Fate of urea-N-15 in a soil-wheat system as influenced by urease inhibitorhydroquinone and nitrification inhibitor dicyandiamide

By applying labeled urea into a loamy meadow brown soil, a pot experiment w ith spring wheat as test crop was carried out. The results showed that at t he end of this experiment, the plant recovery, the soil recovery and the to tal loss of applied urea N-15 was 17.7-23.7%, 43.7-56.3% and 20.0-36.8%, re spectively. N-15 recovery by wheat grain in any treatment varied within a r ange of 9.0-14.7% of the applied N-15. A combined application of hydroquino ne (HQ) and dicyandiamide (DCD) gave the lowest loss and the highest recove ries in both the plant and soil, while applying HQ or DCD alone had less ef fect on them. During the whole period of wheat growth, HQ+DCD induced an in creasing N-15 uptake by plant, and even promoted the translocation of absor bed N-15 from stem to grain. In the presence of inhibitors, organic plus ch emically fixed N-15 occupied a large portion of soil N-15 recovery at matur ity stage of wheat growth (34.3-50.6%, in contrast to 9.9% in the absence o f inhibitors), and DCD and DCD+HQ could remarkably reduce the remaining soi l (NO3-+NO2-)-N-15. In this pot experiment, the leaching loss of applied N- 15 was excluded, and hence, the gaseous loss was considered as the main par t of the N-15 loss. Regarding N loss, N2O flux only occupied a very small p art, and its main part was other gaseous N losses. DCD and DCD+HQ retarded N2O flux from the soil-wheat system after treatment with urea and reduced t he total N2O flux during the whole period of wheat growth. Treatment with b oth inhibitors had much lower gaseous N losses than that with HQ or DCD alo ne. Hence, a proper combination application of HQ and DCD is an efficient w ay to improve urea-N efficiency and crop quality, while decreasing its loss to the environment.