Nitrogen fertilization regulates crosstalk between marandu palisadegrass and Herbaspirillum seropedicae: An investigation based on 15N isotopic analysis and root morphology

Strategies seeking to increase the use efficiency of nitrogen (N) fertilizers and that benefit plant growth through multiple mechanisms can reduce production costs and contribute to more sustainable agriculture free of polluting residues. Under controlled conditions, we investigated the compatibility between foliar inoculation with an endophytic diazotrophic bacterium (Herbaspirillum seropedicae HRC54) at control and low, medium and high N fertilization levels (0, 25, 50 and 100 mg of N kg-1 as urea, respectively) in Marandu palisadegrass. Common procedures in our research field (biometric and nutritional assessments) were combined with isotopic techniques (natural abundance - δ15N‰ and 15N isotope dilution) and root scanning to determine the contribution of fixed N and recovery of N fertilizer by the grass. Overall, the combined use of 15N isotopic techniques revealed that inoculation not only improved the recovery of applied N-urea from the soil but also provided fixed nitrogen to Marandu palisade grass, resulting in an increase in the total accumulated N. When inoculated plants grew at control and low levels of N, a positive cascade effect encompassing root growth stimulation (nodes of smaller diameter roots), better soil and fertilizer resource exploitation and increased forage production was observed. In contrast, increasing N reduced the contributions of N fixed by H. seropedicae from 21.5% at the control level to 8.6% at the high N level. Given the minimal to no observed growth promotion, this condition was deemed inhibitory to the positive effects of H. seropedicae. We discuss how to make better use of H. seropedicae inoculation in Marandu palisadegrass, albeit on a small scale, thus contributing to a more rational and efficient use of N fertilizers. Finally, we pose questions for future investigations based on 15N isotopic techniques under field conditions, which have great applicability potential.

Impact of nitrogen fertilizer sustainability on corn crop yield: the role of beneficial microbial inoculation interactions

BACKGROUND

Considering the challenges posed by nitrogen (N) pollution and its impact on food security and sustainability, it is crucial to develop management techniques that optimize N fertilization in croplands. Our research intended to explore the potential benefits of co-inoculation with Azospirillum brasilense and Bacillus subtilis combined with N application rates on corn plants. The study focused on evaluating corn photosynthesis-related parameters, oxidative stress assay, and physiological nutrient use parameters. Focus was placed on the eventual improved capacity of plants to recover N from applied fertilizers (AFR) and enhance N use efficiency (NUE) during photosynthesis. The two-year field trial involved four seed inoculation treatments (control, A. brasilense, B. subtilis, and A. brasilense + B. subtilis) and five N application rates (0 to 240 kg N ha-1, applied as side-dress).

RESULTS

Our results suggested that the combined effects of microbial consortia and adequate N-application rates played a crucial role in N-recovery; enhanced NUE; increased N accumulation, leaf chlorophyll index (LCI), and shoot and root growth; consequently improving corn grain yield. The integration of inoculation and adequate N rates upregulated CO2 uptake and assimilation, transpiration, and water use efficiency, while downregulated oxidative stress.

CONCLUSIONS

The results indicated that the optimum N application rate could be reduced from 240 to 175 kg N ha-1 while increasing corn yield by 5.2%. Furthermore, our findings suggest that replacing 240 by 175 kg N ha-1 of N fertilizer (-65 kg N ha-1) with microbial consortia would reduce CO2 emission by 682.5 kg CO2 -e ha-1. Excessive N application, mainly with the presence of beneficial bacteria, can disrupt N-balance in the plant, alter soil and bacteria levels, and ultimately affect plant growth and yield. Hence, highlighting the importance of adequate N management to maximize the benefits of inoculation in agriculture and to counteract N loss from agricultural systems intensification.

Technological Quality of Sugarcane Inoculated with Plant-Growth-Promoting Bacteria and Residual Effect of Phosphorus Rates

Phosphate fertilization in highly weathered soils has been a major challenge for sugarcane production. The objective of this work was to evaluate the foliar levels of phosphorus (P) and nitrogen (N) and the technological quality and productivity of second ratoon cane as a function of inoculation with plant-growth-promoting bacteria (PGPBs) together with the residual effect of phosphate fertilization. The experiment was carried out at the research and extension farm of Ilha Solteira, state of São Paulo, Brazil. The experiment was designed in a randomized block with three replications in a 5 × 8 factorial scheme. The treatments consisted of five residual doses of phosphorus (0, 45, 90, 135 and 180 kg ha^-1 of P₂O₅, 46% P) applied at planting from the source of triple superphosphate and eight inoculations from three species of PGPB (Azospirillum brasilense, Bacillus subtilis and Pseudomonas fluorescens), applied in single or co-inoculation at the base of stems of sugarcane variety RB92579. Inoculation with PGPBs influenced leaf N concentration, while inoculations with Pseudomonas fluorescens and combinations of bacteria together with the highest doses exerted a positive effect on leaf P concentration. Co-inoculation with A. brasilense + Pseudomonas fluorescens associated with a residual dose of 135 kg ha^-1 of P₂O₅ increased stem productivity by 42%. Thus, it was concluded that inoculations with Pseudomonas fluorescens and their combinations are beneficial for the sugarcane crop, reducing phosphate fertilization and increasing productivity.

