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Response of petunia to wood fibre amended peat substrate under ebb-and-flow irrigation (Abstract)
(2024)
Test von Schnellverfahren zur Bestimmung der Benetzungseigenschaften von Kultursubstraten (Abstract)
(2024)
Enhancing the nutritional value of pears through agronomic biofortification with iodine (Abstract)
(2024)
The development of non-precious metal-based electrodes that actively and stably support the oxygen evolution reaction (OER) in water electrolysis systems remains a challenge, especially at low pH levels. The recently published study has conclusively shown that the addition of haematite to H2 SO4 is a highly effective method of significantly reducing oxygen evolution overpotential and extending anode life. The far superior result is achieved by concentrating oxygen evolution centres on the oxide particles rather than on the electrode. However, unsatisfactory Faradaic efficiencies of the OER and hydrogen evolution reaction (HER) parts as well as the required high haematite load impede applicability and upscaling of this process. Here it is shown that the same performance is achieved with three times less metal oxide powder if NiO/H2 SO4 suspensions are used along with stainless steel anodes. The reason for the enormous improvement in OER performance by adding NiO to the electrolyte is the weakening of the intramolecular O─H bond in the water molecules, which is under the direct influence of the nickel oxide suspended in the electrolyte. The manipulation of bonds in water molecules to increase the tendency of the water to split is a ground-breaking development, as shown in this first example.
The development of base metal electrodes that can act as active and stable oxygen generating electrodes in water electrolysis systems, especially at low pH levels, remains a challenge. The use of suspensions as electrolytes for water splitting has until recently been limited to photoelectrocatalytic approaches. A high current density (j=30 mA/cm2) for water electrolysis has been achieved at a very low oxygen evolution reaction (OER) potential (E=1.36 V vs. RHE) using a SnO2/H2SO4 suspension-based electrolyte in combination with a steel anode. More importantly, the high charge-to-oxygen conversion rate (Faraday efficiency of 88% for OER at j=10 mA/cm2 current density). Since cyclic voltammetry (CV) experiments show that oxygen evolution starts at a low, but not exceptionally low, potential, the reason for the low potential in chronoamperometry (CP) tests is an increase in the active electrode area, which has been confirmed by various experiments. For the first time, the addition of a relatively small amount of solids to a clear electrolyte has been shown to significantly reduce the overpotential of the OER in water electrolysis down to the 100 mV region, resulting in a remarkable reduction in anode wear while maintaining a high current density.
Water retention properties of wood fiber based growing media and their impact on irrigation strategy
(2024)
Distribution of water and air in growing media during ebb-and-flow irrigation depends on water storage properties (water retention curve) and water transport properties (hydraulic conductivity) of the materials. Growing media with their high number of coarse pores are known to exhibit strong hysteresis, i.e., differences in the water retention properties during drying and wetting cycles. To account for potential ecological disadvantages of peat, wood fibers are commonly used as substitutes for peat in growing media. However, the wood fibers generally have higher air capacities and hydraulic conductivities and lower water capacities compared to peat which may results in necessary adaptions of the irrigation strategy. Tools to optimize irrigation systems are physically based water transport models, such as HYDRUS-1D, which is commonly used to describe water transport in soils, but not often for growing media. In this study, white peat and pure wood fibers were used to describe differences in their water retention behavior. Water retention curves (drying cycles) and hydraulic conductivities were measured with standard analytical procedures. Hysteresis of the water retention curves was analytically determined based on their capillary rise properties. The results were used with a modified HYDRUS-1D model to test model quality against measured water contents during ebb-and-flow irrigation cycles and to optimize the irrigation strategy for the different materials. The results showed that the model quality was sufficiently good only if the strong hysteresis of the water retention curves was considered during the simulation process. Different strategies were tested to modify ebb-and-flow irrigation (irrigation frequency, irrigation duration and irrigation height) in that way that the water suction in the root zone was similar to that of the peat material. Simulation results showed that significant improvements could only be reached by increasing the flooding depth in ebb-and-flow systems to ensure an optimum water supply of plants in the wood fiber based growing media.
