Soil microbial biomass, measured as total PLFAs,ranged in 52.2–68.0, 54.2–74.8, and 45.6–70.6 nmol g−1 soil DW at the tillering, grain-filling, and maturity stages, respectively (Table IV). Significant differences(P < 0.05) in soil microbial biomass between WLI and WCI were observed at the grain-filling stage,in which soil total PLFAs under WCI were significantly higher than that under WLI. However, there were no significant differences between WLI and WCI both at the tillering and maturity stages. The soil total PLFAs were significantly affected by N fertilizer levels
at each growth stage (Table IV, P < 0.01). During the three growth stages, N application significantly increased the concentration of soil total PLFAs in both irrigation regimes. However, there was no statistical difference between N0 and N1 treatments under WCI at the tillering stage. The average increments of total PLFAs due to N application under WLI were 14.0%,25.4%, and 14.4% at the tillering, grain-filling and maturity
stages, whereas those under WCI were 14.9%,33.3%, and 25.7%, respectively. Clearly, total PLFAs increased as the N level increased, but the values were not statistically different between N2 and N3 treatments.Moreover, there were significant I × N interactions(Table IV) for soil microbial biomass both at the grain-filling (P < 0.05) and maturity (P < 0.01)stages.