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).