2.3.5. Soil P budget and balance
The phosphorus budget in this trial is defined as the difference between P input and P output in spring wheat soil, where P input means P added to the soil with P fertilizer; P output means P taken out by the aboveground biomass of spring wheat. P balance is defined as the P content difference in topsoil (0–0.2 m) between the beginning and the end of the trial in each growing season.