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Scheme of the plant availability of mineral nutrients in dependence of the soil pH 

Scheme of the plant availability of mineral nutrients in dependence of the soil pH 

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Background Due to its unique chemistry magnesium (Mg) is subject to various cycling processes in agricultural ecosystems. This high mobility of Mg needs to be considered for crop nutrition in sustainable agricultural systems. The Mg mobility in soils and plants and its consequences for crop nutrition are understood, but recent findings in crop Mg u...

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... change (Easterling et al. 2000). The roles of Mg in plant metabolism particularly under stress conditions are well known (Cakmak and Kirkby 2008). Magnesium is involved in carbohydrate formation and translocation. However, under Mg deficient conditions these processes of the primary metabolism are severely disturbed. Cakmak and Kirkby (2008) concluded from experiments investigating the effect of light treatments on Mg-deficient leaves that the Mg requirement is increased under high-light conditions. The higher requirement of Mg under high light might be reduced to the fact that under suboptimal Mg supply and high light processes are induced which finally lead to accumulation of reactive oxygen species (ROS) and thus plant damage. Much higher activities of antioxida- tive enzymes such as superoxide dismutase and ascorbate peroxidase in Mg -deficient leaves compared to Mg-adequate leaves indicate that Mg deficiency stress, indeed, induce generation of reactive oxygen species as a consequence of impairments in photosynthetic elec- tron transport and utilization of photoassimilates (Cakmak and Marschner 1992). Hence, the described higher Mg demand is simply due to the essential roles of Mg in primary metabolism, which cannot be optimally fulfilled under Mg deficient conditions. Consequently, in plants well supplied with Mg differences in light stress susceptibility are not observed, so that under optimal Mg supply no further demand for Mg can be suggested. However, as initially mentioned high light, drought, and heat stress typically occur at the same time. Therefore, in agricultural practice there is an increased risk of temporarily occurring Mg deficiency due to reduced delivery of Mg by mass flow. With respect to the crop Mg demand plant biomass production typically follows a sigmoidal curve with low biomass accumulation after emergence, followed by an exponential vege- tative growth and finally a plateau during generative growth and yield formation. Particularly in periods where an increased risk of low Mg availability (e.g. drought) is synchronized with high crop growth rates and therefore high Mg demand, there is an increased risk that the soil Mg pool and soil applicated sparingly water-soluble Mg fertilizers/limes cannot meet the actual crop demand for Mg. This is particularly true for important crops exhibiting extraordinary high growth rates and, therefore, nutrient demands (C4 plants like maize and sugarcane). Here leaf and/or soil application of readily available Mg sources can be advantageous (Römheld and Kirkby 2007). This view was underlined by Härdter et al. (2004), who investigated the effect of different Mg fertilizer sources on Mg availability in soils. The authors recommended that for maximization of crop uptake while minimizing Mg losses Mg sources exhibiting a gradual but strong release matching the plants requirements should be applied. The source of Mg applied to meet actual high demands should among water-solubility also consider the accompanying ion, which is introduced into the system and, particularly for leaf fertilization, the capacity of a specific Mg salt to induce leaf burning symptoms. Figure 4 shows the solubility of some different Mg salts. Römheld and Kirkby (2007) state that foliar Mg fertilization would be effective particularly in combination with N quality fertilization during reproductive stages as the assimilate transport into harvest organs (tubers, grains, fruits etc.) is enhanced and thereby the competition between the root as second strong sink is reduced. However, in terms of yield security maintained root growth further offers the advantage of continuous water and nutrient supply under drought stress. Magnesium deficiency is problem inherent in acid soils due to the high saturation of the soil CEC with H + ions and consequent Mg leaching for long time periods and impaired Mg uptake (see sections above). Indeed, already 60 to 70 years ago first studies reported that a low pH of soils exhibit higher leaching rates for Mg (Schachtschabel 1954, and literature cited therein). Von Uexkull and Mutert (1995) estimated that about 30 % of the total ice-free land area in the world is acidic (defined as pH<5.5 in the top soil layers) representing about 4 billion ha. In view of arable land expansion Haug (1983) even estimated that about 70 % of the potentially arable land is acidic. Soil acidity is not only a soil immanent problem but is additionally further enhanced by agricultural fertilization practice. Indeed, Guo et al. (2010) could measure a significant effect of excessive N and base cation fertilization on soil acidification