4.2. Effect of tillage on soil enzyme activities
The activity of selected enzymes was used in the current study
as an indicator of soil quality and most strikingly, early
environmental changes induced by tillage systems and soil
disturbance (Raiesi and Beheshti, 2014; Paz-Ferreiro and Fu,
2016). The activity of both urease and ALP was greater in RT than
CT and tillage effects on urease activity were more remarkable
than on ALP activity. This suggests that urease activity is
increased to a greater extent than ALP under RT systems and is
more sensitive to tillage than ALP activity in the study soil. Results
also suggest that tillage practices have similar overall effects on
the activities of enzymes involved in N and P cycling in soils. The
positive impact of RT on soil enzyme activities concurs with
findings of previous studies, where the activity of urease and ALP
(Mohammadi et al., 2013) were higher under RT than under CT.
Urease and ALP are both extracellular enzymes involved in N and
P cycling, respectively, thus controlling N and P release for plant
and microbial growth. The increased catalase activity in less
disturbed soils by both chisel and rotary plows under RT is in
agreement with Jin et al. (2009), who observed higher catalase
activity in RT than CT systems. Catalase is an intracellular enzyme
involved in the microbial metabolism in the cell and is an
important oxidoreductase that exists in nearly all aerobic and
facultative anaerobic microorganisms, protecting cellular activity
and metabolism from oxidative stress by hydrogen peroxide (Alef
and Nannipieri, 1995; Trasar-Cepeda et al., 1999). Increased
enzyme activities can be related to higher total microbial biomass
contents in RT soils. Soil enzyme activities were positively related
to microbial biomass but were negatively correlated with
microbial turnover; suggesting the increased microbial biomass
content or the declined microbial turnover also cause an increase