Recycling fishery waste into biobased fertilizers: Agronomic performance and soil health impacts

This study evaluated the agronomic performance and soil impact of biobased fertilizers derived from fishery waste and by-products as circular alternatives to synthetic nitrogen (N) fertilizers in short-term field experiments with broccoli. Four biobased fertilizers — bokashi pellet (BP), nutrient solution with amino acids (NPKA), fish sludge pellet (FSP), and protein fraction (PF) — were obtained from pilot installations across Europe. The evaluation focused on soil mineral N (SMN) dynamics, N use efficiency (NUE), crop yield, and soil biological responses. One week after transplanting and fertilization, SMN levels in the topsoil (0–10 cm) were the highest in the NPKA (253 ± 94 kg ha⁻¹) and PF (181 ± 45 kg ha⁻¹) treatments, comparble to the mineral fertilizer (MF; 237 ± 5 kg ha⁻¹). In contrast, FSP (68 ± 17 kg ha⁻¹) and BP (30 ± 11 kg ha⁻¹) did not significantly differ from the unfertilized soil (40 ± 5 kg ha⁻¹). Early SMN availability showed a strong positive correlation with broccoli yield and N uptake. Crop yields ranged from 8594 to 14,842 kg ha⁻¹ among the organic treatments, with NPKA and PF performing comparably to MF (14,726 kg ha⁻¹) and substantially better than FSP and BP. The control treatment (CON) yielded 9252 kg ha⁻¹ . NPKA and PF also demonstrated the highest NUE values (108 % and 84.8 %, respectively), with estimated mineral fertilizer equivalents of 79.5 % and 62.7 %. Soil biological activity showed treatment-specific responses. Dehydrogenase activity, microbial biomass carbon, and phospholipid fatty acid profiles in the 0–10 cm soil layer were significantly affected by fertilizer treatments, though most microbial indicators returned to baseline levels post-harvest. Soil fauna responses were variable: Springtail abundance declined under MF, whereas mite populations were more sensitive to organic treatments. Overall, the findings suggest that certain biobased fertilizers, particularly NPKA and PF, can effectively replace mineral N fertilizers, maintaining crop productivity while enhancing soil health indicators. These results support the integration of fish waste-based biobased fertilizers into sustainable agricultural practices.