Effect of urease/nitrification inhibitors on the behavior of urea-N in the soil planted to rice

The influences of urease/nitrification inhibitors on urea-derived ammonium and nitrate contents in the soils at increasing distances from rice root rhizosphere were studied by a self-made rhizobox.The results showed that dicyandiamide (DCD) with or without hydroquinone (HQ) significantly improved the growth of rice during the period of cultivation, and decreased the urea-derived ammonium contents in rhizosphere and near rhizosphere soil until 60 days after fertilization.Treatments with DCD and with DCD plus HQ,could remain a much higher ammonium levels in rice non-rhizosphere soil at day 20 after fertilization than the control,but a contrary phenomenon was found afterwards.These two treatments significantly decreased nitrate contents in the soils at some distances from rice root rhizosphere at day 20 after fertilization,and later on,the soil out of the rhizobox remained the similar phenomenon until 40 days.In the presence of DCD,nitrate contents in rice root rhizosphere soil appeared much higher levels during an earlier period than the control.This period was just N utilization peak by rice.Hence,DCD and DCD plus HQ could,to some extent,eliminate the potential for urea-derived N loss in rice root rhizosphere soil.The plant-free soil is apparently not a satisfactory control treatment to study the dynamics of ammonium and nitrate in the rhizosphere soil compared to the non-rhizosphere soil(3 cm from rice rhizosphere).