in China by comparing soil pH and fertilization practice of different Chinese soils in the 1980s and 2000s. Among the quantitative cation composition of soils the soil acidity also impacts Mg uptake by plants as low pH impairs the uptake of base cations. The pH dependency of the plant availability of three base cations is schematically shown in Fig. 5 for a pH range realistic for arable land. The decrease of plant availability particularly of the two base cations Ca and Mg at acidic pH (< pH 6) is a consequence of the increasing inability to build up and maintain a sufficient pH and hence electrochemical gradient across the plasma membrane of root cells (Schubert et al. 1990). Among an impaired availability and uptake of base cations like Ca and K soil acidity leads to several additional adverse effects. At soil pH<4 – 4.5 the root growth is directly inhibited by H + toxicity with severe consequences for crop production (Islam et al. 1980; Koyama et al. 1995; Rangel et al. 2005). However, acid soils bear also the risk of element toxicities, particularly Mn and Al. Manganese is an essential plant micronutrient, whereas Al is not required by plants, even though some plant species accumulate Al in their tissue (Klug and Horst 2010; Ma et al. 2001 [ Fagopyrum esculentum ], Matsumoto et al. 1976 [ Camellia sinensis ], Ma et al. 1997 [ Hydrangea macro- phylla ]) This section is included due the substantial progress made in the last years in clarifying the role of Mg in metal toxicity stress alleviation. Starting with Mn there is a considerable inter- and intraspecific (between plant species and between cultivars within a plant species) variability in tolerance to excess Mn (Foy et al. 1978). However, several studies report a beneficial effect of Mg supply on Mn tolerance of crops (Le Bot et al. 1990; Goss and Carvalho 1992). For wheat Goss and Carvalho (1992) reported that Mg increased the tolerance of plants to high concentrations of manganese in shoot tissue and also increased the ability of the plant to discriminate against manganese ions in translocation of nutrients from roots to shoots. ” Le Bot et al. (1990) found that increasing the Mg/Mn ratio in the plant tissue alleviates Mn toxicity in tomato and wheat. It is noteworthy here that obviously Mg reduced Mn toxicity not only by reducing Mn uptake (cation antagonism) but also by increasing the plant tissue tolerance. Malcová et al. (2002) found that the toxic effect of excess Mn can be alleviated by adding Mg. This was not only true for in-vitro experiments but also for the symbiotic association between the arbuscu- lar mycorrhizal fungi and maize as host plant. To our knowledge the mechanisms underlying the increasing effect of Mg on Mn tissue tolerance are not yet understood. The alleviative effect of Mg on Al toxicity is recognized for a long time in several plant species (Edmeades et al. 1991 [ Triticum aestivum ], Keltjens and Tan 1993 [Helinathus annuus , Glycine max , Vigna unguiculata , Arachis hypogaea , Cucumis sativus , Lycopersicum esculentum , Brassica capitata ssp., Oryza sativa , Zea mays , Secale cereale , Sorghum bicolor , Triticum aestivum , Hordeum vulgare , Avena sativa ]; Tan and Keltjens 1995 [ Sorghum bicolor ]; Silva et al. 2001 [ Glycine max ]; Hecht-Buchholz and Schuster 1987 [ Hordeum vulgare ]), but up to date the exact mechanisms underlying this phenomenon are not yet fully understood as well. Bose et al. (2011) summarized the potential positive effects of Mg in the plants ’ physiology to increase the resistance/tolerance of crop plants to toxic Al 3+ . It appears that there is not a single reason responsible for the alleviative effect of Mg on Al toxicity expression but a coordinated interplay between several factors including better carbohydrate partitioning and organic acid synthesis and secretion (see also Ma et al. 2001), enhanced phosphatase activity, better H -ATPase activity and cytoplasmic pH regulation, protection from Al- induced increase in cytosolic Ca concentrations and reactive oxygen species. Interestingly, Deng et al. (2006) provided evidence that overexpression of a magnesium transport gene from Arabidopsis thaliana ( AtMGT1 ) conferred tolerance to Al in Nicotiana ben- thamiana indicating that increased internal Mg concentrations are necessary for this effect. The association of increased Mg uptake and Al tolerance was also very recently verified for rice, an extraordinary Al tolerant plant species (Chen et al. 2012; Chen and Ma 2012). The expression of a rice Mg transporter ( OsMGT1 ) was regulated by Al availability, and knockout of this gene enhanced Al sensitivity of rice. The upregulation of a Mg transporter under Al stress was accompanied by increased Mg uptake by the rice plant through enhanced V max of the protein. Whether the increased tolerance of rice due to increased Mg uptake is a consequence of a specific Mg function or of the more efficient metabolic regulation of Mg-associated pathways in the plant as described by Bose et al. (2011), remains to be elucidat- ed. Future work should clarify the exact underlying mechanisms as well. Moreover, it would be interesting to investigate whether Al stress induces a higher Mg demand for optimal plant growth also in the field, and when yes, to which extent (Is an adaption of the ...

