| Application of nitrogen (N) fertilizer in paddy fields can easily result in N loss with low N use efficiency. Urea is an important N fertilizer widely used in agricultural production of China. According to the biological chemical transformation process of N in soil, urease inhibitor/ nitrification inhibitor in two-way regulation was one effective measure to realize the efficient utilization of urea-N, and controll N pollution from the source in farmland. It was investigated of the effects of a urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), a nitrification inhibitor 2-chloro-6-(trichloromethyl) pyridine (CP) and their combined application on urea-N transformation, NH3 volatilization rate, NH3 accumulation and dynamic characteristic in yellow clayey soil, using an incubation experiment under constant temperature and humidity. It was investigated of the inhibition effect of combined biochemical inhibitors on soil N transformation as affected by interaction of soil temperature and soil water content in yellow clayey soil. An incubation experiment was conducted to investigate the urease inhibition effect of N-(n-propyl) thiophosphoric triamide (NPPT)in different texture soils and jackbean urease with NBPT by different dosages of urea adding.A soil column leaching experiment was conducted in a greenhouse to observe N and K transformation and leaching loss following the application of urea and UAN with NBPT, CP, or both. A static chamber and gas chromatograph were used to collect and determine CO2, CH4, and N2O fluxes. The global warming potentials(GWP) based on the cumulative emissions of N2O and CH4 were also compared for the various soil treatment combinations.It was conducted to study the effects of biochemical inhibitor combinations(NBPT/NPPT+CP) and fertilization models (one-off and three-time fertilization), and their interactions on yield, yield components, and economic benefit of rice; population quality of rice; nutrient absorption, utilization and distribution of rice,and the relationship between nutrient uptake and grain yield; N dynamic change characteristics in the surface water and leachate; NH3 volatilization and greenhouse gases (CH4 and N2O) emission flux during rice growing season, and calculated GWP and greenhouse gas emissions intensity (GHGI) in yellow clayey field using two factor randomized block design.Results showed that:1. Effects of combined biochemical inhibitors on urea-N transformation,ammonia volatilization and cumulative characteristics in yellow clayey soil:Differernt dosages of NBPT can slower urea release in soil for 3-9 days, and effectively inhibit the urease activity, and thus delay the hydrolysis of urea, and significantly reduce the peak of NH3 volatilization rate by 34.98%. Differernt dosages of CP can inhibit the transformation from NH4+-N to NO3--N, with the effective regulation time over 72 day, but aggravate soil NH3 volatilization loss, and significantly increase the peak of NH3 volatilization rate by 10.89%. Compared with application of NBPT or CP alone, their combination can effectively inhibit urea hydrolysis and maintain large amounts of N in soil in the form of NH4+-N, decrease NH3 volatilization rate at the early stage, and thus reduce NH3 volatilization loss. The best option is application of NBPT? 0.5% and CP?0.3% to urea in yellow clayey soil.2. Comparison of N-(n-propyl) thiophosphoric triamide and N-(n-butyl)thiophosphoric triamide as urease inhibitors: The effective reaction time of urea was less than 9 d in the loamy and clay soil. Addition of NBPT/NPPT for retardation of urea hydrolysis was more than 3 d. In sandy soil, urea decomposition was relatively slow, and adding inhibitor significantly inhibited soil urease activity, and reduced NH4+-N content. During the incubation time, the inhibition effect of high dosage urea in the soil was better than that of low dosage. The urease inhibition effects both in different texture soils were in the range of sandy soil> clayey soil> loamy soil. NPPT applied by different rates of urea with soil or purified jackbean urease significantly delayed urea hydrolysis, similar to the trend with NBPT. Molecular docking was performed to investigate the potential binding mode. NPPT/NBPT penetrated the active catalytic site of jackbean urease deeply, interacted with nickel ions and different amino acid residues around the catalytic site of urease. The docking energies(?Gdock) of NPPT and NBPT with jackbean urease were -66.04 kcal·mol-1 and -66.36 kcal mol-1. In addition, NPPT was shown an effective and promising urease inhibitor due to its high thermostability in product processing of urea melt in favor of urea-based fertilizer applications in the future.3. Inhibition effect of combined biochemical inhibitors on N transformation in yellow clayey soil affected by