Assessment of the Role of Bulking Agents and Composting Phases on the Quality of Compost Tea from Poultry Wastes

In this study, the effects of composting phase and bulking agent on macronutrient extraction and the chemical, physicochemical, and biological properties of 20 compost teas from poultry waste composting mixtures were evaluated. Phosphorus (P) extraction was more efficient during stabilization after the thermophilic phase; however, water-soluble P declined as composting progressed. K was more amenable to extraction, with yields ranging from 30% to 70%, followed by N (2% to 12%) and P (1% to 7%). Compost tea quality was clearly affected by both the bulking agent and the composting stage. Bulking agents that accelerate the process, such as cotton waste (CW) and Napier grass (NG), contributed to nutrient mineralization, increasing availability in the compost tea but also raising salt contents responsible for phytotoxicity. In contrast, tree trimmings (TT), sawdust (S), and sugarcane bagasse (SCB) showed better results, striking a balance between nutrient availability and salt content. The period between the thermophilic phase and cooling was the most suitable for extraction, providing the greatest contribution of water-soluble nutrients. This study highlights the influence of bulking agents and composting phases on nutrient extraction and phytotoxicity of compost teas and provides new insights into the role of electrical conductivity as a threshold indicator for safe agricultural application.