Universal Probability Distribution Function for Bursty Transport in Plasma Turbulence

Bursty transport phenomena associated with convective motion present universal statistical characteristics among different physical systems. In this letter, a stochastic univariate model and the associated probability distribution function for the description of bursty transport in plasma turbulence is presented. The proposed stochastic process recovers the universal distribution of density fluctuations observed in plasma edge of several magnetic confinement devices and the remarkable scaling between their skewness $S$ and kurtosis $K$. Similar statistical characteristics of variabilities have been also observed in other physical systems that are characterized by convection such as the X-ray fluctuations emitted by the Cygnus X-1 accretion disc plasmas and the sea surface temperature fluctuations.Comment: 10 pages, 5 figure

Exploring the Simultaneous Effect of Total Ion Concentration and K:Ca:Mg Ratio of the Nutrient Solution on the Growth and Nutritional Value of Hydroponically Grown Cichorium spinosum L.

Nutrient-efficient plants and agricultural systems could tackle issues resulting from conventional agriculture. Spiny chicory (Cichorium spinosum L.), a very adaptive, wild edible vegetable, is gaining commercial interest as a functional food. Floating-raft hydroponics is a method commonly used for the commercial cultivation of leafy vegetables due to numerous advantages compared to soil cultivation. In this paper, the simultaneous effects of different potassium, calcium and magnesium ratios and different electrical conductivity (EC) levels on the growth and mineral composition of hydroponically grown C. spinosum were investigated. Four nutrient solutions (NS) were compared, two NS with low EC (L, 2.4 dS/m) and two with high EC (H, 3.6 dS/m) with K:Ca:Mg ratios of either 50:40:10 or 40:50:10. The results showed no interactions between the two factors. No significant effects were observed on the fresh and dry weight, leaf number and leaf area. High EC levels increased the K content and decreased the Mn and Zn content in the leaf tissues. The 40:50:10 ratio led to increased Ca content in plant tissues. The Nitrate-N was only affected by the EC level and was increased under H conditions, whereas the total-N was not affected

Current situation of greenhouse vegetable production in Greece

The total greenhouse area in Greece amounts to about 5,600 ha, which corresponds to approximately 0.12% of the total cultivated area of the country. Of this area, 92% (5,200 ha) is used for vegetable production and only 8% (400 ha) is occupied by ornamental crops. Nearly 93% of the total greenhouse area of Greece is plastic-covered but nearly 96% of the greenhouses used for vegetables in Greece are plastic-covered. Glasshouses are used mainly in floriculture. The main vegetable crops in the Greek greenhouses are tomato and cucumber followed by pepper. Crete is the leading region of Greece in greenhouse production, followed by Peloponnese, Macedonia, Thessaly, Central Greece, Epirus and Aegean Islands. A significant proportion of the greenhouse area used for vegetables is occupied by high tunnels. Low tunnels are used to a large extent too, particularly for early melon, watermelon and strawberry production. Only a minor percentage (about 17%) of the greenhouse area used for vegetable production is heated in Greece. The level of automation in the greenhouses used for vegetable production in Greece is unsatisfactory. Computer controlled automation systems are only exceptionally used in greenhouse vegetable production. The fuel cost for greenhouse heating is relatively high in Greece and, therefore, most vegetable greenhouses are not heated. However, heating in the winter is necessary to attain proper temperature levels for high yield and good quality products. Currently, soilless culture in Greece occupies approximately 180 ha, which is nearly 3.3% of the total greenhouse area. Soil solarization and soilless culture in combination with grafting seem currently the safest and most effective practices to overcome the problem of soil-borne pathogens in intensively cultivated greenhouses in Greece

Impact of cultivar and grafting on nutrient and water uptake by sweet pepper (capsicum annuum l.) grown hydroponically under mediterranean climatic conditions

In closed-cycle hydroponic systems (CHS), nutrients and water should be delivered to the plants at identical ratios to those they are removed via plant uptake, to avoid their depletion or accumulation in the root zone. For a particular plant species and developmental stage, the nutrient to water uptake ratios, henceforth termed “uptake concentrations” (UC), remain relatively constant over time under similar climatic conditions. Thus, the nutrient to water uptake ratios can be used as nutrient concentrations in the nutrient solution (NS) supplied to CHS to compensate for nutrient and water uptake by plants. In the present study, mean UC of macro- and micronutrients were determined during five developmental stages in different pepper cultivars grown in a closed hydroponic system by measuring the water uptake and the nutrient removal from the recirculating NS. The experiment was conducted in a heated glasshouse located in Athens Mediterranean environment and the tested cultivars were ‘Orangery,’ ‘Bellisa,’ ‘Sondela,’ ‘Sammy,’ self-grafted and ‘Sammy’ grafted onto the commercial rootstock ‘RS10’ (Capsicum annuum). ‘Sondela’ exhibited significantly higher NO3 -, Mg2+, Ca2+ and B UC, while Bellisa exhibited higher K UC in comparison with all other cultivars. The UC of all nutrients were similar in the grafted and the non-grafted ‘Sammy’ plants, which indicates that this Capsicum annum rootstock does not modify the uptake of nutrients and water by the scion. The UC of macronutrients estimated in the present study (mmol L-1) ranged from 2.4 to 3.7 for Ca, 1.0 to 1.5 for Mg, 6.2 to 9.0 for K, 11.7 to 13.7 for N, and 0.7 to 1.1 for P. The UC of N, K, Ca, and Mg were appreciably higher than the corresponding values found in Dutch tomato glasshouse, while that of P was similar in both locations during the vegetative stage and higher in the present study thereafter. The UC of Fe, Zn and B tended to decrease with time, while that of Mn increased initially and subsequently decreased slightly during the reproductive developmental stage. © 2018 Ropokis, Ntatsi, Kittas, Katsoulas and Savvas

