2.2.5 Crop uptake
Total nutrients were estimated by multiplying crop production data by crop-specific nutrient content (Li and Jin, 2011) for the following crops: maize, wheat, beans, rapeseed, vegetables, melon, kiwi and apple. We assumed that the nutrient content of each crop remained constant over time. Table S3 lists the values of the parameters used in this study to convert crop yield data to crop N, P, and K uptake. The crop uptake output was calculated as follows:
Outputc = Cy × p (4)
Where
Outputc nutrient output of crop uptake (kg ha-1 yr-1);
Cy different annual crop yields (kg);
p nutrient content in N, P, K of the different crops (%).