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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%.
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.
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®.
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.
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.
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.
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.
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.
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.