Nitrogen fixation and calcium activation of oyster shell during composting and its performance on acidic soil amendment

Chicken manure, corn straw and oyster shell powder (OSP) were used as raw materials for organic-inorganic combined composting. Experiments were designed by adding different amounts of OSP (0 %, 20 %, and 40 %), designed as CK, T1, and T2, respectively. In final composts, the pH value increased to 8.72–9.08, and the electrical conductivity ranged from 2.08–3.82 mS·cm⁻¹. The co-composting could effectively reduce ammonia emissions by 54.65 % and could activate the calcium component by 37.5 %. Addition of OSP promoted the humification and the humic acid could increased 86.1 %. This calcium-based compost of oyster shells (OSs) activated by composting was used to plant Brassica napus by pot experiment. Compared with the addition of OSP after composting, the calcium-based compost activated by composting significantly promoted the growth of Brassica napus because of more nitrogen, humus and available calcium in the calcium-based compost. In addition, this calcium-based compost significantly increased pH, organic matter (OM) and exchangeable calcium content in the acidic soil. In general, composting is an effective method to realize the fertilizer utilization of OSs. This composting process could make full use of calcium in oyster shells to achieve nitrogen retention and humification enhancement during composting, meanwhile calcium morphology in oyster shells can be activated and high-quality acidic soil conditioner can be obtained.