Common Bean Productivity and Micronutrients in the Soil-Plant System under Residual Applications of Composted Sewage Sludge

Composted sewage sludge (CSS) is an organic fertilizer that can be used as a source of micronutrients in agriculture. However, there are few studies with CSS to supply micronutrients for the bean crop. We aimed to evaluate micronutrient concentrations in the soil and their effects on nutrition, extraction, export, and grain yield in response to CSS residual application. The experiment was carried out in the field at Selvíria-MS, Brazil. The common bean cv. BRS Estilo was cultivated in two agricultural years (2017/18 and 2018/19). The experiment was designed in randomized blocks with four replications. Six different treatments were compared: (i) four increasing CSS rates, i.e., CSS5.0 (5.0 t ha^-1 of applied CSS, wet basis), CSS7.5, CSS10.0, CSS12.5; (ii) a conventional mineral fertilizer (CF); (iii) a control (CT) without CSS and CF application. The available levels of B, Cu, Fe, Mn, and Zn were evaluated in soil samples collected in the 0-0.2 and 0.2-0.4 m soil surface horizons. The concentration, extraction, and export of micronutrients in the leaf and productivity of common beans were evaluated. The concentration of Cu, Fe, and Mn ranged from medium to high in soil. The available levels of B and Zn in the soil increased with the residual rates of CSS, which were statistically not different from the treatments with CF. The nutritional status of the common bean remained adequate. The common bean showed a higher requirement for micronutrients in the second year. The leaf concentration of B and Zn increased in the CSS7.5 and CSS10.0 treatments. There was a greater extraction of micronutrients in the second year. Productivity was not influenced by the treatments; however, it was higher than the Brazilian national average. Micronutrients exported to grains varied between growing years but were not influenced by treatments. We conclude that CSS can be used as an alternative source of micronutrients for common beans grown in winter.

Integrated use of plant growth-promoting bacteria and nano-zinc foliar spray is a sustainable approach for wheat biofortification, yield, and zinc use efficiency

Introduction and aims

The intensive cropping system and imbalance use of chemical fertilizers to pursue high grain production and feed the fast-growing global population has disturbed agricultural sustainability and nutritional security. Understanding micronutrient fertilizer management especially zinc (Zn) through foliar application is a crucial agronomic approach that could improve agronomic biofortification of staple grain crops. The use of plant growth-promoting bacteria (PGPBs) is considered as one of the sustainable and safe strategies that could improve nutrient acquisition and uptake in edible tissues of wheat to combat Zn malnutrition and hidden hunger in humans. Therefore, the objective of this study was to evaluate the best-performing PGPB inoculants in combination with nano-Zn foliar application on the growth, grain yield, and concentration of Zn in shoots and grains, Zn use efficiencies, and estimated Zn intake under wheat cultivation in the tropical savannah of Brazil.

Methods

The treatments consisted of four PGPB inoculations (without inoculation, Azospirillum brasilense, Bacillus subtilis, and Pseudomonas fluorescens, applied by seeds) and five Zn doses (0, 0.75, 1.5, 3, and 6 kg ha^-1, applied from nano ZnO in two splits by leaf).

Results

Inoculation of B. subtilis and P. fluorescens in combination with 1.5 kg ha^-1 foliar nano-Zn fertilization increased the concentration of Zn, nitrogen, and phosphorus in the shoot and grain of wheat in the 2019 and 2020 cropping seasons. Shoot dry matter was increased by 5.3% and 5.4% with the inoculation of P. fluorescens, which was statistically not different from the treatments with inoculation of B. subtilis as compared to control. The grain yield of wheat was increased with increasing nano-Zn foliar application up to 5 kg Zn ha^-1 with the inoculation of A. brasilense in 2019, and foliar nano-Zn up to a dose of 1.5 kg ha^-1 along with the inoculation of P. fluorescens in the 2020 cropping season. The zinc partitioning index was increased with increasing nano Zn application up to 3 kg ha^-1 along with the inoculation of P. fluorescens. Zinc use efficiency and applied Zn recovery were improved at low doses of nano-Zn application in combination with the inoculation of A. brasilense, B. subtilis, and P. fluorescens, respectively, as compared to control.

Discussion

Therefore, inoculation with B. subtilis and P. fluorescens along with foliar nano-Zn application is considered a sustainable and environmentally safe strategy to increase nutrition, growth, productivity, and Zn biofortification of wheat in tropical savannah.

Beneficial Microorganisms Improve Agricultural Sustainability under Climatic Extremes

The challenging alterations in climate in the last decades have had direct and indirect influences on biotic and abiotic stresses that have led to devastating implications on agricultural crop production and food security. Extreme environmental conditions, such as abiotic stresses, offer great opportunities to study the influence of different microorganisms in plant development and agricultural productivity. The focus of this review is to highlight the mechanisms of plant growth-promoting microorganisms (especially bacteria and fungi) adapted to environmental induced stresses such as drought, salinity, heavy metals, flooding, extreme temperatures, and intense light. The present state of knowledge focuses on the potential, prospective, and biotechnological approaches of plant growth-promoting bacteria and fungi to improve plant nutrition, physio-biochemical attributes, and the fitness of plants under environmental stresses. The current review focuses on the importance of the microbial community in improving sustainable crop production under changing climatic scenarios.

