mg yield kg–1 N from low, 28%, to high, 80%, NDFA); (ii) N-gap increased faster when NDFA values were above 80% and after plant N content was above 370 kg N ha–1 suggesting that the crop needs additional N for coping yield potential; and (iii) when excluding roots, the partial N balance calculation revealed negative values across all NDFA levels. Future studies should consider a holistic approach to quantify the contribution of BNF in overall N cycling, including N contribution from roots, and to better understand the soil × plant × rhizobia interactions. EEA Oliveros Fil: Ciampitti, Ignacio A. Kansas State University. Department of Agronomy; Estados Unidos Fil: Salvagiotti, Fernando. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Oliveros. Departamento de Agronomía; Argentina