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Cambridge tap water ICP-MS results

It is <"back to the chalk">. It is very nearly pure CaCO3, you can tell this by the colour, if it had anything else in it the <"white cliffs of Dover"> would be a lot less white.
TBH, I am just not sure about one thing: how comes that the tap water has a lot of NO3 (30ppm) and has almost no K. I know that agriculture does not usually use KNO3 preferring urea or NH4NO3 as nitrogen source (that is all nitrified towards soluble nitrates apparently). However, K is also used in all fertilizing techniques and all K salts are very soluable. Finally it turns out that the tap water has very few K comparing to NO3, which is good to know as is, so I'm mostly curious here.
 
Hi all,
how comes that the tap water has a lot of NO3 (30ppm) and has almost no K.
However, K is also used in all fertilizing techniques and all K salts are very soluble.
The simple answer is I don't know and I would have expected that there should be appreciable levels of potassium (K) for that reason. A little bit of digging may have found the answer.

The <"Soil Minerals and Plant Nutrition: The Nature Education Knowledge Project"> (which looks a very useful resource) suggests that the differences are mainly to do with differences in cation and anion exchange capacity. For nitrogen (N) it says:
..... In soils, N applied through fertilizers and mineralized N from organic matter mostly ends up in the NO3- form. Due to the limited anion exchange capacity of most soils, leaching of applied N in the form of NO3- ions is a common water quality problem, particularly in agricultural regions. It also represents an important economic inefficiency, because producers apply excessive amounts of fertilizer to compensate for the leaching.......
and for potassium (K):
...........Phyllosilicates retain and release K for plants from non-exchangeable or fixed (i.e., exchanged very slowly and only when the K concentration in soil water drops below a threshold value) and exchangeable forms. Potassium ions present on the exchange sites are adsorbed by outer-sphere complexation and are readily available for plant uptake....... On the other hand, illite, vermiculite, and interstratified 2:1 clay minerals release fixed or non-exchangeable K from interlayer sites through cation exchange and diffusion processes at slower rates than the exchangeable K........
<"Zörb C, Senbayram M, Peiter E. Potassium in agriculture--status and perspectives. J Plant Physiol. 171(9) pp 656-69"> suggests that the plant roots play an important part in potassium acquisition.
...... Average soil reserves of K are generally large, but most of it is not plant-available. Therefore, crops need to be supplied with soluble K fertilizers) ......... Recent investigations have shown that organic exudates of some bacteria and plant roots play a key role in releasing otherwise unavailable K from K-bearing minerals.
I know <"that similar processes"> makes iron (Fe) plant available.

cheers Darrel
 
I did some digging also yesterday and as Darrel mentions CEC, yes it’s the action of Illite clays in the overlying landscape around Cambridgeshire and in soil that retain the K leaving an average of 2-3ppm K in surface waters, the number can go up to about 20ppm if there is heavy rainfall. It’s actually surprising how much K and other major Ions like Mg can be bound up and retained in soil and clays. Tangentially to the conversation Clay can uptake maximally saturated solutions of Magnesium Sulphate to form a silky gel like compound, this is how you make the glue for pottery called ‘Slip’.

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:)
 
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