Inoculation with Plant Growth-Promoting Bacteria and Nitrogen Doses Improves Wheat Productivity and Nitrogen Use Efficiency

Wheat is one of the staple foods of the global population due to its adaptability to a wide range of environments. Nitrogen is one of the crucial limiting factors in wheat production and is considered a challenge to food security. Therefore, sustainable agricultural technologies such as seed inoculation with plant growth-promoting bacteria (PGPBs) can be adopted to promote biological nitrogen fixation (BNF) for higher crop productivity. In this context, the objective of the current study was to evaluate the effects of nitrogen fertilization and seed inoculations with Azospirillum brasilense, Bacillus subtilis and A. brasilense + B. subtilis on agronomic and yield attributes, grain yield, grain N accumulation, N use efficiency and applied N recovery in Brazilian Cerrado, which consists of gramineous woody savanna. The experiment was carried out in two cropping seasons in Rhodic Haplustox soil under a no-tillage system. The experiment was designed in a randomized complete block in a 4 × 5 factorial scheme, with four replications. The treatments consisted of four seed inoculations (control-without inoculation, inoculation with A. brasilense, B. subtilis and A. brasilense + B. subtilis) under five N doses (0, 40, 80, 120 and 160 kg ha^-1, applied from urea) at the wheat tillering stage. Seed co-inoculation with A. brasilense + B. subtilis increased grain N accumulation, number of spikes m^-1, grains spike^-1 and grain yield of wheat in an irrigated no-tillage system of tropical savannah, regardless of the applied N doses. Nitrogen fertilization at a dose of 80 kg ha^-1 significantly increased grain N accumulation and number of grains spikes^-1 and nitrogen use efficiency. Recovery of applied N was increased with inoculation of B. subtilis and co-inoculation of A. brasilense + B. subtilis at increasing N doses. Therefore, N fertilization can be reduced by the inclusion of co-inoculation with A. brasilense + B. subtilis in the cultivation of winter wheat under a no-tillage system of Brazilian Cerrado.

Nanozinc and plant growth-promoting bacteria improve biochemical and metabolic attributes of maize in tropical Cerrado

Introduction

Plant growth-promoting bacteria (PGPBs) could be developed as a sustainable strategy to promote plant growth and yield to feed the ever-growing global population with nutritious food. Foliar application of nano-zinc oxide (ZnO) is an environmentally safe strategy that alleviates zinc (Zn) malnutrition by improving biochemical attributes and storage proteins of grain.

Methods

In this context, the current study aimed to investigate the combined effect of seed inoculation with PGPBs and foliar nano-ZnO application on the growth, biochemical attributes, nutrient metabolism, and yield of maize in the tropical savannah of Brazil. The treatments consisted of four PGPB inoculations [i.e., without inoculation, Azospirillum brasilense (A. brasilense), Bacillus subtilis (B. subtilis), Pseudomonas fluorescens (P. fluorescens), which was applied on the seeds] and two doses of Zn (i.e., 0 and 3 kg ha-1, applied from nano-ZnO in two splits on the leaf).

Results

Inoculation of B. subtilis with foliar ZnO application increased shoot dry matter (7.3 and 9.8%) and grain yield (17.1 and 16.7%) in 2019-20 and 2020-2021 crop seasons respectively. Inoculation with A. brasilense increased 100-grains weight by 9.5% in both crop seasons. Shoot Zn accumulation was improved by 30 and 51% with inoculation of P. fluorescens in 2019-20 and 2020-2021 crop seasons. Whereas grain Zn accumulation was improved by 49 and 50.7% with inoculation of B. subtilis and P. fluorescens respectively. In addition, biochemical attributes (chlorophyll a, b and total, carotenoids, total soluble sugar and amino acids) were improved with inoculation of B. subtilis along with foliar nano ZnO application as compared to other treatments. Co-application of P. fluorescens with foliar ZnO improved concentration of grains albumin (20 and 13%) and globulin (39 and 30%). Also, co-application of B. subtilis and foliar ZnO improved concentration of grains glutelin (8.8 and 8.7%) and prolamin (15 and 21%) in first and second seasons.

Discussion

Therefore, inoculation of B. subtilis and P. fluorescens with foliar nano-ZnO application is considered a sustainable and environmentally safe strategy for improving the biochemical, metabolic, nutritional, and productivity attributes of maize in tropical Savannah regions.

Azospirillum brasilense and Zinc Rates Effect on Fungal Root Colonization and Yield of Wheat-Maize in Tropical Savannah Conditions

A successful microbial inoculant can increase root colonization and establish a positive interaction with native microorganisms to promote growth and productivity of cereal crops. Zinc (Zn) is an intensively reported deficient nutrient for maize and wheat production in Brazilian Cerrado. It can be sustainably managed by inoculation with plant growth-promoting bacteria and their symbiotic association with other microorganisms such as arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE). The objective of this study was to evaluate the effect of Azospirillum brasilense inoculation and residual Zn rates on root colonization and grain yield of maize and wheat in succession under the tropical conditions of Brazil. These experiments were conducted in a randomized block design with four replications and arranged in a 5 × 2 factorial scheme. The treatments consisted of five Zn rates (0, 2, 4, 6 and 8 kg ha^-1) applied from zinc sulfate in maize and residual on wheat and without and with seed inoculation of A. brasilense. The results indicated that root colonization by AMF and DSE in maize-wheat cropping system were significantly increased with interaction of Zn rates and inoculation treatments. Inoculation with A. brasilense at residual Zn rates of 4 kg ha^-1 increased root colonization by AMF under maize cultivation. Similarly, inoculation with A. brasilense at residual Zn rates of 2 and 4 kg ha^-1 reduced root colonization by DSE under wheat in succession. The leaf chlorophyll index and leaf Zn concentration were increased with inoculation of the A. brasilense and residual Zn rates. The inoculation did not influence AMF spore production and CO₂-C in both crops. The grain yield and yield components of maize-wheat were increased with the inoculation of A. brasilense under residual Zn rates of 3 to 4 kg ha^-1 in tropical savannah conditions. Inoculation with A. brasilense under residual Zn rates up to 4 kg ha^-1 promoted root colonization by AMF and DSE in the maize cropping season. While the inoculation with A. brasilense under 2 and 4 kg ha^-1 residual Zn rates reduced root colonization by AMF and DSE in the wheat cropping season. Therefore, inoculation with A. brasilense in combination with Zn fertilization could consider a sustainable approach to increase the yield and performance of the maize-wheat cropping system in the tropical savannah conditions of Brazil.