Wood fibers can contribute to replacing peat in growing media and thus help to protect peatlands. As domestic, renewable raw materials, they represent a sustainable option for this purpose. To date, however, wood fibers are usually used as a peat substitute at a maxi-mum of 30% (v/v). A main reason for this limitation is the insufficient microbial stability of wood fibers, which favors nitrogen immobilization and can thus impair nitrogen supply of plants. To address this drawback, in this study wood fibers were subjected to different thermal or thermal-hydrolytic treatments. Seedling tests with napa cabbage were conducted to determine whether treated wood fibers were free of phytotoxic substances. Mixtures with 50% (v/v) wood fiber and white peat each were used. In addition, three wood fiber varieties were evaluated in the cultivation of petunia. Two wood fiber proportions (30 and 60% v/v) and two nitrogen fertilization rates (common and increased supply) were included in each case. In the seedling trial with napa cabbage, no phytotoxic effects were detectable in any of the wood fiber variants investigated. However, when cultivating petunias, both shoot mass growth and number of flowers decreased with increasing wood fiber content. In substrates with a wood fiber content of 60% (v/v), plant development was inhibited so severely that the petunias no longer achieved marketable quality. Increased nitrogen fertilization was able to compensate for this negative effect only in few cases. This suggests that other factors than nitrogen limited plant growth in wood fiber-rich substrates. Among others, physical proper-ties such as the lower water capacity of wood fibers may be a cause. More in-depth investigations are still required in this regard.
Boron dynamics in a peat-based growing medium and its impact on the growth of basil (Abstract)
(2021)
As allergy towards apples is widespread, the evaluation of various cultivation and postharvest influences on the allergenic potential is of great importance. Therefore, the analysis of the Mal d 1 content was the focus of this study, originally dealing with investigating the influence of a selenium biofortification on apple quality. The Mal d 1 content of apples was in most cases reduced when the fruits were biofortified with selenium. Apple variety and climatic conditions were identified as further influencing factors for the Mal d 1 content of the fruits. The separate analysis of the peel and the fruit flesh showed that the content of Mal d 1 in the fruit flesh was significantly lower in the biofortified samples than in the controls. In conclusion, the results indicate that the selenium biofortification of apples and biochemical mechanism behind can reduce the allergenic potential regarding the content of Mal d 1.
Perceptions of German consumers regarding methods for fortifying foods with iodine (Abstract)
(2022)
Aus dem Brutschrank ins Gewächshaus – Bewertung des Stickstoffhaushalts in Substraten (Abstract)
(2022)
Einfluss einer Selen-Biofortifikation auf verschiedene Qualitätsparameter von Äpfeln (Abstract)
(2022)
Spinach is a nitrogen (N)-demanding crop characterized by a shallow root architecture. Especially in the first weeks after sowing, significant N uptake is limited to the uppermost few centimetres of the soil. However, base fertilization is usually based on the soil mineral N (Nmin) concentration in the upper 30 cm. Therefore, the objective of this study was to examine whether the soil sample depth for calculating the base N fertilization can be reduced to the 0-15 cm layer. In seven field trials, conducted during spring, summer and autumn seasons, either a low or high base fertilization dose was applied at sowing. Until top dressing, soil samples were frequently taken in the upper 0-15 and 15-30 cm layers to determine the average Nmin concentration in each layer. Top dressing was applied when the first true leaves had unfurled. With this fertilizer application, the total N supply was aligned between both treatments based on the Nmin concentration in the upper 30 cm of the soil. Aboveground fresh and dry masses were determined after reaching a fresh mass yield of 15-20 t ha‑1 and related to the mean Nmin concentration in the first 3 to 4 weeks of cultivation between sowing and top dressing. It was shown that the Nmin concentration in the upper 0-15 cm of the soil highly reflects the base fertilization rate. By contrast, the Nmin concentration in the 15-30 cm layer remained unaffected. However, the Nmin concentration of both top soil layers can affect fresh and dry mass yield at harvest. Therefore, the entire 0-30 cm soil layer should be considered when calculating the base N fertilization rate in field-grown spinach. Measurements revealed that spinach fresh and dry masses were increased until the N availability of between 54 and 59 kg ha‑1 (0-30 cm) was reached at the seedlings stage, respectively.
