Soil Mechanical Composition and Moisture Enhanced the Improvement of Mealworm Casting Amendment on Different Land Use Soils

To investigate the effects of mealworm casting amendment on different land-use soils and find out the optimal soil moisture content for application, three distinct soils of different soil texture were selected for soil incubation experiment, one of which was set to two moisture levels. Soil samples were collected on days 14 and 28 of the incubation. Research findings indicate that soil mealworm casting amendemnt stimulates soil carbon and nitrogen cycling, facilitating the conversion of nutrients into forms readily absorbed by plants. The most pronounced effect is observed in soil ammonium nitrogen content, with an average increase of 620.7%; the average increases in soluble carbon and soluble organic carbon were 80.7% and 92.5%, respectively. Adding insect manure significantly increased the abundance of microorganisms involved in the soil carbon cycling, such as Proteobacteria and Bacteroidetes. The mealworm manure also increased beneficial taxa such as Chitinophaga and suppressed disease-associated microorganisms, thereby improving the soil microbial community structure. Moisture conditions and soil mechanical composition were key factors influencing the effectiveness of mealworm castings. The optimal moisture content for mealworm castings application is 60% of the field capacity, while higher moisture (80% of the field capacity) inhibits casting mineralization and reduces soil nitrate nitrogen content by 73.2% at day 28. Suitable moisture contents promoted mineralization of Tenebrio molitor castings, whereas excessive clay content constrained both mineralization and the frass-induced increase in soil pH.