3.3. Enzyme activities
FDA hydrolase activity was highest under GP managed soils,
but similar levels were observed in soils under AgB, GB and
RC treatments (Table 2). There were no significant differences
among treatments. Soils under perennial vegetation treatments
had 1.1–1.3 times the FDA activity compared to soils from cultivated
land (RC). The average FDA hydrolase activity for the
perennial vegetation treatments was found to be 937g fluorescein
g−1 dry soil while the activity on the conventionally managed
RC treatment was only 749g fluorescein g−1 dry soil.
There were significant differences between GP and RC treatments
for dehydrogenase activity. The GP treatment showed the
highest activity (225.6g TPF g−1 dry soil) and the RC treatment
showed the lowest activity (62.4g TPF g−1 dry soil; Table 2).
Similar dehydrogenase activities were observed in soils of the treatments
AgB and GB.
Analysis of-glucosidase and-glucosaminidase enzyme activity
revealed significant differences (p≤0.01) between the RC
treatment and all other treatments (Table 2). The GP (243 and
159g PNP g−1 dry soil) treatment showed the highest activity and
RC (123 and 74g PNP g−1 dry soil) showed the lowest activity for
-glucosidase and -glucosaminidase enzyme activities, respectively.
We observed that -glucosidase and -glucosaminidase
enzyme activities were more than two times higher under perennial
vegetation treatments than the RC treatment.
3.4. Soil carbon and nitrogen
The soil organic carbon (SOC) and total nitrogen (TN) contents
were significantly higher in perennial vegetation treatments compared
to the RC treatment (Table 3). The SOC content for the RC
treatment was 1.2% while those of other three treatments were
greater than 1.7%. Similarly, the TN content for the RC treatment
was 0.13%, while in other treatments it was greater than 0.19%. The
GP treatment had the highest SOC content while the TN content
was highest both in GP and AgB. However, the differences among
perennial vegetation treatments were not significant. These results
followed the same pattern as-glucosidase and-glucosaminidase
enzyme activities as well as WSA.
3.5. Depth effects
The depth effect was significant for all parameters at p≤0.01
(Table 4). This supports the hypothesis that enzyme activities and
water stable aggregates are greater in the surface soil compared
to sub-surface soil. Among the treatments, the AgB showed the
greatest differences in WSA, and FDA hydrolase and -glucosidase
enzyme activities between the two depths. Similarly for dehydrogenase
and -glucosaminidase enzyme activities, the highest
difference was observed in GP and GB treatments, respectively.
The smallest differences were observed in the RC treatment for
all parameters. The treatment by depth interaction was significant
only for -glucosidase and -glucosaminidase enzyme activities
(Figs. 2 and 3). This indicates that the slopes for the enzyme
activities were different between the perennial vegetation treatments
and the RC treatment. In essence, greater differences existed
between the two depths for measured parameters in perennial vegetation
treatments compared to the RC treatment.