MadSci Network: Earth Sciences

Re: What is the best method for testing soil acidity and nutrient levels?

Date: Mon Jan 22 23:39:22 2001
Posted By: Maggie Guo, Grad student, Plant Physiologu and Molecular Biology Program, Dept.of Plant Biology, UIUC
Area of science: Earth Sciences
ID: 976392134.Es


This is a good question. In a scientific lab environment, it is easy to use 
some specific instruments, such as specific chromatography for testing ion 
concentrations, and PH meter for checking acidity. But if you do not need 
very precise data, general chemical knowledge is enough. My proposal only 
requires PH test paper (which is always short, slip of paper), beakers, 
several chemicals, water, fire and your chemical knowledge.

For acidity: 
Put your soil sample into small volume of water, stir and leave for a while, 
you should get a small amount of solution cover the soil. Now wet your PH 
test paper in the solution, compare to the instruction of the test paper, 
you can know the approximate PH of your soil sample.

For nutrient levels:
Generally speaking, the most important nutrients in soil including organic 
components and inorganic components [nitrogen (NO3- or NH4+), potassium (K+
), phosphorus (HPO42+ or H2PO4+), sulfur (SO42-) and some elements like Fe 
and Cu}, so you will know nutrient level of your sample after you know the 
concentration these components. For organic components, you can heat your 
sample until no visible fumes, compare the weight before/after heating, you 
can know the amount of organic components. About the inorganic components, 
the first step is to get clean solution from your sample. You need to stir 
your sample in a larger amount of water, get through the filter, and maybe 
your need to heat your sample to get crystals of salt. After get solution of 
your sample which contains all the salts, you can do a series of chemical 
experiment to figure out the components and their concentration. For 
example, NH4+ is not very stable and may form NH3 after heating. So if you 
feel stimulus smell, your sample may contain NH4+; Ca++ can form 
precipitation with SO42-, so if you add Ca++ and see white precipitation, 
it's possible that your sample contains SO42-. 


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