2.2 Soil sampling and chemical analysis
Soil samples were collected from three replicate plots for each treatment. In each 33 m2 plot, five soil cores were taken from the four layers at 0−10, 10–20, 20–30, and 30–40 cm depths and mixed thoroughly. The composite soil samples were immediately placed in a gas-permeable plastic bag and stored at 4°Cuntil analysis. Subset soil samples were air-dried and sieved through a 2-mm mesh to remove plant debris and stones. The physical and chemical properties of the soil were then analysed, as presented in Table 2.
Microbial biomass carbon (MBC) and nitrogen (MBN) were determined using the fumigation-extraction method (Brookes et al., 1985; Wu et al., 1990) and analysed using a total organic carbon analyser (TOC-VWP; Shimadzu Corporation, Kyoto, Japan) and flow-injection auto-analyser (Tecator FIA Star 5000 Analyzer, Foss Tecator, Sweden), respectively. Soil pH was measured using a pH meter (Delta 320; Mettler Toledo, Columbus, OH, USA) with a soil/water ratio of 1:2.5. SOC content was determined using dry combustion in an elemental analyser (VarioMAX C/N; Elementar, Langenselbold, Germany). The soil alkali-hydrolysable nitrogen content (available N) was determined using alkali solution diffusion absorption. Olsen-P was extracted using 0.5molL−1NaHCO3(Olsen et al., 1954).