Co-Inoculation with Azospirillum brasilense and Bradyrhizobium sp. Enhances Nitrogen Uptake and Yield in Field-Grown Cowpea and Did Not Change N-Fertilizer Recovery

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.

Use of Repeated Measures Data Analysis for Field Trials with Annual and Perennial Crops

Field studies conducted over time to collect any type of plant response to a set of treatments are often not treated as repeated measures data. The most used approaches for statistical analyses of this type of longitudinal data are based on separate analyses such as ANOVA, regression, or time contrasts. In many instances, during the review of manuscripts, reviewers have asked researchers to treat year, for example, as a random effect and ignore the interactions between year and other main effects. One drawback of this approach is that the correlation between measurements taken on the same subject over time is ignored. Here, we show that avoiding the covariance between measurements can induce erroneous (e.g., no differences reported when they exist, or differences reported when they actually do not exist) inference of treatment effects. Another issue that has received little attention for statistical inference of multi-year field experiments is the combination of fixed, random, and repeated measurement effects in the same statistical model. This type of analysis requires a more in-depth understanding of modeling error terms and how the statistical software used translates the statistical language of the given command into mathematical computations. Ignoring possible significant interactions among repeated, fixed, and random effects might lead to an erroneous interpretation of the data set. In this manuscript, we use data from two field experiments that were repeated during two and three consecutive years on the same plots to illustrate different modeling strategies and graphical tools with an emphasis on the use of mixed modeling techniques with repeated measures.

Diazotrophic Bacteria Is an Alternative Strategy for Increasing Grain Biofortification, Yield and Zinc Use Efficiency of Maize

Biofortification of cereal crops with zinc and diazotrophic bacteria is a sustainable solution to nutrient deficiency and hidden hunger. The inoculation of staple grain crops such as maize is increased with reducing productivity losses while improving nutrition and use efficiency under climatic extremes and weathered soils of tropical savannah. Therefore, objectives of our study were to evaluate the influence of seed inoculation with diazotrophic bacteria (No inoculation-Control, Azospirillum brasilense, Bacillus subtilis, and Pseudomonas fluorescens) together with residual effect of soil Zn (absence and presence) on growth, yield, Zn nutrition, Zn use efficiencies, and intake of maize in 2019 and 2020 cropping seasons. The inoculation of B. subtilis increased hundred grain mass and yield (14.5 and 17%), while P. fluorescens under residual Zn fertilization has improved shoot and grain Zn concentration in shoot (29.5 and 30.5%). and grain (25.5 and 26.2%), while improving Zn accumulation in shoot (33.8 and 35%) and grain (37.2 and 42%) of maize. The estimated Zn intake in maize was also increased with A. brasilense inoculation and residual Zn application. The Zn use efficiencies including Zn use efficiency, agro-physiological, and utilization efficiency was increased with B. subtilis, while applied Zn recovery was increased with A. brasilense inoculations under residual Zn fertilization. Zinc use efficiency was increased by 93.3 and 397% with inoculation of B. subtilis regardless of Zn application. Therefore, inoculation with B. subtilis and P. fluorescens along residual Zn fertilization is considered the most effective and sustainable strategy for agronomic biofortification of maize under harsh tropical conditions of Brazil.

Improving Sustainable Field-Grown Wheat Production With Azospirillum brasilense Under Tropical Conditions: A Potential Tool for Improving Nitrogen Management

Sustainable intensification of cropping systems requires to increase productivity and nutrients use efficiency while reducing negative impacts of agricultural management practices on ecosystem and environment. Plant growth-promoting rhizobacteria (PGPR) inoculations are considered one of the most promising and safe strategy to alleviate environmental alterations in context of climatic extremes to improve plant nutrition while reducing dependency of nitrogen (N) fertilizer application. This study investigated the interactive effects of N levels and inoculation with A. brasilense on plant biomass, grain yield, agronomic efficiency (AE) of applied N, apparent N-fertilizer recovery (AFR) and N content in plant targeting economic feasibility of wheat production system. The field trial tested 4 N application levels applied in side-dressing (control, low, average and high; named 0, 50, 100 and 200 kg N ha−1) and two inoculations (without and with A. brasilense seed inoculation). The results exhibited that inoculation with A. brasilense enhanced AE, AFR and N uptake in wheat plants with increased root and shoot N accumulation and grain N accumulation under average and high N application levels. In addition, inoculation increased root and shoot biomass, leading to a yield increase of 10.3% compared with non-inoculated plants. Wheat plant inoculation associated with application of the average N level provided the greatest profitability. Furthermore, results showed that reducing N fertilization from 100 to 50 kg N ha−1 along A. brasilense inoculation led to an increase in operating profit of 10.5%. In view of low economic cost, ease of application, and high probability of a positive response by wheat crops, even associated with different N application levels, the inoculation with A. brasilense prone to be a key sustainable management practice to improve wheat production under tropical conditions. This practice has the potential to increase wheat grain yield, N use and uptake, and overall farm profitability.

