| Soil carbon and nitrogen processes play an important role in the budget of atmospheric greenhouse gases, such as carbon dioxide (CO2) and nitrous oxide (N2O). N2O is naturally produced through soil microbial processes of nitrification and denitrification. Certainly, quantifying soil nitrification and denitrification or assessing their relative contribution to soil N2O flux is essential to understand the nature of N2O production in the soil. On the other hand, soil respiration has become one of the hotspots in global carbon cycling field. A study on soil respiration and its components will help to understand carbon cycling processes in agroecosystem. Moreover, exploring the possible relationship between carbon and nitrogen processes in the soil will be an important aid in the processes of CO2 and N2O production.In this study, a BaPS (Barometric Process Separation) system was introduced to measure soil respiration rate, gross nitrification and denitrification rate in the wheat, soybean and maize fields. As a new technique determining soil carbon and nitrogen transformation, the BaPS worked under the theory that in a closed, isothermal system, the gross nitrification, denitrification, soil rerspiration rate can be calculated from the balances of O2, CO2, and the total gas amount. Intact soil cores from winter-wheat, maize, and soybean fields were sampled through three successive growing seasons to determine the gross nitrification, denitrification, respiration rate. Meanwhile, CO2 and N2O concentration in headspace of the BaPS system was simultaneously detected by a gas chromatograph (GC/Agilent4890D) to verify the result from the BaPS technique. Soil parameters and biological parameters were determined by routine method. The objective of this study was to explore the seasonal dynamics of soil nitrification-denitrification, soil respiration dependent on crop root development and agricultural practices, and to exercise their possible relationships under different agricultural management.The effect of tillage and previous crop type on nitrification-denitrification was studied during wheat-growing season. Nitrification rate depended on soil temperature over the entire wheat-growing season. In contrast with the conventional tillage, no-tillage increased soil nitrification, but decreased soil NH4+-N and NO3--N content. Compared with the previous crop type of soybean, rice planting in the previous season accelerated soil nitrification-denitrification rate in the following wheat season.Seasonal dynamic of nitrification rate in soybean and maize fields was closely associated with soil moisture. The optimal range of soil moisture to soil nitrification was estimated to be 30~50%WFPS (Water-filled-pore-space). Soil nitrificaion rate in the rhizosphere increased with crop root development, which produced a linear relationship between them over the entire season.Nitrification contributed 88.3% to soil N2O flux of wheat season. Similarly, N2O was primarily produced through nitrification in the soybean and maize growing season. Soil N2O emissions were significantly affected by precipitation event, which gave rise to soil moisture as an important factor to N2O emissions. Soil N2O flux peak occurred at high soil mositure. When N2O flux is less than 2.0 μgN·kg-1·h-1, however, it was exponentially correlated with soil nitrification rate. On the other hand, soil N2O flux was higher in the rhizosphere than in the non-rhizosphere, suggesting that crop root involvement favor soil nitrification and N2O emissions in the soybean and maize uplands.Seasonal variation of soil respiration rate in the rhizosphere depended obviously on root biomass, while that in the non-rhizosphere was not pronounced. Seasonal soil respiration rate in the rhizosphere averaged 29.8±6.4 mgC·kg-1·d-1 and 70.8±38.6 mgC·kg-1·d-1 for the soybean and maize fields, respectively. In contrast, the soil respiration rate was relatively lower in the non-rhizosphere, with the seasonal average of 14.4±5.1 mgC·kg-1·d-1 for the soybean field and 18.1±8.7 mgC·kg-1·d-1 for...
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