Hermetia illucens L., known as Black Soldier Fly (BSF) appear as an opportunity to reuse vegetable by-products, as it is easy to reproduce and can be reared in agricultural side streams, allowing the production of both, animal feed (the larvae, after recycling of the vegetal debris) and soil organic fertilizer (insect frass). Although several organic fertilizers, from long ago, have been used in agriculture, there is yet a paucity of experimental data on the evaluation of the fertilization potential of BSF larvae frass (BSFF). The present study is a contribution to access the agronomic and environmental potential of the BSFF as an organic fertilizer. Within this aim, it was conducted a greenhouse experiment with ryegrass, using seven treatments of BSFF. Under the experimental conditions, the results showed a significant effect of BSFF on the overall ryegrass production, with a steady increase (significant at p ≤ 0.05, as accessed through the Tukey test) up to the treatment with a greater rate of application. In what concerns sustainability of soil productivity, at the end of the experiment, there was also positive indications, namely, a significant increase of OM, P and K, for treatments with higher N endowments, together with a constant increase of dehydrogenase activity, from the control to the higher treatment, which was significant for treatments receiving the higher dose of BSFF.

To evaluate the distribution and source of nitrogen (N) in non-bearing orange trees (Citrus sinensis L. Osbeck cv. ‘Lane Late’ grafted on ‘Carrizo’ citrange), an orchard was established in a Gleyic Podzol (South Portugal). Trees were labelled with ¹⁵N-enriched ammonium nitrate. A set of trees was used for monthly leaf sampling while a second set was destructively harvested in November of each year and separated into different plant organs. Five trees also received unlabelled N after one year of labeling to evaluate the re-distribution of N within the plant. Nitrogen concentration in new leaves tended to decrease following the growth flushes of March, June, and August. The N derived from fertilizer (%Ndff) was small in April suggesting the importance of internal N reserves for new development in spring. Fertilizer use efficiency was 6, 20, and 30% in the 1^st, 2^nd, and 3^rd years, respectively. More than half of the ¹⁵N absorbed by plants each year was allocated to young organs, but the %Ndff was practically the same for all plant organs in the three years. Of the total N content of trees in November 2001, about 35% derived from fertilizer applied that year, 16% from fertilizer applied the previous year, and the remaining 49% came from other N sources.

Diagnosing nutrient insufficiencies or toxicities in sorghum through foliar analysis is still unusual and mainly used for grain sorghum. The influences of the combinations of four nitrogen (N) rates with three sodium chloride (NaCl) rates on the leaf N, phosphorus (P), calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na) concentrations of sweet sorghum [Sorghum bicolor (L.) Moench ssp. saccharatum], cropped for ethanol production, and on biomass and sugar yields were evaluated in three consecutive years of an experiment established on a Eutric Fluvisol equipped with a trickle irrigation system (“triple emitter source”). The relationships among leaf nutrient concentrations, dry matter, and sugar yields were also examined. Nitrogen, much more than salinity, affected leaf nutrient concentration, stem dry weight, and sugar yield. Leaf N concentration was the best indicator for predicting sugar production of sweet sorghum.

Cropping systems are strongly dependent on mineral fertilisers, which are effective in achieving high crop productivities. However, these chemical inputs end up compromising soil quality in the long-term. Frass from black soldier fly (BSF) larvae is a novel organic fertiliser that is rich in organic matter and advocated as a material that can sustain crop productivity while increasing soil quality. This study aimed at evaluating distinct fertilisation regimes in the cultivation of ryegrass ( Lolium multiflorum Lam. or annual ryegrass) in soils of different types (sandy, loamy and clay) and fertility levels. In a 7-month pot experiment conducted in a glass greenhouse, plants were cultivated with exclusive mineral (MT) or organic (OT) fertilisation, in addition to combinations between both (mineral and organic, MOTs) in different proportions (25:50; 50:50 and 75:25), considering a 140 kg per hectare N demand. Crop yield was favoured by the combination of organic and mineral fertilisers in all soils, which also had its fertility increased, especially regarding organic matter build-up and nutrient accumulation. In addition, the presence of frass in the sandy soil stimulated microbial activity, which was measured by the enzyme dehydrogenase. Frass derived from BSF larvae can be considered an adequate organic fertiliser in the cultivation of ryegrass in distinct soil types, when applied in partial (25% to 75%) replacement of mineral fertilisers, enabling high crop productivity and nutritional quality of the crop, while increasing soil fertility.