Festuca glyceriantha Biochar as a Carrier for Trichoderma harzianum Immobilization: Physicochemical Characterization and Effects on Wheat Yield, Grain Protein, and Soil Organic Carbon Storage in Andean Soils

Biochar and beneficial microorganisms have gained increasing attention as alternatives for improving soil properties and crop performance under sustainable agricultural systems. Wheat (Triticum aestivum L.), one of the major crops in the Andean region, requires management strategies that enhance productivity while improving soil quality. This study evaluated the effects of biochar from the native high-Andean grass Festuca glyceriantha Pilger, Trichoderma harzianum, and their combination (Trichoderma harzianum immobilized on biochar) on the growth, yield, grain protein, and soil organic carbon (SOC) storage of wheat (Triticum aestivum L.) in Ayacucho, Peru. A 2 × 2 factorial randomized complete block design with four replicates was used (biochar rate: 0.96 t ha−1). Colonization of biochar by Trichoderma harzianum yielded 5 × 108 spores mL−1 in the recovered suspension, supporting its use as a microbial carrier. Both inputs improved root length, plant height, and biomass accumulation, with responses varying across phenological stages. Grain yield exceeded the control (1.86 t ha−1) by 32.26% with biochar (2.46 t ha−1), 17.74% with Trichoderma harzianum (2.19 t ha−1), and 30.11% with both (2.42 t ha−1). The combination did not outperform biochar alone. The significant biochar × Trichoderma harzianum interaction (yield, p = 0.03; grains per spike, p = 0.02) cannot be interpreted as biological antagonism because inoculum dose and delivery method were not equivalent between treatments (two drench applications in T03 vs. a single application of colonized biochar in the sowing furrow in T04), and the significant biochar × Trichoderma harzianum interaction (yield, p = 0.03; grains per spike, p = 0.02) reflected a less-than-additive response. Trichoderma harzianum increased grain protein content (p < 0.01), whereas biochar did not (p = 0.90); thousand-grain weight and chlorophyll content were unaffected. SOC storage did not differ among treatments (p = 0.101; 156.5–228.4 Mg C ha−1), so no carbon sequestration benefit can be concluded after one growing season. Biochar mainly enhanced grain yield, whereas Trichoderma harzianum mainly improved grain protein. These results support applying each input independently according to the agronomic objective, pending multi-season and multi-site validation with equivalent inoculum doses and complete control treatments.