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

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.

Thermochemical digestate fertilizer from solid waste: Characterization, labile carbon dynamics, dehydrogenase activity, water holding capacity and biomass allocation in banana.

Thermochemical digestion is a rapid technology of biowaste management resulting in the instant production of organic fertilizer. Characterization and assessment of its suitability as an organic fertilizer is essential for recommendation for crop application. Biowaste and the thermochemical digestate were subjected to physicochemical and biochemical characterization and the compost maturity parameters assessed. The product integrated with inorganic fertilizers was tested in an Ultisol grown with banana in comparison with farmyard manure based fertilizers. Temporal variation in soil reaction, water holding capacity, carbon dynamics, dehydrogenase activity and plant biomass were determined. The thermochemical digestate fertilizer had a bulk density (0.76 Mg m-3), pH (neutral), C:N ratio (16.26), CEC (85.70 cmol(+) kg-1), CEC/ TOC ratio (3.99), Fertilizing index (4.7) and a Clean index (5.0). Field evaluation revealed enhanced water holding capacity (38.75-83.17%). Total carbon increased with consistently high labile (R2 = 0.9551) and non labile carbon fractions and the lowest average lability index (0.78). Dehydrogenase activity at harvest enhanced by 72.81%. An even biomass allocation resulted in 38.84% more biomass production in the fruit over farmyard manure based treatments. In addition to ensuring the safety of the environmental ecosystem, the thermochemical digestate conformed to be a quality resource favoring microbial proliferation and carbon sequestration, thereby restraining carbon dioxide emission. The thermochemical digestate fertilizer based nutrition serves the key deliverables of natural resource management, ecofriendly rapid disposal of biowaste and quality organic fertilizer for banana in Ultisols.