Effects Of Urease/Nitrification Inhibitors On Soil Nitrogen Transformation And Nitrogen Use Efficiency Of Wheat

With the combination of laboratory incubation test, field plot and pot experiments, the effects of urease/nitrification inhibitors on soil nitrogen transformation and nitrogen use efficiency of wheat in Hebei Province were investigated. In this study, hydroquinone (HQ) was as urease inhibitor, dicyandiamide (DCD) and 3,5- dimethylpyrazole (DMP) were as nitrification inhibitors. The results showed that:1) Under the condition of constant temperature and constant humidity, the urea-N transformation in Aqiuc cinnamon soil and Fluvo-aquic soil were significantly inhibited by nitrification inhibitors DCD and DMP. Compared the two inhibitors, the soil nitrification was stronger inhibited by DMP on two soils. While compared the regulation effect of DCD or DMP on nitrogen transformation in the two soils, the better effect was observed in Fluvo-aquic soil than in Aqiuc cinnamon soil.2) In-situ incubation experiment was conducted in the field during the growth of wheat. The results indicated that compared with urea, applying optinum amount of DMP could prolong soil nitrification by about six months. But in wheat field, urea combined with DCD and DMP could prolong soil nitrification by 40 and 155 days, respectively, which further showed that the oxidation of soil ammonium was better inhibited by DMP than DCD.3) The soil nitrification was significantly inhibited by DMP or DCD combined with HQ. Hydrolysis of urea was temporally inhibited by HQ which mainly inhibited the activity of urease. Compared with urea, applying inhibitors could decrease total amount of volatilized ammonia by more than 10%.4) After harvesting wheat, soil NH₄⁺-N contents in all treatments were less than 10 mg/kg, and there was no significantly difference. The accumulated peak of soil NO₃^--N in treatment of urea combined with DMP equivalent to 2% of urea-N was observed in 0～30 cm soil layer, while that in urea treatment was observed in 30～60 cm soil layer, which maybe increased nitrate leaching losses.5) The results of two field experiments indicated that applying inhibitors, especially DMP, could increase wheat yield through by increasing effective panicles. Compared with those in urea treatment, wheat yield, nitrogen use efficiency, agronomic efficiency and physiological efficiency in treatment with DMP equivalent to 1.5% of urea-N were increased by 11.63%, 11.20 percent point, 54.38% and19.61%, respectively, and those in treatment with DMP equivalent to 2% of urea-N were 38.03%, 12.89 percent point, 212.87% and 142.70%, respectively. Meanwhile, the total amount of nitrogen in the part of above ground was increased in treatment with inhibitors through increasing nitrogen accumulation in grain, but the straw biomass and nitrogen accumulation were not affected.6) The regulation mechanism of urease/nitrification inhibitors was studied by pot experiment. The results indicated that DCD and DCD combined with HQ showed a positive effect on promoting the growth of wheat seedling, especially on wheat root, enhancing the accumulation of dry matter and nitrogen, and increasing the ratio of root to plant. It was related with that the applications of urease/nitrification inhibitors changed the ratio of NH₄⁺-N to NO₃^--N in rhizosphere soil, and improved nitrate reductase activity in leaves and roots, which could promote the nitrogen assimilation and metabolization of wheat.