Finn Petersen

Vanilla is a high-value crop whose demand exceeds supply, yet evidence-based nutrient management remains unexplored. This study investigated the effect of nitrogen form on vegetative growth, biomass allocation, and physiology of Vanilla planifolia in soilless culture. Ninety-five plants were assigned to five NO₃⁻-N: NH₄⁺-N ratios (0:100 to 100:0; n = 17 each) at 47 mg nitrogen L⁻¹ and a nitrogen-free solution ( n = 10), over 140 days under controlled conditions. Total dry mass declined linearly with increasing ammonium proportion ( p < 0.001), with relative growth rate the most responsive parameter: ammonium nutrition reduced total dry mass by 28% and relative growth rate by 36% relative to purely nitrate-fed plants. Increasing ammonium supply acidified the rhizosphere (substrate pH declined by 1.2 units, from 5.93 to 4.72) and tended to reduce leaf biomass fraction and total root length; tissue nitrogen concentration increased linearly with increasing ammonium proportion across all organs. A treatment × shoot-position interaction revealed temporally compounding growth advantages under nitrate nutrition. These results provide first evidence that nitrogen form, together with the accompanying shift in rhizosphere pH, shapes early vegetative growth in vanilla, with nitrate‑dominated supply producing the highest vegetative growth under the controlled soilless conditions tested.

This study quantified the individual and interactive effects of photosynthetic photon flux density (PPFD) and nitrate-nitrogen supply on vegetative growth of Vanilla planifolia (V. planifolia) in a factorial experiment combining four PPFD levels (10‑208 µmol m⁻ ² s⁻ ¹ ) and six nitrogen concentrations (6.9‑60.5 mg NO₃⁻‑N L⁻ ¹ ) over 154 days. Light intensity was the dominant factor, affecting 16 of 20 parameters. Biomass gain saturated at 125 µmol m⁻ ² s⁻ ¹ (daily light integral ~ 5.4 mol m⁻ ² d⁻ ¹ ), while specific leaf area halved, indicating structural acclimation. Non-photochemical quenching rose 20‑fold without an increase in non‑regulated dissipation, consistent with regulated photoprotection. Nitrogen optimised biomass production efficiency at approximately 50‑56 mg L⁻ ¹ , and leaf nitrogen saturated near 2.1‑2.2% dry mass. Light × nitrogen interactions were scarce (4 of 20 parameters), indicating that nitrogen demand was largely independent of light within the range tested. PSII fluorescence parameters responded exclusively to light; Y(NO) was unresponsive to both factors. The results provide the first combined PPFD and nitrogen dose–response data for V. planifolia under controlled conditions and, as an outcome from this soilless system, support a target of 125 µmol m⁻ ² s⁻ ¹ PPFD for highest growth and 50–56 mg NO₃⁻-N L⁻ ¹ for optimal nitrogen use efficiency in vegetative cultivation.

Global population growth is expected to increase poultry meat demand, intensifying the need for sustainable protein sources. Soybean meal, the primary protein feed for poultry, has negative associations with deforestation and long transport distances. Duckweed has emerged as a possible, more sustainable alternative due to its high growth rate and protein yield. The nutrient digestibility and performance effects of the duckweed species Lemna minor (L. minor) in broiler diets were investigated in two experiments. Experiment 1 determined the ileal digestibility of crude protein, amino acids, phosphorus, and metabolizable energy in L. minor. The digestibility of most amino acids in L. minor ranged from 70% to 96%, with lysine and methionine at 87% and 86%, respectively. At 48%, the digestibility of cysteine was markedly lower than that of the other amino acids. However, the digestibility of P exceeded 90%. The energy values of dry matter were 7.05 MJ AME and 6.13 MJ. Experiment 2 tested the inclusion of L. minor (up to 10%) in isoenergetic and isonitrogenous diets. No significant effects on nutrient digestibility, weight gain, feed intake, or feed conversion ratio were observed. Both experiments demonstrate that L. minor cultivated under controlled conditions is a highly digestible, reliable feed source. Its inclusion in broiler diets is feasible, as it does not impair performance, yet provides amino acid balance whilst ensuring biomass quality. These findings support L. minor as a novel protein alternative and warrant further research on higher inclusion rates.

The production of duckweed (Lemnaceae) as a novel protein source could make a valuable contribution to human nutrition. The greatly reduced habitus of duckweed enables simple cultivation with extremely low space requirements, making this free-floating freshwater plant ideal for substrate-free and vertical cultivation in controlled environment agriculture. Of particular importance in the design of a plant-producing Indoor Vertical Farming process is the determination of light intensity, as artificial lighting is generally the most energy-intensive feature of daylight-independent cultivation systems. In order to make the production process both cost-effective and low emission in the future, it is, therefore, crucial to understand and mathematically describe the primary metabolism, in particular the light utilization efficiency. To achieve this, a growth model was developed that mathematically describes the combined effects of plant density and light intensity on the growth rate of Lemna minor L. and physiologically explains the intraspecific competition of plants for light through mutual shading. Furthermore, the growth model can be utilized to derive environmental and process parameters, including optimum harvest quantities and efficiency-optimized light intensities to improve the production process.