The mineralization of soil organic nitrogen (N) and crop residues can significantly contribute to the N supply of vegetable crops. However, short-term mineralization dynamics are difficult to predict. On the other hand, fast-growing crops like spinach are highly sensitive to N shortage. Therefore, in situ soil columns have been tested to estimate the actual N supply via mineralization in field-grown spinach. In ten fertilization trials covered soil columns (20 cm in diameter) were driven into the soil to a depth of 30 cm at the start of the cultivation. Eight columns were repeated in three blocks within a total trial area of 0.10 to 0.25 ha. Net N mineralization was derived by subtracting the soil mineral N concentration (Nmin) in the upper 30 cm before installation from the concentration inside the columns at harvest. For comparison, a balance sheet was calculated for spinach plots receiving no N fertilization (zero plots) as well as fertilized plots and used as a proxy for net N mineralization. In this approach the initial Nmin concentration in the upper 30 cm of the soil, the N supply via irrigation, and fertilization as well as the total aboveground N uptake by spinach and the Nmin residue were considered. By using soil columns, N mineralization was determined with a mean coefficient of variation of 18%. A higher spatial variability of up to 43% was observed when spinach was grown as a second crop. The average net N mineralization rate ranged between 2 kg ha‑1 week‑1 (0-30 cm) in winter-grown spinach and 3-7 kg ha‑1 week‑1 (0-30 cm) in the other seasons. Nitrogen mineralization measured by the soil columns was qualitatively confirmed with the data obtained by the balance sheet. Soil columns enable repeated samplings during the spinach cultivation. In this way, top dressing rates can be adjusted to the actual N supply.
Iron deficiency is still widespread as a major health problem even in countries with adequate food supply. It mainly affects women but also vegans, vegetarians, and athletes and can lead to various clinical pictures. Biofortification of vitamin C-rich vegetables with iron may be one new approach to face this nutritional challenge. However, so far, little is known about the consumer acceptance of iron-biofortified vegetables, particularly in developed countries. To address this issue, a quantitative survey of 1000 consumers in Germany was conducted. The results showed that depending on the type of vegetable, between 54% and 79% of the respondents were interested in iron-biofortified vegetables. Regression analysis showed a relationship between product acceptance, gender, and area of residence. In addition, relationships were found between consumer preferences for enjoyment, sustainability, and naturalness. Compared to functional food and dietary supplements, 77% of respondents would prefer fresh iron-rich vegetables to improve their iron intake. For a market launch, those iron-rich vegetables appear especially promising, which can additionally be advertised with claims for being rich in vitamin C and cultivated in an environmentally friendly way. Consumers were willing to pay EUR 0.10 to EUR 0.20 more for the iron-biofortified vegetables.
Iron deficiency is a global issue and can lead to a variety of clinical pictures. The biofor-tification of vegetables with iron could complement the existing portfolio of iron-rich products, thus improving iron supply in the long term. In order to determine whether the iron-biofortified vegetables could meet this demand and would address appropriate target groups, a quantitative online survey was conducted in Germany. Based on 1000 consumer responses, a cluster analysis was performed. The results showed a four-cluster solution. The first cluster was holistically engaged, the second was fitness-affine but health unconcerned, the third cluster consists frugal eaters with a focus on medical prevention, and the fourth cluster are hedonists. No cluster focused its consumption on iron-enriched products, but instead all developed an individual mix of the three product groups.
This research project focused on the consumers' acceptance of a newly developed apple in order to encourage the purchase behavior in the supermarket. It was enriched with selenium via biofortification in order to address the undersupply with the trace element in the German population. The study included online surveys and a market test in food retail. The results were used as preparation for the design of a marketable apple product. In the online pretest, the most popular apple cultivars, the most popular health benefits of selenium, as well as the respondents' preferences for the name of the new apple: Selstar® were detected. These results were included in an online survey which encompassed n=1042 interviews from German households. The sample was recruited according to national representative distribution of age groups, gender, and regions. The results show that the majority of the respondents were not sure what exactly selenium is and what it is used or needed for. Therefore, the product package included information about the health benefits of selenium, for e.g. the immune system. The stepwise approach of the research and the implementation of the results helped the targeted navigation of the market launch of the Selstar®.
