Organic fertilizers in organic greenhouse production systems – a review

From a sustainability point of view, there are strong arguments of nutrient recycling within the society, which means more use of organic nutrient sources within agriculture and horticulture. At the same time, there is an increasing consumer demand for certified organic products, and incentives from governments to increase the conversion of production areas to organic production. This also applies to greenhouse horticulture. Many different raw materials for organic fertilizers are used as of today, such as animal manures, slaughterhouse byproducts, vegetable byproducts, green manure, algae, composts, anaerobic digestates etc. In common for all these fertilizer types is that they are limited in availability, not always consistent with respect to nutrient content, and that they require microbial degradation in order to mineralize its content of nutrients, and are thereby more or less to be characterized as slow release fertilizers. Greenhouse horticulture is different from open field agriculture in several ways with respect to nutrient supply. Firstly, the use of fallow crops and crop rotation is not practical due to the high investment costs bound in the greenhouse structure. Secondly, growth per unit area is significantly higher than in outdoor production, with subsequently higher nutrient demand, often concentrated to a relatively short period of time. On the other hand, climatic factors such as soil temperature and moisture can be controlled which is beneficial for the control of nutrient release. Traditionally, animal by-products such as manure and slaughterhouse wastes have been widely used as organic fertilizers. However, limited availability and ethical concerns is currently driving forces in the search for alternative nutrient sources. The use of solid and liquid anaerobic digestates as fertilizers is a promising practice for greenhouse horticulture. Energy is a “by product” from the production and the nutrient content of the digestates can be modified by feeding the anaerobic reactor with different stock. Furthermore, it is suggested that techniques for fine-tuning the nutrient supply in organic greenhouse horticulture is further developed and adopted, such as the use of microbial biofertilizers and foliar sprays

Nutrient utilization and growth of tomato crops fertilized with solid anaerobic digestate

Anaerobic digestate is a valuable resource for horticultural production, as it contains nutrients and fibers that can be used in plant growing medium. However, compared with hydroponic production based on mineral fertilizers, obtaining accurate nutrient supply at each stage of the growth cycle may be challenging. In an experiment using container-grown tomato crops, we evaluated different fertilization regimes with solid anaerobic digestate (SAD). Four different treatments were compared, two involving different proportions (19 % and 37 % by volume) of SADs in the peat-based growing medium, one treatment where growing medium with 37 % SAD was inoculated with active nitrifying bacteria, and one treatment where 15 % (v/v) of the peat in growing medium with 37 % SAD was replaced with sawdust to control nitrogen (N) availability during cultivation. A mineral-fertilized treatment (N-P-K 5–1-5) with approximately similar N amount as in the treatment with 37 % SAD was used as reference. Nutrient availability, nutrient uptake efficiency, crop performance (plant growth, biomass accumulation), and plant stress (chlorophyll fluorescence) were monitored during cultivation. The concentration of ammonium was initially high (190–416 mg/L substrate) in the growing media fertilized with anaerobic digestate, while the concentration of nitrate was low. Readily available ammonium concentration decreased rapidly during cultivation, to around 50 % after 10 days and to almost 100 % by the end of the cultivation. Available nitrate concentration was initially low (0–8 mg/L in the different treatments) and decreased to zero within a week, but increased slightly from day 40 of cultivation. Nutrient use efficiency was generally higher (15–50 % for different nutrients) in the treatment with 19 % digestate. Inclusion of sawdust in the growing medium decreased nutrient use efficiency by 30–50 %. Compared with the mineral-fertilizer reference, biomass production was lower in all treatments fertilized with digestate, with 37 % and 19 % SAD resulting in 62 % and 47 % of total biomass obtained in the reference, and similar reductions in yield of harvestable fruits. Chlorophyll fluorescence measurements indicated elevated plant stress in the treatments fertilized with SAD. Addition of sawdust or nitrifying bacteria did not help to control nitrogen availability during cultivation. Therefore, anaerobic digestate fertilizers need further optimization before they can be a competitive alternative to mineral fertilizers

Utilizing Anaerobic Digestates as Nutrient Solutions in Hydroponic Production Systems