Effects of temperature and grafting on yield, nutrient uptake, and water use efficiency of a hydroponic sweet pepper crop

In areas characterized by mild winter climate, pepper is frequently cultivated in unheated greenhouses in which the temperature during the winter may drop to suboptimal levels. Under low temperature (LT) conditions, the uptake of nutrients may be altered in a different manner than that of the water and thus their uptake ratio, known as uptake concentration, may be different than in greenhouses with standard temperature (ST) conditions. In the present study, pepper plants of the cultivars “Sammy” and “Orangery”, self-grafted or grafted onto two commercial rootstocks (“Robusto” and “Terrano”), were cultivated in a greenhouse under either ST or LT temperature conditions. The aim of the study was to test the impact of grafting and greenhouse temperature on total yield, water use efficiency, and nutrient uptake. The LT regime reduced the yield by about 50% in “Sammy” and 33% in “Orangery”, irrespective of the grafting combination. Grafting of “Sammy” onto both “Robusto” and “Terrano” increased the total fruit yield by 39% and 34% compared with the self-grafted control, while grafting of “Orangery” increased the yield only when the rootstock was “Terrano”. The yield increase resulted exclusively from enhancement of the fruit number per plant. Both the water consumption and the water use efficiency were negatively affected by the LT regime, however the temperature effect interacted with the rootstock/scion combination. The LT increased the uptake concentrations (UC) of K, Ca, Mg, N, and Mn, while it decreased strongly that of P and slightly the UC of Fe and Zn. The UC of K and Mg were influenced by the rootstock/scion combination, however this effect interacted with the temperature regime. In contrast, the Ca, N, and P concentrations were not influenced by the grafting combination. The results of the present study show that the impact of grafting on yield and nutrient uptake in pepper depend not merely on the rootstock genotype, however on the rootstock/scion combination. © 2019 by the authors

Responses of sweet pepper (Capsicum annum L.) cultivated in a closed hydroponic system to variable calcium concentrations in the nutrient solution

BACKGROUND: The use of water containing calcium bicarbonate (Ca(HCO3)2) at excessively high concentrations in closed hydroponic crops can cause calcium ion (Ca2+) accumulation in the recycled nutrient solution (NS) and concomitantly negatively affect yield and product quality. The aim of the study was to determine maximum Ca2+ concentrations that do not harm the crop and to simulate the pattern of Ca2+ accumulation when the Ca2+ concentration in the irrigation water, and concomitantly in the replenishment nutrient solution (RNS), is excessive. In the current study, irrigation water containing 1.5, 3.0, 4.5 and 6.0 mmol L−1 Ca2+ was used to prepare the RNS supplied to pepper cultivated in a closed hydroponic system. RESULTS: At 1.5 mmol L−1 Ca2+, no Ca2+ accumulation was observed in the recirculating NS. However, at 3.0, 4.5 and 6.0 mmol L−1 in the irrigation water, the Ca2+ concentration in the recirculating NS, increased by the latter cropping stages to 17, 28 and 37 mmol L−1, corresponding to 6.4, 9.0 and 10.8 dS m−1. The accumulation of Ca2+ in the recirculating NS affected both tissue nutrient concentrations and uptake concentrations of Ca2+, sulphate ion (SO42−) and magnesium ion (Mg2+), but this was not the case for nitrogen (N) or potassium ion (K+). Growth, yield and plant water uptake were restricted at moderate (3.0 and 4.5 mmol L−1) and high (6.0 mmol L−1) external Ca2+ levels. CONCLUSION: In soilless pepper crops with zero discharge of fertigation effluents, the Ca2+ concentration in the irrigation water and the RNS should be lower than 3.0 mmol L−1 to avoid yield restrictions due to salinity. © 2021 Society of Chemical Industry. © 2021 Society of Chemical Industr

