Black soldier fly larvae frass increases the soil’s residual nutrient content and enzymatic activity – a lettuce production trial

Abstract

The aim of this study was to evaluate the potential agronomic value of black soldier fly larvae frass (BSFF) as an organic fertiliser in short-cycle crops, using lettuce as the test plant. Treatments consisted in applying different fertilisers (BSFF and mineral) at different doses and combinations. The experiment was carried out for 42 days and plants were analysed in terms of biomass production, while the soil was chemically characterised before and after fertilisation, in order to assess the residual nutrient concentrations. In addition, soil microbial activity was assessed through the activity of the enzymes dehydrogenase and β-glucosidase. The highest yields were obtained with an exclusive mineral fertilisation (162.5±61.8 g fresh weight) and with a mixture of organic/mineral fertilisation (144.5±16.8 g) in comparison to exclusive fertilisation with BSFF, probably due to the immobilisation and slow mineralisation rate of the N provided by frass, along with the choice of the short-cycle plant, which requires readily available nutrients. Nevertheless, the BSFF increased the soil’s organic matter and residual nutrient content after 42 days of experiment, as well as the enzymatic activity of dehydrogenase and β-glucosidase, by at least 121 and 24% in the soils fertilised with BSFF, respectively. Thus, despite not being effective as an exclusive fertiliser for a short cycle culture, the BSFF included in a mixture with mineral fertilisation, may compete with exclusive mineral fertilisation with the benefit of improving the sustainability of soil fertility and crop production.

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“…However, it should be noted, that in the reference trial we were dealing with a short-lived crop and the mineralization of nutrients from the organic fertilizer is a slow process. With regard to the pH (H 2 O) of the soil after harvest, as shown in the reference study, 4 the beneficial effect of the crop in raising the pH was significant, except for the treatment with exclusively mineral fertilization, which however did not differ from the initial soil value. With regard to the residual OM content after harvest, the positive difference was significant for the T100, T150 and Tmix treatments (23 g kg -1 ), in relation to T0 and TM (18 g kg -1 ).…”

“…The results, previously evaluated for production, 4 had revealed no significance between TM and Tmix, as well as for the other treatments among themselves, the results between these two groups being significantly different, which was already to be expected from what can be seen in Figure 1. This endorses the thesis that, as far as biomass production is concerned, and in the experimental situation in question, organic fertilization alone does not compete with exclusively mineral fertilization, as far as immediate soil fertility for the crop in question is concerned, unless adequately supplemented with the latter.…”

“…Crispa) in Haplic Fluvisol (ISSS-ISRIC-FAO, 2006) mixed with perlite, in a proportion of 4:1 respectively, and fertilized with a biodigested by the larvae of the black soldier fly (BSFL) -opportunely reported. 4 The mineral fertilizer used was Foskasuper®, considering 100% of the expected N requirement. Entomocompost was produced by Entogreen® and resulted from the black soldier fly larvae (BSFL) digestion of agro-industrial by-products (from potato and onion), without any stabilizers or preservatives added, and in accordance with the Portuguese legislation.…”

“…Despite progress already achieved through increased research and experimental development in this area, 3 triggered in particular by the need to promote the innocuous disposal of organic waste that is being produced in overwhelming proportion, justified doubts remain about the possibility of total replacement of mineral fertilizers without affecting agricultural productivity levels compatible with the scale to be expected for long term global needs. In the present case study, without doctrinal prejudices on the use of chemical fertilizers, but with a view to a scale of production compatible with the current and prospective global needs of agricultural production, the aim is to show an illustration of the effect on plant regrowth after the aerial part has been harvested, taken from a pot experiment, 4 where modalities without fertilization, with mineral fertilization, with organic fertilization and with mixed fertilization were contrasted.…”

Hermetia illucens frass improves the physiological state of basil (Ocimum basilicum L.) and its nutritional value under drought

“…Quality of the HI frass is high in terms of N, P, and K levels [ 15 ]. Use of HI frass from larvae increased the soil organic matter and the residual nutrients content, as well as the enzymatic activity of dehydrogenase and β-glucosidase [ 16 ].…”