LFL: Soil Inorganic NItrogen
Soil Nitrate is sampled approximately every 2 weeks through growing season (April – October) through 1999; not all years were sampled every 2 weeks depending on ground conditions; only spring and fall sampling from 2000 on.
Soil cores are taken at 5 areas per plot at a depth of 25 cm. Three soil cores (1.9 cm diameter cylinder wet tip hand probe) are taken in a zigzag pattern up between rows 2 & 3 and two soil cores are taken in a zigzag pattern between down rows 4 & 5. The cores are taken on either side of the row. The cores are combined in a pail, hand crumbled, hand mixed and put into a cardboard soil box. Any remaining soil is placed backed into the plot.
The boxes are then placed (within 2-3 hrs of sampling) into the soils dryer (low temperature convection oven) at 110-140 ° F until dry (at least 48 hrs).
After removal from the dryer, the soils are then ground using a Hammermill Grinder through a 2 mm sieve and placed back into the box.
The soils are then taken to the laboratory for analysis.
A 10 g sub-sample is weighed into a 100 ml plastic specimen cup and 50 ml of 1N KCl is added. The cup is shaken for 30 minutes on a reciprocal shaker (approx. 180 strokes per minute). The cup is removed from the shaker and allowed to stand for 15 minutes. The supernatant is then filtered through a Whatman No. 1 filter paper and collected into a small plastic vial. The samples are then analyzed for inorganic N (N-NO3- and N-NH4+) concentrations using a Lachat automated colorimetric analyzer. If analysis cannot be preformed immediately, the vials can be frozen until they can be analyzed.