ABSTRACT An important by‐product of insect rearing is the frass, a mixture of excrements, shed exoskeletons, and undigested feed. The recycling of frass as biofertilizer in agriculture is gaining attention as potential alternative to mineral fertilizers. A better understanding of how frass affects soil fertility and crop growth is crucial to provide recommendations about benefits and limits of insect frass as biofertilizer. To reach this goal, in this study we aim at comparing how different mealworm frass amounts, that is, alone or in combination with mineral fertilizer, can affect soil fertility and spring wheat nitrogen nutrition. After a 8‐week long greenhouse experiment, we observed lower soil mineral nitrogen concentration in the treatments receiving the frass either alone or in combination with the mineral fertilizer, so suggesting a potential reduction of nitrogen loss with the biofertilizer. Mealworm frass addition significantly increased the aboveground biomass compared to both the mineral fertilizer alone and the control, particularly by stimulating the growth during the initial phases of crop development. Similarly, greater belowground biomass was also associated with frass treatments where plants invested more biomass in roots with wider diameters. Based on nitrogen nutrition index, both the mineral fertilization and the frass in combination with mineral fertilizer provided the best nitrogen nutrition. Instead, the frass alone treatment, by promoting biomass growth and a dilution of nitrogen concentration, showed a nitrogen deficient status like the control even if the nitrogen export of the frass alone was like that of the frass in combination with the mineral fertilizer. We observed that frass alone stimulated biomass growth to such an extent to reduce the recovery efficiency but, on the other hand, it increased the nitrogen physiological efficiency. Overall, our study shows that the combination of mealworm frass and mineral fertilizer provides promising synergic effects at both soil and crop level.
Fontana et al. (Sun,) studied this question.