Citations

... Generally, magnesium (Mg) plays an important role in plant photosynthesis, assimilation product production and allocation Tian et al., 2021). However, the importance of Mg in crop production has been largely underestimated in recent decades (Cakmak and Yazici, 2010;Gransee and Führs, 2013;Guo et al., 2016). Previous studies have shown that adequate Mg fertilizer application can increase the main crop yield by an average of 8.5% globally (Wang et al., 2020b) and has a positive effect on a crop's ability to access and utilize N even under N-deficient conditions (Grzebisz et al., 2010;Grzebisz, 2013). ...
... Magnesium is abundant in the Earth's crust, however, various factors (e.g., source rocks, cation competition, Mg leaching) restrict the absorption of Mg by crops (Senbayram et al., 2015;Gransee and Führs, 2013). Concretely, most Mg is fixed in the soil mineral lattice and is not easily absorbed by plants (Senbayram et al., 2015;Tian et al., 2021). ...
... In addition, the cation antagonism of Mg 2+ with potassium (K + ) and calcium (Ca 2+ ) occurs due to the properties of soil parent materials and unreasonable fertilization, which hinders the effective absorption of Mg by plants (Farhat et al., 2013;Xie et al., 2021). In addition, the properties of a large hydrated radius make free Mg 2+ bind weakly to negatively charged soil surface and root cell walls and thereby easily lead to soil Mg leaching, particularly in acidic soil and areas with high precipitation (Gransee and Führs, 2013). Consequently, the shortage of available Mg in soils is becoming the key limiting factor affecting crop growth in agricultural systems (Edmeades, 2004;Guo et al., 2016;Chowdhury, 2017;Chen et al., 2022b), and the deficiency of Mg in crop production is gradually becoming common worldwide (Römheld and Kirkby, 2009). ...
Article
Magnesium (Mg) plays an important role in controlling the biological utilization and dispersion of nitrogen (N) in crops and the environment; however, the application of Mg fertilizer is often neglected in crop nutrient management globally. Can intensified Mg management optimize the agronomic and environmental benefits of tea production? To answer this question, four trials of Mg fertilizer levels in oolong tea (Camellia sinensis L.) garden were designed, i.e., 0 (Mg0), 35 (Mg1), 70 (Mg2) and 140 (Mg3) kg MgO ha⁻¹ yr⁻¹, and the tea yield and quality, N use efficiency (NUE) and reactive N losses were assessed. Compared with Mg0, Mg applications significantly increased tea yield by an average of 14.1% (spring tea), 18.4% (autumn tea) and 15.8% (annual total tea), improved tea quality, and increased the partial factor productivity of applied N (PFPN) and NUE by 13.9–17.2% and 17.8–25.5% after the four-year trial, respectively. The N uptake of young shoots (i.e., harvest part) in Mg1, Mg2 and Mg3 was higher than that in Mg0 by 19.5%, 25.8% and 21.5%, respectively. Simultaneously, Mg fertilization significantly decreased the N surplus and reduced the risk of reactive N loss. There was no significant difference in the indicators mentioned above or in the economic benefits among the Mg fertilizer treatments. In conclusion, if the risk of soil nitrate leaching is not considered, the recommended Mg application rate is 35 kg MgO ha⁻¹ yr⁻¹; otherwise, it is 70 kg MgO ha⁻¹ yr⁻¹. These results indicated that Mg could be a key limiting factor and have positive effects on tea production, and reasonable Mg fertilization is beneficial to the sustainability of tea production.
