Sample Collection and Analyses of Physical-Chemical properties
Soils were sampled from each treatment plot. Nine soil cores (3.8 cm diameter, 25 cm depth) were taken randomly from each plot, and mixed thoroughly to form one composite sample. Each sample was placed in a sterile plastic bag, sealed, and placed on ice when transported to the laboratory. The fresh soil was used for microbial parameters determination. Air-dried samples were used for physicochemical properties determination. Soil moisture content was measured gravimetrically, and the soil pH was measured in 1 M KCl (1:5, w/v). NH4+-N, and NO3-N were extracted with 2 M KCl. NH4+-N, and NO3-N concentrations were detected using a flow injection analyzer (Tecator Inc., Hoganas, Sweden). Soil organic carbon and total nitrogen concentrations were analyzed using the CHNS-analyzer system (Elementar Analysensysteme GmbH, Hanau, Germany). Soil microbial biomass was estimated using the chloroform fumigation-extraction method (Vance et al. 1987).