| Puding County of Guizhou Province was selected as the study area in the paper. Based on the data of the measured field sampling in2011and the second soil survey data in1980, and the soil utilization map of Puding County、soil type map of Puding County were collected. The soil organic carbon database of0-20cm and0-100cm layer of soil were established according to using ArcGIS software. Soil organic carbon storage of0-20cm and0-100cm layer of soil in cropland in Puding County was estimated. The accumulation of soil organic carbon pool in different soil types of cropland was analyzed. The variation of soil organic carbon pool in cropland during past30years was revealed, and the carbon sequestration potential of farmland was predicted. Combined the field survey data, the main effect factors of soil organic carbon pool of Puding County was analyzed. Meanwhile, the main measures of agricultural production of land sustainable utilization and further stability improve soil organic carbon stock for cropland in Puding County were discussed. The main results were as follows:(1) SOC density of the cultivated horizon (0-20cm) in cropland in Puding County was4.90kg/m2. SOC density of paddy field was6.53kg/m2and SOC density of dry land was4.30kg/m2. The order of SOC density of the cultivated horizon (0-20cm) in different soil groups were paddy soil (6.53kg/m2)> mountain yellow brown soil (5.53kg/m2)> alpine shrub meadow soil (4.98kg/m2)=alluvial soil (4.98kg/m2)>calcareous soil (4.40kg/m2)> purple soil (4.26kg/m2)> yellow soil (4.19kg/m2). Among them, the SOC densities in three kinds of soil (calcareous soil, yellow soil and purple soil) were lower than the average lever of Puding County. SOC density in0-100cm layer of farmland in Puding County was15.88kg/m2on average. The highest SOC density in0-100cm layer of different soil groups was paddy soil (24.96kg/m2). Alluvial soil, mountain yellow brown soil and alpine shrub meadow soil, which were also higher and more than15.00kg/m2. The lowest density of SOC was calcareous soil (12.03kg/m2).(2) The SOC storage in0-20cm layer of cropland in Puding County was2707.89×109g. SOC storage in0-100cm layer of soil was8775.29×109g. In0-20cm soil layer, SOC storage in paddy field and in dry land were975.17×109g and1732.72×109g, both accounted for36.0%and64.0%of the total SOC storage in0-20cm layer of cropland in Puding County. Moreover, in0-100cm soil layer, SOC storage in paddy field and in dry land accounted for42.49%and57.51%of the total SOC storage in0-100cm layer. Thus, the distribution area of paddy field accounted for only27.02%of the total area, but the SOC storage of0-100cm layer accounted for nearly1/2. So the paddy field is the most important SOC pool in Puding County and is the focus of increasing and sequestration of carbon. For SOC storage in0-20cm layer and0-100cm layer of different soil types, the SOC stocks of paddy soil, yellow soil and calcareous soil were higher. And the sum of SOC stock of which accounted for97.25%of the total SOC storage in0-20cm layer, and accounted for97.49%of the total SOC storage in0-100cm layer. Therefore, paddy soil, yellow soil and calcareous soil are the main objects for implementation measures to improve SOC content of cropland in Puding County.(3) The SOC storage capability of paddy soil was the strongest in0-20cm layer of soil, and yellow soil was the weakest. Considering SOC storage capability in0-100cm layer of soil, Paddy soil was obviously stronger than any other soil especially calcareous soil. The SOC storage capacity of soil in different soil genus was different. The SOC storage capacity of the soil genus for rust poison field, cold soak field and mud duck feces field was higher than200.00in0-20cm layer of soil. And SOC abundance was lower than55.00in the soil genus of slope rim loess field, white cement field, white eel mud field and purple sand soil. The highest value still appears in paddy field, while yellow calcareous soil was the lowest, the SOC abundance of which was only38.38in0-100cm layer soil. Therefore, as the most widely distributed soil in Puding County, calcareous soil and yellow soil were the main objects for implementation measures to improve carbon sequestration of cropland.(4) Since1980, nearly30years of human disturbance had a good effect to SOC accumulation of cropland in Puding County. The SOC storage of0-20cm layer and0-100cm layer of cropland showed an increasing trend, which were increased0.95%and47.16%. For soil groups, the SOC storage of alluvial soil, yellow soil and paddy soil showed an increasing trend and played a "carbon sink" effect in0-20cm soil layer, in which SOC stock of paddy soil was most increased, up to218.96x109g. while SOC stock of calcareous soil decreased of the maximum. In0-100cm soil layer, increased of SOC storage was due to three types of soil (paddy soil, yellow soil, and calcareous soil), and which SOC storage added value accounted for the proportion of total SOC storage added value in0-100cm soil layer of Puding County was53.83%,32.01%and17.19%.(5) Taking SOC density and storage in2011for basic point and maintaining the present land area, SOC density potential in0-20cm soil layer was2.13kg/m2, and the SOC storage potential the same depth was1177.88×109g. In addition, SOC density potential in0-100cm soil layer was3.60kg/m2, the SOC storage potential was1990.80×109g. It showed that there was a potential of SOC sequestration of cropland in Puding County. For soil groups, there was relatively rich potential in the follow soil group to increase SOC storage, yellow soil, calcareous soil, and paddy soil. The potential of SOC sequestration for yellow soil and calcareous soil accounted for the total SOC sequestration potential was49.0%,41.05%in0-20cm soil layer of Puding County. The potential of SOC sequestration in0-100cm soil layer mainly existed in yellow soil and calcareous soil. In terms of soil genus, the greatest potential of SOC sequestration in0-20cm soil layer was gathered white cement field, white eel mud field and purple sand soil. And secondary yellow calcareous soil had the highest potential in0-100cm soil layer.(6) This study found that no significant difference for the SOC density in different altitudes in Puding County, which indicated that altitudes was not the main factor for SOC density of cropland in Puding County. While the slope and SOC density was highly significant negative correlation (p <0.01), showed that gentle slope was beneficial to the accumulation of SOC. SOC density and available phosphorus (AP), total nitrogen (TN), total phosphorus (TP), C/N, silt-content were showed a highly significant positive correlation (p<0.01); SOC density and gravel volume, sand-content were a significantly negatively correlated (p<0.05). The order of SOC density in different cropping systems and different crops were Double-crop (rice-rape)> One-crop (rice)> Double-crop (other)> One-crop (corn)> Double-crop (corn-rape). After the analysis of SOC density and different types of fertilizer, the amount of straw returned, this indicated that there was a significant positive correlation (p<0.05) between SOC density and organic fertilizer. The result showed that applying more organic fertilizer was conducive to the accumulation of SOC. Through a comprehensive analysis of all the factors including terrain factors, soil physical and chemical factors, and factors such as farm management measures and so on, that can be considered preliminary the indicators of total nitrogen (TN), carbon to nitrogen ratio (C/N), gravel volume ratio (9) and soil bulk density (pb) were very important factors affecting agricultural soil organic carbon in Puding County. |
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