Bio-based Fertilizers Research Articles

Green synthesis of Spirulina-based carbon dots for stimulating agricultural plant growth

In this study, photoluminescent carbon quantum dots (CQDs) were synthesized by thermal pyrolysis of the microalgae spirulina without any surface passivating agent. The CQDs showed ~10 nm average size and exhibited blue photoluminescence emission around 450 nm under 340–400 nm excitation wavelength. A quantum yield of 23.5% was attained at 300 °C for 2 h. Thermodynamic and kinetic investigations about pyrolysis reaction showed that CQDs synthesis occurs slowly and non-spontaneously, with a mean activation energy of 192.6 kJ/mol. The final product showed a broad range of solubility, besides being efficient for lentil seed growth when dispersed in 0.05–0.1 mg/mL aqueous solutions. The CQDs reported here may be considered a promising renewable bio-based fertilizer for crop species in the sustainable agriculture field.

An examination of maximum legal application rates of dairy processing and associated STRUBIAS fertilising products in agriculture

The dairy industry produces vast quantities of dairy processing sludge (DPS), which can be processed further to develop second generation products such as struvite, biochars and ashes (collectively known as STRUBIAS). These bio-based fertilizers have heterogeneous nutrient and metal contents, resulting in a range of possible application rates. To avoid nutrient losses to water or bioaccumulation of metals in soil or crops, it is important that rates applied to land are safe and adhere to the maximum legal application rates similar to inorganic fertilizers. This study collected and analysed nutrient and metal content of all major DPS (n = 84) and DPS-derived STRUBIAS products (n = 10), and created an application calculator in MS Excel™ to provide guidance on maximum legal application rates for ryegrass and spring wheat across plant available phosphorus (P) deficient soil to P-excess soil. The sample analysis showed that raw DPS and DPS-derived STRUBIAS have high P contents ranging from 10.1 to 122 g kg−1. Nitrogen (N) in DPS was high, whereas N concentrations decreased in thermo-chemical STRUBIAS products (chars and ash) due to the high temperatures used in their formation. The heavy metal content of DPS and DPS-derived STRUBIAS was significantly lower than the EU imposed limits. Using the calculator, application rates of DPS and DPS-derived STRUBIAS materials (dry weight) ranged from 0 to 4.0 tonnes ha−1 y−1 for ryegrass and 0–4.5 tonnes ha−1 y−1 for spring wheat. The estimated heavy metal ingestion to soil annually by the application of the DPS and DPS-derived STRUBIAS products was lower than the EU guideline on soil metal accumulation. The calculator is adaptable for any bio-based fertilizer, soil and crop type, and future work should continue to characterise and incorporate new DPS and DPS-derived STRUBIAS products into the database presented in this paper. In addition, safe application rates pertaining to other regulated pollutants or emerging contaminants that may be identified in these products should be included. The fertilizer replacement value of these products, taken from long-term field studies, should be factored into application rates.

Restoring nutrient circularity in a nutrient-saturated area in Germany requires systemic change

Regions with intensive agriculture often encounter environmental problems caused by nutrient excess of agro-food-waste systems that have become increasingly linear over previous decades. In this study, nitrogen (N), phosphorus (P), potassium (K) and carbon (C) flows in the whole agro-food-waste system of district Cleves in Germany were quantified simultaneously using substance flow analysis. Moreover, nutrient use inefficiency hotspots were identified to establish options to improve nutrient self-sufficiency as a first step towards nutrient circularity. Data on mass flows and nutrient contents was acquired for the year 2016 from stakeholders, statistical databases, literature and modelling. Organic C was included for flows with potential as organic fertilizer. Results show that animal production drives the nutrient flows in the export-oriented district, with feed import, manure application and losses from housing and manure storage accounting for 40, 45 and 60% of all N, P and K flows, respectively. In particular agriculture is responsible for N losses, with 150 kg N lost ha−1 agricultural land. Crop production surplus and with that soil accumulation of P and K are 515 t and 4100 t respectively. Stoichiometry of N:P:K:C in the different organic materials does not allow direct application and meeting crop requirements without exceeding demand of especially P. Processing of biomass is therefore required. Based on mass, especially manure holds potential for processing into bio-based fertilizers. To improve nutrient cycling and soil C conservation, being an important element for a sustainable agricultural sector, local balances between crop and animal production need to be considered.

