Soil Tests for P, K, N, Ca, S, Mg

[pyroglycerine]

Hi,

 

I need to conduct soil tests for the plant macronutrients: P, K, N, Ca, S, and Mg.

 

A test for Nitrogen seems fairly straightforward using the Kjedahl Method.

 

According to several online University sources, tests for Phosphorus and Potassium each require the use of a rotating shaker. Is there a method which does not, or an alternative device to the rotating shaker? (I don't have $200+ to spend on a rotating shaker right now).

 

Where can I find detailed methods for determining Ca, S, and Mg content in soil?

 

NOTE: Accuracy should be within +/-0.1%, higher accuracy is not necessary.

 

Thanks,

pyroglycerine

 

 

[John Cuthber]

Which interpretation of 0.1% do you mean?

The one that's probably unachievable, or the one that's meaningless?

For example, more than 330 parts per million or 0.003% nitrogen is considered high

http://www.ksre.ksu.edu/kswater/images/nitrogen.htm

So all results would be reported as 0.0%

 

Or do you hope to measure ti so that you can tell the difference between 0.003% and 0.003003%

[pyroglycerine]

The latter. For example John, if the correct measurement is 0.003%, then I need an accuracy of 0.1% error within that number.

So, 0.003% + 0.1% = 0.003003 or -0.1% =0.002997%

 

''Chemistry Expert'', I'm yearning for the day when you give a useful answer.

Of course, it's up to you, but I would ask you to kindly stop commenting on my threads unless you have a direct answer to my question(s).#

 

Thanks

[Fuzzwood]

Then provide a better description of what you need in the future. Besides, I cannot remember you paying anything for being helped out. People who answer you do that from their own good heart. You could be a bit more appreciative.

[John Cuthber]

The latter. For example John, if the correct measurement is 0.003%, then I need an accuracy of 0.1% error within that number.

So, 0.003% + 0.1% = 0.003003 or -0.1% =0.002997%

 

''Chemistry Expert'', I'm yearning for the day when you give a useful answer.

Of course, it's up to you, but I would ask you to kindly stop commenting on my threads unless you have a direct answer to my question(s).#

 

Thanks

"Your question does not make sense" is a direct answer.

Please stop posting threads which ask questions too poorly constructed to answer.

And good luck finding someone who can reliably measure anything in soil to that accuracy.

If you find someone who says they can, let me know and I will ask them some awkward questions.

The first one is how to weigh out soil to that precision because it's always gaining or losing water?

There's also the problem of the buoyancy correction since you don't know (in advance) the density of the soil.

You can't use the "traditional" approach of weighing in vacuo because of the loss of volatiles.

 

Seriously, when I said "probably unachievable" I meant it.

 

It would also be interesting to know why you think that level of precision is important.

[pyroglycerine]

"Your question does not make sense" is a direct answer.

Please stop posting threads which ask questions too poorly constructed to answer.

And good luck finding someone who can reliably measure anything in soil to that accuracy.

If you find someone who says they can, let me know and I will ask them some awkward questions.

The first one is how to weigh out soil to that precision because it's always gaining or losing water?

There's also the problem of the buoyancy correction since you don't know (in advance) the density of the soil.

You can't use the "traditional" approach of weighing in vacuo because of the loss of volatiles.

 

Seriously, when I said "probably unachievable" I meant it.

 

It would also be interesting to know why you think that level of precision is important.

 

I don't think that level of precision is important. I lied because I was wrong.

I got annoyed because you showed me I was wrong. Quite childish.

My apologies for the outburst.

I am appreciative for your input, although you may now think otherwise.

I should have done some research first before posting.

 

So, if I may be so bold, could you help me with that? - What level of accuracy would I need for analysing effect on plants of moderating macro-nutrient content in soil? (i.e developing a chemical fertilizer)

 

Thanks

Edited April 23, 2014 by pyroglycerine

[John Cuthber]

Well, there are kits on the market that let you measure most of those nutrients.

I don't know what precision they offer, but it's reasonable to assume that they are adequate, or they wouldn't sell.

For what it's worth, my guess would be that, if the results are good to +/- 10% relative then the effects of temperature, water level and sunlight will make more difference than the concentrations of nutrients.

Also, with "colour change" tests 10% relative is about as good as it gets.

If there was an easy, simple or cheap way to do it that information would be all over the web so...

 

The simple answer to the question in the OP is that, for small numbers of sample, you can shake things by hand.

 

Googling hydroponics will probably get you some information (oddly, a lot of the people doing that only seem to be interested in one crop, but the advice is probably applicable to other plants).

[pyroglycerine]

Well, there are kits on the market that let you measure most of those nutrients.

I don't know what precision they offer, but it's reasonable to assume that they are adequate, or they wouldn't sell.

For what it's worth, my guess would be that, if the results are good to +/- 10% relative then the effects of temperature, water level and sunlight will make more difference than the concentrations of nutrients.

Also, with "colour change" tests 10% relative is about as good as it gets.

If there was an easy, simple or cheap way to do it that information would be all over the web so...

 

The simple answer to the question in the OP is that, for small numbers of sample, you can shake things by hand.

 

Googling hydroponics will probably get you some information (oddly, a lot of the people doing that only seem to be interested in one crop, but the advice is probably applicable to other plants).

I have heard of the kits, however they are not easy to find here in China, maybe I can bring one back from the UK.

Yes, I have actually been thinking of setting up a hydroponics system for a more controlled environment.

 

Thanks for your help