Trash Amended with Trichoderma Effects on Cane Yield, Soil Carbon Dynamics, and Enzymatic Activities under Plant–Ratoon System of Sugarcane in Calcareous Soil

Soil organic carbon (SOC) management is crucial for promoting crop growth and maintaining sustainability. In calcareous soils, there is a consistent decline in SOC in agricultural soils, with many soils exhibiting notably low SOC content. In this context, evaluating the potential of sugarcane–ratoon systems should be a priority, as these trashes play a vital role in sustaining SOC levels, enhancing soil health, and ultimately influencing cane yield positively. We investigated the effects of trash management and the application of Trichoderma on the growth, yield, SOC, and its fractions in a sugarcane plant–ratoon system. Thus, a field experiment was conducted in a randomized block design with five replications with four treatments, which consisted trash mulching (RM) or incorporation (RI), or removal (RR) with or without Trichoderma (T). RI + T influenced the growth and yield attributes viz. plant height, tillers, cane diameter, and millable canes positively. An improvement of 12.0 and 21.3% in cane yield was recorded after the harvest of the third ratoon crop as compared to RM and RR, respectively. The highest SOC stock (28.84 Mg ha⁻¹) was recorded with RI + T treatment. Furthermore, RI + T plots had 35.9% higher total organic carbon (TOC) with 31.9, 31.8, 32.0, and 32.1% higher very labile, labile, less labile, and non-labile C fractions, respectively, than RR plots. Moreover, trash incorporation with Trichoderma inoculation treatment improved soil respiration, soil microbial biomass carbon, soil microbial biomass N, and soil protein by 38.4, 20.1, 45.2, and 31.1%, respectively, as compared to trash mulching without Trichoderma. Similarly, RI + T treatment recorded higher C sequestration rate (0.89 Mg ha⁻¹ year⁻¹) and C sequestered (3.56 Mg ha⁻¹). Significantly higher dehydrogenase activity (19.8%) and alkaline phosphatase activity (28.0%) were observed in RI + T treatment as compared to RM treatment. Thus, trash incorporation with Trichoderma is recommended for higher soil C sequestration and soil health for sustained sugarcane–ratoon productivity.