User friendly reagents for rapid thermochemical processing of Biowaste

Abstract

A study entitled ‘User friendly reagents for rapid thermochemical processing of biowaste’ was carried out at the Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani during 2022-2024. The objective of the study was to standardize user friendly and easily available alternate reagents for rapid thermochemical processing of biowaste, study the nutrient release and retention characteristics of the resultant thermochemical organic fertilizer and test its crop suitability. The study included standardization of reagent protocol for production of thermochemical organic fertilizer (TOF) by testing of resultant products and selecting the best three alternate reagent combinations, characterization of those products, an incubation study, leaching study and field experiments using cowpea var. Kanakamony as test crop. Production of TOF was as per patented KAU rapid thermochemical processing technology developed by Sudharmaidevi et al. (2017). The acid-alkali components were substituted with reagents such as acetic acid (5% and 10%), calcium hydroxide (5%, 10%, 15%), and calcium oxide (10%, 15%). All formulations were neutral to slightly alkaline with TOC content ranging from 33.94% to 38.21%. Phytotoxicity assessment based on the germination index (GI) of cowpea, bhindi, and amaranthus indicated values exceeding 60% for TOFs prepared from 5 % Acetic acid + 10 % Ca(OH)2 [TA5CH10], 5 % Acetic acid + 15% Ca(OH)2 [TA5CH15], 10 % Acetic acid + 5 % Ca(OH)2 [TA10CH5], 10 % Acetic acid + 10 % Ca(OH)2 [TA10CH10], and the patented TOF (P), suggesting their safety and non-toxic nature for seed germination and seedling growth. In pot culture studies, TOF (P) recorded the highest yield (68.70 g/plant), which was statistically on par with TA10CH10 (65.83 g/plant). Number of fruits per plant, pod length and pod weight were statistically comparable for both TOF (P) and TA10CH10. This was followed by TA5CH10 which was statistically similar to that of TOF (P) in plant height, length and weight of pod. This was followed by TA5CH15. So TA10CH10, TA5CH10 and TA5CH15 were selected for further analysis. Characterization of these three selected TOFs showed physical and chemical properties meeting FCO standards. Among them, TA10CH10 recorded the highest levels of total N (2.08%), K (1.42%), Mg (0.71%), S (301.33 mg/kg), and all micronutrients. These findings emphasized the superior nutrient profile of TA10CH10 formulation. The incubation study for 90 days revealed the nutrient release pattern of organic fertilizers. The 100 and 75 per cent of TOF from the three selected reagent combinations, and TOF (P), FYM as per POP were incubated (17.85 g per container pot). TOF was applied in N equivalence of FYM (8.9 g per container pot for 100 % TOF and 6.69 g per container pot for 75 %TOF). Soil alone was kept as control. Soil pH in all treatments recorded a decreasing trend up to 60 days. EC of the soil was found increasing till 60 days followed by a slight decrease till 90 days. Soil organic carbon content and available N content was found increasing up to 30 days followed by a decrease till 90 days. Available P content was found to be higher in treatment where FYM was applied and an increasing trend was observed up to 30 days followed by a decline till 60 days and then an increase. Available K was found increasing till 60 days followed by a decrease and was recorded highest for TOF (P). Soil OC, available N, Mg, S and micronutrients were highest from TOF (P) and was significantly on par with TA10CH10. In the leaching study, sieved samples (40 g) were mixed with 800 mL distilled water and filtered samples were analyzed at different time intervals. Ammoniacal N increased, while total and nitrate N decreased. Leaching of other macronutrients increased over time. Micronutrients exhibited varying patterns with majority following an increasing trend. Overall, TOF (P) and TA10CH10 had the highest nutrient release, indicating greater leaching potential. Field trials showed that 100% TOF (P) + STBR (T5) recorded the highest cowpea yield in Rabi (33.48 g/plant) and Kharif (34.56 g/plant). STBR+ TA10CH10 (T4) was statistically on par with T5 in both seasons (31.86 g/plant and 31.45 g/plant). Plant height, number of nodules, number, length and weight of pod were found statistically similar between T5 and T4. Available nutrient content in post-harvest soil, whole plant analysis and crude protein content of T4 was found statistically on par with T5. The study concluded that application of TA10CH10 (TOF prepared from 10 % acetic acid and 10 % calcium hydroxide) at 10 t ha⁻¹, in combination with soil test based fertilizer recommendation (STBR), proved to be best for cowpea var. Kanakamony compared to both FYM + STBR and TOF formulations prepared using other alternate reagent combinations. Overall, TOF prepared from 10 % acetic acid and 10 % calcium hydroxide (TA10CH10) emerged as a promising, user-friendly, and sustainable alternative to the patented TOF—matching its nutrient efficiency and yield benefits while being easily produced from biowaste using vinegar and lime, making it ideal for small-scale household adoption.