2.3 Determination of soil physicochemical properties
The fresh soil sample was divided into two parts. One fresh soil sample was used for the determination of soil ammonium nitrogen content (NH4+-N) and nitrate nitrogen content (NO3--N), and the other was naturally air-dried and screened for the determination of other indices. Soil weight water content (SWW) and soil bulk density (SBD) were measured by the drying method. Soil pH was determined by a glass electrode pH meter (STARTER 300, Shanghai) (soil‒water ratio 1:5). The soil total carbon content (TC) was determined by a total organic carbon analyser (Vario, German). The soil total nitrogen content (TN) was measured by the Kjeldahl method. NH4+-N and NO3--N in soil were extracted by 1 mol/L KCl (soil‒water ratio 1:10), and the extract was determined by a continuous flow analyser (SEAL Analytical AA3, German). The content of available phosphorus (AP) in soil was determined by the molybdenum-antimony resistance colorimetric method after leaching with sodium bicarbonate.