Assessing Nitrogen Availability in Biobased Fertilizers: Effect of Vegetation on Mineralization Patterns

Biobased nitrogen (N) fertilizers derived from animal manure can substitute synthetic mineral N fertilizer and contribute to more sustainable agriculture. Practitioners need to obtain a reliable estimation of the biobased fertilizers’ N value. This study compared the estimates for pig slurry (PS) and liquid fraction of digestate (LFD) using laboratory incubation and plant-growing experiments. A no-N treatment was used as control and calcium ammonium nitrate (CAN) as synthetic mineral fertilizer. After 100 days of incubation, the addition of PS and LFD resulted in a net N mineralization rate of 10.6 ± 0.3% and 20.6 ± 0.4% of the total applied N, respectively. The addition of CAN showed no significant net mineralization or immobilization (net N release 96 ± 6%). In the pot experiment under vegetation, all fertilized treatments caused N immobilization with a negative net N mineralization rate of −51 ± 11%, −9 ± 4%, and −27 ± 10% of the total applied N in CAN, PS, and LFD treatments, respectively. Compared to the pot experiment, the laboratory incubation without vegetation may have overestimated the N value of biobased fertilizers. Vegetation resulted in a lower estimation of available N from fertilizers, probably due to intensified competition with soil microbes or increased N loss via denitrification.

Antibiotic residues in substrates and output materials from biogas plants – Implications for agriculture

Bio-based fertilizers including farmyard manure, sewage sludge, meat and bone meal, composts, digestates and derived products are nutrient-rich fertilizers. They deliver organic matter but may pose the risk to contaminate soils by pollutants such as pharmaceuticals, heavy metals, resistance genes or pathogens. Manure and sewage sludge are increasingly used in biogas plants for energy production with the residue being used as fertilizer. It is therefore important to understand the fate of pharmaceuticals during anaerobic digestion. In the present study, 29 biogas plants from three countries were studied. The different input materials and output after digestion were analyzed for selected examples of antibiotics from three different classes, namely tetracyclines (TCs), sulfonamides (SAs) and fluoroquinolones (FQs). These classes are frequently found in animal manures and sewage sludge and display differing mobility and persistence. The results revealed that antibiotics could be detected in 81% of the substrates derived from animal manures and sewage sludge and in 83% of the digestates. Antibiotics were determined with the highest frequency of 100% in sewage sludge where especially ciprofloxacin and tetracycline were found. Highest concentrations were analyzed in poultry dung with in maximum of 8.6 and 8.2 mg/kg DW of enrofloxacin and tetracycline, respectively. After digestion, slightly lower concentrations of antibiotics were determined for most substrates. However, in one biogas plant using poultry dung as an input material a maximum concentration of 15.2 mg/kg DW of tetracycline was determined in the digestate, which after separation accounted for 29.8 mg/kg DW of tetracycline in the liquid phase.

Wastewater nutrient recovery using twin-layer microalgae technology for biofertilizer production.

This study evaluates the feasibility of advanced biofilm microalgae cultivation in a twin layer (TL) system for nutrient removal (N and P) as the tertiary treatment in small wastewater treatment plants (WWTPs) located in sensitive areas. Furthermore, the potential valorisation of microalgae biomass as a component of bio-based fertilizers is assessed. Scenedesmus sp. was chosen among 33 microalgae strains for inoculation of TL due to its high growth rate and its nutrient uptake capacity. The tests carried out in the prototype were markedly efficient for total soluble and ammoniacal nitrogen removal (up to 66 and 94%, respectively). In terms of potential valorisation of microalgae, the nutrient content was 5.5% N (over 40% protein), 8.8% P2O5 and 1.5% K2O, high enzymatic activity, very low levels of heavy metals and no detectable pathogen presence. However, in the formulation of solid-state bio-based fertilizers, the microalgae proportions in blends of over 2% of microalgae led to negative effects on ryegrass (Lolium perenne L. ssp.) and barley (Hordeum vulgare ssp.). The obtained results demonstrate that TL represents a promising technology, which allows efficient tertiary treatment of urban wastewater and the production of high-quality bio-based fertilizer.

