Potassium in soil

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. 

Table 4.4. Some extractants for potassium in soils used by various regional laboratories.

Martin, H.W., and D.L. Sparks. 1985. On the behavior of nonexchangeable potassium in soils. Commun. Soil Sci. Plant Anal. 16 133-162. 

Selim, H.M., R.S. Mansell, and L.W. Zelazny. 1976b. Modeling reactions and transport of potassium in soils. Soil Sci. 122 77-84. 

Total potassium in soils or minerals is best determined by decomposition of the sample by means of HF followed by flamephotometric determination. 

Like other alkali metals, pure rubidium does not exist in nature due to its high reactivity. Rubidium is often found with potassium in soils and minerals such as lepidolite and carnalite. There is little demand for rubidium in industries other than the pharmaceutical industry. The little that is produced—as a byproduct when lithium is extracted from lepidolite—is typically used for research purposes. The compound rubidium chloride has, however, been found effective in treating people with depression. 

Column 2 of Table 1.1 shows the ratio of plant content to soil content of important ions. The hydrogen, carbon, and oxygen ratios are omitted because these ions are not derived directly from soils. The ratios are crude indices of the relative availability of soil components to plants. Calcium, sulfur, nitrogen, and potassium in soils are more available than iron and manganese. One goal of soil chemistry is to explain why ions in soils vary widely in their degree of plant availability. 

From Tables 7.2 and 7.4, calculate the average residence times of calcium, magnesium, and potassium in soils. 

Figure 2.2. Routine assay of (a) sulfate in soil extracts by spectrophotometry [355] and (b) of potassium in soil extracts by flame photometry [43] as performed by the Analytical Laboratory of the Centro de Energia Nuclear na Agricultura, Piracicaba, Sao Paulo, Brazil. Note that the large series of routine assays, all performed in duplicate, are bracketed by serial calibration of standards injected in triplicate.

In order to determine wither potassium fertilization is needed or not, it is important to determine the exchangeable potassium in soil samples [53]. The ion-selective potassium electrode proved applicable for these measurements [54]. A potentiometric flow injection manifold and method was worked out for solving that task by Almeida and coworkers [55]. They used the ion-selective potassium electrode built in a flow through cell. 

Wang, J. and Scott, A.D. (2001) Determination of exchangeable potassium in soil using ion-selective electrodes in soil suspensions. Eur. J. Soil ScL, 52, 143-150. 

Almeida, M.I.G.S., Segundo, M.A., Lima, J.L.E.C. and Rangel, A.O.S.S. (2006) Potentiometric multi-syringe flow injection system for determination of exchangeable potassium in soils with in-line extraction. Microchem. J., 83, 75-80. 

Grygolowicz-Pawlak, E., Pachecka, K.A., Wolanin, B. and Malinowska, E. (2006) Towards miniaturized sensors for determination of exchangeable potassium, in soil samples. Int. Agrophys., 20,101-105. 

The study of all the forms of potassium in soils will no doubt be an important topic in the forthcoming volume on soil chemistry of the present encyclopedia. There have, however, been a reasonable number of laboratory studies on the extraction and availability of from feldspars and micas under varying conditions of temperature, pH and buffering, and over various particle-size ranges. A typical recent paper is that by Stohlberg [1959], and a recent summary of forms of potassium in the soil is that of Wiklander [1955]. The results of these studies can be very broadly summarized as follows. Potassium in feldspars is a major source of the potassium required for plant growth in many soils. It is, however, virtually nonexchangeable by comparison with the potassium in the micaceous clay minerals, and... 

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