Dust Emission From Farmland Of Lou Soil And Authentication Of DPM Model

The urban air quality was adversely affected by dust emitted from farmland surface of countryside, and the particle pollution was intensified. Moreover, soil productivity was declined by the wind erosion of farmland surface, and the sustainability of farmland using was also undermined. DPM (Dust Production Model) model was mainly used for large-scale of the simulation of dust emission, but in the medium and small-scale was not been verified.The aerodynamic roughness length and threshold frictional velocity of farmland surface at different crop growing stage (earing stage, nudity stage and reviving stage) were compared in this paper. The result implied that the farmland was a source of dust at the nudity stage of wheat, then the dust emission was observed and the authentication of DPM model was verified at this stage. The parameter scheme for computed dust emission flux was established, and the modification of DPM model which can be used on farmland of lou soil was also discussed. The main findings are as follow:(1) According to the result of soil dry sieving, the micro-aggregates size distribution was can be expressed as a mixture of two lognormal mass size distribution populations, the mass median diameters were 193μm and 619μm, and the standard deviation of them were 1.40 and 1.25, the ratio of the micro-aggregates mass was 19:81.(2) The average value of roughness length in reviving stage, earing stage and nudity stage of wheat were 0.7211cm, 6.0078cm and 0.0797cm, respectively. The range of roughness length at different stages was 0.004～17.929 cm.(3) In case of Z₀= Z_0s, the threshold frictional velocity of the experiment farmland of lou soil was 24.89cm s^-1. The threshold frictional velocity in reviving stage, earing stage and nudity stage of wheat were 46.85 cm s^-1, 98.93 cm s(-1) and 29.05 cm s^-1. (4)The farmland at whest's nudity stage was a source of dust, the measured and computed vertical fluxes were 2～11μg·m^-2·s^-1 and 15～71μg·m^-2·s^-1 respectively, both at the range of 10⁰～10¹Î¼g·m^-2·s^-1. The preliminary results show that the DPM can be applied to predict the dust emission flux in experiment area, and experience parameter C for value of 0.02.(5) The parameter scheme for computed dust emission flux was established, and the modified model of farmland of lou soil at nudity stage:F_h=2．6*10³U^*3·∫_Dp(1+R)(1-R²)dS_rel(D_p)dD_pF_dust,i=4.6*10³d_i³/e_i·∫_Dp^∞p_i(D_p)dF_h(D_p)(6) According to the research, for farmland, the traditional tilling methods should be replaced with no-tillage or shallow-tillage, vegetation covering, and band tilling of muloh cover, for weaking the soil erosion.