Soil quality (SQ) pertains to the intricate and ongoing capacity of soil to function as a thriving ecosystem that supports the growth of plants and animals. However, there is a limited understanding of SQ assessment in mixed forest plantations. Therefore, we formulated and tested the hypothesis that the inclusion of a nitrogen-fixing tree species (such as Acacia mangium) improves SQ indicators in mixed treatments involving Eucalyptus trees. To evaluate the changes in SQ, we conducted a field experiment that employed the Soil Management Assessment Framework (SMAF) tool to analyze pure and mixed plantations of Eucalyptus grandis and A. mangium. Soil samples were collected at a depth of 0–20 cm from different treatments, including pure E. grandis without nitrogen fertilization (E), pure A. mangium (A), pure E. grandis with nitrogen fertilization (E + N), and mixed E. grandis and A. mangium (E + A). Sampling took place at 27 and 39 months after planting. We selected seven indicators of SQ: two biological indicators (soil microbial biomass carbon and β-glucosidase enzyme activity), four chemical indicators (soil organic carbon, pH, available phosphorus, and potassium), and one physical indicator (bulk density). By applying the SMAF tool, we determined the SQ scores for each indicator. The results revealed that E + A stands exhibited higher SMAF scores than pure stands, particularly in terms of pH (0.49 and 0.52 at 27 and 39 months, respectively) and phosphorus levels (0.84 and 0.82, at 27 and 39 months), respectively. Forest management practices and the sampling period had the most pronounced impact on biological and chemical indicators. Notably, significant positive correlations were observed between SMAF scores and pH, available phosphorus content, enzymes, soil organic carbon, and microbial biomass in both sampling periods. This study effectively provided novel information that introducing a nitrogen-fixing tree species in combination with eucalyptus trees enhances SQ, as indicated by the SMAF tool, which could reduce the need for external inputs (e.g., mineral fertilizers) by the farmers. Future studies should analyze the effects of A. mangium not only with other E. grandis varieties but also with other forestry essences.

Summary: Bibliometric research illuminates the scientific development of soil health (SH) studies in the Brazilian Semiarid, which are crucial for sustainable agriculture and mitigating climate change impacts. However, research trends on SH in the Brazilian Semiarid are still not well understood. This study aimed to illustrate how SH has been addressed in research concerning the Brazilian Semiarid. Terms such as ‘soil health,’ ‘soil quality,’ ‘biological quality,’ ‘chemical quality,’ ‘physical quality,’ as well as ‘Caatinga,’ ‘Brazilian Semiarid,’ and ‘Brazilian Northeast’ were searched in the Scopus® database. Bibliometric parameters were catalogued by the number of publications per year, most cited articles, primary institutions, main journals, and keyword frequency. The articles were evaluated based on the examination of chemical, physical, and biological indicators, and a similarity test was conducted to group articles according to these indicators. The bibliometric analysis reveals a significant increase in scientific output since 2020. Embrapa research centres contribute significantly to this expanding body of knowledge, with the leading journal ‘Revista Caatinga’ reflecting a specialized focus on the region’s unique challenges. The most evaluated indicators were pH, soil organic carbon, P, Ca²⁺, Mg²⁺, K⁺, and bulk density, but the prevalence of biological indicators, such as soil organic carbon (SOC), activity of enzymes such as alkaline and acid phosphatase, and ß-glucosidase, microbial activity, and soil fauna, underscores key research themes. These findings highlight the practical implications of SH research, but while increased research is commendable and increasingly necessary, studies are still scarce. Increased research is vital for the development of strategies that contribute to the long-term sustainability of the Brazilian Semiarid region.

Summary: Globally, the use of biological products, including biological control agents, biofertilizers, and bioinoculants, has increased significantly as a strategy to reduce dependence on synthetic inputs and promote sustainable agriculture. However, its effects on soil health are still poorly explored. Therefore, this study aimed to analyse the multifunctionality of biological products in agriculture, focusing on soil health, using a systematic review and bibliometric analysis approach. This analysis involves summarizing their mechanisms of action, categories, and impacts. Parameters such as the number of publications per year, the most cited articles, the frequency of keywords and international scientific collaboration networks between countries were analysed. The results showed an expansion in the number of publications on biological products and biological products over the years, with a significant growth in recent years, with emphasis on Brazil and Russia. The most frequent keywords include ‘biological products’, ‘biological product’, ‘soil’, ‘fungi’, ‘bacteria’, and ‘biological control’, and the most cited articles address topics such as the use of Azospirillum sp. in agriculture, the combined application of biological products to control soil diseases, and the inoculation of seeds with Bacillus subtilis. Although few studies have directly evaluated soil health, the results indicate that biological products are related to improvements in soil health, which stimulate the microbiota and promote greater productivity, thereby positively impacting the physical and chemical properties, highlighting the importance of an integrated approach for soil health.