Moving food production into the urban and peri-urban areas is one way of facilitating a closed-loop approach, integrating waste handling with food production in order to recirculate nutrients and at the same time reduce the use of mined and fossil resources in the production. Using anaerobic digestion as a way of converting urban wastes to an energy source (methane) and a nutrient-rich biodigestate with subsequent use as fertilizer for food production seems like a feasible approach. However, utilizing urban wastes in plant production systems implies some challenges, such as high salinity of the waste, imbalanced composition of nutrients, and abundance of less favorable forms of nitrogen. In a series of experiments, these problems were addressed. Vegetables (Pak Choi) were cultivated hydroponically in a controlled climate. Experiments included increased salinity, elevated levels of nitrite, and different concentrations of the biogas digestate-based nutrient solution, with mineral based solutions as controls. In general, the mineral controls yielded around 50% higher fresh biomass than the organic solutions. However, the quality of the produce with respect to content of secondary metabolites such as vitamins was enhanced when the plants were cultivated with organic nutrient solutions. Increasing the concentration of NaCl to 241 mg Cl L−1 did not negatively affect plant performance. Increasing the concentration of nitrite negatively affected plant growth, with reductions in biomass production by up to 50%. Given this well-functioning nitrification process that did not result in high nitrite concentrations, the use of anaerobic digestates seems feasible for hydroponic production of vegetables

Fosforrestriktion som retarderingsmetod för krukväxter?

Fosfor är nödvändigt för cellens uppbyggnad och funktioner. Vid produktion av krukväxter i odlingssubstrat tillförs vanligen ett överskott av fosfor. Kan en begränsad tillförsel av fosfor (”fosfor-restriktion”) användas för att kontrollera krukväxters tillväxt? Vi har gjort en sammanfattning av publicerade studier för att få svar på frågan

Benefits and drawbacks of combined plant and mushroom production in substrate based on biogas digestate and peat

Production of plants and mushrooms in substrate based partly on anaerobic digestate from biogas production (30%) and peat (70%) was studied in experiments performed using oyster mushroom (Pleurotus ostreatus) and basil (Ocimum basilicum). Biogas digestate was included in order to decrease use of peat and fertilizer. In separate experiments, combined greenhouse production of mushrooms and plants in fresh substrate, mushroom production in bags of fresh substrate or spent substrate from plant production, and plant production in spent substrate from mushroom production were studied. In terms of plant yield, positive impacts of combined culture were observed, with significantly higher yield of basil when mushroom spawn was added to fresh substrate at a concentration of 2% (p 0.04). Increasing the concentration to 10%, which was sufficient for fruiting body formation in parallel with plant production, did not increase basil yield compared with the control. When fresh substrate was partly replaced with spent substrate from mushroom production, significantly higher yield of basil was obtained (p 0.001). Mushroom production had an impact on the nutritional composition of the substrate, resulting in changes in nitrogen dynamics, a significant decrease in phosphorus concentration by 14% (p 0.001), and a change in extractable concentrations of five of 10 elements studied. In terms of mushroom yield, the impacts of combined production with plants were generally negative

Consumer attitudes towards hydroponic cultivation of vegetables - Specifically exploring the impact of the fertilisation strategy (using mineral origin or food waste as fertiliser)

This study explores consumer attitudes and beliefs towards hydroponics (growing without soil), as well as the willingness to eat vegetables grown using two different fertilisation strategies (mineral and food waste). The impact of food neophobia, connectedness to nature and awareness of ongoing climate change is also explored. Data were collected through a survey (October 2021) with 1,000 Swedish respondents. Less than half of the respondents were aware of hydroponics, with no differences due to gender or age. Nonetheless, education turned out to be a predictor. No differences were seen in attitude due to gender or level of education, yet a slightly more positive attitude was found among older respondents and a more positive attitude among those who had not heard about hydroponic systems before. Food neophobia and higher age only (negatively) predicted the willingness to eat food with input from food waste, whereas connectedness to nature did not predict willingness to eat vegetables from any of the two fertilising systems. A belief in climate change had a positive impact on the willingness to eat vegetables from both systems. The results revealed significant differences between the two systems, with the circular perceived as significantly more natural, environmentally friendly, more exciting, representing the future, more energy efficient, more innovative as well as more positive overall, compared to the mineral. These qualities could be used by stakeholders when communicating these new systems. The results support the understanding that hydroponics is a food technology to which consumers express positive attitudes and beliefs

Production of oyster mushroom (Pleurotus ostreatus) on sawdust supplemented with anaerobic digestate

