Potassium, in fertilizer

Most potassium in fertilizers is the simple chloride salt, having a 60-62% K2O equivalent. Certain crops such as potatoes and tobacco do not like high amounts of chloride. For these crops KNO3, K2SO4, or K2Mg(S04)2 may be used. Florida citrus crops need magnesium nutrients so K2Mg(S04)2 is favored there. 

Gehrke, C.W., Ussary, J.P. and Kramer, G.H. Jr (1 964) Automation of the AOAC flame photometric method for potassium in fertilizers. Journal of the Association of Official Agricultural Chemists 47, 459 69. 

Fertilizers have potassium, nitrogen, and phosphorus in a form that dissolves easily in water so that plants can absorb them. The potassium in fertilizer is in an ionic compound called potassium carbonate. Two ionic compounds in the fertilizer contain the nitrogen—ammonium nitrate and ammonium sulfate. The phosphorus supplied is in another ionic compound, calcium dihydrogen phosphate. 

Use of potassium in fertilizers. The current world consumption of KjO is approximately 20 Tg y" (Table 9.5). The amount of K applied per sq. metre of arable land varies widely among different countries of the world. In 1966, for example, Italy averaged about 1 gK m , while Belgium applied 16 gK m . The Netherlands and West Germany also apply high rates of K, while France, Denmark, the United Kingdom, and the U.S.A. average 6 gm" or lower. However, the U.S.A. uses about 25% of the world s present consumption (Barber et al., 1968). 

S. Vicente, E.P. Borges, B.F. Reis, E.A.G. Zagatto, Exploitation of tandem streams for carry-over compensation in flow analysis. I. Turbidimetric determination of potassium in fertilizers, Anal. Chim. Acta 438 (2001) 3. 

Fig. 4.10 Scheme of continuous segmented analyser with continuous filtering system for the determination of potassium in fertilizers. (Reproduced from [5] with permission of Pergamon Press). 

Millions of tons of ammonia are used worldwide each year to supply crops with nitrogen. Ammonia is either added to irrigation water or injected directly into the ground. Many other nitrogen fertilizers are synthesized from ammonia. Phosphorus in fertilizers originates from phosphate (P04 ) in rock deposits. Potassium in fertilizers comes from evaporated ancient seabeds in the form of potassium oxide (K2O). 

Water-soluble potassium (expressed as K2O) can be determined by manual or automated flame photometric and tetraphenylboron titration methods for all types of fertilizer samples. Atomic absorption can be used for samples below 5% K2O to maintain the highest degree of precision and accuracy. (Note Tetraphenylboron method for potassium is being used less often because of safety issues associated with formaldehyde.) Methods using ICP-OES for high concentration of potassium are currently being developed. Note Potentiometric measurements can be used to determine potassium in fertilizers but are not official approved methods and do not meet the accuracy and precision requirements as current methods. 

KCl —NaCl —MgS04) and in many brines. Separated by fractional crystallization, soluble water and lower alcohols. Used in fertilizer production and to produce other potassium salts. 

The legal basis for the sale of fertilizers throughout the world is laboratory evaluation of content as available nitrogen, phosphorus, and potassium. By convention, numerical expression of the available nutrient content of a fertilizer is by three successive numbers that represent the percent available of N, P20, and K O, respectively. Thus, for example, a 20—10—5 fertilizer contains available nitrogen in the amount of 20% by weight of N, available phosphoms in amount equivalent to 10% of P2O5, and available potassium in amount equivalent to 5% K O. The numerical expression of these three numbers is commonly referred to as the analysis or grade of the fertilizer. Accepted procedures for laboratory analysis are fixed by laws that vary somewhat from country to country. 

In the United States the analytical methods approved by most states are ones developed under the auspices of the Association of Official Analytical Chemists (AOAC) (3). Penalties for analytical deviation from guaranteed analyses vary, even from state to state within the United States (4). The legally accepted analytical procedures, in general, detect the solubiUty of nitrogen and potassium in water and the solubiUty of phosphoms in a specified citrate solution. Some very slowly soluble nutrient sources, particularly of nitrogen, are included in some specialty fertilizers such as turf fertilizers. The slow solubihty extends the period of effectiveness and reduces leaching losses. In these cases, the proportion and nature of the specialty source must be detailed on the labeling. 

Some of the principal forms in which sulfur is intentionally incorporated in fertilizers are as sulfates of calcium, ammonium, potassium, magnesium, and as elemental sulfur. Ammonium sulfate [7783-20-2] normal superphosphate, and sulfuric acid frequendy are incorporated in ammoniation granulation processes. Ammonium phosphate—sulfate is an excellent sulfur-containing fertilizer, and its production seems likely to grow. Some common grades of this product are 12—48—0—5S, 12—12S, and 8—32—8—6.5S. 

Economic Aspects and Uses. Total world production of potassium products is 29,000,000 tons per year (65). Potassium chloride is removed from brine at Moab, and Wendover, Utah, and at Seades Lake, California. Potassium sulfate is made from Great Salt Lake brine by Great Salt Lake Minerals Corp., which is the largest producer of solar potassium sulfate in the wodd. Combined, these U.S. faciUties stiU produce a relatively small percentage of potash fertilizers in the wodd. Production from the Dead Sea, for example, is 10 times greater than production of potassium from brines in the United States. More than 95% of all the potassium produced is used in fertilizer blends. The remainder is converted to other potassium chemicals for industdal use (see Potassium compounds). 

Some compounds of the s-block elements are important industrial chemicals, too. For example, more than 1.4 billion kilograms of K2 CO3 (potassium carbonate, whose common name is potash), is produced in the United States each year. This compound, which is obtained from mineral deposits, is the most common source of potassium for fertilizers. Fertilization with potassium is necessary because this element is essential for healthy plant growth. Moreover, potassium salts are highly soluble in water, so potassium quickly becomes depleted from the soil. Consequently, agricultural land requires frequent addition of potassium fertilizers. 

