LaMotte STH Outfit - Manual (Page 16)

16
Nitrite Nitrogen
Nitrites are formed as an intermediate step in the production of nitrates.
Soils that are well drained and aerated contain only small amounts of
nitrite nitrogen. Excessive nitrites, which are toxic to plants, may result
from soil conditions unfavorable to the formation of nitrate, such as
inadequate aeration. High nitrite readings may also be encountered
in soils with large amounts of nitrates, where a portion of the nitrate
nitrogen decomposes to form nitrites.
PROCEDURE
1. Use a transfer pipet (0364) to add 5 drops of soil extract to a large
depression on a spot plate (0159).
2. Add 1 drop of *Nitrite Nitrogen Reagent 1 (5151WT).
3. Add 1 drop of *Nitrite Nitrogen Reagent 2 (5152WT). Mix with
a clean stirring rod.
4. Add 3 drops of *Nitrite Nitrogen Reagent 3 (5153WT). Mix with
a stirring rod. Wait 1 minute.
5. Match sample color to a color standard on the Nitrite Nitrogen Color
Chart (1310). Record as ppm nitrite nitrogen.
6. If sample color matches, or is deeper than, the highest standard,
repeat test on a diluted sample. Transfer one drop of soil extract to
a large depression on a spot plate. Add 4 drops of *Universal
Extracting Solution (5173). Follow Steps 2-5. Multiply fi nal result
by 5. Record as ppm Nitrite Nitrogen.
Ferric Iron
The role of iron in plant nutrition is discussed in the LaMotte Soil
Handbook. Iron is essential to the formation of chlorophyll, and iron
defi ciency causes chlorosis. While most soils contain abundant iron,
only a fraction is soluble and readily available to the growing plant.
This is particularly true in neutral or alkaline soils. Acid soils contain
higher levels of available iron.
PROCEDURE
1. Use a transfer pipet (0364) to transfer four drops of the general soil
extract to one of the larger depressions on a spot plate (0159).
2. Use the 0.05 g spoon (0696) to add one level measure of *Iron
Reagent Powder (5275). Mix with a clean stirring rod (0519).
3. Add one drop of *Ferric Iron Test Solution (5116PS). Mix again.
4. Match the resulting color to the *Ferric Iron Color Chart (1348).
The test result is read in pounds per acre ferric iron.