... In addition, high temperatures and rainfall also cause serious leaching and result in the loss of soil Mg [10]. These Mg fertilizers leach easily and have low utilization rates, leading to a waste of resources [11][12][13]. Hence, it is necessary to find a slow-release Mg (S-Mg) fertilizer, to solve F-Mg fertilizer's shortcomings. ...
... Mg is very mobile in soils, because it is less bound to the soil charges. This results in a relatively high abundance of this element in the soil solution and thus a higher risk of leaching [13,62,63]. Mg in the red soils of southern China is easily leached by rain [10]. ...
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Fertilizer application, especially their physical and chemical composition, substantially regulates crop growth and development. The form in which fertilizers are applied to the soil has always been regarded as a crucial factor regulating nutrient availability. However, the properties and release characteristics of Mg fertilizers, i.e., fast-release Mg (F-Mg) and slow-release Mg (S-Mg), have not been fully elucidated in acidic soils. This study characterized the different Mg fertilizers, and their release characteristics were verified through pot (using soybean) and field (using pomelo) experiments. The results showed that, despite the differences between different Mg fertilizers, the same functional group peaks were recorded among them. F-Mg fertilizers had a low pH and low Mg purity, while S-Mg fertilizers had a high pH and high Mg purity. The release rate and leaching characteristics of the F-Mg fertilizers were higher than the S-Mg fertilizers. The pot experiment showed that the yield and growth of soybean were higher under the S-Mg fertilizer than the F-Mg fertilizer. However, MgSO4·7H2O and MgO had the best effect among the F-Mg and S-Mg fertilizers, respectively. The effects of these two fertilizers were further validated using field experiments, and it was found that MgSO4·7H2O and MgO fertilizers substantially improved the yield and quality of pomelo. However, MgO showed a better effect than MgSO4·7H2O. This study can provide a sound theoretical basis for selecting the most efficient type of Mg fertilizer for acid soils. It can contribute valuable information regarding farmland management strategies and may result in sustainable agricultural productivity.
... High mobility of Mg in the soil as well as in the plants have got attention for its needs to be considered in the nutrient management. Therefore, the understanding of Mg physiology in the plants and its role under stress condition is highly important for successful and sustainable crop production [37]. Thus, for wheat it has been shown that the nitrogen application has not only improved the Mg uptake, but also enhanced the translocation from the root to the shoot. ...
... Particularly, under low Mg conditions, there was a higher risk of Mg deficiency symptom development. Besides, the actual Mg availability over a growing season heavily depends on (i) various environmental factors (rainfall and timing, etc.), (ii) site-specific conditions (soil type, availability of other nutrients, etc.), and (iii) the crop species making a precise prediction almost impossible [37]. Additionally, Mg application significantly improved the kernel yield which might be due the direct role of Mg in plants as well its role in the uptake of other nutrients as reported previously [39]. ...
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Citation: Ali, H.; Sarwar, N.; Muhammad, S.; Farooq, O.; Rehman, A.-u.; Wasaya, A.; Yasir, T.A.; Mubeen, K.; Akhtar, M.N. Foliar Application of Magnesium at Critical Stages Improved the Productivity of Rice Crop Grown under Different Cultivation Systems. Sustainability 2021, 13, 4962. https://
... However, Mg 2+ effects on the Shannon index are in line with the negative effects of the exchangeable Ca 2+ /Mg 2+ ratio on DF1, indicating that a pronounced absence of Mg 2+ has negative effects on the respiratory response of the soil microbial community to soluble low molecular weight substances. It should be noted that the importance of the Ca 2+ /Mg 2+ ratio has been a matter of considerable debate in plant nutrition (Gransee & Führs, 2013), but never in respect to soil microbial communities. ...
