2.2.1 Fertilizer input
The nutrient input in the chemical fertilizer is converted according to the pure nutrient. Fertilizer inputs include elemental fertilizer and compound fertilizer, the proportion of compound fertilizer referenced in Li and Jin. (2011) included the proportion of the northwest region.
The fertilizer input is calculated as follows:
Inputfer = α × Fef + β × Fcf (1)
Where
Inputfer pure nutrient input of fertilizer for the county (kg);
α nutrient content of elemental fertilizer (%);
Fef inputs of elemental fertilizer N, P or K (kg);
β N, P or K ratio of compound fertilizer (%);
Fcf inputs of compound fertilizer N, P or K (kg).
2.2.2Manure input
Manure inputs, which we define as wastes excreted during livestock and human production. Manure inputs were calculated based on the reported number of heads of livestock and head per capita, population, and the product of the manure content produced per head of livestock per year. Nutrients in human feces are estimated by adult numbers, and the total population multiplied by 0.85 equals the number of adults. Additionally, we considered the collection utilization of excreta (pigs, cattle, sheep, poultry and humans) (Le Noë et al. , 2018). See Table S1 for additional details and parameters used.
The manure input is calculated as follows:
Where
Inputman = i × Ed × Nd × Cd + NLi × Eu × Nu × Cu (2)
Inputman pure nutrient input of manure for the county (kg);
i species of livestock;
NLi number of livestock and poultry (head);
Ed, Eu fecal excretion and urine excretion (kg head-1 d-1);
Nd, Nu Fecal and urine nutrient content (%);
Cd, Cu Collection utilization (%).