Effect of dicyandiamide and hydroquinone on the transformation of urea-nitrogen-15 in soil cropped to wheat

A pot experiment with a loam soil and spring wheat as test crop showed that an application of dicyandiamide (DCD), and especially its combination with hydroquinone (HQ), gave a much larger recovery of soil urea(-15)N than tre atments based on the application of urea alone or urea plus HQ. Most of the urea-N-15 applied to soil was present as organic plus chemically fixed N-1 5 in the DCD and DCD plus HQ treatments. These two treatments showed the sm allest accumulation of urea-derived (NO3-+NO2-)-N-15. Under well-drained co nditions. there was a synergistic effect of the nitrification inhibitor DCD and the urease inhibitor HQ on urea-N-15 transformations and the recovery of fertilizer N-15 in soil after the application of urea.