3.3. Treatment effects on enzyme activities, soil respiration, and N
mineralization
The activity of NAGase and β-glucosidase enzymes at the Madison
site was greater in soils treated with pelleted poultry manure compared
to the no-amendment control soils in May 2013 (p b 0.001 and p =
0.005 for NAGase and β-glucosidase, respectively), and β-glucosidase
was higher in the oilseed radish treatment (p = 0.028). No differences,
however, were observed in these enzymes at this site in the July 2013
samples (p = 0.52 and p = 0.08 for NAGase and β-glucosidase, respectively)
(Table 3). While no statistical differences at the Farmington site
were observed for NAGase and β-glucosidase activity in May (p =
0.43 and p = 0.06 for NAGase and β-glucosidase, respectively), both
enyzmes had greater activity in winter rye in July 2013 (p = 0.015
and p b 0.001 for NAGase and β-glucosidase, respectively). Similarly,
β-glucosidase activity was greater in oilseed radish (p = 0.014) and
buckwheat (p = 0.014) than in the control in July 2013. No effects of
treatment on NAGase and β-glucosidase activity were observed at the
Lamberton site (p ≥ 0.36). Interestingly, pelleted poultry manure consistently
increased NAGase activity in May and July at all locations, although
in most cases the increases were not statistically significant.
Phosphatase activity was greater in all amendment treatments compared
to the control in May 2013 at Lamberton. In contrast, there was
a reduction in May phosphatase activity at the Madison site in the oilseed
radish, beef manure, and Sustane® treatments. No significant differences
(p = 0.56) in phosphatase activity among treatments were
observed in the July 2013 soil samples. N mineralization was not affected
by any treatment (p = 0.64).
Soil respiration levels in July were much lower at all locations than
those observed in May. This is likely attributable to increasingly dry conditions
as the growing season progressed. However, despite the overall
decline, 101% greater soil respiration (p b 0.001) was observed in July in
the winter rye treatment compared to the no-amendment control at the
Farmington site. Other cover crops did not significantly affect soil respiration
(p ≥ 0.07). Pelleted poultry manure increased soil respiration in
the May samples by 84% and 104% (p b 0.001) at the Lamberton and
Madison sites, respectively. This spike in microbial activity, however,
was short-lived, and was no longer apparent by the July sampling date
(Fig. 2), perhaps due to lower moisture conditions.