Demand for bio-based fertilizers from dairy manure in Washington State: a small-scale discrete choice experiment

AbstractThe use of bio-based fertilizers derived from dairy manure can provide a valuable source of fertility, improve soil health and provide an outlet for manure from dairy operations. We conducted a small-scale discrete choice survey of crop farmers and crop consultants in Washington State to determine the attributes that were important to them in the potential use of a bio-based fertilizer product derived from dairy manure. Of the attributes examined, distribution channel was not statistically significant. Respondents preferred air-dried or pelletized forms to wet forms, though there was no statistically significant difference between air-dried and pelletized forms. As expected, uptake increased as price decreased. Our results imply that respondents would be willing to pay 23 and 39% more for an air-dried or pelletized product, respectively, than for a ‘semi-wet’ product. Our results indicate that there are other important attributes beyond the ones in the survey that led respondents to stay with their current fertilizer regime. Qualitative responses in the survey pointed to the need for field trial results and data on nitrogen release from the bio-based fertilizer. Greater understanding of willingness-to-pay and attributes important to potential end users is important for the development of markets for bio-based fertilizers.

Estimating and comparing cropland nitrogen need with dairy farm nutrient recovery: a case study in Whatcom County, WA

AbstractIn agricultural regions, like Whatcom County, Washington, crop and dairy production co-exist, but increased agricultural specialization and intensification have divorced what was, historically, an integrated approach to production. This agricultural segregation contributes to farm, regional and watershed-scale nutrient imbalances, and several different management approaches have been devised to improve, correct and close these nutrient cycling disparities. In high-density production regions, utilizing locally produced bio-based fertilizers may provide one avenue toward closing regional nutrient loops. Technologies such as dairy-operated nutrient recovery systems may help improve the flow of nutrients between dairy and cropping systems by extracting nutrients from raw manure and producing materials that are more easily used on farms than raw manure. To evaluate the potential impact of a nutrient recovery system and its related product, we estimated nitrogen balances between cropland use and manure production within Whatcom County, Washington and examined a theoretical scenario in which a specific nutrient recovery product was utilized across the region. We considered one economic barrier, transportation cost, and calculated a hypothetical comparison for transporting nitrogen in two forms, a downstream nutrient recovery product and raw manure. The scenarios presented here demonstrate a potential gap between regional nutrient supply and demand, illustrate the tradeoffs with a technological approach, and make clear that both technological tools and practical management strategies are needed to address the challenges of redistributing nutrients in high-density production areas.

Effect of application of different biogas fertilizer on eggplant production: Analysis of fertilizer value and risk assessment

