Abstract
With the forecasted dramatic growth of insect rearing in the near future, frass (insect excreta) has been increasingly considered a sustainable resource for managing plant nutrition in cropping systems and a promising alternative to conventional fertilizer. However, the impact of soil fauna on its fertilizing effect has not been investigated so far. In this study, we investigated the effect of earthworms (Lumbricus terrestris L.) on nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca) uptake and crop growth in the presence of frass from mealworm (Tenebrio molitor L.). Using a pot experiment, we found that earthworms increased N, P, K and Ca concentration in barley (Hordeum vulgare L.) in the presence of frass, suggesting that earthworm activity enhances the short-term recycling of nutrients from frass. Compared to treatments with and without frass and earthworms, the specific leaf area of barley was the highest in the presence of both earthworms and frass. This confirms that earthworms and frass have a synergistic effect on soil fertility. Overall, our study shows that earthworms may improve the efficiency of organic fertilizers and argues therefore for the importance of developing sustainable agricultural practices that promote earthworm populations.
Highlights
In the context of the massive increase in the human population at an unprecedented level, insect rearing represents an opportunity to answer the growing demand for proteins with a low ecological footprint [1]
Context and the need to contribute to the circular economy, the possibility of recovering frass as a fertilizer has recently been considered by researchers [2,3,4]
It is known that soil fauna, especially earthworms, may positively affect plant growth [8,9] due to, among others, changes in soil structure and water regime [10], improvement of soil organic matter and nutrient cycling [11,12], and stimulation and dispersal of beneficial microorganisms [13]
Summary
In the context of the massive increase in the human population at an unprecedented level, insect rearing represents an opportunity to answer the growing demand for proteins with a low ecological footprint [1]. Houben et al [3] have found that frass from mealworm (Tenebrio molitor L.) might be as efficient as conventional mineral fertilizer to sustain crop growth due to its rapid mineralization after its incorporation into the soil and the presence of nutrients in a readily-available form. It is known that soil fauna, especially earthworms, may positively affect plant growth [8,9] due to, among others, changes in soil structure and water regime [10], improvement of soil organic matter and nutrient cycling [11,12], and stimulation and dispersal of beneficial microorganisms [13]. Adding exogenous organic amendments generally stimulates earthworm activity which reciprocally improves the fertilizing effect of these amendments [13,14,15], even though some contradictory results have been found [12,16]
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