Duckweed is gaining attention in animal nutrition and is considered as a potential alternative protein source for broiler chickens. In order to evaluate the nutritional value of duckweed, three individual batches were investigated. They consisted of a mixture of Lemna minuta and Lemna minor (A, 17.5% crude protein), Spirodela polyrhiza (B, 24.6% crude protein) and Lemna obscura (C, 37.0% crude protein). Treatment diets contained 50% batch A, 50% batch B, and 25, 50 and 75% of batch C. All diets were fed to broiler chickens (Ross 308) from an age of 21 to 27 days. Diets with a share of 50 and 75% of batch C led to decreased feed intake (109.3 and 74.9 g/day, respectively) compared to the control. Standardized ileal digestibility of crude protein and amino acids differed significantly between duckweed batches, at values for methionine between 49.9 and 90.4%. For all amino acids, batch A consistently had the lowest and batch C the highest digestibility. Batches had different tannin contents of 2943, 2890 and 303 mg/kg for batches A, B and C, respectively. The apparent ileal digestibility of phosphorus differed significantly between all batches (50.8–78.9%). Duckweed can be used as a protein feed for broiler chickens. However, a defined and stable biomass composition optimized for the requirements of broiler chickens is needed.

Duckweeds can be potentially used in human and animal nutrition, biotechnology or wastewater treatment. To cultivate large quantities of a defined product quality, a standardized production process is needed. A small-scale, re-circulating indoor vertical farm (IVF) with artificial lighting and a nutrient control and dosing system was used for this purpose. The influence of different light intensities (50, 100 and 150 µmol m⁻² s⁻¹) and spectral distributions (red/blue ratios: 70/30, 50/50 and 30/70%) on relative growth rate (RGR), crude protein content (CPC), relative protein yield (RPY) and chlorophyll a of the duckweed species Lemna minor and Wolffiella hyalina were investigated. Increasing light intensity increased RGR (by 67% and 76%) and RPY (by 50% and 89%) and decreased chlorophyll a (by 27% and 32%) for L. minor and W. hyalina, respectively. The spectral distributions had no significant impact on any investigated parameter. Wolffiella hyalina achieved higher values in all investigated parameters compared to L. minor. This investigation proved the successful cultivation of duckweed in a small-scale, re-circulating IVF with artificial lighting.

Within this paper, the authors explain their transdisciplinary vision of nutrient recovery for sustainable urban plant cultivation in Germany from different but complementary perspectives (SUSKULT vision). Nowadays, the demand for fresh, healthy, locally and sustainably produced food in German urban areas is constantly increasing. At the same time, current agricultural systems contribute significantly to exceeding the planetary boundaries. The disruption of the phosphorus and nitrogen cycles in particular stands out from the manifold effects of modern food production on the Earth system. One central issue that will have to be faced in the future is how increased yields in agriculture will be achieved with high-energy requirements in fertilizer production and pollution of water and soil by phosphorus and reactive nitrogen. City region food systems (CRFS) can be a solution to overcome these issues. Nevertheless, to ensure sustainable CRFS, innovative technologies and methods need to be developed, including nutrient and energy recovery and adapted horticultural cultivation methods that fit complex urban dynamics. Such new strategies need to be integrated in long-term social and political transformation processes to enhance acceptance of food produced by recyclates. The joint contribution of experts from the wastewater, horticultural, and political sciences, together with industrial and societal sector actors, is critical to reach these objectives. The overarching goal of SUSKULT’s vision is the establishment of the field of urban circular agricultural production as an innovative sector of the bio-based economy in Germany.

In order to produce protein-rich duckweed for human and animal consumption, a stable cultivation process, including an optimal nutrient supply for each species, must be implemented. Modified nutrient media, based on the N-medium for duckweed cultivation, were tested on the relative growth rate (RGR) and crude protein content (CPC) of Lemna minor and Wolffiella hyalina, as well as the decrease of nitrate-N and ammonium-N in the media. Five different nitrate-N to ammonium-N molar ratios were diluted to 10% and 50% of the original N-medium concentration. The media mainly consisted of agricultural fertilizers. A ratio of 75% nitrate-N and 25% ammonium-N, with a dilution of 50%, yielded the best results for both species. Based on the dry weight (DW), L. minor achieved a RGR of 0.23 ± 0.009 d⁻¹ and a CPC of 37.8 ± 0.42%, while W. hyalina’s maximum RGR was 0.22 ± 0.017 d⁻¹, with a CPC of 43.9 ± 0.34%. The relative protein yield per week and m² was highest at this ratio and dilution, as well as the ammonium-N decrease in the corresponding medium. These results could be implemented in duckweed research and applications if a high protein content or protein yield is the aim.