Explicating the fertilizer potential of anaerobic digestate: Effect on soil nutrient profile and growth of Solanum melongena L.

The use of anaerobic digestate (ADg), a nutrient-rich residual product of the anaerobic digestion (AD) process, could be a promising strategy for nutrient recycling in agriculture. However, when analyzing the usage of waste digestate as an organic amendment, properties such as organic and nutritional content, hygienic quality, and stability are important factors to consider. In this context, the present study elucidates the suitability of ADg as a fertilizer supplement based on agricultural criteria, including soil nutrient dynamics and the growth performance of brinjal (Solanum melongena L. var. Kashi Uttam). Pot experiments were conducted to explore the viability and response of ADg produced from three different organic wastes viz. the organic fraction of municipal solid waste (OFMSW), sewage sludge (SS), and flower waste (FW). Five fertilization treatments of each ADg, i.e., 0, 25, 50, 75, and 100%, designated as C, T1, T2, T3, and T4, were examined. The findings exhibited a significant (p<0.05) increase in Total Organic Carbon (TOC), exchangeable Na, K, Ca, and available P, while a considerable increment (p>0.05) in TKN was noticed in all the treatments. Biochemical analyses of brinjal depicted significant enhancement (p<0.05) in total chlorophyll (66.7 %) and carotenoid (56.03%) in T1 treatment of OFMSW ADg at 65 DAS. Likewise, maximum protein content increased by 326.8% in T2 of FW ADg at 65 DAS. However, a few of the metal contents also increased with increasing ADg(s) dosage but were well within the permissible limits of the Indian standard. A progressive increase in proline, peroxidase, and lipid peroxidation (p<0.05) was observed with increasing dosages, indicating metal-induced physiological stress in plants. However, improved ascorbic acid and phenol (23.8% at T2 treatment of OFMSW ADg) content allayed oxidative stress. Likewise, augmented morphological and yield (173.4% in T3 treatment of OFMSW ADg and 153.6% in T4 treatment of FW ADg) responses of brinjal in all the treatments showed their aptness for agricultural application with multifaceted environmental benefits. However, more research into the impacts of ADg on soil and plant growth and its transformation during AD is needed to identify the digestate’s end-use value.