Soils essential elements

Fertilizers are immensely important to humanity. Agriculture requires fertilizers because growing plants remove various chemical elements from the soil. In a fully contained ecosystem, decaying organic matter replenishes the soil, but the elements contained in crops that are harvested and shipped elsewhere are not replenished. Thus, intensive agriculture inevitably depletes the soil of essential elements, which must be replaced by fertilization. 

Plants are highly sensitive to soil acidity because many equilibria involving plant nutrients are affected by pH. Phosphorus is a primary example. This essential element for plant growth occurs in soils mainly as phosphates, which are subject to phosphate-hydrogen phosphate equilibria. Consequently, phosphorus is... 

Soil pH is easily tested for and determines the availability of nutrients and the success of white clover. Very acid soils (below pH 5.0) will cause a deficiency of the trace elements iron, boron, copper and molybdenum and conversely will cause injury to plant growth by increasing the availability of aluminium and manganese to toxic levels. Over-liming, on the other hand, which can raise the pH above 6.5, will reduce the availability of certain essential elements such as phosphorus, manganese and boron. 

Water soluble Se in the North West region varied from 0.0002-0.0429 mg/kg. Water soluble Se accounted for 2.13-6.34% of the total Se in the soils of North China. Selenium is an essential element to animals and humans. When water soluble Se in soils is less than 0.003 mg/kg, Se deficiency in animal and human beings may occur. EDTA-extractable Se in the alkali desert soils of North China was in the range of 0.011-0.090 mg/kg this was about 5-11% of the total Se in the soils. Selenium deficiency was mostly found in the Loess Plateau and Tibet region. NH4OAc-cxtractable Ni in soils from Beijing was 0.29 mg/kg. 

System 19. soil (IV) terrestrial plants (VIII) terrestrial animal (IX) forage with including the technological pre-treatments (XIV). This system shows the dependence of essential element contents from environmental conditions. 

Most cobalt found on earth is diffused into the rocks. It also is found in coal and soils, and at trace concentations in animals and plants. It is an essential element for plants and animals (as vitamin B12). Its absence in animals can cause retarded growth, anemia and loss of apetite. The element has been detected in meteorites and in the atmospheres of the sun and other stars. 

Manganese is an essential element for plants and animals. Its shortage in soil can cause chlorosis or lack of chlorophyll in plants—manifested by the appearance of yellow or grey streaks on the leaves or mottling. It activates certain plant enzymes, such as oxalosuccinic decacarboxylase in the oxidation of carbohydrates. Manganese deficiency can cause deformity of bones in animals. 

The presence of iron in vegetable ash has been known since the beginning of the eighteenth century. Although iron is not a constituent of the chlorophyll molecule, a plant grown in a culture medium entirely free from it produces no chlorophyll. According to Roscoe W. Thatcher, plants take iron from the soil in the smallest proportion of any of the essential elements. Since ferrous compounds are toxic to plants, only the soluble ferric compounds can be utilized (195). 

M. O. Schultze stated that cobalt is an essential element for the nutrition of sheep and cattle. Although it is not essential for the growth of the herbage plants, they nevertheless take it up from the soil and make it available for animal nutrition (106) To prevent anemia, even when the diet contains adequate amounts of iron, a small amount of cobalt (not more than four micrograms per day per kilogram of body weight of sheep) is required (124). It is an important constituent of vitamin B 2. 

Agricultural fertilization with sulphur is not a new concept - at the research level at least, sulphur has long been recognised as an essential plant nutrient. However because the complex role of sulphur - in soils, in plant material and in interaction with other essential element cycles - has never been fully understood, sulphur fertilizers have been used mainly on an empirical basis. As a result, sulphur fertilization has shown somewhat erratic performance Measured sulphur deficiency in soils has not always been correlated with poor crop yield and, as a corollary, sulphur fertilization of sulphur deficient soils has not always improved poor crop yields. Thus it has been difficult to routinely demonstrate an economic benefit to the farmer. 

The assessment of plant-available soil contents can frequently be achieved and validated by field experiments for nutritionally essential elements, and, for a few potentially toxic elements such as chromium, nickel and molybdenum, at the moderately elevated concentrations that can occur in agricultural situations. The validation of extraction methods, devised for agricultural and nutritional purposes, is much less easy to achieve when they are applied to heavy metals and other potentially toxic elements, especially at the higher concentrations obtained in industrially contaminated land. This is not surprising in view of the fact that for some heavy metals, for example lead, there is an effective root barrier, in many food crop plants, to their uptake and much of the metal enters plants not from the root but by deposition from the atmosphere on to leaves. In these circumstances little direct correlation would be expected between soil extractable contents and plant contents. For heavy metals and other potentially toxic elements, therefore, extraction methods are mainly of value for the assessment of the mobile and potentially mobile species rather than plant-available species. This assessment of mobile species contents may well, however, indicate the risk of plant availability in changing environmental conditions or changes in land use. 