Silicon Amendment Enhances Agronomic Efficiency of Nitrogen Fertilization in Maize and Wheat Crops under Tropical Conditions

Sustainable management strategies are needed to improve agronomic efficiency and cereal yield production under harsh abiotic climatic conditions such as in tropical Savannah. Under these environments, field-grown crops are usually exposed to drought and high temperature conditions. Silicon (Si) application could be a useful and sustainable strategy to enhance agronomic N use efficiency, leading to better cereal development. This study was developed to explore the effect of Si application as a soil amendment source (Ca and Mg silicate) associated with N levels applied in a side-dressing (control, low, medium and high N levels) on maize and wheat development, N uptake, agronomic efficiency and grain yield. The field experiments were carried out during four cropping seasons, using two soil amendment sources (Ca and Mg silicate and dolomitic limestone) and four N levels (0, 50, 100 and 200 kg N ha⁻¹). The following evaluations were performed in maize and wheat crops: the shoots and roots biomass, total N, N-NO₃⁻, N-NH₄⁺ and Si accumulation in the shoots, roots and grain tissue, leaf chlorophyll index, grain yield and agronomic efficiency. The silicon amendment application enhanced leaf chlorophyll index, agronomic efficiency and N-uptake in maize and wheat plants, benefiting shoots and roots development and leading to a higher grain yield (an increase of 5.2 and 7.6%, respectively). It would be possible to reduce N fertilization in maize from 185–180 to 100 kg N ha⁻¹ while maintaining similar grain yield with Si application. Additionally, Si application would reduce N fertilization in wheat from 195–200 to 100 kg N ha⁻¹. Silicon application could be a key technology for improving plant-soil N-management, especially in Si accumulator crops, leading to a more sustainable cereal production under tropical conditions.

Inoculation With Growth-Promoting Bacteria Azospirillum brasilense and Its Effects on Productivity and Nutritional Accumulation of Wheat Cultivars

Agricultural practices that allow a productive increase in a sustainable manner are becoming increasingly necessary to feed an ever-growing global population. The inoculation with Azospirillum brasilense has the potential to reduce the use of synthetic mineral fertilizers with efficient capacity to promote plant growth and increase nutrition. Therefore, this research was developed to investigate the potential use of A. brasilense to increase the accumulation of macro- and micronutrients and its influence on grain yield, plant height, and spike population in two wheat cultivars (CD1104 and CD150), under irrigated conditions in the Brazilian Cerrado. The study was carried out in a Rhodic Hapludox under a no-tillage system. The experiment was designed in randomized blocks with six replications, arranged in a 2 × 2 factorial scheme: two cultivars (CD150 and CD1104) and two levels of inoculation (control and with A. brasilense). The inoculation with A. brasilense provided greater accumulation of micronutrients in the aerial part of the wheat. In the cultivar CD1104, B and Cu had an accumulation 27.7 and 57.4% higher compared with those of the control without bacteria. In the cultivar CD150, Azospirillum increased the accumulation of B, Fe, and Mn by 43.8, 49.9, and 22%, respectively, and reduced Cu by 21.9%, compared with those of the control. The cultivar CD150 has greater efficiency to accumulate N (+35.5 kg N ha−1) as compared with the cultivar CD1104. Interactions between inoculation and cultivars resulted in greater accumulation of S and K in the shoot of the wheat cultivar CD150, as well greater accumulation of Cu in CD1104. In growth assessments, inoculation or cultivars did not statistically influence wheat grain yield and spike population. Howevere, for plant height, the CD1104 genotype has 13.1% bigger plant height on average than that of the CD150 genotype. Inoculation can contribute more sustainably to wheat nutrition.

Coffea arabica seedlings genotypes are tolerant to high induced selenium stress: Evidence from physiological plant responses and antioxidative performance

Selenium (Se) is considered a beneficial element to higher plants based on its regulation of antioxidative system under abiotic or biotic stresses. However, the limit of beneficial and toxic physiological effects of Se is very narrow. In the present study, the antioxidant performance, nutritional composition, long-distance transport of Se, photosynthetic pigments, and growth of Coffea arabica genotypes in response to Se concentration in solution were evaluated. Five Coffea arabica genotypes (Obatã, IPR99, IAC125, IPR100 and Catucaí) were used, which were grown in the absence and presence of Se (0 and 1.0 mmol L^-1) in nutrient solution. The application of 1 mmol L^-1 Se promoted root browning in all genotypes. There were no visual symptoms of leaf toxicity, but there was a reduction in the concentration of phosphorus and sulfur in the shoots of plants exposed to high Se concentration. Except for genotype Obatã, the coffee seedlings presented strategies for regulating Se uptake by reducing long-distance transport of Se from roots to shoots. The concentrations of total chlorophyll, total pheophytin, and carotenoids were negatively affected in genotypes Obatã, IPR99, and IAC125 upon exposure to Se at 1 mmol L^-1. H₂O₂ production was reduced in genotypes IPR99, IPR100, and IAC125 upon exposure to Se, resulting in lower activity of superoxide dismutase (SOD), and catalase (CAT). These results suggest that antioxidant metabolism was effective in regulating oxidative stress in plants treated with Se. The increase in sucrose, and decrease in SOD, CAT and ascorbate peroxidase (APX) activities, as well as Se compartmentalization in the roots, were the main biochemical and physiological modulatory effects of coffee seedlings under stress conditions due to excess of Se.