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Andosols are generally characterized by strong resilience to degradation and high soil fertility. This may decline during long‐term peanut (Arachis hypogea) monoculture, as indicated by soil chemical and biological properties. The study investigated the monoculture‐induced changes in soil chemical environment as driver for the decline in soil fertility. In this on‐farm study, soils from seven sites cropped with peanut monoculture for different periods between 1 and 20 years were analyzed for soil chemical properties (pH, Al and Fe oxides, soil organic matter) as well as soil microbial biomass and microbial functional diversity, estimated by multiple substrate‐induced respiration (MSIR). Total nitrogen (N), soil organic carbon (SOC), and microbial biomass C (MBC) declined by 57%, 62%, and 73%, respectively, over 20 years of peanut monoculture in comparison with 1 year peanut cultivation. The SOC/total N ratio showed the most consistent decrease during this period. The Shannon diversity index, calculated from the MSIR responses, generally decreased from 2.5 to 2.1 during peanut monoculture, passing a minimum after 10 years. Discriminant function 1 declined with increasing years of peanut monoculture (r = –0.87) and explained 74% of the variance, separating nearly all peanut sites from each other. The main predictors were soil pH, exchangeable Al3+, and the SOC/total N ratio, but dithionite extractable Al and Fe as well the ratio of exchangeable Ca2+/Mg2+ also made significant contributions. Twenty years of peanut monoculture led to a strong decline in soil fertility, as strongly indicated by soil microbiological indices.
... The rest of the soils in the study area have a perfect Ca-Mg (1 < Ca/Mg < 5) balance. This means that these soils are satisfactory and reflect a nutritional balance between Ca and Mg [72,73]. ...
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The presence of a noticeable rate of degradation in the land of the Nile Delta reduces the efficiency of crop production and hinders supply of the increasing demand of its growing population. For this purpose, knowledge of soil resources and their agricultural potential is important for determining their proper use and appropriate management. Thus, we investigated the state of soil fertility by understanding the effect of the physical and chemical properties of the soil and their impact on the state of land degradation for the years 1985, 2002 (ancillary data), and 2021 (our investigation). The study showed that there are clear changes in the degree of soil salinity as a result of agricultural management, water conditions, and climatic changes. The soil fertility is obtained in four classes: Class one (I) represents soils of a good fertility level with an area of about 39%. Class two (II) includes soils of an average fertility level, on an area of about 7%. Class three (III) includes soils with a poor level of fertility, with an area of about 17%. Class four (IV) includes soils of a very poor level of fertility with an area of about 37% of the total area. Principal component analysis (PCA) has revealed that the parameters that control fertility in the studied soils are: C/N, pH, Ca, CEC, OM, P, and Mg. Agro-pedo-ecological units are important units for making appropriate agricultural decisions in the long term, which contribute to improving soil quality and thus increasing the efficiency of soil fertility processes. View Full-Text
... Another two studied elements essential for plant growth and development are magnesium and potassium. They are the 7th and 8th most representative mineral elements on Earth, respectively (Huang 2005;Gransee and Führs 2013). Magnesium in soils originates from rock materials containing various silicates (Gransee and Führs 2013), while potassium-bearing micas and feldspars are the dominant potassium reserves in soils (Huang 2005). ...
... They are the 7th and 8th most representative mineral elements on Earth, respectively (Huang 2005;Gransee and Führs 2013). Magnesium in soils originates from rock materials containing various silicates (Gransee and Führs 2013), while potassium-bearing micas and feldspars are the dominant potassium reserves in soils (Huang 2005). The efficiency of the plant to accumulate metals/metalloids in the aboveground organs or store them within its roots depends on their bioavailability in the soil and the plant's tolerance to their concentrations (Elektorowicz and Keropian 2015). ...
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The mobility of chemical elements in the soil-orchid system has been poorly studied. The aim of this study is to evaluate the uptake and mobility of several trace (Li, Ba, Sr, Ag, Hg, and B) and macronutrients (Ca, Mg, and K) in the orchid Anacamptis morio (L.) R.M.Bateman, Pridgeon & M.W.Chase from soils in western Serbia. The sampling sites are characterized by three different bedrock types—cherts, limestones, and serpentines, which are the source of the significant chemical differences in the elemental status of the soil and plant tissues. The four-step Community Bureau of Reference sequential extraction procedure was used to determine the distribution of fractions and predict their potential phytoavailability. The orchid and soil samples were analyzed for total elemental content analysis using ICP-OES. The greatest potential for plant availability was determined for Ba and Sr, representing about 80% of the total soil content. More than 40% of Li in the soils was found to be potentially phytoavailable. Significant correlations were found between the total content of Li, B, and Sr in soils. Between 38 and 60% of Li content and more than 80% of Ba and Sr content were determined to be potentially phytoavailable by sequential analysis. The highest bioconcentration factor (> 1) was determined in the case of B and Sr for all orchid organs, while translocation factor for Li was highest in tubers and leaves. The studied elements were mainly stored in tubers and roots, indicating the exclusion strategy of A. morio as a metal tolerance mechanism. The data obtained showed significant differences in metal content in soils and plants originating from sites with different parent materials, suggesting that bedrock type and associated soil properties are important factors that determine chemical element mobility and uptake.
