Microbial inoculant-mediated transformation of Jarava ichu biomass: effects on nutrient availability and heavy metal concentrations

Abstract

Introduction: Jarava ichu is an abundant grass species in high-Andean ecosystems but remains underutilised because its slow natural decomposition limits its potential as an organic soil amendment. Its accumulation may also contribute to the retention of heavy metals in soils, potentially affecting soil quality and agricultural productivity. This study evaluated the effects of microbial inoculants on the physicochemical and mineral composition of J. ichu biomass and their potential to reduce heavy-metal concentrations. Methods: A 2 × 2 × 2 factorial experiment was conducted under a randomised complete block design (RCBD), comprising eight treatments, including a non-inoculated control. The microbial inoculants evaluated were Beauveria bassiana, Trichoderma viride, and EM-Compost. After 180 days of incubation, pH, electrical conductivity (EC), organic matter (OM), macronutrients (N, P, K, Ca, and Mg), and heavy metals (Ni, Cr, and Pb) were determined. Treatment and interaction effects were evaluated to identify changes in biomass composition and contaminant concentrations. Results: T. viride and EM-Compost significantly increased EC to 53.57 and 56.83 mS·m⁻¹, respectively, and enhanced macronutrient availability, particularly P (4,455.24 and 4,462.60 mg·kg⁻¹, respectively) and Mg (3,630.33 and 3,706.39 mg·kg⁻¹, respectively). T. viride reduced Ni and Cr concentrations by 15.53% and 19.75%, respectively, whereas EM-Compost reduced Pb concentration by 43.98%. Among the interaction effects, the combination of B. bassiana and EM-Compost produced the highest K concentration (2,659.45 mg·kg⁻¹). Discussion and conclusion: Microbial inoculation promoted substantial changes in the chemical composition of J. ichu biomass after 180 days, particularly by increasing nutrient availability and reducing selected heavy-metal concentrations. T. viride and EM-Compost showed the greatest potential for enhancing nutrient release and reducing contaminants, suggesting that microbial treatment may improve the suitability of J. ichu biomass for subsequent valorisation as an organic soil amendment. Further studies should directly quantify decomposition rates, nutrient mineralisation, and the agronomic effects of the resulting biomass to confirm its potential for soil management.