| As the most important part of the terrestrial carbon pools,the fixation capacity of soil carbon sequestration has arisen attention from scholars all over the world.Current research of soil organic sequestration trait on the Loess Plateau concentrated more on the small watershed,less on regional scale.In this study,we used the environmental factor expansion method estimating soil organic carbon sequestration,analyzing the factors affecting the carbon sequestration,defining the rate and potential of the organic carbon sequestration in the regional cropland soil on the Loess Plateau.Moreover,establishing the method for the design of farmland soil sampling in the different landform regions of the Loess Plateau.It can provide a theoretical basis for regional carbon sequestration and agriculture management.The following main progress has been made in the study:1.The spatial distribution of soil organic carbon density in different landform types on the Loess Plateau is obviously different.The high density area of soil organic carbon is distributed in the Fen River Valley(3.41 kg/m~2).The soil organic carbon density in the other geomorphic regions from large to small in turn is Ledu(3.31 kg/m~2),Wugong(2.70 kg/m~2),Pingluo(2.37 kg/m~2),Zhuanglang(2.14 kg/m~2)and Lishi(1.88 kg/m~2)and the Ning County(1.82 kg/m~2),the lowest area is Zhungeer(1.66 kg/m~2).2.The organic carbon density of cropland soil on the Loess Plateau is 2.27 kg/m~2,and the density of organic carbon is concentrated in two numerical intervals of 0-1 kg/m~2 and 1-2kg/m~2,accounting for 43.91%and 38.32%of the whole loess plateau cropland soil,and the farmland soil with organic carbon density greater than 2 kg/m~2 accounts for 17.78%of the farmland soil in the the Loess Plateau.The soil organic carbon storage in the farmland of the Loess Plateau is 445.47Tg.3.The soil carbon sequestration potential of farmland in different landform types of Loess Plateau is significant different.The potential of soil carbon sequestration is the highest(1.30 kg/m~2)in Ledu.The carbon sequestration potential in other geomorphic areas from large to small is Wugong(1.07 kg/m~2),Pingluo(1.00 kg/m~2),Zhungeer(0.67 kg/m~2),Zhuanglang(0.62kg/m~2),Lishi(0.60 kg/m~2)and Fenhe Valley(0.51kg/m~2),the lowest is Ning county(0.44kg/m~2).The soil carbon sequestration potential of farmland soil in the Loess Plateau is 0.65kg/m~2,and the potential soil organic carbon pool of the farmland plough layer on the Loess Plateau is 125.91 Tg,which still has greater carbon sequestration potential.4.The rate of carbon fixation is 86.47 kg/hm~2·a in the highland area.Compared with the results of the second National Soil Census,the proportion of carbon lost farmland is 7.87%and the carbon fixation ratio is 92.13%.The carbon fixation rate of the plain area in the Loess plateau is 190.62 kg/hm~2·a.The average carbon fixation rate in the hilly area is 113.33kg/hm~2·a,the proportion of carbon loss cultivated land area is 26.97%and the carbon sequestration ratio is 73.03%.5.The methods of reasonable sampling design are different in different landform types on the Loess Plateau.A reasonable sampling method for upland area in the loess plateau was considered to be grid sampling design with a suggested grid interval of 4km.The efficiency of the grid sampling design was 64.3%and 31.8%higher than that of random distribution method and joint unit method,respectively.A reasonable sampling method for the plain area of the Loess Plateau was also grid sampling design with a suggested sampling interval of 2km.The efficiency of the grid layout method in the area was 64.8%and 128.8%higher than that of the random distribution and joint unit,respectively.The reasonable sampling method was joint unit layout method in the hilly and gully region of the loess plateau.The suggested density of the joint unit layout method in the area was 1314 hm~2/unit,and the efficiency of the joint unit distribution was 205.8%and 294.2%higher than that of the random distribution and grid distribution,respectively. |
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