Abstract: A natural field experiment was conducted to investigate the effect of dicyandiamide（DCD）and DCD + S on nitrification-inhibiting on apple orchard soil. The results were as follows：soil NH4+-N contents in N + DCD and N + DCD + S treatments were higher than that of N treatment within 40 days after fertilization，while the NH4+-N content in soil with N + DCD treatment was significantly higher than that of N treatment within 6–20 days after fertilization，yet the NH4+-N content in soil with N + DCD + S treatment was still significantly higher until 30 days after fertilization，prolonging 10 days than DCD for nitrification inhibition；Soil NO3--N content was obviously lower in the two nitrification inhibitor treatments than that of N treatment, decreasing by 18.72%–58.91%. Compared with N treatment，gross nitrification and denitrification rates in soil were low in N + DCD and N + DCD + S treatments，and the biggest difference appeared at early times，this confirmed that nitrification inhibitor could inhibit the transformation of soil NH4+-N to NO3--Neffectively.

Key words: apple, orchard, soil, nitrification inhibitor, ammoniacal nitrogen, nitrate, gross nitrification rate, denitrification rate