nitrates not utilized for crop production were available for leaching. Nitrate leaching did
occur as maximum nitrate concentrations increased at these wells (2, 4, and 6) to 37, 49,
and 37 ppm during the year following application (4/90 - 4/91). In the zone of
contribution to wells 1, 3, and 5, 251 lbs/A of total available N (as manure, whey
permeate and commercial fertilizer) was applied. Corn yields averaged 96 bu/A at this
rate of application which is also below the expected goal. Maximum nitrate
concentrations in wells 1, 3, and 5 reached 64, 56, and 64 ppm during the testing period.
There was a clear difference in nitrate concentrations from the 2 different application
rates (64, 56, and 64 at 251 lbs N/A vs. 37, 49, and 37 at 185 lbs N/A) although all wells
indicate that excess nitrates were reaching the groundwater. Research from the Arena
site in the LWRV indicates that large rainfall events (> 1") can move water beyond the
root zone and a 2 inch event can move water up to 5 feet in 12 hours (Fermanich. 1994).
There were 5 rainfall events during the 1990 growMing season which exceeded 1 inch/day.
Two of these storms exceeded 4 inches/day. Water table elevations increased 2 feet in
June (Table 2) as rapid recharge occurred from 10.8 inches of rain during that month
(Table 3).
The 1991 growing season was drier than normal (Table 3). Total available
nitrogen was applied at a rate of 185 lbs/A for the entire study area and credits were
taken for manure and whey Auhdrous ammonia was side-dressed and a nitrogen
inhibitor (N-Serve) was used in the zone contributing recharge to wells 1. 3, and 5 while
anhydrous ammonia preplant and N-Serve were used near wells 2, 4, and b. Corn yields
of 150 bu/A were obtained from the side-dress application while 119 bu/A was