Nitrate concentrations fluccuated greatly in the 6 monitoring wells throughout the
study period. The highest concentrations in the groundwater occurred from over
application of nitrogen from manure, whey permeate, and commercial fertilizer (at 254
Ibs/A) in a year with several heavy rainfall events. However even when nitrogen was
applied at rates to meet crop needs, deep percolation from these rainstorms moved
nitrates beyond the root zone before it could be utilized by the crop. The lowest nitrate
concentrations (below the drinking water standard) were achieved in a drier year and
with better management practices for sandy soils that included use of a nitrogen inhibitor
and side-dress application of nitrogen. Thus it seems that nitrate leaching seems strongly
related to the amount and timing of rainfall/irrigation with respect to the time and
amount of available nitrogen application in the upper root zone. This means that even
with the best management practices large or unpredicatable rainstorm events can leach
nitrates through these sandy soils to the groundwater thus making it difficult to meet
groundwater quality standards immediately below this field.
Parent atrazine and its metabolites are not nearly as leachable as nitrates. The
study area, with uniform sand particles and small organic matter and clay content had
relatively little capacity to sorb atrazine but nevertheless it's movement was retarded.
Even with several rainfall events in 1990, which caused deep percolation it took about a
year for parent atrazine to reach the water table. If the results of this study had been
based on parent atrazine only, not one of the well samples would have exceeded the ES
and only a few samples from each of the wells would have exceeded the PAL However
with the addition of metabolite analysis, total atrazine concentrations often exceeded