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

By applying labeled urea into a loamy meadow brown soil, a pot experiment with spring wheat as test crop was carried out. The results showed that at the end of this experiment, the plant recovery, the soil recovery and the total loss of applied urea N-15 was 17.7-23.7%, 43.7-56.3% and 20.0-36.8%, respectively. N-15 recovery by wheat grain in any treatment varied within a range of 9.0-14.7% of the applied N-15. A combined application of hydroquinone (HQ) and dicyandiamide (DCD) gave the lowest loss and the highest recoveries in both the plant and soil, while applying HQ or DCD alone had less effect on them. During the whole period of wheat growth, HQ+DCD induced an increasing N-15 uptake by plant, and even promoted the translocation of absorbed N-15 from stem to grain. In the presence of inhibitors, organic plus chemically fixed N-15 occupied a large portion of soil N-15 recovery at maturity stage of wheat growth (34.3-50.6%, in contrast to 9.9% in the absence of inhibitors), and DCD and DCD+HQ could remarkably reduce the remaining soil (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 part of the N-15 loss. Regarding N loss, N2O flux only occupied a very small part, 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 the total N2O flux during the whole period of wheat growth. Treatment with both inhibitors had much lower gaseous N losses than that with HQ or DCD alone. Hence, a proper combination application of HQ and DCD is an efficient way to improve urea-N efficiency and crop quality, while decreasing its loss to the environment.