Simulation Study In CO₂ Emissions Of Farmland Soil In Loess Hilly-gully Region Based On The DNDC Model

This research use loess hilly-gully region of farmland as the study's area, take the field experiment and the method of combining the mechanism model, the effect of, not coated with test of spring corn under different technologies such as irrigation and CO2 emission flux for the continuous field positioning observation, selecting main corn crop rotation system 9 test under different management methods in the field as the research object, from April to October in 2012 and in April 2013 to October 2013 on crop field management, crop production and soil physical and chemical properties and application situation, and investigate the water quality with basic information such as weather, statistical analysis and measurement.Loess hilly-gully region of this study is to find out the upland soil CO2 emission characteristics, reveals the different farmland management system of the seasonal variation of soil CO2 emission flux and the change rule and influence factors, and through the field measured data to construct the DNDC model, quantitative evaluation of different technical measures the net greenhouse effect, and the dry land of spring corn farmland stable, emissions and carbon sequestration" coordinated management technical measures, the main research conclusions are as follows:(1)Dry farmland soil CO2 emission characteristicsSeasonal variation characteristics:corn farmland soil CO2 flux in the study area under the coated and effect of management measures, is maximum in July (maximum soil solute in different conditions 3.5 ?mol/m2/s, not maximum soil solute in different conditions 2.7 ?mol/m2/s, in August fell rapidly, the growth period were lower and more stable. And compared with the bare land, the area of the emission flux is greater than that of bare land.Daily variation characteristics:farmland soil CO2 emissions in the study area is not obvious, but you can see, generally around 2 o'clock at noon, discharge rate is bigger, coated cases up to 3.1 (?mol/m2/s, without effect of up to 2.1 (?mol/m2/s.Bare land conditions are generally lower emission flux is planting condition.(2)The applicability test modelDNDC model established by using the data of 2012 and validation showed that the DNDC model to simulate the well field of corn growth period of CO2 emission flux and the change of precipitation, air temperature and soil surface temperature, simulated values and measured values are close to. Although the model still has some problems, in loess hilly-gully region in the future on CO2 emissions estimation dryland farming has great application value.(3)Sensitivity analysis of the modelWith the increase of soil temperature, CO2 emission simulation value also increase, with the change of the simulation value and the actual situation; Relative to as the change of soil temperature, rainfall changes caused by CO2 emission flux is lesser, at the same time, the temperature and soil moisture for dry farmland soil CO2 emissions are tiny.(4)The model simulation resultsIn 2013, according to the results of simulation in the maize growing season, coated with no effect of two kinds of management under the condition of dryland corn farmland soil CO2 emissions from 3 leaf stage began to rise gradually, until it reached the highest in the summer autumn falling fast. Effects of soil respiration under the condition of management are up to 3.49?mol/m2/s, not coated management under the condition of up to 4.86?mol/m2/s. This period, farmland show the atmospheric CO2 sink. Farmland soil CO2 flux showed "U" type of daily variation rule, whether or not coated, laminating CO2 emission flux is rising in the morning, and are all reached the highest at 12:00 of the day, the effect of management condition, the largest emission flux is 3.43?mol/m2/s, not coated management under the condition of maximum emission flux is 3.91?mol/m2/s. Bare land condition, whether or not coated, laminating CO2 flux are 1?mol/m2/s near fluctuations, and the effect of conditions, relatively stable, the amplitude is smaller.Maize growing season for carbon sequestration, the growing season for carbon emissions, corn after anthesis to silking stage, the CO2 flux reached the maximum value of the year. NEE starting around 7 leaf stage changed from positive to negative, after reaching maturity and changed from negative to positive, from the point of carbon flux change in dynamic, July and August is the highest peak of net carbon absorption, month uptake respectively 364 g, m-2 and 302 g·m-,2, the maize growing season farmland NEE-666g·m-2; And April and November is the highest peak of carbon released, release quantity respectively 89 g·m-2 and 62 g·m-2, the growing season NEE is 403g·m-2. Maize growing season in the carbon balance of payments is 143.0g·m-2, without considering straw grain use scenario performance for carbon sequestration.