The Study Of Inhibitory Effect And Mechanism Of Nitrification Inhibitor DMPP

Urea is widely used in agricultural production as a convenient source of nitrogen. However, when applied to soil, urea has been reported to have low N response efficiencies due to volatilization, nitrification, denitrification, erosion, runoff, and leaching. Previous studies indicate that nitrification inhibitors are useful in improving N use efficiency which can inhibit the oxidation of ammonium. Nitrification inhibitors have also been shown to be effective in reducing nitrate leaching and nitrous oxide emissions. More recently, the nitrification inhibitor,3,4-dimethylpyrazole phosphate (DMPP), has become available and was reported can be used at low application rate with high efficiency, and is also environmentally friendly.The objective of this study was to determine the inhibitory effect of DMPP on particular soil. The effect of DMPP on soil microbes and soil enzymes were also examined in order to demonstrate the mechanism of DMPP on nitrification inhibition. The outcome of this research may help formulate management decisions that aid in improving N application efficiency.The results of this research are as follows:The effect of nitrification inhibitors3,4-dimethylpyrazole phosphate (DMPP) on soil nitrogen transformation in different soils was investigated in a laboratory incubation experiment. During the incubation, soil pH and NH4+-N increased at the beginning of the experiment and then decreased, soil NO3--N and the apparent nitrification rate (ANR) increased throughout the incubation process. The concentration of NH4+-N and the soil pH were significantly higher in the treatments with DMPP compare to the urea-only treatment, which also possessed low concentration of NO3--N and low ANR. In the treatments of paddy soil and fluvo-aquic soil, nitrification was observed from the urea-only treatment until day14. After the addition of DMPP, this process was extended to28days. Nitrification was also found to be slower in black and red soils compare to paddy and fluvo-aquic soils, especially in red soil. The addition of DMPP affected the soil ANR, but this effect was found to be as strong in paddy and fluvo-aquic soils.The effect of the nitrification inhibitor3,4-dimethylpyrazole phosphate (DMPP) on N transformations and composition of ammonia-oxidizing bacteria (AOB) communities was investigated, at centimeter scale in a microcosm experiment under laboratory conditions. After28days samples were collected from soil treated with urea or urea and DMPP at increasing distance from the fertilizer zone; this distance ranged from0to5cm in both horizontal and vertical directions. The results showed that DMPP application significantly increased soil pH, NH4+-N and mineral N (NH4+-N, NO3--N and NO2--N) concentrations but decreased (NO3-+NO2O-)-N concentration and such effect was decreased by increasing the distance from the fertilizer zone. Fingerprint profiles of denaturing gradient gel electrophoresis (DGGE) showed that the number of bands decreased by increasing the distance from the fertilizer zone due to decreasing NH4+-N concentrations in the urea treatment. Compared to urea applied alone, DMPP application increased NH4+-N concentrations and decreased AOB diversity from0to3cm but promoted diversity from3to5cm distance from the fertilizer zone. A phylogenetic analysis showed that the AOB communities were dominated by Nitrosospira cluster3. Therefore, the nitrification inhibitor DMPP modified the composition of AOB communities by increasing the distance from the fertilizer zone and this probably was related to the changes in soil pH and inorganic N concentration.Nitrification was delayed due to the inhibitory effect on the reproduction of AOB when DMPP was applied. Although the addition of DMPP significantly decreased N02--N and N03"-N concentrations, and increased the soil pH and NH4+-N concentration, no significant effect was observed on the AOB community structure. Based on the RT-PCR results, the quantity of AOB was significantly lower in the DMPP treatments compared to the urea-only treatment.Compared to the urea-only treatment, no significant effect was observed on urea hydrolysis and the prosess of nitrate reduction to ammonium when the DMPP was added. There was no significant difference in the activity of soil urease, nitrate reductase, nitrite reductase and hydroxylamine reductase between different DMPP application rates.The addition of DMPP significantly reduced the emission of N2O and CO2compare to the urea-only treatment, however, ammonia volatilization was increased during the incubation period due to the high concentration of NH4+-N inside the soil. The same trends of N2O and CO2emissions were observed from different treatments of soil. In the urea-only treatment, N2O and CO2peak emissions were observed in the first week, whereas N2O and CO2peak emissions in the DMPP treatments occurred after20days of incubation. The cumulative emissions of N2O or CO2were significantly lower in the DMPP treatments compared to the urea-only treatment. There was no significant effect of DMPP application rate on ammonia volatilization. However, N2O and CO2emissions were increased when the DMPP application rate was lower than1%. Hence, we suggested that1%of N is the best application rate of DMPP.