2.3. Sampling and measurements
2.3.1. Soil sampling
Six soil cores (diameter 0.08 m, height 0.2 m) were randomly taken in each plot at a depth of 0–0.2 m before sowing and fertilization, and in the middle of each growth stage of spring wheat (i.e. seedling, heading, grain-filling and maturity) in both years.
Sampling dates were 0, 40, 70, 100 and 130 days after sowing (DAS). Each soil sample was divided in half for fresh and air-dried soil samples. Fresh soil samples were used to measure microbial biomass carbon content (MBC), acid phosphatase activity (APA) and alkaline phosphatase activities (ALP). Air-dried samples were used to measure soil pH, organic carbon, total N, total phosphorus, Olsen-P and inorganic P fractions.