Basic Properties Spatial-temporal Variation And Heavy Metal Environmental Risk Assessment Of Calcic Black Soil In Henan Province

Soil is the most basic and important natural resource to human survival. Basic properties of soil are important indexes for soil fertility evaluation, affecting the level of crop production, and the soil environmental quality and safety have a Close relationship to the heavy metal risk grades. Basic properties spatial-temporal variation and heavy metal pollution risk assessment of calcic black soil in Henan province are studied through outdoor sampling and indoor determination by the special project funding of national science and technology basic work. The following conclusions are obtained:(1) The main texture is silt loam for calcic black soil, the top soil average pH value declines from 7.8 to 6.9 with the lowest variable coefficient above 14.2%. The average CEC value declines 1.13 cmol/kg and the variable coefficient is 39.8%. The average content of the upper soil organism and total nitrogen rises from 12.6g/kg and 0.83 g/kg to 13.11 g/kg and 1.2 g/kg over time, the average content of the upper soil available phosphorus show an obvious increasing trend with average value increasing from 4.8 mg-kg-1 to 33.6 mg·kg-1 and the highest variable coefficient at 71.2%. the rapidly available potassium average content increases 51.3 mg·kg-1 and the variable coefficient is 44.8%.Basic causes of these changes due to natural factors and human factors. The human factors are mode change of land management, straw returned and fertilization, etc.(2) The calcic black soil surface pH and total nitrogen contents are similar in different areas. Besides of Zhoukou, soil surface CEC content in three other areas are basically identical. The surface soil organic matter contents vary from 8.9 g/kg to 24.3 g/kg.The maximum contents of available phosphorus and rapidly-available potassium are respectively 42.7 mg/kg in Xuchang and 255.3 mg/kg in Nanyang while the minimum of those are respectively 15.4 mg/kg in Zhoukou and 141.7 mg/kg in Zhumadian.(3) The calcic black soil pH values keep unchanged along with the profile down, Soil CEC and rapidly-available potassium contents are different in different regions with different profiles. Soil organic matter and available phosphorus contents are declining in the profile from top to bottom, and the trend of the total nitrogen contents remains a generally slow decline.(4) soil Hg, As are excess levels with 50% and18.2% respectively, Cd, Cr, Cu, Ni, Pb, zinc are under standard. The calcic black soil heavy metals pollution rank is Pb(0.070)< Cu(0.130)< Cr(0.328)< Zn(0.392)< Cd(0.401)< Ni(0.520)< As(0.806)< Hg(1.743) with single factor pollution index evaluation method. By the Nemerow comprehensive pollution index, the maximum value is 5.273, the minimum value is 0.438 and the mean value is 1.506. There is a sample belongs to strong risk level, four samples belong to medium level of risk, the others all belong to slight risk level by Hakanson potential ecological risk evaluation method. Eir, the single factor potential ecological harm coefficient, is Pb(0.350)< Zn(0.392)< Cu(0.650)< Cr (0.656)< Ni(2.601)<< As(8.059)< Cd(12.018)<< Hg(69.707). The calcic black soil heavy metals pollution rank is Pb(-0.97)< Ni(-0.75)< Cu(-0.62)= Cr (-0.62)< Zn(-0.25)< Cd(0.04)< As(0.21)< Hg(1.99) by the geo-accumulation index evaluation. Pb is no pollution, Hg pollution frequency is 90.9%, As is 63.6%, Cd is 59.1% and others are under 20%. The calcic black soil in the study area is low risk level by the methods of single factor pollution index evaluation, Nemerow pollution index evaluation, Hakanson potential ecological risk evaluation and the geo-accumulation index evaluation.