The soil organic matter C contents ranged between 23.8 and 29.9 g kg−1 (Table I). The NPK2
treatment showed the highest soil organic matter C, and the PK treatment showed the lowest. Compared
to the initial result in 1990, the soil organic C of the PK treatment decreased by 15% and that of
control by 10%. N-fertilizer application showed positive effects on maintaining and even increasing the
soil organic matter content. Fertilizing also affected the soil available-N contents. The PK and NPK2
treatments had the highest available-N contents (65.7 mg kg−1), followed by the NPK, NK, and NP2K
treatments, and then by the NP and control treatments (57.8 mg kg−1). All treatments with P-fertilizer
showed a higher soil available P content than those without P. Compared to the initial available P in1990,