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Soil acidity limits crop growth and yield all over the world. Low grain yields is usually associated with poor soil fertility; however, little attention has been given to the nitrogen-based fertilizer use efficiency in soils managed with lime. Given the current scenario of uncertainties regarding the availability and prices of fertilizers, our study aimed to understand how maize intercropped with ruzigrass and soybean plants develop in long-term soils managed with lime rates, and what the fate of the 15N–labeled ammonium sulfate [(15NH 4) 2 SO 4 ] applied in the soil-plant system. The treatments consisted of four dolomitic lime rates applied to the soil surface [control, half the recommended lime rate (½ RLR), full recommended lime rate (1 RLR) and double the recommended lime rate (2 RLR)]. The higher lime rate (2 RLR) improved fertility, carbon and nitrogen stocks in the soil profile, and grain and/or stover production of maize, ruzigrass and soybean. As a consequence, maize and ruzigrass recovered a high amount of 15N-fertilizer. On the other hand, soybean recovered less 15N-fertilizer, regardless of treatment, but a greater amount was found in acidic soils. At the end of the maize and soybean growth cycles, our results showed that in 2 RLR-amended soil, the 15N unrecovered was 71% lower than control. Finally, our results suggested that the use of low lime rates (½ RLR) may increase the 15N losses potential to deep layers, whereas low amounts of 15N were found in the subsoil when higher lime rates were applied. Soil acidity management through higher lime rates leads, over time, to increased soil fertility, resulting in a favorable environment for plant growth and the use of nitrogen fertilizers. In this way, it is possible to obtain a more productive and less costly agricultural system, and with less potential to pollute the environment. • Soil fertility increases after long-term liming with higher lime rates. • The 15N-fertilizer recovery by crops is proportional to the soil fertility level. • Low lime rates increased the concentration of 15N-fertilizer in deep soil layers. • The higher 15N recovery leads to higher yields and lower N-fertilizer losses. [ABSTRACT FROM AUTHOR]

• Deep root growth was improved by increasing soil fertility with lime. • Photosynthesis and water use efficiency are enhanced in high fertile soils. • Long-term liming increased soybean grain yield proportionally to the lime rate. Soil acidity is one of the major drivers of yield-limited crop productivity, particularly when combined with dry spells during crop development. Liming is a widely used strategy for alleviating the negative effects of soil acidity, ensuring greater crop root development to assist the plant in periods of low water availability, promoting full photosynthetic activity and, consequently, increasing crop yield. Here, we investigated the long-term effects of surface liming on soil chemical properties as well as soybean root growth, nutrition, photosynthetic parameters and grain yield during three growing seasons (2016–2019) in a region prone to dry spells. The long-term liming experiment was established in 2002. We evaluated the long-term effects of four surface lime rates: control, soil not treated with lime; ½ RLR, soil treated with half the recommended lime rate; 1 RLR, soil treated with the full recommended lime rate; and 2 RLR, soil treated with twice the recommended lime rate. The last lime application occurred in 2016. Our results revealed that increasing lime rates applied to soil surface up to 2 RLR increased soil fertility and root growth, besides to enhance the root distribution along soil profile. These changes contributed to boost soybean leaf photosynthetic pigments and gas exchange, leading to better growth, nutrition and grain yields, despite periods of dry spells. Our results suggested that in tropical agricultural systems with intensive cultivation throughout the agricultural year, higher lime rates can be applied without nutritional imbalances in the soil and plants. Our study provided important clues on how long-term liming changes soil fertility and triggers the cascading effects in improving root growth and distribution, as well as soybean photosynthetic metabolism and yield. [ABSTRACT FROM AUTHOR]

• Liming impacts micronutrient availability, which affects microbial N-cycle genes. • Gypsum and lime increase Ca, Mg and Mn in the rhizosphere of intercropped plants. • The amendments increase abundance of genes related to biological nitrogen fixation in soil and rhizosphere. • The amendments reduce nitrification and denitrification gene abundances in soil and rhizosphere. • Liming and lime + gypsum enhance N uptake by plants and maize grain yield. Liming is widely used to decrease soil acidity, and the application of lime alone or in combination with other amendments, such as gypsum, is a viable agricultural practice to improve soil nutrient status and crop yield. However, the effects of applying lime and gypsum alone or in combination on the microbial population and N cycle in intercropped no-till tropical systems are largely unknown. Here, we determined the lasting effects of applying lime and gypsum individually or in combination on soil chemical properties, N uptake by intercropped plants, maize yield, archaeal and bacterial abundances, and N cycle genes in the maize and ruzigrass rhizospheres in a long-term field experiment in tropical soil with a no-till maize and forage ruzigrass intercropping system. Our results showed that the application of lime or lime + gypsum increased soil fertility and the gene abundances of microorganisms responsible for biological nitrogen fixation and reduced gene abundances of nitrification and denitrification in the soil and rhizosphere of ruzigrass and maize. The accompanying increases in Ca2+ and Mg2+ availability, reduced Al3+ levels, and balance of micronutrient availability, mainly Mn, in the soil strongly influenced the responses of N cycle genes and enhanced plant N-acquisition and maize yield. [ABSTRACT FROM AUTHOR]