McCracken et al. 164) compared atomic absorption with the tetraphenyl-boron method for determining potassium in 1190 fertilizers, and very close agreement was found between the two methods. Hoover and Reagor 16S) also found good agreement between the two methods, and atomic absorption was far more rapid. They reported that the 7665 A potassium line was more subject to interference than the less sensitive 4044 A line. Temperli and Misteli 166> reported far better results for low concentrations of potassium in soil extracts by atomic absorption spectroscopy than by flame emission spectroscopy. 

The inhibition of amino-acid transport has been regarded as the main toxic effect of mercury compounds [82], The biochemical mechanism underlying the inhibition is unclear. In unfertilized sea-urchin eggs an interaction with the amino-acid carrier was found, whereas in fertilized eggs inhibition of amino-acid transport was indirect and might result from an elevation of the Na + content of the egg caused by the inhibition of the Na+ pump [83]. The action on the diffusional process could be mediated by an effect on membrane phospholipids or on membrane proteins, or by interaction with Ca2+ which stabilizes membrane structure. Mercuric chloride in skate liver cells inhibited amino acid transport, decreased Na + /K + -ATPase (adenosinetriphosphatase) activity, impaired volume regulatory mechanisms and increased the permeability of the plasma membrane to potassium [84]. It has been suggested that... 

Occasionally, especially In alkaline soil, trace elements, although present, may not be soluble due to the high pH, and are therefore unavailable to the plant. On these occasions, additional supplies might be needed (see pp.54-55). Mineral deficiencies can also be caused by too much of another element overdo potassium-rich fertilizers, for example, and you may "lock up" magnesium so that plants develop symptoms of magnesium deficiency. 

Examples of the use of FIA with ISE detection involve the determination of nitrate and total nitrogen in environmental samples [48, 49, 125, 166], potassium, sodium [125], calcium [51] and urea [124] in serum or major nutrients in fertilizers [73]. An interesting combination of an ISFET sensor with the FIA principle [52] is shown in fig. 5.17. This is a simultaneous determination of potassium, calcium and pH in serum during dialysis on an artificial kidney. 

As with other alkali metals, potassium compounds have many uses. For example, almost all of the compound potassium chloride is used in fertilizers. Currently potassium chloride is mined or derived from seawater. Many years ago, potassium was secured for human use by burning wood and plant matter in pots to produce an ash called potash, which was mostly potassium carbonate and used as a caustic, mainly for making soap when mixed with fats. 

The second reason for acid-digestion is the determination of the total soil elemental content of, e.g. potassium, phosphorus or trace elements. This is seldom done for potassium in normal soil samples, mainly because the total K in soils is of no value as an index to the availability of K to plants, nor is it always of value in tracing the movement or accumulation of applied fertilizer K (Pratt, 1965). The unreactive soil phosphorus is obtained by subtracting the naturally leached reactive phosphorus from the total phosphorus, and a method for determining the latter by extraction with sulphuric acid and potassium persulphate is cited by Turner and FHaygarth (2000). They analysed... 

Potassium chloride is the most important salt of potassium from the perspective of its abundant occurrence and apphcations. This salt, along with potassium sulfate, is used heavily in fertilizers as the primary source of potassium, an essential element for crops. Over 90% salt manufactured is consumed as fertilizer. Also, potassium chloride is a raw material for producing potassium metal and several important potassium salts including potassium nitrate, potassium hydroxide, and potassium sulfate. Other applications are in electrode cells photography buffer solutions and measurement of salinity in water. 

Potassium sulfate is used in fertilizers as a source of potassium and sulfur, both of which are essential elements for plant growth. Either in simple form or as a double salt with magnesium sulfate, potassium sulfate is one of the most widely consumed potassium salts in agricultural apphcations. It is preferred over potassium chloride for certain types of crops such as, tobacco, citrus, and other chloride—sensitive crops. Some other applications include making gypsum cements to make potassium alum in the analysis of Kjeldahl nitrogen and in medicine. 

The reputations of the elements continue to be shaped by folklore and received wisdom as much as by an understanding of their quantitative effects. Is aluminium, then, good in the mineral brighteners of washing powders but bad in pots and pans Copper salts can be toxic, but copper bracelets are rumoured to cure arthritis. We take selenium supplements to boost fertility, while selenium contamination of natural waters devastates Californian ecosystems. Which of us can say whether 0.01 milligrams of potassium in our bottled water is too little or too much ... 

Potassium carbonate is used in the chemical industry as a source of inorganic potassium salts (potassium silicates, potassium bicarbonate), which are used in fertilizers, soaps, adhesives, dehydrating agents, dyes, and pharmaceuticals. Potassium carbonate used to make potassium lye produces soft soaps, which are liquids or semisolids rather than solids. Other uses of potassium carbonate includes use as a fire suppressant in extinguishers, as a C02 absorbent for chemical processes and pollution control, an antioxidant in rubber additives, and in pharmaceutical formulations. 

Although the most prominent use of saltpeter is for the production of black powder, potassium nitrate is also used as fertilizer. In the first half of the 17th century, Johann Rudolf Glauber (1604-1668) obtained saltpeter from animal pens and discovered its use to promote plant growth. Glauber included saltpeter with other nutrients in fertilizer... 

Potassium is found in feldspars and micas, and is the fourth most abundant cation in seawater (390 mg kg-1). Potassium compounds are usually obtained from evaporites (i.e., residues from evaporated water) as KC1 ( potash ) or carnallite, mainly for use in fertilizers. 

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