Stainless steel made to rust: a robust water-splitting catalyst with benchmark characteristics
(2015)
The oxygen evolution reaction (OER) is known as the efficiency-limiting step for the electrochemical cleavage of water mainly due to the large overpotentials commonly used materials on the anode side cause. Since Ni–Fe oxides reduce overpotentials occurring in the OER dramatically they are regarded as anode materials of choice for the electrocatalytically driven water-splitting reaction. We herewith show that a straightforward surface modification carried out with AISI 304, a general purpose austenitic stainless steel, very likely, based upon a dissolution mechanism, to result in the formation of an ultra-thin layer consisting of Ni, Fe oxide with a purity >99%. The Ni enriched thin layer firmly attached to the steel substrate is responsible for the unusual highly efficient anodic conversion of water into oxygen as demonstrated by the low overpotential of 212 mV at 12 mA cm−2 current density in 1 M KOH, 269.2 mV at 10 mA cm−2 current density in 0.1 M KOH respectively. The Ni, Fe-oxide layer formed on the steel creates a stable outer sphere, and the surface oxidized steel samples proved to be inert against longer operating times (>150 ks) in alkaline medium. In addition Faradaic efficiency measurements performed through chronopotentiometry revealed a charge to oxygen conversion close to 100%, thus underpinning the conclusion that no “inner oxidation” based on further oxidation of the metal matrix below the oxide layer occurs. These key figures achieved with an almost unrivalled-inexpensive and unrivalled-accessible material, are among the best ever presented activity characteristics for the anodic water-splitting reaction at pH 13.
Soil versus foliar iodine fertilization as a biofortification strategy for field-grown vegetables
(2015)
Iodine (I) biofortification of vegetables by means of soil and foliar applications was investigated in field experiments on a sandy loam soil. Supply of iodine to the soil in trial plots fertilized with potassium iodide (KI) and potassium iodate directly before planting (0, 1.0, 2.5, 7.5, and 15 kg I ha-1) increased the iodine concentration in the edible plant parts. The highest iodine accumulation levels were observed in the first growing season: In butterhead lettuce and kohlrabi the desired iodine content [50–100 μg I (100 g FM)-1] was obtained or exceeded at a fertilizer rate of 7.5 kg IO3--I ha-1 without a significant yield reduction or impairment of the marketable quality. In contrast, supplying KI at the same rate resulted in a much lower iodine enrichment and clearly visible growth impairment. Soil applied iodine was phytoavailable only for a short period of time as indicated by a rapid decline of CaCl2-extractable iodine in the top soil. Consequently, long-term effects of a one-time iodine soil fertilization could not be observed. A comparison between the soil and the foliar fertilization revealed a better performance of iodine applied aerially to butterhead lettuce, which reached the desired iodine accumulation in edible plant parts at a fertilizer rate of 0.5 kg I--I ha-1. In contrast, the iodine content in the tuber of sprayed kohlrabi remained far below the targeted range. The results indicate that a sufficient spreading of iodine applied on the edible plant parts is crucial for the efficiency of the foliar approach and leafy vegetables are the more suitable target crops. The low iodine doses needed as well as the easy and inexpensive application may favor the implementation of foliar sprays as the preferred iodine biofortification strategy in practice.
Iodine biofortification of butterhead lettuce (Lactuca sativa)viafoliar sprays was investigated infield trials, focusing on assessing the influence of the time and application method. The iodine (I)concentrations in the edible plant parts increased when potassium iodide (KI) and potassiumiodate (KIO3) solutions were sprayed at doses up to 0.25 kg I ha–1on different dates close to har-vest. Crop yield and marketable quality were not significantly affected by I treatments. A greaterefficacy of KI was frequently observed and probably related to its lower point of deliquescenceand smaller anion size in comparison with KIO3. KI sprays on butterhead lettuce at different timesof the day resulted in a higher I enrichment when applied at 11:00 and 15:00 h. The diurnal varia-tion in I uptake may reflect the impact of fluctuating climatic conditions at the time of application.Iodine treatments at different application dates near harvest led to an increasing I concentrationin the vegetable produce that could be related to the rising shoot fresh mass and leaf area.When KI and KIO3were sprayed simultaneously with commercial calcium fertilizers, fungicidesor insecticides, I accumulation in butterhead lettuce was not negatively affected or in some caseseven significantly enhanced. The results show that foliar sprays of KI and KIO3are an effectivemethod to biofortify butterhead lettuce with I and this approach may easily be implemented as aroutine method in commercial cultivation.