Selenium toxicity stress-induced phenotypical, biochemical and physiological responses in rice plants: Characterization of symptoms and plant metabolic adjustment

Selenium (Se) at low concentration is considered benefit element to plants. The range between optimal and toxic concentration of Se is narrow and varies among plant species. This study aimed to evaluate the phenotypic, physiological and biochemical responses of four rice genotypes (BRS Esmeralda, BRSMG Relâmpago, BRS Bonança and Bico Ganga) grown hydroponically treated with sodium selenate (1.5 mM L^-1). Selenium treated plants showed a dramatically decrease of soluble proteins, chlorophylls, and carotenoids concentration, resulting in the visual symptoms of toxicity characterized as leaf chlorosis and necrosis. Selenium toxicity caused a decrease on shoot and root dry weight of rice plants. Excess Se increased the oxidative stress monitored by the levels of hydrogen peroxide and lipid peroxidation. The enzymatic antioxidant system (catalase, superoxide dismutase, and ascorbate peroxidase) increased in response to Se supply. Interestingly, primary metabolism compounds such as sucrose, total sugars, nitrate, ammonia and amino acids increased in Se-treated plants. The increase in these metabolites may indicate a defense mechanism for the osmotic readjustment of rice plants to mitigate the toxicity caused by Se. However, these metabolites were not effective to minimize the damages on phenotypic traits such as leaf chlorosis and reduced shoot and root dry weight in response to excess Se. Increased sugars profile combined with antioxidant enzymes activities can be an effective biomarkers to indicate stress induced by Se in rice plants. This study shows the physiological attributes that must be taken into account for success in the sustainable cultivation of rice in environments containing excess Se.

Influence of Azospirillum brasilense associated with silicon and nitrogen fertilization on macronutrient contents in corn

Information regarding the interaction between biological nitrogen fixation (BNF) with Azospirillum brasilense inoculation and the use of silicon (Si) is needed. Silicon exerts numerous benefits on grasses, especially when the plants are subjected to biotic and abiotic stresses, affecting plant nutrition. The aim of this research was to determine if there is a synergistic effect between the inoculation with A. brasilense and Si use, on macro-nutrient content in corn shoot and root. The field trial was performed in Selvíria, Brazil, on a Typic Rhodic Hapludox soil under no-till system. The experimental design was a completely randomized block design with four replicates arranged in a 2 × 5 × 2 triple factorial arrangement, consisting of two soil acidity corrective sources (dolomitic limestone and Ca and Mg silicate as sources of Si); five N doses (0, 50, 100, 150 and 200 kg ha-1 applied in topdressing); with and without seed inoculation with A. brasilense. The inoculation favored N concentration in shoots and increased the N and S concentration even when associated to high N rates in topdressing. The Si as Ca and Mg silicate associated with the increment of N rates does not promote an increase in the macronutrients uptake. Although it did not favor the N use, the Si also did not negatively affect the benefits of the A. brasilense.

Inoculation of Azospirillum brasilense associated with silicon as a liming source to improve nitrogen fertilization in wheat crops

This research was developed to investigate whether inoculation with Azospirillum brasilense in combination with silicon (Si) can enhance N use efficiency (NUE) in wheat and to evaluate and correlate nutritional and productive components and wheat grain yield. The study was carried out on a Rhodic Hapludox under a no-till system with a completely randomized block design with four replications in a 2 × 2 × 5 factorial scheme: two liming sources (with Ca and Mg silicate as the Si source and limestone); two inoculations (control - without inoculation and seed inoculation with A. brasilense) and five side-dress N rates (0, 50, 100, 150 and 200 kg ha-1). The results of this study showed positive improvements in wheat growth production parameters, NUE and grain yield as a function of inoculation associated with N rates. Inoculation can complement and optimize N fertilization, even with high N application rates. The potential benefits of Si use were less evident; however, the use of Si can favour N absorption, even when associated with A. brasilense. Therefore, studies conducted under tropical conditions with Ca and Mg silicate are necessary to better understand the role of Si applied alone or in combination with growth-promoting bacteria such as A. brasilense.

Can silicon applied to correct soil acidity in combination with Azospirillum brasilense inoculation improve nitrogen use efficiency in maize?

Alternative management practices are needed to minimize the need for chemical fertilizer use in non-leguminous cropping systems. The use of biological agents that can fix atmospheric N has shown potential to improve nutrient availability in grass crops. This research was developed to investigate if inoculation with Azospirillum brasilense in combination with silicon (Si) can enhance N use efficiency (NUE) in maize. The study was set up in a Rhodic Hapludox under a no-till system, in a completely randomized block design with four replicates. Treatments were tested in a full factorial design and included: i) five side dress N rates (0 to 200 kg ha-1); ii) two liming sources (Ca and Mg silicate and dolomitic limestone); and iii) with and without seed inoculation with A. brasilense. Inoculation with A. brasilense was found to increase grain yield by 15% when N was omitted and up to 10% when N was applied. Inoculation also increased N accumulation in plant tissue. Inoculation and limestone application were found to increase leaf chlorophyll index, number of grains per ear, harvest index, and NUE. Inoculation increased harvest index and NUE by 9.5 and 19.3%, respectively, compared with non-inoculated plots. Silicon application increased leaf chlorophyll index and N-leaf concentration. The combination of Si and inoculation provided greater Si-shoot accumulation. This study showed positive improvements in maize growth production parameters as a result of inoculation, but the potential benefits of Si use were less evident. Further research should be conducted under growing conditions that provide some level of biotic or abiotic stress to study the true potential of Si application.