... According to Oliveira et al. [102], in maize the proportion of mass flow contribution to Ca, Mg, N, S and K transport was as follows: 100, 63, 56, 45 and 10%, respectively. This series clearly shows that the supply of plants with Ca and Mg may be severely limited in drought conditions, despite their relatively high concentration in the soil compared to other macronutrients [103]. Taking into account the diffusion processes, a water shortage in the soil will primarily limit the mobility of phosphate ions and micronutrients. ...
... However, in relation to Mg, the degree of soil moisture has a greater practical importance, as this element is assimilated by plants as a result of a mechanism known as mass flow. Contrary to K, Mg is less readily absorbed [103]. This is one of the reasons for the relatively easy leaching of Mg from the soil. ...
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Article
Fertilizer Use Efficiency (FUE) is a measure of the potential of an applied fertilizer to increase its impact on the uptake and utilization of nitrogen (N) present in the soil/plant system. The productivity of N depends on the supply of those nutrients in a well-defined stage of yield formation that are decisive for its uptake and utilization. Traditionally, plant nutritional status is evaluated by using chemical methods. However, nowadays, to correct fertilizer doses, the absorption and reflection of solar radiation is used. Fertilization efficiency can be increased not only by adjusting the fertilizer dose to the plant’s requirements, but also by removing all of the soil factors that constrain nutrient uptake and their transport from soil to root surface. Among them, soil compaction and pH are relatively easy to correct. The goal of new the formulas of N fertilizers is to increase the availability of N by synchronization of its release with the plant demand. The aim of non-nitrogenous fertilizers is to increase the availability of nutrients that control the effectiveness of N present in the soil/plant system. A wide range of actions is required to reduce the amount of N which can pollute ecosystems adjacent to fields.
... Magnesium (Mg 2+ ) is mobile in soils, but it is also highly subjected to leaching [20]. Moreover, competition among cations may also become disadvantageous to Mg 2+ during a plant's uptake [11], while productivity and fruit quality are strongly influenced by the morphology of the tomato field as it can affect water availability for plants. ...
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As the productivity and quality of tomato fruits are responsive to Mg applications, without surpassing the threshold of toxicity, the assessment of potential levels of Mg accumulation in tissues, as well as the interactions with Ca and physicochemical properties, prompt this study. An agronomic workflow for Mg enrichment, consisting of six foliar applications of MgSO4 with four concentrations (0%, 0.25%, 1% and 4%), equivalent to 0, 43.9, 175.5 and 702 g ha-1 , was applied on two tomato (Lycopersicum esculentum L.) genotypes (Heinz1534 and Heinz9205). During fruit development, leaf gas exchange was screened, with only minor physiological deviations being found. At harvest, Mg contents among tissues and the interactions with Ca were analyzed, and it was found that in both varieties a higher Mg/Ca ratio prevailed in the most external part of the fruit sprayed with 4% MgSO4. However, Mg distribution prevailed relatively near the epidermis in H1534, while in H9205 the higher contents of this nutrient occurred in the core of the fruit, which indicated a decrease of the relative proportion of Ca. The morphologic (height and diameter), physical (dry weight and density) and colorimetric parameters, and the total soluble solids of fruits, did not reveal significant changes in both tomato varieties. It was further concluded that foliar application until 4% MgSO4 does not have physiological impacts in the fruit’s quality of both varieties, but in spite of the different patterns of Mg accumulation in tissues, if the mean value in the whole fruit is considered, this nutrient prevails in H1534. This study thus suggests that variety H1534 can be used to attain tomato fruits with added value, providing an option of further processing to achieve food products with functional properties, ultimately proving a beneficial option to producers, the food processing industry and consumers. Moreover, the study reinforces the importance of variety choice when designing enrichment workflows.