Fruit Volatiles, Quality, and Yield of Watermelon as Affected by Grafting

The aim of the present study was to examine the effect of grafting of watermelon hybrids 'Obla F-1' and 'Vanessa F-1' on to Cucurbita maxima x Cucurbita moschata rootstock TZ 148 and Lagenaria sp. rootstock 'Dias F-1', on the volatiles and yield of fruit and the plant growth. Fruit volatiles analysis showed the presence of two aldehydes, namely (E)-2-nonenal and (E, Z)-2,6-nonadien-1-al, with (E)-2-nonenal being present at higher concentrations in grafted than in un-grafted plants. Grafted plants had also higher growth rate, total yield, and fruit number than un-grafted plants, whereas the percent dry matter of leaves and shoots was higher in ungrafted plants. No differences were observed for mean fruit weight, fruit shape, and rind thickness. Fruit from grafted plants had more compact flesh and less acid fruit juice than fruit from ungrafted plants. Fruit volatile components differed between ungrafted and grafted plants. With regards to sugar content, no significant differences between grafted and ungrafted plants were observed, except in the case of 'Obla F-1' hybrids. Sodium concentration of plant tissues and fruit was higher in 'Obla F-1' ungrafted plants, as well as carotenoid, lycopene, and vitamin C content in fruit, but only in the second year. In conclusion, rootstock-scion combination implemented in the present study affected plant growth and fruit yield and quality, rendering the choice of rootstocks and scions of major importance in order to achieve the highest yield and quality of watermelon fruit

Responses of sweet pepper (Capsicum annum L.) cultivated in a closed hydroponic system to variable calcium concentrations in the nutrient solution

BACKGROUND: The use of water containing calcium bicarbonate (Ca(HCO3)2) at excessively high concentrations in closed hydroponic crops can cause calcium ion (Ca2+) accumulation in the recycled nutrient solution (NS) and concomitantly negatively affect yield and product quality. The aim of the study was to determine maximum Ca2+ concentrations that do not harm the crop and to simulate the pattern of Ca2+ accumulation when the Ca2+ concentration in the irrigation water, and concomitantly in the replenishment nutrient solution (RNS), is excessive. In the current study, irrigation water containing 1.5, 3.0, 4.5 and 6.0 mmol L−1 Ca2+ was used to prepare the RNS supplied to pepper cultivated in a closed hydroponic system. RESULTS: At 1.5 mmol L−1 Ca2+, no Ca2+ accumulation was observed in the recirculating NS. However, at 3.0, 4.5 and 6.0 mmol L−1 in the irrigation water, the Ca2+ concentration in the recirculating NS, increased by the latter cropping stages to 17, 28 and 37 mmol L−1, corresponding to 6.4, 9.0 and 10.8 dS m−1. The accumulation of Ca2+ in the recirculating NS affected both tissue nutrient concentrations and uptake concentrations of Ca2+, sulphate ion (SO42−) and magnesium ion (Mg2+), but this was not the case for nitrogen (N) or potassium ion (K+). Growth, yield and plant water uptake were restricted at moderate (3.0 and 4.5 mmol L−1) and high (6.0 mmol L−1) external Ca2+ levels. CONCLUSION: In soilless pepper crops with zero discharge of fertigation effluents, the Ca2+ concentration in the irrigation water and the RNS should be lower than 3.0 mmol L−1 to avoid yield restrictions due to salinity. © 2021 Society of Chemical Industry

Nutrient uptake concentrations of a pepper crop under Mediterranean climate conditions

Knowledge of nutrient to water uptake ratios which are commonly termed "uptake concentrations", are especially important in greenhouse crops when plants are grown in closed-cycle cultivation systems. In such systems, the input ratio between the mass of a nutrient and the volume of water should be equal to the corresponding nutrient to water uptake ratio by the plants, so as to avoid accumulation. Thus, if data about the mean uptake concentrations are known, they can be used to establish nutrient solutions for closed-cycle hydroponic cultivations. Preliminary observations indicated that the nutrient-to-water uptake ratios in crops grown hydroponically in Mediterranean greenhouses may be substantially different than in north-European greenhouses, due to differences in climatic conditions. Furthermore different genotypes or different rootstocks in the case of grafted plants may have an impact on nutrient and water uptake. In the present study, the uptake of water and nutrients was measured in 4 different pepper genotypes ['Orangery', 'Bellisa', 'Sondela', 'Sammy' self-grafted and 'Sammy' grafted onto a commercial rootstock 'RS10' (Capsicum annum L.)]. All plants were grown in a closed NFT system. Mean water uptake ratios (uptake concentrations) of macro- and micronutrients for two time intervals, namely vegetative and 1st reproductive stage, were determined through the estimation of nutrient removal from the recycled nutrient solution. The results of this study indicated that 'Sondela' exhibited the highest uptake concentrations of NO3, Mg nd Ca in comparison with all other treatments In contrast, the uptake concentrations of all nutrients were similar in the grafted and the nongrafted 'Sammy' plants and that must be due to the genotype of the rootstock and the specific combination of the rootstock-scion. © 2017 ISHS