2
INTRODUCTION .................................................................................................... 4
THE NITROGEN CYCLE ........................................................................................... 4
WHY AND WHEN TO TEST FOR NITROGEN .............................................................. 5
HOW TO COLLECT SOIL SAMPLES ............................................................................. 5
FERTILIZATION RECOMMENDATIONS ...................................................................... 6
HOW TO PROGRAM NITROGEN FERTILIZATION ........................................................ 7
CONVERSION FACTORS .......................................................................................... 8
WARNING ............................................................................................................ 8
CHEMICAL REACTION ............................................................................................. 8
SPECIFICATIONS .................................................................................................... 8
TEST PROCEDURE FOR DETERMINING NITRATE IN IRRIGATION WATER .................... 9
TEST PROCEDURE FOR DETERMINING NITRATE IN SOIL SAMPLES .......................... 10
Calcium Sulfate Extraction ................................................................................ 10
Nitrate Determination ...................................................................................... 11
Index
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.
11
15- Separate one side from the other
three to form a cone.
16- Place the folded filter disc into the funnel and filter the
sample. The extracted sample in the beaker is now ready for
analysis.
NITRATE DETERMINATION
17- Use a pipette to fill each glass vial with 5 mL of the extracted
sample and follow the test procedure as for irrigation water (steps
2 to 5).
18- Keep it at a distance of 30-40 cm (12-16") from the eyes to match the color.
Rotate the disc while looking at the color test windows and stop when you find the
color match.
19- Read the value in the result window and multiply it by 2 to obtain mg/L (ppm)
of nitrate-nitrogen (N-NO
3
-
). Multiply the reading value by 8.86 to obtain mg/L
of nitrate (NO
3
-
).
For best results:
Intensely colored samples will make the color matching determination
difficult and they should be adequately treated before performing the test. Suspended
matter in large amounts should be removed by prior filtration.
Caution:
Ultraviolet radiation may cause fading of colors. When not in use, keep the
disc protected from light, in a cool and dry place.
Interference:
Strong oxidizing and reducing substances; ferric ion (positive interfer-
ence); chloride above 100 ppm (negative interference).
5 mL