The use of plant growth promoting bacteria (PGPB) that can solubilize phosphorus (P) has shown potential to improve nutrient availability in grass crops such as corn (Zea mays L.) This study was developed to investigate if inoculation with Azospirillum brasilense, Bacillus subtilis or Pseudomonas fluorescens associated with P₂O₅ rates can improve phosphorus use efficiency (PUE) reflecting on greater corn development and yield. The field trial was set up in a Rhodic Hapludox under no-till system under Savannah conditions, in a completely randomized block design with four replicates. Treatments were tested in a full factorial design and included: (i) five P₂O₅ rates (0 to 105 kg ha^–1) and (ii) four PGPB seed inoculation (Control–without inoculation, A. brasilense, B. subtilis or P. fluorescens). Inoculation was found to increase grain yield by 39.5, 29.1, and 15.9% when B. subtilis was inoculated in the absence of P₂O₅ rates and associated with 17.5 and 70 kg P₂O₅ ha^–1 and by 34.7% when A. brasilense was inoculated with application of 105 kg P₂O₅ ha^–1. In addition, inoculation with B. subtilis and A. brasilense were found to increase P uptake, benefiting productive components development, leading to an improved PUE, and greater corn grain yield. The results of this study showed positive improvements in P uptake as a result of B. subtilis and A. brasilense inoculation, with an increase of 100.5 and 54.6% on PUE, respectively; while the P. fluorescens inoculation were less evident. Further research should be conducted under biotic or/and abiotic conditions such as attack of pathogens and insects, drought, salinity, water flooding, low and high temperature to better understand the role of PGPB, inoculated alone or in combination as the co-inoculated method.

Sugarcane holds the prominent position in global economy. Extensive research is needed to enhance the efficiency of phosphorous fertilizers which increase the cost of sugarcane production more specifically in the less fertile soils which are weathered and phosphorous deficit as tropical region soils. We are currently living in a transitional period called the “Green Micro-revolution,” in which the use of plant growth-promoting bacteria (PGPB) is justified and although bacteria such as Azospirillum brasilense, Bacillus, and Pseudomonas fluorescens in other crops are recognized for increasing production however, little is known about the effects of these microorganisms on sugarcane. The current study aimed to evaluate the effect of inoculation with three species of plant growth promoting bacteria (A. brasilense, Bacillus subtilis, and P. fluorescens) without or with combine application of reduced doses of phosphate fertilizer, in the P soil available, P leaf concentration, shoot yield and P accumulation in sugarcane (cane-plant) at the end of the cycle. The experiment was carried out with a sugarcane crop in a Hapludox Rhodic with low available P content, in a randomized block design with 8 × 5 factorial scheme, being eight inoculations and five P doses (0, 45, 90, 135, and 180 kg ha⁻¹ P₂O₅) as triple superphosphate. The bacterial inoculations influenced the leaf P content, so that inoculation with B. subtilis + P. fluorescens provided the highest concentration of phosphorus in the sugarcane leaf. Both the layers of the soil were differently influenced by inoculation and P doses whereas inoculation with A. brasilense + P. fluorescens at 135 kg P₂O₅ ha⁻¹ provided the highest soil P content in the soil layer of 0–0.25 m. Although, maximum stalk yield was obtained with inoculation of B. subtilis + P. fluorescens at the dose of 135 kg ha⁻¹ P₂O₅. The inoculation of A. brasilense + B. subtilis with application of 45 kg P₂O₅ ha⁻¹ improved dry matter, total P accumulation and stalk production by 38% in sugarcane variety (RB92579) and reduced P fertilization by 75% for the same variety grown in low-P soil.

The relationship between zinc mineral nutrition and plant growth-promoting bacteria (PGPB) is pivotal in enhancing agricultural productivity, especially in tropical regions characterized by diverse climatic conditions and soil variability. This review synthesizes and critically evaluates current knowledge regarding the synergistic interaction between zinc mineral nutrition and PGPB in tropical agricultural systems. Zinc is an essential and fundamental micronutrient for various physiological and biochemical processes in plants. Its deficiency affects plant growth and development, decreasing yields and nutritional quality. In tropical regions, where soil zinc availability is often limited or imbalanced, the PGPB, through different mechanisms such as Zn solubilization; siderophore production; and phytohormone synthesis, supports Zn uptake and assimilation, thereby facilitating the adverse effects of zinc deficiency in plants. This review outlines the impacts of Zn–PGPB interactions on plant growth, root architecture, and productivity in tropical agricultural systems. The positive relationship between PGPB and plants facilitates Zn uptake and improves nutrient use efficiency, overall crop performance, and agronomic biofortification. In addition, this review highlights the importance of considering indigenous PGPB strains for specific tropical agroecosystems, acknowledging their adaptability to local conditions and their potential in sustainable agricultural practices. It is concluded that Zn fertilizer and PGPBs have synergistic interactions and can offer promising avenues for sustainable agriculture, addressing nutritional deficiencies, improving crop resilience, and ensuring food security.

