H o w t o P e r f o r m a N iit r o g e n E x t r a c t iio n o n S o iill
How to Perform a N trogen Extract on on So
M che e Knabb
Determining the nitrogen content in soil samples is useful for a variety of reasons,
from understanding how much fertilizer to add to a field to determining how nitrogen
pollution has affected a forest. One procedure that has been developed to analyze
nitrogen content in soil is to perform an extraction using a concentrated salt solution,
such as potassium chloride. Once the nitrogen has been extracted, it can easily be
analyzed using instrument such as a Lachat or a microplate reader.
The process that will be described here will only include the extraction procedure.
This means that soil samples must already be taken prior to this treatment and
chemical analyses will not be discussed. The steps necessary to perform this task are
label the containers, homogenize the soil, weigh the soil, add potassium chloride,
shake the samples, set up filtration apparatus, filter the samples, sieve the remaining
soil, and finally, clean up. The task should take about 3 hours and should be
performed in a laboratory.
In order to explain the process, the RAMP project will be used as an example. There
may be minute differences between this procedure and others, but the general
process is the same. Additionally, there is a glossary at the end of this document if
you are unsure of the meaning of any terms.
When completing any process in a lab, there should be knowledge of the risks
o Potassium Chloride (KCl) is corrosive and contact with skin and eyes should be
o Never ingest anything in the lab
o If something is ingested, consider contacting poison control
o Do not wear latex gloves if you are allergic to latex
o Do not overfill samples
Before the steps of the process are described, the materials should be collected.
Mater a s_________________________________________________
The following items are needed for this process and are listed according to when they
will be needed:
o Permanent Marker
o 125 mL plastic cups and tops
o Metal tins
o Plastic scintillation vials and lids
o Soil samples
o Nitrile gloves
o Data sheet
o Metal spoon
o 1 gallon bottle filled with 2 M Potassium Chloride (KCl)
o Cardboard box
o Packing paper
o filtration rack
o Plastic funnels
o filter paper
o 1 L squirt Bottle with deionized water
o flat pieces of cardboard
o large plastic bag
Additionally, the process will require the use of the following devices:
o Mettler Toledo balance
o 100 mL dispensette
o Drying oven
o 2 mm sieve
1.. Labell the contaiiners..
1 Labe the conta ners
1..1 Label the plastic cups, metal tins, and scintillation vials with the project
title (RAMP), sample number, and date.
1..2 Prepare blank samples that do not contain soil, but treat them the same as
the soil samples.
This image shows what the containers should look like once they have been labeled.
2.. Homogeniize the soiill..
2 Homogen ze the so
2..1 Note: Put on gloves before this step to avoid
2..2 Open a bag that contains soil and remove any
2..3 Break up any clumps of soil and mix it up so
that it forms a homogenous mass.
2..4 Complete this task for all of the samples.
The image above shows a sample
3.. Weiigh the soiill..
3 We gh the so
3..1 Turn on the balance and make sure it is reading 0.00 g.
3..1..1 Press TARE to zero the balanceif it does not read 0.00
3..2 Place the plastic cup on the balance
3..3 Write down the mass of the cup on the data sheet.
3..4 Using the plastic spoon add 20± 0.2 g of soil to the cup and write its mass.
3..5 Complete this task for each of the samples.
The image above shows a soil sample being weighed on
the balance. The yellow button is the TARE button.
4.. Add Potassiium Chlloriide..
4 Add Potass um Ch or de
Warning: be careful when working with KCl because it is
corrosive. Avoid contact with skin and eyes. If contact occurs,
flush immediately with cold water.
4..1 Obtain the dispensette and a 1 gallon bottle filled
with 2M KCl.
4..2 Remove the lid from the bottle and screw on the
4..3 Make sure that the measurement will be taken to 100
4..4 Turn the red dial so that it is perpendicular to the
4..5 Pull the top and fill the pipette and then push it back
down so that the KCl returns into the bottle.
4..6 Turn the dial so that it is parallel to the spout and
pull the top. Put a cup under the spout and push down
the top so that the KCl is dispensed into the cup.
4..7 Screw the cap on the cup and fill each cup with KCl.
The image to the right
shows the dispensette
filled with KCl.
5.. Shake the samplles..
5 Shake the samp es
5..1 Place all of the samples in a cardboard box and add packing paper as
necessary to ensure that the samples will not move around in the box.
5..2 Close the box and secure it on the shaker so that it will not slide around.
5..3 Turn the shaker on high for 1 hour.
The images below show the samples placed in the box (left) and then on the shaker (right).
6.. Set up fiilltratiion apparatus..
6 Set up f trat on apparatus
6..1 Place the funnels in the rack corresponding to the number of samples that
6..2 Obtain a piece of filter paper and fold it twice so that it looks like one
fourth of the original area. Open the paper so that one fourth is on one side
and three fourths are on the opposite side and place it in the funnel.
6..3 Wet the filter paper with the deonized water so that it lays flat on the
funnel. Tap the funnels so that all of excess water is removed.
6..4 Put the pieces of cardboard on the bottom of the rack to provide a flat
surface to place a scintillation vial under each funnel.
The image above shows the filtration apparatus set up after deionized has been used
to wet the filter paper.
7.. Fiillter the samplles..
7 F ter the samp es
Warning: be careful not to overfill the vials because the liquid will expand when they
are frozen and may cause the container to burst.
7..1 Remove the samples from the cardboard box and organize them so that
each sample is next to the corresponding funnel/scintillation vial set-up.
7..2 Carefully pour the extraction solution into the funnel for each sample and
fill each vial so that it is 2/3 full. It may take a while for some of the samples
to filter depending on the soil type.
7..3 Cap each of the vials, place them in a labeled plastic bag, and place them
in the freezer until they will be chemically analyzed.
The image above shows the samples filtering.
8.. Siieve remaiiniing soiill..
8 S eve rema n ng so
8..2 Place the 2 mm sieve in the sink and pour the remaining contents of the
cup into the sieve.
8..2 Turn the water on and push the soil through the sieve.
8..3 Collect the rocks that remain in the sieve and put them in the metal tin
corresponding to the sample
8..4 Place the tins in the oven
at 105 ˚C.
8..5 After 2 days the tins can
be removed from the oven
and weighed to determine
the amount of soil present in
The image at left shows a sample
being sieved. The rocks are placed
in the metal tins, which are seen at
the back right of the image.
9.. Cllean up..
9 C ean up
9..1 Return all of the used items to where they were found.
9..2 Any dirty materials, such as the plastic cups, should be washed with soapy
water and then an acid bath. Make sure you do not put any metal in the acid
bath because it will cause the metal to rust.
By following all of the steps outlined above, it should be clear how to complete this
process. To reiterate, you should label all of your containers, homogenize the soil,
weigh the soil, add KCl, shake the samples, set up the filtration apparatus, filter the
samples, sieve the remaining soil, and clean up. Overall, each of the steps is
straightforward and with practice can be completed without additional instruction.
Balance-instrument that measures mass
Deionized water- water that has had the dissolved solids in it removed
Extraction-method of separation which uses the differences in solubility of desired
products from undesired products
Homogenize- to make a mixture uniform throughout
Sieve- a device used to separate wanted material from unwanted material; in this
case it separates particles larger than 2 mm from particles smaller than 2 mm