Humification evaluation and carbon recalcitrance of a rapid thermochemical digestate fertiliser from degradable solid waste for climate change mitigation in the tropics

Abstract

Indiscriminate, unhygienic and unscientific disposal of solid wastes poses significant risks leading to soil, water and air pollution. Abiotic and nonenzymatic rapid thermochemical processing technology provides a solution for the management of degradable solid waste at the source, converting it to organic digestate fertiliser within a day, thus overcoming the main drawback of the long time span required for composting. A study was performed to evaluate the maturity parameters and the extent of humification of the thermochemical digestate fertiliser and the raw biowaste substrate. We made an objective assessment of the recalcitrance efficiency of the added thermochemical digestate fertiliser on tropical Ultisol soil grown with two cycles of tomato and amaranthus crop sequences. Unlike the raw biowaste substrate, the thermochemical digestate complied with the threshold standards of compost maturity parameters and humification indices. Soil application of the thermochemical digestate fertiliser brought significant additions to the labile, microbial biomass and recalcitrant fractions of soil organic carbon within a year after four cycles of crop growth, as revealed by principal component analysis. Linear regression analysis revealed a strong and significant fit of the labile and microbial biomass carbon fractions with the total dry biomass of amaranthus and tomato. The thermochemical digestate fertiliser imparted a recalcitrance index of 85.57 % and enhanced the soil carbon stock by 4.81 % over the compost-based treatments with a superior soil carbon sequestration rate. The study confirmed that thermochemical digestate fertiliser is a fairly humified, high-resource organic fertiliser input with enhanced agronomic biomass production and recalcitrance efficiency, favouring soil carbon sequestration in Ultisol soils of the tropics.