Carbon Pools and Indices Under Activated Trash Treatments in Sugarcane Plant–Ratoon System Grown in Calcareous Soil of Subtropics

A field investigation was conducted at Sugarcane Research Institute, RPCAU, Pusa, Bihar, India during 2020–2022 on sugarcane plant–ratoon system to investigate the effect of trash mulching treatments applied either alone or activated with urea (25 kg N ha −1 )/farmyard manure (5 t ha −1 )/vermicompost (2.5 t ha −1 )/ Trichoderma viride/Azotobacter + PSB inoculated trash and direct incorporation of trash in soil with no trash control. The dose of chemical fertilizer for plant and ratoon was applied as per recommendation in all the treatments. The results revealed that the CO 2 evolution decreased continuously with the advancement of crop growth. The very labile (1.62–2.76 g kg −1 ), labile (1.09–2.17 g kg −1 ), less labile (1.55–2.21 g kg −1 ) and non-labile carbon (2.18–2.95 g kg −1 ) varied significantly after two crop cycles. The carbon fractions were in order of non-labile-C > very labile-C > less labile-C > labile-C. The mean soil TOC (6.26–9.79 g kg −1 ), organic carbon stock (14.70–20.76 Mg ha −1 ), SMBC (110.73–265.16 mg kg −1 ) and microbial quotient (1.77–2.71%) differed significantly due to trash mulching treatments after harvest of ratoon. The CPI (1.00–1.57) and CMI (138.36–238.30) varied significantly in trash-treated plots than no trash. The results revealed that mean cane yield of plant (65.96–83.31 t ha −1 ) and ratoon crop (54.20–71.99 t ha −1 ) differed significantly among the treatments. The mean sugar yield varied significantly in plant (7.22–9.97 t ha −1 ) and ratoon crop (5.78–8.58 t ha −1 ) due to various trash mulching treatments. The positive relationship was found among cane and sugar yield with TOC and CMI. Our findings suggest that trash mulching (10 t/ha) treatments either activated with urea/vermicompost/FYM or inoculated with Trichoderma viride significantly improved soil carbon pool parameters, fractions of carbon and carbon stock over the two crop cycles with improvement in the carbon indices, viz. carbon pool index and carbon management index. It brings significant enhancement in quality of soil and productivity of sugarcane plant–ratoon system in subtropics.