Anaerobic digestion (AD) is an important technology for manure treatment in livestock farms, but when a large amount of biogas slurry (BS), and biogas residues (BR) from large-scale farms are used as fertilizer, there are usually main ways to utilize the raw digestate (untreated BS, and BR), as a bio-based fertilizer. In this study, the effects of direct application of digestate and bio-based ammonium sulfate (AS) fertilizer obtained by ammonia stripping of BS on the cultivation of eggplant and crop yield were compared. Eggplant growth, nitrogen fertilizer efficiency, crop yield, and heavy metals accumulation were studied under the normal-dose application and double-dose application of digestate. In addition, the fertilizer efficiency and safety risk assessments of bio-based AS liquid fertilizer and bio-based AS solid fertilizer were also discussed. A comprehensive comparison of N-fertilizer efficiency and yield showed that the bio-based AS liquid fertilizer had the best fertilizer efficiency, followed by double-dose digestate, and the bio-based AS solid fertilizer, while the normal-dose digestate had poor efficiency. The application effect of bio-based AS liquid fertilizer was closer to the traditional urea N fertilizer. The results showed that compared with the bio-based AS solid fertilizer, the apparent recovery efficiency of N (ARE N ) of eggplant with bio-based AS liquid fertilizer increased by 2.8 times, and the eggplant yield increased by 24.5%. Moreover, the yield of eggplant with bio-based AS liquid fertilizer was increased by 28% compared to the direct application of digestate. Furthermore, no seedling burning and growth inhibition occurred with double application of digestate, but the content of heavy metal (Pb) increased significantly. The results can be used as a reference for understanding the effect of digestate and bio-based AS fertilizer on the cultivation of eggplant and the correlated safety risks assessment. • Comparison of application efficiency of biogas digestate and bio-based AS fertilizer. • Upgraded biofertilizer has the potential to replace digestate and synthetic nitrogen. • No seedling burning or growth inhibition with normal and double-dose of digestate. • Bio-based AS liquid fertilizer has the best comprehensive fertilizer effect. • Double-dose of digestate increases eggplant yield, but the heavy metal risk exists.

Carbon and nutrient recycling ecotechnologies in three Baltic Sea river basins – the effectiveness in nutrient load reduction

There exist numerous ecotechnologies for recovery and reuse of carbon and nutrients from various waste streams before they are lost to runoff. However, it remains largely unknown how growing implementation of such ecotechnologies affect nutrient emissions to surface waters at catchment scale. Here, this knowledge gap is addressed by application of SWAT model in three case study catchments draining to the Baltic Sea: Vantaanjoki (Finland), Fyrisån (Sweden) and Słupia (Poland). Sustainability analysis with Multi-Criteria Analysis was applied in the stakeholder workshops in the case study areas to assess different ecotechnology alternatives. The following ecotechnologies received the highest sustainability scores: in Vantaanjoki anaerobic digestion, based on mostly agricultural residues; in Fyrisån source-separation of wastewaters; in Słupia nutrient extraction within the wastewater treatment process. The effect of application of digestate on agricultural soils in the Vantaanjoki catchment was simulated by adjusting the model parameters describing the organic carbon content and physical properties of soil. The results showed small reductions of nutrient loads to the Gulf of Finland. Larger reductions of nutrient loads to Lake Mälaren in Sweden and the Baltic Sea in Poland were achieved as a result of the wastewater treatment upgrades. In the Fyrisån catchment, higher relative reductions were simulated for TN than TP, and in dry years than in wet years. Although the studied ecotechnologies did not show as high effectiveness in nutrient load reduction as combinations of traditional Best Management Practices reported in literature, they do have other multiple benefits including crop yield increase, electricity, heat and bio-based fertilizer production.

Wastewater-grown Algae Pellets and Paste as Fertilizers for Containerized Crops

Drawbacks of traditional synthetic fertilizer led us to explore a biologically based (bio-based) alternative. Our objective was to quantify the efficacy of wastewater-grown algae pellets and pastes harvested from rotating algal biofilm systems as fertilizers for three crops, ‘Honeycomb’ marigold (Tagetes patula L.), ‘Beefsteak’ tomato (Solanum lycopersicum L.), and ‘Ambrosia’ sweet corn (Zea mays L.). Factorial experiments were designed for each crop with fertilizer type (algae pellets, algae paste, a synthetic controlled-release fertilizer, or a commercially available bio-based fertilizer from wastewater treatment) and substrate (commercial or custom-made) as factors. Shoot growth, shoot nutrient concentration, and substrate pH and electrical conductivity (EC) were affected by fertilizer, substrate, or their interaction. Algae pellets and paste supplied nutrients to all three species effectively, increasing shoot size, dry weight, perceived health, and nutrient concentrations compared with unfertilized controls. Notwithstanding some variability among crops, performance of algal materials was similar to that of the synthetic fertilizer and better than that of the commercial bio-based fertilizer. As a bio-based fertilizer that supplies plants with recycled nutrients sequestered from wastewater, wastewater-grown algae can reduce the impacts of mineral nutrition management in container-crop production by partially supplanting synthetic fertilizer use.

