The domestication of wild-growing plants, including cultivation and fertilization protocols, is able to alleviate the ecological risks posed by the uncontrolled harvesting of range-restricted local endemic plants. In this field study focused on Verbascum arcturus, a vulnerable local endemic of Crete (Greece), the effect of two kinds of fertilization applied by two methods (foliar/root) was investigated. The foliar application included conventional or integrated nutrient management (INM) fertilization. Root application included the application of conventional fertilizers, biostimulants, or INM with biostimulants. Several properties of plant growth, physiology and nutrition were determined. The results showed that fertilization treatment affected neither leaf color and shape nor plant growth, morphology, dry mass partitioning or nutrient content. However, both kinds of foliar-applied fertilization enhanced Zn and B in leaves and soil-applied biostimulant increased leaf Ca. Considering both chlorophyll and antioxidant compounds’ content, foliar application of the INM fertilizers, as well as soil application of the conventional fertilizers or biostimulants, could be considered as accepted options. This study reports for the first time an assessment of the total phenolic and flavonoids content evidenced in V. arcturus and encourages the use of fertilization in promoting the herbal antioxidant profile without compromising visual quality or yield. The findings of this study could be considered as a documented contribution toward the sustainable exploitation of V. arcturus.

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Soil contamination with potentially toxic elements (PTEs) is considered one of the most severe environmental threats, while among remediation strategies, research on the application of soil amendments has received important consideration. This review highlights the effects of biochar application on soil properties and the bioavailability of potentially toxic elements describing research areas of intense current and emerging activity. Using a visual scientometric analysis, our study shows that between 2019 and 2020, research sub-fields like earthworm activities and responses, greenhouse gass emissions, and low molecular weight organic acids have gained most of the attention when biochar was investigated for soil remediation purposes. Moreover, biomasses like rice straw, sewage sludge, and sawdust were found to be the most commonly used feedstocks for biochar production. The effect of biochar on soil chemistry and different mechanisms responsible for PTEs’ immobilization with biochar, are also briefly reported. Special attention is also given to specific PTEs most commonly found at contaminated soils, including Cu, Zn, Ni, Cr, Pb, Cd, and As, and therefore are more extensively revised in this paper. This review also addresses some of the issues in developing innovative methodologies for engineered biochars, introduced alongside some suggestions which intend to form a more focused soil remediation strategy.

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The objective of this study was to elucidate how changes on illite K and vermiculite content affect cation exchange capacity (CEC) and K availability and to evaluate the ability of different extraction methods to predict respective soil K fixation and release capacities. A greenhouse pot experiment with winter wheat was conducted on K-deficient soils with different K application rates and soil K was extracted with ammonium acetate (NH 4 OAc) and sodium tetraphenylboron (NaBPh 4). Illite K and vermiculite contents were determined and a modified Mitscherlich equation was applied to predict critical levels of K availability with respect to a minimum soil K status which could be considered as a constrain fixation factor (z factor). The study showed that z factor was strongly correlated with NaBPh 4-K of K-deficient soils (r = 0.97). In addition, illite K and vermiculite content satisfactorily predicted both the saturation ratio of NH 4 OAc-K (KSR) (r 2 = 0.83) and K buffering properties of K-deficient soils (r 2 = 0.75), while illite K alone well predicted available NaBPh 4-extracted K (r 2 = 0.78). Finally, strong correlations were found between critical levels of K addition and K availability of NaBPh 4-K (r = 0.92). The study suggests that potassium-fixing clay minerals can predict K availability of K-deficient soils, while CEC found to improve the above relationships. Furthermore, the amount of K that represents a minimum K status (z factor) consists of both exchangeable and non-exchangeable K, documenting the superiority of NaBPh 4 over the conventional method of NH 4 OAc in predicting fixation capacities.

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Wild phytogenetic resources are threatened by overexploitation. This pressure on species and natural ecosystems can be alleviated in part by recruiting and domesticating wild-growing species under pilot cultivation with tailor-made fertilization schemes. This study focused on the pilot cultivation of Origanum microphyllum—a critically endangered local endemic plant of Crete, Greece—investigating the effect of conventional and integrated nutrient management (ΙΝΜ) fertilizers by foliar or root application and biostimulant. Above-ground biomass together with leaf chlorophyll fluorescence and color (SPAD meter, DA meter, Chroma Meter) were determined. Leaf chlorophyll, antioxidant compound (carotenoids, phenols, flavonoids), and nutrient contents were also assessed. The results showed that fertilization did not significantly affect plant growth and leaf nutrient content. Root fertilization was associated with greener leaves compared to foliar. The same trend was generally evident for antioxidant compound content. The small size of leaves may have impeded the efficiency of the foliar application. In conclusion, root application of conventional or INM fertilizers seems more suitable to promote visual quality and herbal antioxidant profile of O. microphyllum, than the foliar one.

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