years 2009–2011, the mean CMR and NMR values in RT soils were
much lower (19–30% for CMR and 27–28% for NMR) than those in
CT soils (Table 4). The CMR/NMR ratio, an indicator of microbial N
demand and immobilization, varied from 41 to 44 and was not
affected by tillage treatment after all (Table 3), while tended to
decline over time from 52 in 2008 to 37 in 2011 when averaged
across tillage treatments (Table 5). The reduced tilled plots had also
lower C (CMR/OC; P < 0.001) and N (NMR/TN; P < 0.05) mineralization
coefficients than the conventionally tilled soils (Tables 3 and
5). There was a good correlation between MTR and CMR (r = 0.70,
P < 0.001) and between MTR and NMR (r = 0.53, P < 0.01) (Table 6).
The linear regression between MBC/MBN ratios and mineralization
rates of SOM was highly significant (Fig. 3). The linear regression
between the MBC/MBN ratios and CMR values was significant at
P < 0.005, and accounted for 82% of the variation in CMR. The
regression of the NMR against the MBC/MBN ratio was also
significant (P < 0.001), and explained 60% of the variability.
Positive correlations between the qCO2 values and SOM mineralization
rates were observed (Table 6).