Effects of Biochar Based Fertilizer on Soil Nutrient Content and Maize Yield of Acidic Soil in Heilongjiang Province

Unreasonable fertilizer input and low fertilizer utilization seriously restrict the development of maize in Heilongjiang province. In this paper, the effects of biochar based fertilizer on the nutrient content of acidic soil and corn yield in Heilongjiang province were studied. The random block design was adopted, and seven treatments were set with four repetitions. The results showed that biochar based fertilizer increased the soil organic matter content in the mature stage of maize. The S1 (The biochar biobased fertilizer treatment 1 in acid soil), S2 (The biochar biobased fertilizer treatment 2 in acid soil), and S3 (The biochar biobased fertilizer treatment 3 in acid soil) treatments organic matter contents increased by 15.96%, 11.06% and 10.03% than SCK (The Acid Soil Control Check) respectively. The total nitrogen, total phosphorus, total potassium, total calcium of S1 treatment corn plants increased 16.81%, 15.34%, 31.20% and 22.96% than SCK. The S1 treatment increased the yield of corn, which was 1.94% higher than SCK. There was no significant difference between the yield of S2, S3 with SCK treatments, which achieved the effect of fertilization reducing.

Nutrient recovery from digested waste: Towards a generic roadmap for setting up an optimal treatment train

This paper aims to develop a generic roadmap for setting up strategies for nutrient recovery from digested waste (digestate). First, a guideline-based decision-tree is presented for setting up an optimal bio-based fertilization strategy as function of local agronomic and regulatory criteria. Next, guidelines and evaluation criteria are provided to determine the feasibility of bio-based fertilizer production as function of the input digestate characteristics. Finally, a conceptual decision making algorithm is developed aiming at the configuration and optimization of nutrient recovery treatment trains. Important input digestate characteristics to measure, and essential factors for monitoring and control are identified. As such, this paper provides a useful decision-support guide for wastewater and residuals processing utilities aiming to implement nutrient recovery strategies. This, in turn, may stimulate and hasten the global transition from wastewater treatment plants to water resource recovery facilities. On top of that, the proposed roadmap may help adjusting the choice of nutrient recovery strategies to local fertilizer markets, thereby speeding up the transition from a fossil-reserve based to a bio-based circular nutrient economy.

Farmers' reasons to accept bio-based fertilizers: A choice experiment in seven different European countries

European agriculture is a large importer of nutrients in the form of chemical fertilizers. Additionally, countries with livestock-intensive farming face problems with disposal of nutrients in animal manure. The availability of chemical fertilizers has changed farmers' past dependence on manure. Nowadays, despite its nutrient content, manure is sometimes considered as a waste product. However, if the characteristics of manure and other waste streams could be enhanced through processing, it could be transformed into an alternative bio-based fertilizer recycling the nutrients within the farming sector. This would also create opportunities for nutrient exchange between different European regions. However, a key question is what is needed for farmers to accept these products as replacements for their current chemical fertilizer use? In this paper, key attributes determining the acceptance of alternative bio-based fertilizer products are identified. Based on the identified attributes, a discrete choice experiment was designed to reveal farmers' preferences and Willingness-To-Pay for these attributes. Identical experiments were conducted in seven different European countries. The results indicate that farmers from the different countries have common preferences for concentrated products that have certainty in the nitrogen content and at a lower price than chemical fertilizer. Other attributes such as the presence of organic carbon, hygienization of the product and fast release of nutrients were only statistically significant in some countries. The results imply that a bio-based fertilizer similar to chemical fertilizers could be sold at around 65% of the price of mineral fertilizer. Additionally, we show which attributes industry should take into consideration when estimating the demand for new bio-based fertilizer products. (C) 2018 Elsevier Ltd. All rights reserved.

