Mounting evidence indicates that fall-applied nitrogen (N) is
converted to nitrate much more rapidly than has been generally
believed in Iowa. Observations made last December add to this
evidence. Soil samples were collected in mid-December from three
fields that received anhydrous ammonia in mid-November. The
fields were in Greene County, and soil samples were collected
from a total of 25 test areas within the fields. The test areas
were selected to represent the range in soil characteristics
within each field. Samples were collected to a depth of 18
inches in and between injection bands within each test area.
Concentrations of ammonium and nitrate were measured in each
sample. Fertilizer N was distinguished from soil N by
subtracting concentrations found between bands from those found
in bands. Percentage of nitrification of fertilizer N was
calculated by expressing amount of fertilizer nitrate as a
percentage of fertilizer N found as exchangeable ammonium and
nitrate. Percentage of nitrification increased