2.2.6 N, P and K balances
The balance was defined as the sum of N inputs through mineral
fertilizers, manure, wet and dry atmospheric deposition, symbiotic
N2 fixation, straw return and irrigation, minus N output
through crop uptake. The N, P and K balances in cropland are calculated
as follows:
Bc = Input - Output
Efficiency (%) = (nutrient output) / (nutrient input) × 100 (5)
Where
Bc nutrient balance in cropland (kg
ha-1 yr-1);
Input include fertilizers, manure, wet, dry atmospheric deposition,
symbiotic N2 fixation and straw return and irrigation
(kg ha-1 yr-1);
Output include crop uptake (kg ha-1yr-1).