... These symptoms are a result of impaired C metabolism and a decrease in the overall chlorophyll and C fixation rates [88,89]. Mg deficiencies in the soil can be ascribed to a number of factors, such as high Na, K or Ca levels or leaching, especially in sandy soils [89,90]. Na, K and Ca are strong competitors and can replace Mg, leading to decreased availability of this element [89]. ...
... Na, K and Ca are strong competitors and can replace Mg, leading to decreased availability of this element [89]. In the Molopo, Mg leaching occurs due to the soil's high infiltration rates [46,52] and the high mobility of Mg in soil [90], possibly explaining the low levels of Mg found in the soil of the study sites. ...
... Ca plays a crucial role in the strengthening of cell walls and the protection of the plant against diseases and, most importantly, heat stress (especially in the dry Molopo region) [90,91]. Ca deficiency in plants can lead to the dieback or scorching of young leaves due to reduced transpiration rates [91], and Ca shortages can be caused by acidic soils or high levels of other positively charged ions, including Mg, Na and K [90,91]. ...
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Various factors lead to increased woody species density, biomass and cover (so-called ‘bush encroachment’) that influence ecosystem functioning and services in semi-arid rangelands. Ultimately, bush encroachment has adverse effects on human livelihoods. An increased understanding of ecosystem functioning in bush-encroached rangelands could contribute to improved management, conservation and restoration. This study, therefore, aimed to determine landscape functioning of bush-encroached and controlled savanna rangelands in the Molopo region, South Africa, by using the landscape function analysis (LFA) monitoring procedure. Mixed models revealed no significant differences based on LFA indices between bush-thickened and bush-controlled sites due to drought conditions that prevailed while the survey was carried out. Stability, which revealed the largest LFA contributing factors, always had the highest numerical value for sites that were still bush-encroached. Soil analyses revealed that grass litter patches from aeroplane-controlled sites had the highest average nutrient levels. As expected, high percentages of carbon and calcium levels were found in bush-encroached shrub litter patches. Bush-encroached landscapes are fully functional areas, especially under drought conditions. Long-term research is required to determine the effects successful management has on ecosystem functioning, especially during periods of higher rainfall.
... Mg absorption will be inhibited if the concentration of K + is more than 20 mol L -1 (Shaul, 2002). Furthermore, the K and Mg elements would be easily leached if they cannot be properly bound in the soil solution (Gransee and Führs, 2013). The research from Tito et al. (2020) showed that the application of 5 t ha -1 biochar from poultry litter improved soil chemical properties, especially for available P and exchangeable K in the soils, which were in line with the results of this experiment. ...
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The inorganic fertilizer that is used excessively in tea plantations causes soil health degradation. Tea pruning residue and tea fluff are local biomass that has the potential to be used as alternatives to soil nutrient input that is not well conducted in the tea plantation. This study evaluated biochar from the residue of tea pruning and tea fluff compost as potential organic materials to improve the chemical properties of soil in tea plantations. The tea pruning residue biochar and tea fluff compost were mixed in Inceptisols in a pot experiment with treatment combinations of A = control, B = 2.5 t manure compost/ha, C= 0.25% biochar + 1 t tea fluff compost/ha, D = 0.50% biochar + 1 t tea fluff compost/ha, E= 0.75% biochar + 1 t tea fluff compost /ha, F = 0.25% biochar + 1 t tea fluff compost/ha + 2.5 t manure compost/ha, G = 0.50% biochar + 1 t tea fluff compost/ha + 2.5 t manure compost/ha, and H = 0.75% biochar + 1 t tea fluff compost/ha + 2.5 t manure compost/ha. Soil incubation was conducted for 90 days, and soil samples were analyzed for pH, organic C, available P, exchangeable Mg, and exchangeable K contents. The results showed that the mixture of 0.50% biochar + 1 t tea fluff compost /ha + 2.5 t manure compost/ha gave the most optimal improvement in soil properties. The improvement percentages of soil properties obtained were available P of 334%, Exchangeable Mg of 38%, exchangeable K of 244% and pH of 4.6.