Nitrogen and phosphorus release from organic wastes and suitability as bio-based fertilizers in a circular economy

ABSTRACTThe drive to a more circular economy has created increasing interest in recycling organic wastes as bio-based fertilizers. This study screened 15 different manures, digestates, sludges, composts, industry by-products, and struvites. Nitrogen (N) and phosphorous (P) release was compared following addition to soil. Three waste materials were then ‘upgraded’ using heating and pressure (105°C at 220 kPa), alkalinization (pH 10), or sonification to modify N and P release properties, and compared in a second soil incubation. Generally, maximum N release was negatively correlated with the CN ratio of the material (r = −0.6). Composted, dried, or raw organic waste materials released less N (mean of 10.8 ± 0.5%, 45.3 ± 7.2%, and 47.4 ± 3.2% of total N added respectively) than digestates, industry-derived organic fertilizer products, and struvites (mean of 58.2 ± 2.8%, 77.7 ± 6.0%, and 100.0 ± 13.1% of total N added respectively). No analyzed chemical property or processing type could explain differences in P release. No single upgrading treatment consistently increased N or P release. However, for one raw biosolid, heating at a low temperature (105°C) with pressure did increase N release as a percentage of total N added to soil from 30% to 43%.

Fertilizer performance of liquid fraction of digestate as synthetic nitrogen substitute in silage maize cultivation for three consecutive years

Following changes over recent years in fertilizer legislative framework throughout Europe, phosphorus (P) is taking over the role of being the limiting factor in fertilizer application rate of animal manure. This results in less placement area for spreading animal manure. As a consequence, more expensive and energy demanding synthetic fertilizers are required to meet crop nutrient requirements despite existing manure surpluses. Anaerobic digestion followed by mechanical separation of raw digestate, results in liquid fraction (LF) of digestate, a product poor in P but rich in nitrogen (N) and potassium (K). A 3-year field experiment was conducted to evaluate the impact of using the LF of digestate as a (partial) substitute for synthetic N fertilizer. Two different fertilization strategies, the LF of digestate in combination with respectively animal manure and digestate, were compared to the conventional fertilization regime of raw animal manure with synthetic fertilizers. Results from the 3-year trial indicate that the LF of digestate may substitute synthetic N fertilizers without crop yield losses. Through fertilizer use efficiency assessment it was observed that under-fertilization of soils with a high P status could reduce P availability and consequently the potential for P leaching. Under conditions of lower K application, more sodium was taken up by the crop. In arid regions, this effect might reduce the potential risk of salt accumulation that is associated with organic fertilizer application. Finally, economic and ecological benefits were found to be higher when LF of digestate was used as a synthetic N substitute. Future perspectives indicate that nutrient variability in bio-based fertilizers will be one of the greatest challenges to address in the future utilization of these products.

Bioextraction potential of seaweed in Denmark — An instrument for circular nutrient management

The aim of the study is to assess the efficacy of seaweed for circular nutrient management to reduce eutrophication levels in the aquatic environment. We performed a comparative Life Cycle Assessment (LCA) of two reference waste management systems treating seaweed as biowaste, i.e. landfill disposal and combustion, and an alternative scenario using the seaweed Saccharina latissima as a resource for biobased fertilizer production. Life Cycle Impact Assessment (LCIA) methods were improved by using a cradle-to-cradle approach, quantifying fate factors for nitrogen and phosphorus loss from fertilized agriculture to the aquatic environment. We also differentiated between nitrogen- and phosphorus-limited marine water to improve the traditional freshwater impact category, making this indicator suitable for decision support in relation to coastal water management schemes. Offshore cultivation of Saccharina latissima with an average productivity of 150Mg/km2 in Danish waters in 2014 was applied to a cultivation scenario of 208km2. The bioresource scenario performs better than conventional biowaste management systems, delivering a net reduction in aquatic eutrophication levels of 32.29kgNeq. and 16.58kgPO43−eq. per Mg (dry weight) of seaweed, quantified by the ReCiPe and CML impact assessment methods, respectively. Seaweed cultivation, harvest and reuse of excess nutrients from the aquatic environment is a promising approach for sustainable resource cycling in a future regenerative economy that exploits manmade emissions as a resource for closed loop biobased production while significantly reducing eutrophication levels in 3 out of 7 Danish river basin districts. We obtained at least 10% bioextraction of phosphorus manmade emissions (10%, 89% and >100%) and contributed significantly to local nitrogen reduction goals according to the Water Framework Directive (23%, 78% and >100% of the target).

