Preliminary Studies on the Impact of Sericultural Compost on Soil Quality and Bombyx mori Nutrient Intake Dynamics

Sericulture generates large volumes of organic residues that are rarely reintegrated into production systems. We evaluated a closed-loop system in which silkworm (Bombyx mori) frass, uneaten leaves and larval litter were composted for 2.5 months in an aerated, moisture-controlled vessel and applied (1.74 kg/m2) to a mulberry (Morus alba L.) plantation following a 2024 baseline period, with compost amendments and subsequent assessments carried out over the 2024–2026 seasons, in a randomized paired-plot field comparison design (one control and one compost-amended plot). The preliminary results showed that compost amendment was associated with an increase, compared to the control group, in soil humus by 44% (5.20% vs. 3.61%), organic carbon by 44% (3.01% vs. 2.09%) and total nitrogen by 60% (0.32% vs. 0.20%), while lowering the C/N ratio from 10.37 to 9.36 (all p ≤ 0.011), without altering pH (p = 0.153); sodicity indicators remained low (exchangeable sodium percentage ≤ 2.3%). Exchangeable K+ increased 2.6-fold (5.85 vs. 2.28 me/100 g soil). In leaves, compost amendment correlated with a significant increase in the experimental group compared to the control group for Ca by 51% (3.05% vs. 2.02%), Mg by 19% or 1.19-fold (0.31% vs. 0.26%), Cu by 36% (8.38 vs. 6.14 mg/kg) and Mn by 96% (59.20 vs. 30.28 mg/kg) (p ≤ 0.02), while chlorophyll A and carotenoids increased by 12% (20.78 vs. 18.61 mg/100 g FW) and 31% (10.76 vs. 8.19 mg/100 g FW), respectively. Fifth-instar larvae fed leaves from amended plots ingested 14% more dry matter (524.63 g vs. 459.64 g) and 8% more nitrogen (26.16 mg/day vs. 24.29 mg/day) and 33% more ether extract (8.88 vs. 6.69 mg/day) relative to the control group (p ≤ 0.001). These preliminary observational results suggest that the application of sericulture waste compost is linked to trends of enhanced soil fertility and higher leaf nutrient content. Unlike previous studies that evaluated sericulture by-products as isolated soil amendments, this work provides an associative assessment of parameters measured across the soil–plant–silkworm–compost loop, offering evidence for the potential benefits of diverting sericulture by-products away from landfills and converting them into high-quality organic compost, although final crop yield and sericultural performance endpoints remain to be quantified.