Introduction The hydrochar (HC) produced from the hydrothermal carbonisation at mild temperature (190-220°C) of several typologies of organic wet waste, among which agro-industrial waste, seems very promising as amendment/fertilizer. The aerobic post-treatment of HC improves its agronomic properties (Bona et al., 2022). The project “HYDRORG” founded by VRT (Fondazione Valorizzazione Ricerca Trentina) studied the agro-environmental properties and effect on soil of HC compared to compost (COM) and HC aerobically post treated (MIX) (Bona et al., 2023). Methodology The HC (190° C for 2 h) was produced at the HTC pilot plant using winery and dairy agro-industrial sludges. The HC properties have been compared to COM and MIX, obtained by mixing HC and COM in a ratio 1:1 (w/w), monitored in an aerated pile for 1 month, by measuring temperature, oxygen uptake (by dynamic respiration index), and water content. The Growth Index (GrI) has been assessed by testing the growth of Lactuca sativa L., at increasing doses. The three amendments were chemically characterised, studying the quality of carbon content by measuring dissolved organic carbon (DOC) by 1HNMR liquid state, and the soil recalcitrant organic matter (ROC) fraction (alkaline extracted) by 13C NMR liquid state. Finally, the short and long-term effects on soil have been considered. The HC, COM, and MIX were added to the soil and incubated at controlled conditions (25°C and 50% of WHC). The soils have been analysed considering the dynamic of nutrient (N,P,K, and Mg) and the evolution of organic carbon, by applying different analytical methods: thermal analysis of TOC400 and recalcitrant oxidable carbon (ROC) (UNI EN 17505:2024 method), soil respiration, DOC/ROC by 1HNMR liquid state and 13C NMR liquid state of soil alkaline extract, and POXC (permanganate oxidable carbon) (following the methods of Weil et al., 2003). Results and discussion The MIX aerated pile determines a faster decrease of oxygen uptake (from 1789 to 421 mgO2 kgVS-1 h-1). HC has a higher content of both TOC and TKN compared to other products (47 and 4.8 g kg-1) HC has a higher content of P compared to COM (41 and 4.5 g kg-1 respectively) and the MIX has an intermediate value (12.9 g kg-1). The K content was higher in the COM (14.2 g kg-1). The HC induces toxicity on seed germination while COM does not show adverse effect (GrI always >1). And MIX30 was able to double the plant growth in comparison to COM (GrI always ≫1). The analysis of DOC and ROC fractions showed the presence of aliphatic components, greater than aromatic ones in HC, with a higher proportion of less complex and thermally stable molecular compounds (Bona et al., 2023). COM, HC, and MIX were used for soil incubation at two agronomic doses (10 and 20 Mg/ha). After 1 month, the soil amended with HC differed from COM for P and N dynamics; MIX have an intermediate effect. The data suggest a role of HC and MIX as slow-release fertilizers. In the short-term the quantitative effect on TOC were negligible for all the amended soil compared to the Control, and the analysis of DOC and ROC demonstrated slightly differences due to the addition of different quality of organic carbon. These slightly differences were confirmed of the ratio TOC400/ROC. In the long-term the effect TOC400 are similar for all amended soil, but the analysis of POXC highlighted the presence of more active carbon of HC compared to other. Conclusion The chosen approach allowed to verify the effect of new organic fertilizers. The work contributes to the knowledge on their agro-environmental properties, aiming to more define the role in carbon storage, soil fertility management, and mineral fertilizers input reduction.
New amendment: agro-environmental properties of hydrochar and post-treated hydrochar
Bona D.
;Zaccone C.;
2025-01-01
Abstract
Introduction The hydrochar (HC) produced from the hydrothermal carbonisation at mild temperature (190-220°C) of several typologies of organic wet waste, among which agro-industrial waste, seems very promising as amendment/fertilizer. The aerobic post-treatment of HC improves its agronomic properties (Bona et al., 2022). The project “HYDRORG” founded by VRT (Fondazione Valorizzazione Ricerca Trentina) studied the agro-environmental properties and effect on soil of HC compared to compost (COM) and HC aerobically post treated (MIX) (Bona et al., 2023). Methodology The HC (190° C for 2 h) was produced at the HTC pilot plant using winery and dairy agro-industrial sludges. The HC properties have been compared to COM and MIX, obtained by mixing HC and COM in a ratio 1:1 (w/w), monitored in an aerated pile for 1 month, by measuring temperature, oxygen uptake (by dynamic respiration index), and water content. The Growth Index (GrI) has been assessed by testing the growth of Lactuca sativa L., at increasing doses. The three amendments were chemically characterised, studying the quality of carbon content by measuring dissolved organic carbon (DOC) by 1HNMR liquid state, and the soil recalcitrant organic matter (ROC) fraction (alkaline extracted) by 13C NMR liquid state. Finally, the short and long-term effects on soil have been considered. The HC, COM, and MIX were added to the soil and incubated at controlled conditions (25°C and 50% of WHC). The soils have been analysed considering the dynamic of nutrient (N,P,K, and Mg) and the evolution of organic carbon, by applying different analytical methods: thermal analysis of TOC400 and recalcitrant oxidable carbon (ROC) (UNI EN 17505:2024 method), soil respiration, DOC/ROC by 1HNMR liquid state and 13C NMR liquid state of soil alkaline extract, and POXC (permanganate oxidable carbon) (following the methods of Weil et al., 2003). Results and discussion The MIX aerated pile determines a faster decrease of oxygen uptake (from 1789 to 421 mgO2 kgVS-1 h-1). HC has a higher content of both TOC and TKN compared to other products (47 and 4.8 g kg-1) HC has a higher content of P compared to COM (41 and 4.5 g kg-1 respectively) and the MIX has an intermediate value (12.9 g kg-1). The K content was higher in the COM (14.2 g kg-1). The HC induces toxicity on seed germination while COM does not show adverse effect (GrI always >1). And MIX30 was able to double the plant growth in comparison to COM (GrI always ≫1). The analysis of DOC and ROC fractions showed the presence of aliphatic components, greater than aromatic ones in HC, with a higher proportion of less complex and thermally stable molecular compounds (Bona et al., 2023). COM, HC, and MIX were used for soil incubation at two agronomic doses (10 and 20 Mg/ha). After 1 month, the soil amended with HC differed from COM for P and N dynamics; MIX have an intermediate effect. The data suggest a role of HC and MIX as slow-release fertilizers. In the short-term the quantitative effect on TOC were negligible for all the amended soil compared to the Control, and the analysis of DOC and ROC demonstrated slightly differences due to the addition of different quality of organic carbon. These slightly differences were confirmed of the ratio TOC400/ROC. In the long-term the effect TOC400 are similar for all amended soil, but the analysis of POXC highlighted the presence of more active carbon of HC compared to other. Conclusion The chosen approach allowed to verify the effect of new organic fertilizers. The work contributes to the knowledge on their agro-environmental properties, aiming to more define the role in carbon storage, soil fertility management, and mineral fertilizers input reduction.
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