Plant growth-promoting bacteria (PGPB) are an effective tool for improving nutrients in agricultural systems; however, their efficacy depends on successful colonization in soils. To address this challenge, biochar has been identified as an effective material for enhancing soil ecosystem services and can serve as a protective for PGPB. However, the impact of biochar and PGPB on soil health indicators and plant growth remains poorly understood. This study aimed to evaluate the effects of biochar and PGPB on soil chemical and biological properties in cowpea. We used biochar from bean husk (BHB) and grape fermentation residue (GFB) and Bradyrhizobium elkanii USDA 76 (BRA), Burkholderia cepacia ATCC 25416 (PRB), or Rhizobium altiplani BR10423 (RHI). BHB and PRB stimulated cowpea growth, while GFB and PRB promoted soil phosphatase activity. Overall, different combinations of biochar and PGPR increased soil pH, phosphorus, potassium, organic carbon content, and urease activity, but did not affect microbial biomass carbon and β-glucosidase activities. The biochars inoculated with the BRA showed the highest productivity. For example, plants subjected to the BRA + GFB treatment exhibited a 3.85-fold increase in productivity compared to the additional treatment that involved the use of commercial peat. The study demonstrated a positive effect of biochar and PGPB on soil enzymatic activity, nutrient content, and cowpea growth suggesting a sustainable alternative to chemical fertilizers, especially in poor soils. These findings highlight the potential of biochar as an environmentally sustainable carrier of PGPB while addressing the issue of agricultural waste reuse.

The application of biochar is extensively recognized as an effective strategy to enhance soil ecosystem services. However, its combined effect with beneficial microorganisms, such as Trichoderma, still requires further investigation to understand its impact on soil microbiota and nutrient cycling processes. To address this gap, this study aimed to evaluate the effect of biochar produced from on-farm winery waste, specifically grape stalks (GSB) and grape fermentation residues (GFB), generated after wine production, when co-applied with Trichoderma aureoviride URM 5158 and Trichoderma hamatum URM 6656 in soil cultivated with Malbec grapevines. Our findings reveal that both types of biochar and Trichoderma promoted changes in soil properties. The application of GSB biochar combined with T. hamatum increased grape productivity, while GFB biochar enhanced soil enzymatic activities, particularly those expressed per unit of microbial biomass carbon. Additionally, biochar applications increased pH, phosphorus, potassium, organic carbon, and microbial biomass carbon of the soil. Soils treated with the GFB + T. hamatum treatment exhibited an increase of 569.23% in microbial biomass carbon compared to the control. The results of this study provide substantial evidence that biochar and Trichoderma can be used to improve the chemical and biological properties of vineyard soils, increasing nutrient availability, especially carbon. These effects may contribute to soil fertility by promoting a more favorable environment for microbiota development and grapevine growth. This is the first field study to investigate the impact of on-farm winery waste transformed into biochar, combined with Trichoderma isolates, on Malbec grapevines.

Phosphorus (P) plays a vital role in many aspects of plant growth and development. The low amount of available P in agricultural soils reduces crop productivity and phosphate fertilizers are often applied. However, due to the high affinity of P for the soil constituents, the availability of this element becomes limited to plants. Thus, alternative, ecological, and low-cost techniques have been studied to improve P acquisition by crops. Microorganisms able to solubilize P, mainly phosphate-solubilizing bacteria (PSB) have stood out, since they offer an approach to overcome P scarcity by their introduction in agricultural systems via inoculants. In this paper, we showed the potential of P-solubilizing microorganisms and their mechanisms of action, the potential of different inoculation vehicles, also highlighting the biochar as a viable biological product for production of inoculants. The combined effects of these factors (PSB and biochar) add several benefits to the soil-plant system. Results from this review demonstrate that biochar amendments have great potential as a vehicle for inoculation of PSB. However, studies of biochar combined with PSB is still incipient. Future research should focus efforts on exploring highly efficient strains, optimizing conditions, and assessing several sources of waste for production of biochar and their efficiency in field experiments.