Phosphorus Use Efficiency of Bio-Based Fertilizers: Bioavailability and Fractionation

Although to date some technologies producing bio-based phosphorus (P) fertilizers have been proposed and implemented, the efficient use of the recovered products is still limited due to legislative constraints and lack of insights in the P release with time and in the corresponding mechanisms. The aim of this work was to evaluate the fertilizer performance in terms of P release and use efficiency of recovered struvite, FePO4-sludge, digestate, and animal manure as compared to fossil reserve-based mineral triple superphosphate (TSP). First, product physicochemical characteristics and P fractions in the context of European fertilizer legislation were assessed. Next, a controlled greenhouse experiment was set up to evaluate plant reactions as well as changes of P availability in a sandy soil with high P status and a Rheinsand soil with low P status. Soil P fractions were determined in the extracts with water, ammonium lactate and CaCl2, and in soil solution sampled with Rhizon soil moisture samplers. Based on all results, it is worth conducting long-term field trials to evaluate the P release effect of struvite and digestate as compared to animal manure and TSP on different soil types with varying P status. These products showed promise as sustainable substitutes for conventional P fertilizers and could contribute to a more efficient use of P in agriculture. A refined classification of P application standards/recommendations in terms of soil P status, soil texture, and fertilizer characteristics, next to the crop P demand, is recommended. Moreover, the additional use of Rhizon samplers for determination of direct available P, including dissolved organic P, is proposed for better understanding and categorization of different P fertilizers in environmental and fertilizer legislations.

Biobased Fertilizers - Comparison of Nutrient Content of Digestate/Compost

Biobased Fertilizers - Comparison of Nutrient Content of Digestate/Compost

Utilization of derivatives from nutrient recovery processes as alternatives for fossil-based mineral fertilizers in commercial greenhouse production of Lactuca sativa L.

The production of vegetables relies on the use of mineral fertilizers which are based either on fossil fuel (e.g., nitrogen fertilizers based on Haber–Bosch process) or on fossil ore deposits (phosphate rock). On the other hand, nutrient recovery processes generate various end and side products that can provide a sustainable alternative for fossil-based mineral fertilizers. Their use however, is currently limited by insufficient knowledge about the properties and the impact of these products on soil quality and crop yield. This research was aimed to evaluate the use of the liquid fraction of digestate, effluent from constructed wetlands originating from a manure/digestate treatment facility, air scrubber water and struvite in the cultivation of lettuce (Lactuca sativa L.) compared to their conventional fossil-based counterparts. In accordance with the crop nutrient requirements, different fertilization treatments were set up in which individual products and combinations were tested. At harvest time, assessment of soil physicochemical properties was conducted, along with crop quality control. Nutrient balances were determined and an economic and environmental assessment was evaluated. There were no significant differences in crop yield and soil quality at harvest time between conventional fossil-based mineral fertilizers and selected bio-based mineral alternatives. Nitrogen and potassium use efficiencies were slightly lower in treatments with bio-based fertilizers. Moreover, economic and ecological assessment have shown higher benefits for the farmer when bio-based alternatives were used as a replacement for synthetic fertilizers. Re-use of these products should be stimulated in European legislation.