Effect of Sulfur-Enriched Vermicompost on the Growth of Brassica chinensis L. and the Spodoptera litura Fabricius Larvae Feeding

(1) Background: Vermicompost is enriched with plant essential nutrients and has been shown to suppress the incidence of pests; however, its potential is affected by its food sources. (2) Methods: Earthworms were fed cabbage or pig manure to produce two vermicomposts enriched in sulfur and nutrients, respectively. A pot experiment and a feeding experiment were then conducted to determine whether the application of the vermicomposts and sulfur could increase soil fertility, promote the growth of Brassica chinensis L., and inhibit the growth of Spodoptera litura Fabricius larvae. (3) Results: The characteristics of the vermicomposts were mainly affected by the food sources, and vermicomposted cabbage was found to have a higher sulfur content than vermicomposted pig manure. The application of the vermicomposts enhanced the concentrations of organic matter and available phosphorus, as well as the exchange concentrations of potassium, cadmium, and magnesium in the soil. Moreover, the growth of and the accumulated phosphorus and sulfur in the B. chinensis L. samples significantly increased when the plants were grown in soils treated with the two vermicomposts. Hence, the addition of vermicomposted cabbage and sulfur fertilizers can decrease the relative growth rate, total consumption, efficiency of conversion of ingested food, and relative consumption rate of S. litura larvae, possibly due to the increase in leaf sulfur concentration.