Elemental iron, the major element in Earth s core, is the fourth most abundant element in Earth s crust (about 5.0% by mass overall, 0.5%-5% in soils, and approximately 2.5 parts per billion in seawater.) In the crust, iron is found mainly as the oxide minerals hematite, Fe203, and magnetite, Fe304. Other common mineral forms are siderite, FeC03, and various forms of FeO(OH). Iron is an essential element in almost all living organisms. In the human body, its concentration ranges between 3 and 380 parts per million (ppm) in bone, 380-450 ppm in blood, and 20-1,400 ppm in tissue. 

Mn is an essential element and is taken up in the reduced Mn2+ form. Often the first symptom of Mn-deficiency is Fe-deficiency, but the appearance of a number of necrotic areas is a distinguishing feature. Mn-deficiency is widespread in areas of high organic carbon, particularly where these have been limed. Under these conditions Mn2+ is oxidised by soil microorganisms to Mn3+, followed by irreversible dismuta-tion to Mn2+ and Mn(IV) as Mn02. The MnOz is not available under alkaline conditions and Mn deficiency results. 

Sodium is an essential element and additions of sodium chloride to soils can provide increased yields of some plants. There is some degree of overlap in the roles of sodium and potassium in plant nutrition. Both Na and Rb are beneficial in K-deficiency. 

It has not been possible so far to establish that Cr is an essential element required by plants, however, addition of Cr to soils deficient in the element has been shown to increase growth rates and yields of potatoes, maize, rye, wheat or oats (Scharrer and Schropp, 1935 Huffman and Allaway, 1973 Bertrand and De Wolf, 1986). Nickel appears to be an essential element for plants (Farago and Cole, 1988). Zerner and coworkers (Dixon et al., 1975) demonstrated that urease isolated from jack bean (Canavalia ensiformis) was a nickel enzyme. Eskew et al. (1983) have shown that Ni is an essential micronutrient for legumes. Most plants contain nickel in the range 1 - 6 mg kg-1 (Vanselow, 1966 Hutchinson, 1981). The uptake of Ni is enhanced by low pH values, and available nickel increases at pH less than 6.5 as a consequence of the breakdown of Ni complexes in the soil with Fe and Mn oxides. Uptake of nickel by plants and questions of toxicity and tolerance have been reviewed by Farago and Cole (1988). Nickel toxicity toward plants has been reviewed by Vanselow (1966) and Hutchinson (1981). 

Finally, it must be noted that the evolution of tolerance is a necessary condition for the evolution of a population able to colonize a mine, but it may not be sufficient. Mines differ from normal habitats in many ways apart from mere metal contamination the soil structure is usually worse, and the organic content less, so that the soils dry out quickly the soils are frequently very deficient in nitrogen and phosphorus and other essential elements and wind and water erosion may mean that seedling establishment is very difficult (Baker and Proctor, 1990). The result is that plants have to be able to adapt to all these conditions as well as to the metal contamination in practice, only those species which show at least some preadaptation to these harsh conditions are going to be able to evolve tolerant races. It may well be that it is this factor, rather than the evolution of tolerance per se, that is most important in determining which species are able to evolve tolerant races. Such arguments may be relevant when comparing the evolution of tolerance in mine environments and aerially-contaminated sites such as those around smelters, where soil conditions and selective forces are markedly different (Baker, 1987). 

Zinc is easily taken up by plants from the soil where it accumulates in the shoots. It is an essential element for plant nutrition (Marschner, 1986) and is important in both carbohydrate metabolism and protein synthesis. 

Se 0.02 Toxic to plants at concentrations as low as 0.025 mg L-1 and toxic to livestock if forage is grown in soils with relatively high levels of added selenium. As essential element to animals but in very low concentrations... 

Element uptake from soil and transfer into the edible parts of plants have been addressed in several other studies. Soil-to-plant transfer factors in fruit and vegetables grown in various agricultural conditions have been determined for, for example, Pt [100], T1 [101], and various other metal contaminants [102], In a study on stable isotopes of fission product elements (Ce, Cs, Sr), an in vitro enzy-molysis method has been applied to investigate the solubilization of the analytes from fodder in a simulated ruminant digestion [103], The effect of inhibitors of fission product solubility was also considered and essential elements were determined simultaneously to evaluate potential nutrition problems for the animals from the use of such inhibitors. Selective leaching of individual classes of metal complexes with different ligands and sequential enzymolysis have been recently applied to estimate the potential bioavailability to humans of Cd and Pb in cocoa powder and related products [104]. 

What evidence is there that root crops that pick up elements and ions from the soil are essential for a balanced diet and healthy living What would happen if we did not take in sufficient quantities of micro quantities of these essential elements Discuss examples of three such ions. 

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