Nutritional assessment and yield of corn as a function of boron rates and zinc fertilization

Brazilian Cerrado soils are commonly deficient in boron (B) and zinc (Zn). It is still debated whether B and Zn interaction has a synergistic or antagonistic effect on the absorption thereof. Thus, we conducted this study to evaluate the effect of boron rates (0, 1, 2, 3, and 4 kg ha?1, as boric acid), with or without zinc fertilization (2 kg ha?1 Zn, as zinc sulfate), on corn nutritional status and grain yield. We also assessed the residual effect of such fertilization on the fall corn crop grown on an Oxisol in a no-tillage system. A synergistic effect between B and Zn was observed on corn nutritional status when applied to the soil at rates of up to 2 kg ha?1, with higher soil contents resulting from the interaction between these micronutrients. Zinc fertilization and increasing boron rates had no significant influence on corn grain yield in both spring/summer and fall crops, grown on a boron-deficient, clayey soil of Cerrado biome.

Nitrogen rates associated with the inoculation of Azospirillum brasilense and application of Si: Effects on micronutrients and silicon concentration in irrigated corn

The aim of this study was to analyze whether there are differences between the inoculation with Azospirillum brasilense and the silicon application, thus enabling a higher efficiency of nitrogen fertilization, evaluating micronutrients and silicon concentration in shoots and roots of irrigated corn (Zea mays). The experiment was conducted in Selviria, Brazil, under a no-till system, on a Typic Rhodic Hapludox. The experiment was set up as a randomized block design with four replications, in a 2 × 5 × 2 factorial arrangement consisting of two soil corrective sources (dolomitic limestone and Ca and Mg silicate as source of Si); five N rates (0, 50, 100, 150 and 200 kg ha-1); with and without inoculation with A. brasilense. N rates increased B, Cu and Fe concentrations in shoots and B, Cu, Fe, Mn, Zn and Si in roots. Inoculation provided greater concentrations of B and Fe in shoots, and B in roots. Although inoculation with A. brasilense favored micronutrient uptake, it negatively affected Si concentration in shoots in 2015/16 crop. The use of Si in the form of Ca and Mg silicate promotes an increase in Mn, Si and Zn uptake in shoots and Mn and Si concentration in roots.

Depicting the physiological and ultrastructural responses of soybean plants to Al stress conditions

Aluminium (Al) is a toxic element for plants living in soils with acidic pH values, and it causes reductions in the roots and shoots development. High Al concentrations can cause physiological and structural changes, leading to symptoms of toxicity in plant tissue. The aim of this study was to describe the Al toxicity in soybean plants through physiological, nutritional, and ultrastructure analyses. Plants were grown in nutrient solution containing increasing Al concentrations (0; 0.05; 0.1; 1.0, 2.0 and 4.0 mmol L-1). The Al toxicity in the soybean plants was characterized by nutritional, anatomical, physiological, and biochemical analyses. The carbon dioxide assimilation rates and stomatal conductance were not affected by the Al. However, the capacity for internal carbon use decreased, and the transpiration rate increased, resulting in increased root biomass at the lowest Al concentration in the nutrient solution. The soybean plants exposed to the highest Al concentration exhibited lower root and shoot biomass. The nitrate reductase and urease activities decreased with the increasing Al concentration, indicating that nitrogen metabolism was halted. The superoxide dismutase and peroxidase activities increased with the increasing Al availability in the nutrient solution, and they were higher in the roots, showing their role in Al detoxification. Despite presenting external lesions characterized by a damaged root cap, the root xylem and phloem diameters were not affected by the Al. However, the leaf xylem diameter showed ultrastructural alterations under higher Al concentrations in nutrient solution. These results have contributed to our understanding of several physiological, biochemical and histological mechanisms of Al toxicity in soybean plants.

Effect of phosphorus applied as monoammonium phosphate-coated polymers in corn culture under no-tillage system

The use of phosphate fertilizers as coated polymers reduces phosphorus losses that occur by adsorption of P to soil particles, thereby providing this essential nutrient for a longer period. The objective of this study was to evaluate the effect of phosphorus doses applied as conventional monoammonium phosphate or as coated polymers on corn grown in a clayey Oxisol, in the Cerrado region. The experiment was conducted in Selvíria - MS, located at 22°22? S and 51°22? W. The experiment was laid out in a randomized block design arranged as a 4 × 2 factorial, with four doses of P2O5 (0, 50, 100, and 150 kg ha-1) and two sources of phosphorus (monoammonium phosphate (MAP) and monoammonium phosphate coated polymers). The experiment was conducted under no-tillage system during the cropping seasons in 2008/09 and 2009/10. The MAP and MAP-coated sources did not differ in most of the yield components in either of the two seasons. We found a quadratic function adjustment for P doses up to 117 and 98 kg ha-1 of P2O5 for P concentration in leaf tissue and grain yield in the 2008/2009 crop, respectively. We also obtained a quadratic function adjustment for P rates for grain yield and number of plants, up to 118 and 113 kg ha-1 of P2O5, respectively, in the 2009/2010 harvest.

