Agronomic Performance and Elemental Uptake of a Potential Fertilizer Derived from Microwave-Treated Animal By-Products in Lepidium sativum and Lactuca sativa

The aim of this study was to characterize a fertilizer derived from microwave-treated animal by-products consisting of processed animal proteins (PAPs), and to assess its preliminary agronomic performance. Germination tests, hydroponic cultivation, pot trials and elemental analyses of the fertilizer and plant tissues helped to identify suitable application rates, nutrient uptake response and potential limitations. The results reported in this study suggest that PAPs may affect plant growth and nutrient uptake in a species- and treatment-dependent way. In fact, among the tested concentrations, the most favorable responses were obtained with 0.75 g L−1 PAPs in hydroponic systems and 5 g kg−1 PAPs in pot trials, while higher concentrations progressively inhibited plant development. In the hydroponic experiments, Lepidium sativum treated with 0.75 g L−1 PAPs reached a mean length of 10 ± 1 cm, compared with 10.9 ± 0.4 cm for plants supplied with the commercial nutrient solution. In Lactuca sativa treated with 0.75 g L−1 PAPs, Ca and P concentrations were comparable to those measured in the plants treated with the commercial-nutrient-solution, whereas Mg increased by 60 % and K decreased by 73 %. The tested PAPs batch, deriving from fish-waste material, had an Hg content of 1.3 ± 0.1 mg kg−1 dry weight, highlighting the need for feedstock control and batch-specific compliance assessment. Despite the limitations of this preliminary study, the findings highlight promising application ranges, as well as critical methodological and compositional aspects to be addressed in future, in fully replicated investigations.