Im ökologischen Anbau von Topfbasilikum treten des Öfteren Wachstums- und Qualitätsbeeinträchtigungen auf. Diese machen sich bereits an den Jungpflanzen in Form chlorotischer und nekrotischer Keimblätter bemerkbar. Nachfolgend können Infektionen mit Schwächeparasiten wie Botrytis auftreten. Im Rahmen eines Düngungsversuches sollte geklärt werden, inwieweit diese Probleme im Zusammenhang mit der Anreicherung von Ammonium stehen, welches durch die Mineralisierung organischer Dünger in das Kultursubstrat freigesetzt wird. Versuchsfaktoren waren das Ammonium-N/Nitrat-N-Verhältnis (100/0; 50/50; 0/100) und die Stickstoffkonzentration in der Nährlösung (8, 12 und 16 mmol N/L). Ammonium wurde mittels des Nitrifikationshemmstoffes 3,4-Dimethylpyrazolphosphat (DMPP) stabilisiert. Zusätzlich war in den Versuch eine organische N-Düngevariante einbezogen, die neben einer Grunddüngung mit festen Düngern (Hornspäne und DCM ECO-MIX 4) eine flüssige Nachdüngung (Organic Plant Feed) beinhaltete. Die Kultur der Pflanzen erfolgte in einem Torfsubstrat, das zu Versuchsbeginn auf pH 6,5 eingestellt war.
Mit Nitrat (NO3-) als alleiniger Stickstoffquelle zeigte Basilikum über den gesamten Kulturzeitraum ein vitales Wachstum. Ein reines Ammoniumangebot (NH4+) ging, unabhängig von der N-Stufe, mit einer geringeren Keimrate sowie mit verminderten Pflanzenhöhen- und Frischmassezuwächsen einher. Außerdem waren hier chlorotische Keimblätter und eine verringerte Turgeszenz des Sprosses zu beobachten. In der organischen N-Düngevariante blieb das Pflanzenwachstum zunächst ebenfalls hinter dem mit NO3--Angebot zurück. Des Weiteren waren hier die Schadsymptome an den Keimblättern besonders stark ausgeprägt. Im Zuge der Ammonifikation der organischen N-Dünger kam es in den ersten Versuchswochen zu einer Anreicherung von bis zu 350 mg NH4+-N/L Substrat als alleiniger mineralischer Stickstoffform. Mit fortschreitender Nitrifikation setzte dann ein stimuliertes Pflanzenwachstum ein. Zu Versuchsende wiesen die organisch gedüngten Pflanzen den höchsten NO3--Gehalt im Spross auf. Der kompakteste Wuchs und die höchste Turgeszenz der Pflanzen konnten mit ausgeglichenem NH4+/NO3--Angebot erzielt werden.
The present study investigates consumers’ acceptance of Se-biofortified apples, as well as Se health and nutrition claims that have been approved by the European Commission. Despite indications that such statements are more likely to be accepted if the carrier product itself has a healthy image, unprocessed fruits biofortified with Se have not been investigated in this context yet. Apples as the most frequently-consumed type of fresh fruit in Germany may offer the potential to improve the Se status of consumers when the produce is enriched with Se. Therefore, an online survey of 356 German adults was conducted to analyze different aspects that could affect the perception of and preference for the proposed product concept by consumers. The findings indicate a moderate acceptance of Se-biofortified apples, as well as of Se health and nutrition claims among the participants. Additional information about beneficial health effects of Se had a significant impact on consumer acceptance. People who regularly eat convenience food and prefer to buy apples at supermarkets were particularly attracted by the product idea. In conclusion, the results of the study indicate good prospects for a successful introduction of Se-rich apples in the German food market, if the produce is advertised with approved health and nutrition claims.
In the organic production of pot grown basil, yield depressions and quality impairments are often observed. During the early development stage, cotyledons become chlorotic and necrotic. Subsequently, fungal diseases such as botrytis occur. One possible reason for this problem could be the high concentration of ammonium in the growing media released by the mineralization of organic fertilizers. Therefore, a fertilization trial was carried out to investigate the effect of ammonium (NH4+) on basil in comparison to nitrate (NO3-). The experiment included different NH4+-N/NO3--N ratios (100/0, 50/50 and 0/100) and nitrogen (N) concentrations in the nutrient solution (8, 12 and 16 mmol N L‑1). Plants were cultivated in a peat substrate and fertilized with a nutrient solution which, in addition to the different N sources, contained equal concentrations of a base fertilizer as well as the nitrification inhibitor DMPP. Furthermore, an organic fertilization treatment was realized. Basil fertilized solely with NH4+ showed a diminished growth in comparison to well-developed plants receiving NO3- as N source. Germination rate, plant height and fresh matter yield were significantly reduced by NH4+ nutrition. Similar results occur in the organic treatment where the NH4+ concentration rose up to 350 mg NH4+-N L‑1 substrate at the beginning of the cultivation period. Along with a reduction in biomass production, chlorotic cotyledons were observed. These effects might have been caused by NH4+. When N mineralization declined and NH4+ was largely converted to NO3-, plants exhibited improved growth. Within the mineral N treatments, rising NO3- concentration and NO3--N/NH4+-N ratio promoted plant height and reduced plant compactness due to an increased internode elongation. At the end of the experiment, the NO3- content in basil shoots was highest in the organic treatment and lowest with NH4+ as the sole N source. The best herb quality in terms of plant compactness, turgidity and healthiness of cotyledons was observed when basil was fertilized with ammonium nitrate.
