Combination of Humic Substances and Arbuscular Mycorrhizal Fungi Affecting Corn Plant Growth

This study evaluates the interaction effects on corn (Zea mays L.) growth between intact humic substances (HS) extracted in an alkaline medium from three different origins (an Organosol [HS-Org], an Andisol [HS-And], and vermicompost [HS-Vc]) and the arbuscular mycorrhizal fungus (AMF) Dentiscutata heterogama. The HS were characterized by spectroscopic techniques, and different biochemical, morphological, nutritional, and AMF colonization parameters were evaluated in corn plants. The experiment was conducted in a greenhouse, and low-fertility soils sterilized after solarization were used as the substrate. Hybrid corn BR-3025 was planted, and the HS concentrations used were 5, 10, and 20 mg carbon L-1 for HS-And, HS-Vc, and HS-Org, respectively, applied 15, 25, and 45 d after emergence close to the roots. The results show that HS application and D. heterogama inoculation significantly stimulated the biomass in relation to the treatments without AMF. Carbohydrate and protein content were stimulated by HS-AMF interaction. A higher leaf content of nutrients was observed in the AMF- and HS-inoculated plants. The HS-Vc application and AMF inoculation resulted in intense stimulation, which was confirmed with a high mycorrhizal efficiency. The spore density and glomalin content were also stimulated by the three different HS applications independently of their source. The HS-Vc has intermediate structural chemical characteristics in terms of polarity and aromaticity compared with HS-Org and HS-And. The HS-Vc more strongly stimulated the plant physiological parameters when combined with the AMF inoculation. These results may indicate that the HS formed in soil and characterized by structures that are more balanced may function more effectively.