interaction of soil temperature and water content:Soil temperature and water content had significant effects on the inhibition effects of biochemical inhibitor combinations in yellow clayey soil, especially in soil temperature. With the increase of soil temperature, urea hydrolysis increased by the effective time of the combinations reduced, and the inhibition effect of urease and nitrification weakened accompanied by increase in nitrification. With the decrease of soil water content, urea hydrolysis tended to slow by the effective time of the combinations prolonged, and the inhibition effect of urease and nitrification increased accompanied by nitrification weakened. NBPT/NPPT or combined with CP treatments can effectively inhibit soil urease activity, and slow urea hydrolysis. CP or combined with NBPT/NPPT treatments can effectively inhibit the transformation of NH4+-N to NO3--N, and keep high NH4+-N content in soil for longer time under different soil temperature and water conditions. The optimum condition of soil temperature and water content by the application of biochemical inhibitor combinations in yellow clayey soil were 25? and 60%WHC, respectively.4. Effects of nitrogen fertilization combined with biochemical inhibitors on leaching loss of nitrogen, potassium, and greenhouse gas emissions in yellow clayey soil: NBPT treatment can slow urea hydrolysis, and effectively inhibit the generation of NH4+-N,to retard the peak time and reduce the NH4+-N loss of leacheate. CP treatment can effectively inhibit the change of NH4+-N to NO3--N to reduce NO3--N loss, and its effective regulation time was more than 72 d. NBPT+CP treatment can not only slow down urea hydrolysis and keep high NH4+-N content in soil, but also reduce NO3--N content in the leacheate. Compared with addition of NBPT alone, combined with CP can reduce NO3- leaching, and increase K+ fixed by soil lattice, and mitigate the leaching risk of K+ for more than 72 days in yellow clayey soil. The N2O flux peaks were delayed and significantly decreased by adding CP to both N fertilizer applications. Application of CP to both fertilizers with the absence and presence of NBPT reduced N2O emissions by 32.66% and 24.72% (U),and by 29.85% and 29.44% (UAN), respectively. Addition of NBPT alone also significantly reduced N2O emissions from U application (10.56%) other than UAN.Furthermore, the GWPs between fertilizers were reduced by the addition of inhibitors,and the largest decrease (24.68%) was obtained by NBPT+CP.5. Effects of combined biochemical inhibitors and fertilization models on yield, population quality, nutrient uptake and use efficiency of rice in yellow clayey field: Urea by three-time fertilization treatment significantly increased grain yield and economic benefit than those of one-off fertilization treatment by 14.2% and 14.6%; significantly increased productive tillers, effective LAI, SPAD value at heading stage and dry matter accumulation from heading to maturity of rice by 0.8%,24.0%, 9.3%, and 1.5%; significantly increased N, P, and K uptake at maturity by 11.0%, 0.9% and 4.2%, and N recovery efficiency and N agronomic efficiency by 27.5% and 70.8%, respectively. Addition of biochemical inhibitor combinations(NBPT/NPPT+CP) significantly increased productive tillers, panicle setting rate,efficient LAI, and SPAD value at heading stage of rice, and also improved the grain to leaf ratio, to enhance the source-sink relationship; increased N, P, K uptakes of rice,and dry matter production and N accumulation after heading stage, and improved the allocation of nutrients in grain and N use efficiency under different fertilization modes.6. Effects of combined biochemical inhibitors and fertilization models on nitrogen dynamics in surface water, leachate, ammonia volatilization and greenhouse gas emission from yellow clayey paddy field: Urea by three-time fertilization treatment significantly reduced net NH3 volatilization loss rate by 24.6%than that of one-off fertilization treatment during rice growing season; significantly reduced CH4 and N2O emissions, GWP and GHGI by 13.5%, 20.7%, 14.4% and 25.0%, respectively. Addition of CP significantly increased the peak value of NH4+-N concentration in surface water and NH3 volatilization rate, and thus enhanced NH3 volatilization loss. Addition of NBPT/NPPT or combined with CP effectively reduced the peak value of NH4+-N in the surface water and NH3 volatilization rate, and thus mitigated NH3 volatilization loss. On the other hand, CP significantly decreased NO3--N concentration of the leachate, and significantly reduced the peak of N2O emission flux, and CH4 and N2O emissions. CP or combined with NBPT/NPPT effectively reduced the peak value of NO3--N in the leachate, CH4 and N2O emissions,GWP and GHGI. |
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