Biofortified apples seem to be a suitable produce. In this study, different selenium forms and application levels were applied to the two apple varieties ‘Golden Delicious’ and ‘Jonagold’, grown in the years 2017 and 2018 in order to increase the selenium uptake within a typical Western diet. It was shown that the biofortification, which was performed as a foliar application implemented in usual calcium fertilization, led to significantly increased selenium contents in the fruits. Furthermore, biofortification affected the total phenolic content (TPC), the polyphenol oxidase activity (PPO), as well as the antioxidant activity (AOA), the latter measured with the two well-known assays Trolox Equivalent Antioxidant Capacity Assay (TEAC) and Oxygen Radical Absorbance Capacity Assays (ORAC). The varying selenium forms and application levels showed a differing influence on the parameters mentioned before. Higher fertilizer levels resulted in higher selenium accumulation. It was found that PPO activity fluctuates less in biofortified apples. With regard to TPC, selenate led to higher amounts when compared to the untreated controls and selenite resulted in lower TPC. AOA analysis showed no clear tendencies as a result of the selenium biofortification. In the case of ‘Jonagold’, a higher AOA was generally measured when being biofortified, whereas, in the case of ‘Golden Delicious’, only one form of application led to higher AOA. Additionally, differences in the amount of major phenolic compounds, measured with High Performance Liquid Chromatography Mass Spectrometry (HPLC-DAD-ESI-MSn), were observed, depending on the conditions of the biofortification and the variety.
Selenium and iodine are essential micronutrients for humans. They are often deficient in food supply due to low phytoavailable concentrations in soil. Agronomic biofortification of food
crops is one approach to overcome micronutrient malnutrition. This study focused on a pre-launch exploration of German consumers’ willingness to purchase selenium- and/or iodine-biofortified apples. For this purpose, an online survey was carried out. In this context, consumers were asked to choose their most preferred apple product from a set card of product alternatives in a discrete choice experiment (DCE). The multinomial logit model results demonstrated that German consumers’ have a particular preference for iodine-biofortified apples. Furthermore, apple choice was mainly influenced by price, health claims, and plastic-free packaging material. Viewed individually, selenium did not exert an effect on product choice whereas positive interactions between both micronutrients exist.
Notable parts of the population in Europe suffer from allergies towards apples. To address this health problem, the analysis of the interactions of relevant allergens with other substances such as phenolic compounds is of particular importance. The aim of this study was to evaluate the correlations between the total phenolic content (TPC), polyphenol oxidase (PPO) activity, antioxidant activity (AOA), and the phenolic compound profile and the content of the allergenic protein Mal d 1 in six apple cultivars. It was found that the PPO activity and the content of individual phenolic compounds had an influence on the Mal d 1 content. With regard to the important constituents, flavan-3-ols and phenolic acids, it was found that apples with a higher content of chlorogenic acid and a low content of procyanidin trimers and/or epicatechin had a lower allergenic potential. This is probably based on the reaction of phenolic compounds (when oxidized by the endogenous PPO) with proteins, thus being able to change the conformation of the (allergenic) proteins, which further corresponds to a loss of antibody recognition. When apples were additionally biofortified with selenium, the composition of the apples, with regard to TPC, phenolic profile, AOA, and PPO, was significantly affected. Consequently, this innovative agronomic practice seems to be promising for reducing the allergenic potential of apples.
