<p>We tested frass and poultry manure (PM) as soil amendments with the aim of evaluating their effect on soil health and nutrient dynamics, and on the nutrition of two important high-value sweet pepper varieties. We conducted a set of two 90-day incubation experiments of three soils (A, B, and C) with different fertility levels, amended with frass and PM; also, a pot growth experiment was performed with soils A and B to evaluate the effects on two varieties of sweet pepper under these amendments. Frass and PM increased the levels of soil N and P in all tested soils (incubation tests) and in both soil and plant (growth test). Both materials added to soil ca. 10&#xa0;mg&#xa0;kg⁻¹ of NO₃-N, a highly significant increase, while the P and K additions were dependent on their contents in the organic materials. PM, applied at 5%, significantly increased organic carbon (OC), rising it to as high as 3.7% in soil A (from 1.12% in the control) and up to 2% in soil B (from 0.97% in the control), a remarkable increase signifying a trend towards restored soil health. Even in the infertile soils in both the incubation and the growth experiments, frass applied at 1% boosted their fertility and productivity to the extent that they matched the more fertile soil. In the pot experiment, both amendments significantly improved pepper growth and nutrient uptake in soils, with PM slightly more effective than frass. Our findings demonstrate the role of frass, but also of PM, in increasing soil health and plant performance, by increasing nitrate–N, available P, and OC. We recognize the need for future work concerning experimentation of frass with vital crops used as food or feed under real field conditions.</p>