• Bacterial consortium improved the soybean gas exchange. • Bacterial consortium alleviates oxidative damage by improving antioxidant metabolism. • Dry spells causes less damage to the soybean yield treated with bacterial consortium. Short dry spells are an important grain yield constraint in tropical regions. Plant growth-promoting bacteria (PGPB) and their metabolites can mitigate the impact of drought stress by promoting changes in plant metabolism, physiology, and biochemistry. However, the effects of PGPB on soybean Glycine max (L.) Merril] under drought stress in tropical regions have not been established. The experiments were carried out under tropical field conditions with short dry spells. Therefore, in this study we used a three-factorial trial to evaluate the effects of bacterial consortium consisting of N 2 -fixing Bradyrhizobium japonicum (strain SEMIA 5079) and Bradyrhizobium diazoefficiens (strain SEMIA 5080), the biocontrol agent Bacillus subtilis (strain QST 713), and the plant growth-promoting Azospirillum brasilense (strains Ab-V5 and Ab-V6) with or without application of microbial secondary metabolites (MSM, rhizobial metabolites enriched in lipo-chitooligosaccharides (LCOs)) during two growing seasons. Photosynthetic pigments, gas exchange parameters, antioxidant enzyme activity and proline concentrations in leaves, nodulation, plant growth development and grain yield were evaluated. The bacterial consortium comprising Bradyrhizobium spp., A. brasilense strains and MSM application increased the contents of chlorophyll a (14.5 %), chlorophyll b (30.8 %), total chlorophyll (17.2 %), and total carotenoids (27.3 %) compared with Bradyrhizobium spp. treatment alone. This consortium also increased the net photosynthetic rate (17.7 %), stomatal conductance (56.5 %), internal CO 2 concentration in the substomatal chamber (8.3 %), and transpiration (44 %) compared with plants that received the standard inoculation (Bradyrhizobium spp. only), while reducing the leaf contents of hydrogen peroxide (−18.8 %) and proline (−29.4 %), lipid peroxidation (−15.9 %), and the activities of superoxide dismutase (−18.2 %), catalase (−21.2 %), and ascorbate peroxidase (−19.1 %). Taken together, the results indicate that a beneficial bacterial consortium comprising Bradyrhizobium spp. and A. brasilense strains combined with MSM application can alleviate oxidative damage during dry spells. Furthermore, this consortium improved soybean nodulation, plant growth development, and grain yield by up to 12.2 %. [ABSTRACT FROM AUTHOR]

Azospirillum brasilense is a plant-growth promoting bacteria used as a bioinoculant in agriculture. However, the capacity of A. brasilense to establish itself in the soil and rhizosphere of different plants, as well as its interactions with the native soil bacterial community, are not fully understood. This knowledge gap can be attributed to inconsistencies in the quantity of the inoculant delivered (population size) and abiotic and biotic factors that modulate its performance. In this study, our objective was to gain a better understanding of how different-sized populations (sub-dose, recommended dose, and super-dose) of A. brasilense affect and interact with the structure, diversity, and connections of the native bacterial community in both bulk soil and rhizosphere of maize plants at different growth stages. Furthermore, we aimed to assess the effectiveness of these different-sized populations of A. brasilense in promoting plant growth. The introduction of a large population (recommended dose and super-dose) of A. brasilense significantly improved maize growth parameters, while a small population (sub-dose) did not. In the bulk soil, we observed that a large population of A. brasilense was capable of initially disrupt the native soil bacterial community. However, the native soil bacterial community was able to recover from the momentary disturbance and return to its initial state. In the rhizosphere of maize plants, large populations of A. brasilense extended their impact on the native bacterial community, possibly due to permanent changes in plant traits, such as root morphology and exudation. Furthermore, the co-occurrence network analysis revealed shifts in keystone taxa (i.e. , taxa that confer high connectivity) in the rhizosphere of maize plants. A. brasilense played a key role at the early stages, but it was later replaced by Rhizobiales, a native soil bacterium. This study presents novel evidence of how different-sized populations of A. brasilense can influence microbe-microbe and plant-microbe interactions, ultimately affecting maize growth. • Large populations of Azospirillum brasilense had positive impacts on maize growth. • Large populations of A. brasilense were initially able to disrupt the native soil bacterial community. • The native soil bacterial community recovered from the momentary disturbance caused by A. brasilense inoculation. • Network analysis revealed shifts in keystone taxa, with A. brasilense occupying a key role in the early stage of maize growth. [ABSTRACT FROM AUTHOR]