The following observations may be made from the data of Figure 14.
1.  Fertilizer has a range of 615N lower than animal waste with no
overlap of the range of values as presented by Gormly and Spalding (1979) and
Kreitler (1979). However, Wolerink et al. (1979) present a wider range of
615N for septic tank waste and animal waste with the lower 61N values for
septic tank waste slightly overlapping with the higher 6N values for
fertilizer.
2. Unfertilized soil has a range of 61SN isotope values generally
between the range of values for fertilizer and animal waste.
3. Ground water beneath the potato farm and golf course in the Long
Island study has higher 615N (6.2 and 6.5 respectively) than the fertilizer
used at the earth's surface (0.2 and -5.9 respectively).    Flipse, Jr. and
Bonner (1985) attribute this increase in 515N to fractionation processes that
occur within the soil during infiltration.    Flipse, Jr. and Bonner (1985) also
state that nitrogen-isotope ratios of fertilizer-derived nitrate were not
altered to an extent that would make them indistinguishable from animal-waste-
derived nitrates in ground water. However, this statement may assume that the
lowest 615N for animal waste is greater than 10.
4. Cultivated land in West Texas has a wide range of 615N isotope
values with the range wider than and not overlapping with the range for
fertilizer used in West Texas. The range of 61SN for cultivated land does
overlap with the range of values for animal waste of West Texas.
5. The range of S N (3.6 to 10.5) for the subdivisions in Wisconsin
overlaps with the range of values for cultivated and unfertilized soil in
Texas (Kreitler, 1975), unfertilized soil in Nebraska (Gormly and Spalding,
1979), septic tank waste of Wolterink et al. (1979) and, in part, with animal
*       waste of Gormly and Spalding (1979).
Denitrification and volatilization are possible fractionation processes

15
that increase 6 N (Flipse, Jr. and Bonner, 1985). The denitrification of
25