Anaerobic digestion of organic waste results in production of biogas and a nutrient-rich digestate that has an established use as fertilizer in plant production. This study evaluated use of anaerobic digestate based on a high concentration of organic household waste as a fertilizer in sawdust-based production of oyster mushrooms (Pleurotus ostreatus). Inclusion of 0.5 L of anaerobic digestate (AD) per kg sawdust gave similar productivity in terms of biological efficiency (79.5 +/- 5.4 %), and protein concentration (24.7 +/- 2.4 % of dry weight (dw)) as standard mushroom substrate (78.1 +/- 5.3 %, and 21.9 +/- 3.0 % of dw, respectively). However, mushroom growth was impaired at the highest concentration of anaerobic digestate tested, 1 L digestate per kg dw sawdust. Comparison of the AD-fertilized substrate with a mushroom substrate with standard components (sawdust, wheat bran, calcium sulfate) and with similar C/N-ratio revealed some differences in elemental composition of the fruiting bodies, with an major increase in sodium concentration for the AD-fertilized substrate compared with the standard substrate (413.3 +/- 28.9 and 226.7 +/- 30.6 mg kg(-1) dw, respectively). This difference can be explained by high sodium concentration in the anaerobic digestate, most likely due to inclusion of food scraps from households and restaurants in the biodigester feedstock. Screening of both substrates for a total of 133 micro -pollutants revealed that total sum of micropollutants was significantly higher in the AD-fertilized substrate (258 +/- 12 ng/g dw substrate) than in the standard substrate (191 +/- 35 ng/g dw substrate). Nitrogen losses during preparation of the AD-fertilized substrate were negligible

The power of light: Impact on the performance of biocontrol agents under minimal nutrient conditions

BackgroundThe spectral distribution of light (different wavelength) has recently been identified as an important factor in the dynamics and function of leaf-associated microbes. This study investigated the impact of different wavelength on three commercial biocontrol agents (BCA): Bacillus amyloliquefaciens (BA), Pseudomonas chlororaphis (PC), and Streptomyces griseoviridis (SG). MethodsThe impact of light exposure on sole carbon source utilization, biofilm formation, and biosurfactant production by the selected BCA was studied using phenotypic microarray (PM) including 190 sole carbon sources (OmniLog (R), PM panels 1 and 2). The BCA were exposed to five monochromatic light conditions (420, 460, 530, 630, and 660 nm) and darkness during incubation, at an intensity of 50 mu mol m(-2) s(-1). ResultsLight exposure together with specific carbon source increased respiration in all three BCA. Different wavelengths of light influenced sole carbon utilization for the different BCA, with BA and PC showing increased respiration when exposed to wavelengths within the blue spectrum (420 and 460 nm) while respiration of selected carbon sources by SG increased in the presence of red light (630 and 660 nm). Only one carbon source (capric acid) generated biosurfactant production in all three BCA. A combination of specific wavelength of light and sole carbon source increased biofilm formation in all three BCA. BA showed significantly higher biofilm formation when exposed to blue (460 nm) and green (530 nm) light and propagated in D-sucrose, D-fructose, and dulcitol. PC showed higher biofilm formation when exposed to blue light. Biofilm formation by SG increased when exposed to red light (630 nm) and propagated in citraconic acid. ConclusionTo increase attachment and success in BCA introduced into the phyllosphere, a suitable combination of light quality and nutrient conditions could be used

Stress Detection Using Proximal Sensing of Chlorophyll Fluorescence on the Canopy Level

Chlorophyll fluorescence is interesting for phenotyping applications as it is rich in biological information and can be measured remotely and non-destructively. There are several techniques for measuring and analysing this signal. However, the standard methods use rather extreme conditions, e.g., saturating light and dark adaption, which are difficult to accommodate in the field or in a greenhouse and, hence, limit their use for high-throughput phenotyping. In this article, we use a different approach, extracting plant health information from the dynamics of the chlorophyll fluorescence induced by a weak light excitation and no dark adaption, to classify plants as healthy or unhealthy. To evaluate the method, we scanned over a number of species (lettuce, lemon balm, tomato, basil, and strawberries) exposed to either abiotic stress (drought and salt) or biotic stress factors (root infection using Pythium ultimum and leaf infection using Powdery mildew Podosphaera aphanis). Our conclusions are that, for abiotic stress, the proposed method was very successful, while, for powdery mildew, a method with spatial resolution would be desirable due to the nature of the infection, i.e., point-wise spread. Pythium infection on the roots is not visually detectable in the same way as powdery mildew; however, it affects the whole plant, making the method an interesting option for Pythium detection. However, further research is necessary to determine the limit of infection needed to detect the stress with the proposed method