Background
Spinach is a nitrogen (N) demanding crop with a weekly N uptake of up to 60 kg ha–1. Consequently, a high N supply is required, which can temporarily lead to high quantities of nitrate (NO3–) being at risk of leaching.
Aims
The objective of this study was to develop a N fertilization approach to reduce the risk of NO3– leaching in field-grown spinach production without adversely affecting crop yield and quality at an early and late harvest stage.
Methods
Ten fertilization trials were conducted to compare different base fertilization rates and splits of top dressings. For top dressings, granulated fertilizers or foliar sprays were used. In a further treatment, N supply was reduced by withholding the second top dressing of 50–70 kg ha−1.
Results
Nitrate concentration at risk of leaching was considerably reduced by decreasing the base fertilizer rate as well as by splitting the top dressing. However, at an early harvest stage, total aboveground dry mass was reduced by, on average, 6% by these measures across all seasons. In contrast, at a later harvest stage, spinach was less affected by the fertilizer schedule. Urea foliar sprays proved to be insufficient in promoting plant growth and caused leaf necrosis. A reduced N supply led to impaired plant growth and yellowish leaves in both spring and winter.
Conclusions
Base N fertilization of spinach is only required in spring, but not in other seasons. Despite slight yield reduction, the top dressing should be split to reduce the risk of NO3− leaching after an early harvest.
In open-field vegetable production, high quantities of soil mineral nitrogen (Nmin) and N-rich crop residues often remain in the field at harvest. After the harvest of crops in autumn, this N can lead to considerable nitrate (NO3−) losses during the subsequent winter leaching period. In four field trials, different tillage depths (3–4, 10, 30 cm) and dates (early autumn, late autumn, early spring) were investigated to reduce N losses after growing spinach in the autumn. In a further treatment, the nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) was directly applied to the crop residues. Potential N losses were calculated by a balance sheet approach based on Nmin concentration (0–90 cm), measured N mineralization and N uptake by catch crops. By postponing the tillage date from early to late autumn or spring, resprouting spinach stubbles acted as a catch crop, reducing N losses by up to 61 kg ha−1. However, if the spinach biomass collapsed, the N losses increased by up to 33 kg ha−1 even without tillage. The application of DMPP as well as the tillage depth were less effective. Overall, postponing tillage to spring seems to be the most promising approach for reducing N losses during the off-season.
Consumer Acceptance and Market Potential of Iodine-Biofortified Fruit and Vegetables in Germany
(2021)
Biofortification of food crops with iodine is a novel approach to preventing iodine deficiency in humans. The present study analyses the consumer target groups and the market potential of iodine-biofortified fruit and vegetables in Germany. For this purpose, an online survey of 1016 German fruit and vegetable consumers was conducted to investigate the acceptance of different product categories as well as relevant criteria for the market launch. The results show that io-dine-biofortified fruit and vegetables are particularly attractive to consumers who purchase at farmers’ markets, organic food shops, and farm stores. Out of this group, 39% of consumers rate such iodine-rich foods as very appealing. They attach importance to food that naturally contains iodine and prefer produce from integrated domestic cultivation. With their focus on sustainability and naturalness, this group of consumers clearly differs from typical users of dietary supplements, who are primarily concerned with health benefits. However, overall about 85% of respondents would prefer biofortified fruits and vegetables to supplements to improve their iodine supply. The greatest market potential for iodine-biofortified fruit and vegetables is to be expected in super-markets, as this is the preferred food shopping location for most consumers. A total of 28% of those who buy here rate the biofortified foods presented as very appealing. Nevertheless, a successful market launch requires that the benefits of the new products are communicated according to the potential consumer group needs.