Technical and economic feasibility of irrigated wheat as a function of nitrogen doses, sources, and inoculation with Azospirillum brasilense

Azospirillum brasilense is a bacterium known for its biological nitrogen fixation (BNF) in wheat crops. However, there is a lack of comprehensive research defining how much mineral N should be applied to maximize the efficiency of BNF and attain high, economically sustainable yields. Moreover, it would be interesting to investigate whether adding urea with N- (n-butyl) thiophosphoric triamide (NBPT) urease inhibitor might increase BNF in grasses. The objective was to study the effect of inoculation with A. brasilense, associated with varying doses and sources of N, and economically evaluating the yield of irrigated wheat. The experiment was conducted in Selvíria - MS in crop years 2014 and 2015 in Oxisol soil type that was not-tilled. The experimental design was a randomized block with four replications, in a 2 × 5 × 2 factorial scheme, where 2 N sources (urea and Super N - urea with urease inhibitor enzyme), 5 nitrogen fertilization doses in top-dressing (0, 50, 100, 150, and 200 kg ha-1), were applied to wheat crops with or without the inoculation of A. brasilense. Our results showed that the supply of N through Super N was not economically superior to the use of conventional urea; therefore, we recommend the use of urea because of the ease of acquisition. The application of 140 kg ha-1 of N combined with inoculation with A. brasilense showed higher grain yield. However, the 50 kg ha-1 dose of urea in the absence of inoculation provided greater economic viability in wheat cultivation, but was not sufficient to ensure high profitability with grain productivity.

Wheat yield in the Cerrado as affected by nitrogen fertilization and inoculation with Azospirillum brasilense

Abstract: The objective of this work was to evaluate the effect of inoculation with Azospirillum brasilense, associated with N rates and sources, in soil of the Cerrado (Brazilian savanna), on the grain yield of irrigated wheat (Triticum aestivum). The experiment was carried out under a no-tillage system in a Typic Haplustox. The experimental design was randomized complete blocks with four replicates, in a 2x5x2 factorial arrangement: two N sources (urea and urea with NBPT urease inhibitor); five N rates applied as topdressing (0, 50, 100, 150, and 200 kg ha-1); and with or without seed inoculation with A.brasilense. The increase in the N rates positively affected spike length, number of spikelets and of grains per spike, number of spikes per meter, N accumulation in the straw, leaf chlorophyll content, and grain yield of irrigated wheat, regardless of the use of NBPT urease inhibitor with conventional urea. Singly, inoculation with A.brasilense does not affect production components and grain yield, despite the increase in N content in wheat straw. The inoculation with A.brasilense, associated with the application of 140 kg ha-1 N, provides the highest grain yield of irrigated wheat cropped after corn in low-altitude Cerrado.

Economic analysis of corn inoculated with Azospirillum brasilense associated with nitrogen sources and doses

Azospirillum brasilense is a bacterium known for its biological nitrogen fixation (BNF) in corn crops. However, there is a lack of comprehensive research defining how much mineral N should be applied to maximize the efficiency of BNF and attain high, economically sustainable yields. Moreover, it would be interesting to investigate whether adding urea with NBPT urease inhibitor might increase BNF in grasses. Therefore, the aim of this study was to determine the effect of inoculation with Azospirillum brasilense associated with N sources and doses in a Cerrado biome soil by evaluating the grain yield of irrigated corn in economic terms. The experiment was conducted in Selvíria, MS, Brazil under a no-till system on a Latossolo Vermelho distrófico (Oxisol). The experiment was set up as a randomized block design with four replications in a 2 × 5 × 2 factorial arrangement consisting of two sources of N (urea and urea with NBPT urease enzyme inhibitor) and five N doses applied as top-dressing (0, 50, 100, 150, and 200 kg ha-1), with and without the inoculation of seeds with A. brasilense. Inoculation with Azospirillum brasilense makes corn growth much more profitable, irrespective of the dose and source of N. Addition of 200 kg ha-1 N in the form of conventional urea coupled with inoculation with Azospirillum brasilense increases grain yield; however, the highest economic return is obtained with N applied at 100 kg ha-1 with conventional urea and inoculation.

Chemical soil attributes after wheat cropping under nitrogen fertilization and inoculation with Azospirillum brasilense

Azospirillum brasilense plays an important role in biological nitrogen fixation (BNF) in grasses. However, further studies are needed to define how much mineral N can be applied while simultaneously maintaining BNF contribution and maximizing crop yield and to determine the impact of these practices on soil fertility. Thus, we aimed to investigate the effect of inoculation with A. brasilense, in conjunction with varying N doses and sources in a Cerrado soil, on soil chemical attributes after two years of irrigated wheat production. The experiment was initiated in Selvíria - MS under no-tillage production in an Oxisol in 2014 and 2015. The experimental design was a randomized block design with four replications, and treatments were arranged in a 2 x 5 x 2 factorial arrangement as follows: two N sources (urea and Super N - urea with inhibitor of the enzyme urease NBPT (N - (n-butyl thiophosphoric triamide))), five N rates (0, 50, 100, 150 and 200 kg ha-1), and with or without seed inoculation with A. brasilense. The increase in N rates did not influence the chemical soil attributes. Super N acidified the soil more compared to urea. A. brasilense inoculation reduced the effect of soil acidification in intensive irrigated wheat cultivation; however, the base extraction was higher, resulting in a lower soil CEC after cultivation with inoculation. Therefore, the cultivation of wheat inoculated with A. brasilense was not harmful to soil fertility because it did not reduce the base saturation and organic matter content (P, K, Ca, Mg, and S).