The response of soil Olsen-P to the P budgets of three typical cropland soil types under long-term fertilization
Fig 8
CK: Unfertilized control; NK: Nitrogen and potassium; NPK: Nitrogen, phosphorous, and potassium; NPKS: Nitrogen, phosphorous, potassium and straw; and NPKM: Nitrogen, phosphorous, potassium and manure (NPKM).