Many people across the world suffer from iodine (I) deficiency and related diseases. The I content in plant-based foods is particularly low, but can be enhanced by agronomic biofortification. Therefore, in this study two field experiments were conducted under orchard conditions to assess the potential of I biofortification of apples and pears by foliar fertilization. Fruit trees were sprayed at various times during the growing season with solutions containing I in different concentrations and forms. In addition, tests were carried out to establish whether the effect of I sprays can be improved by co-application of potassium nitrate (KNO3) and sodium selenate (Na2SeO4). Iodine accumulation in apple and pear fruits was dose-dependent, with a stronger response to potassium iodide (KI) than potassium iodate (KIO3). In freshly harvested apple and pear fruits, 51% and 75% of the biofortified iodine was localized in the fruit peel, respectively. The remaining I was translocated into the fruit flesh, with a maximum of 3% reaching the core. Washing apples and pears with running deionized water reduced their I content by 14%. To achieve the targeted accumulation level of 50–100 μg I per 100 g fresh mass in washed and unpeeled fruits, foliar fertilization of 1.5 kg I per hectare and meter canopy height was required when KIO3 was applied. The addition of KNO3 and Na2SeO4 to I-containing spray solutions did not affect the I content in fruits. However, the application of KNO3 increased the total soluble solids content of the fruits by up to 1.0 °Brix compared to the control, and Na2SeO4 in the spray solution increased the fruit selenium (Se) content. Iodine sprays caused leaf necrosis, but without affecting the development and marketing quality of the fruits. Even after three months of cold storage, no adverse effects of I fertilization on general fruit characteristics were observed, however, I content of apples decreased by 20%.
Background and Aims: Agronomic biofortification of food crops with iodine may improve the dietary intake of this trace element, which is essential for human development and health. So far, little is known about the suitability of this technique in pome fruits. The objectives of this study were (1) to investigate uptake and translocation of exogenously applied iodine in apple trees, (2) to identify possible strategies of iodine biofortification for this type of fruit, and (3) to evaluate interactions between foliar applied iodine and selenium.
Methods: Apple trees were cultivated in a plastic tunnel for two growing seasons. Iodine was applied via leaves or substrate. During the 2nd year, simultaneous foliar application of iodine and selenium were tested as well. At harvest time, iodine and selenium content in leaves and fruits were determined. The phytoavailable iodine concentration in the growing medium was analyzed following an extraction with calcium chloride. In addition, the dynamics of iodine applied as potassium iodide and iodate in a peat‐based substrate was investigated in an incubation experiment without plants.
Results: The iodine concentration in washed apples increased more than 100‐fold, valuing around 50 µg (100 g FM)−1 by foliar application of iodine as compared to the control treatment. However, this level was only achieved in fruits which were directly wetted by the spray solution. The translocation of leaf‐absorbed iodine to fruits was negligible. Following a substrate fertilization, the fruit iodine content remained rather low due to a strong retention of iodine in the growing medium. When using foliar sprays, the addition of selenium did not affect the iodine enrichment of the apple fruits.
Conclusions: Foliar fertilization of iodine seems to be a promising method to biofortify apples with iodine. The level of I achieved in apple fruits by means of foliar fertilization can significantly contribute to the daily I intake requirement of humans.
Organic pot-based production of basil (Ocimum basilicum L.) often has lower biomass yield than conventional cultivation. Previous investigations indicate that this growth impairment is related to high ammonium (NH4+) concentrations in the growing media released by the mineralization of organic nitrogen (N) fertilizers. However, as a result of this ammonification process substrate pH may also increase. Under neutral to alkaline conditions NH4+ is converted to ammonia (NH3), which is known to be phytotoxic even at low concentrations. Therefore, we investigated the impact of both ammonical N species on basil grown in a peat substrate. In total, three fertilization pot experiments were conducted in a greenhouse in order to compare the effect of different organic base dressings [250 and 750 mg N (L substrate)-1 mainly supplied by a liquid amino acid fertilizer (AAF)] and two initial substrate pH levels (5.5 and 6.5). In two treatments, 5% (v/v) mature compost was mixed into the peat 1 day and 12–days before the substrate was used for sowing, respectively. The aim of this procedure was to stimulate nitrification in this way to reduce ammonical N concentration. Ammonia concentration in the aerial plant surrounding environment was measured by using NH3 detector tubes in combination with an open-top chamber method. The results showed that the growth of basil (number of plants, fresh matter yield, plant height) was significantly inhibited in the second and third week of cultivation by rising NH3 and NH4+ exposure, as well as by a substrate pH ≥ 7.0. These adverse effects were reduced by lowering the organic base dressing rate and adjusting the initial substrate pH to 5.5. Furthermore, the addition of mature compost to peat in combination with a 12-day storage was proven to be effective for promoting nitrification in the organically fertilized substrate. As a result, plant growth was improved by both lower NH3 and NH4+ exposure as well as a faster supply of nitrate (NO3-) as an additional N source. Using this approach, it was possible to feed organically fertilized basil right from the seedling stage with a NO3--N/NH4+-N-balanced and later on providing a predominant NO3--N supply.