Core Ideas: Urea with N‐(n‐butyl thiophosphoric) triamide provided similar effects to conventional urea in tropical edaphoclimatic conditions. Azospirillum brasilense increased maize grain yield, independently of the nitrogen source. Seed inoculation increase maize grain yield even with high nitrogen rates. Inoculation with A. brasilense increases profit in maize production. New studies are needed to optimize the nitrogen amount that can be applied to utilize the Azospirillum brasilense benefits in maize cropping systems. In addition, information regarding the interaction between the urease inhibitor N‐(n‐butyl) thiophosphoric triamide (NBPT) and biological nitrogen fixation (BNF) and how they affect the crop development and yield is also needed. The objective of this study was to evaluate the effect of rates and sources of N in combination with A. brasilense, on leaf chlorophyll index (LCI), N leaf concentration, production components, and maize grain yield in the Brazilian Cerrado region. The study was performed in a Typic Rhodic Hapludox under no‐tillage system. The experimental design was a randomized complete block design with four replications arranged in a 2 × 5 × 2 factorial scheme: two N sources (urea and urea with NBPT) and five N rates (0, 50, 100, 150, and 200 kg ha⁻¹), with and without A. brasilense inoculation. The increase in N rates significantly enhance LCI, N leaf concentration, plant height, ear diameter, mass of 100 grains, and grain yield. No significant differences were observed among the N sources. Inoculation with A. brasilense increased LCI, stem diameter, ear length, and nitrogen use efficiency (NUE), with a positive effect on grain yield. The increase in N rate up to 200 kg ha^‐–1 with A. brasilense inoculation increased grain yield, independently of the N source. The application of 100 kg ha⁻¹ of N as urea, with inoculation of A. brasilense produced the highest profit in maize production.

The biological nitrogen fixation (BNF) process in grasses is caused by diazotrophic bacteria, particularly Azospirillum brasilense. However, studies are lacking on BNF efficiency to define how much mineral nitrogen (N) can be applied to achieve more sustainable high yields. Furthermore, there should be an analysis of whether urea with the urease enzyme inhibitor NBPT is less harmful, benefiting BNF in grasses. The objective of this study was to evaluate the effect of N sources and N rates associated with inoculation with Azospirillum brasilense regarding foliar diagnosis and leaf chlorophyll index (LCI), agronomic efficiency (AE), and corn grain yield in the Cerrado (Brazilian tropical savanna) region. The experiment was conducted in a no-tillage system in a Latossolo Vermelho Distroférrico (Oxisol). A randomized block experimental design was used with four replications in a 2 × 5 × 2 factorial arrangement as follows: two N sources - urea and Super N, urea with urease enzyme inhibitor NBPT [N - (n-butyl thiophosphoric triamide)]; five N rates (0, 50, 100, 150, and 200 kg ha-1) applied in topdressing; and two seed inoculation treatments, one with and one without A. brasilense. N rate positively influenced the LCI and concentrations of N, S, and Mn in leaves, and may increase the concentrations of P, Cu, and Fe; however, higher N rates can reduce AE. The N sources had similar effects, and therefore urea is recommended for N fertilization. Inoculation with A. brasilense decreased leaf concentration of Fe and increased LCI, leaf concentration of P, AE, and corn grain yield; the use of this diazotrophic bacterium is therefore viable even when high rates of N are applied

Phosphorus (P) is a critical nutrient for high sugarcane yields throughout its cultivation cycles, however, a higher amount of P becomes rapidly unavailable to plants due to its adsorption to soil colloids. Some plant growth-promoting bacteria (PGPBs) may be able to enhance P availability to plants and produce phytohormones that contribute to crop development, quality, and yield. Thus, this study aimed to evaluate leaf concentrations of nitrogen (N) and P, yield, and technological quality of sugarcane as a function of different levels of phosphate fertilization associated with inoculation of PGPBs. The experiment was carried out at Ilha Solteira, São Paulo—Brazil. The experimental design was randomized blocks with three replications, consisting of five phosphorus rates (0, 25, 50, 75, and 100% of the recommended P₂O₅ rate) and eight inoculations, involving three species of PGPBs (Azospirillum brasilense, Bacillus subtilis, and Pseudomonas fluorescens) which were applied combined or in a single application into the planting furrow of RB92579 sugarcane variety. The inoculation of B. subtilis and P. fluorescens provided a higher concentration of leaf P in sugarcane. The P₂O₅ rates combined with inoculation of bacteria alter technological variables and stalk yield of sugarcane. The excess and lack of phosphate fertilizer is harmful to sugarcane cultivation, regardless of the use of growth-promoting bacteria. We recommend the inoculation with A. brasilense + B. subtilis associated with 45 kg ha⁻¹ of P₂O₅ aiming at greater stalk yield. This treatment also increases sugar yield, resulting in a savings of 75% of the recommended P₂O₅ rate, thus being a more efficient and sustainable alternative for reducing sugarcane crop production costs.