Effects Of Agricultural Management Changes Towards Soil Organic Carbon Of Upland In Northern Jiangsu Province Based On 1:50000 Soil Database

As a major food production area in China, it was a vital role that studing the dynamics change of agriculture soil organic carbon pool in Huang-Huai-Hai region to improve soil fertility and make polices of carbon sequestration and mitigation CO2 emissions. The study utilized the DNDC (DeNitrification and Decomposition) model, which was relatively mature in modeling biogeochemical process, to simulate soil organic carbon (SOC) dynamics based on specified and common of the 14 agricultural management practices scenarios in IPCC report from 2010 to 2039 of the upland in the 29 counties (or cities) in northern Jiangsu Province, a part of Huang-Huai-Hai region, which systematically analyze the variations of SOC in the whole region, differences of soil groups and administrative under different agricultural management practices. The results would provided scientific evidence for making the reasonable strategy for farmland management and carbon sequestration in Huang-Huai-Hai region. The main research conclusions were as follows:1、 Scenario analysis of the traditional agricultural management of upland in the northern Jiangsu Province from 2010 to 2039 showed that, the average annual carbon sequestration rate(dSOC) under the current agricultural management was 355 kg C hm-2 y-1, with the total SOC increase of 41.75 Tg C. With the average annual carbon sequestration rate of fluvo-aquic soil, saline soil, cinnamon soil, lime concretion black soil, purplish soil and brown soil were almost above 300 kg C hm-2 y-1; while lithosols soil and limestone soil almost were below 210 kg C hm-2 y-1; furthermore, the different counties (or cities) turned out the "carbon sink" effect in the whole region. Therefore, the current agricultural management practices were good for carbon sequestration of the region.2、Scenario analysis of upland in the northern Jiangsu Province from 2010 to 2039 showed that, the whole region turned out "carbon sink" effect. When at no nitrogen fertilizer application and fertilizer nitrogen application rates were 0.5 times of the traditional level scenarios showed a relatively-slower carbon sequestration rate, the average annual SOC changes were 59 kg C hm-2 y-1 and 259 kg C hm-2 y-1, the total SOC changes were 6.93 Tg C and 30.47 Tg C, respectively; while at fertilizer nitrogen application rates were 1.5 and 2.0 times of the traditional level; the application rates of organic manure increased at 2.0,3.0, and 4.0 times than the traditional management scenarios, the rate of crop residue incorporation increased from the traditional management 15%) to 30%,50% and 90%, type 1 of recommended management practices(30% of crop residue incorporation and manure), type II of recommended management practices(50% of crop residue incorporation and manure), type III of recommended management practices(90% of crop residue incorporation and manure) scenarios showed the high carbon sequestration rate, whose average annual SOC changes were between 381 kg C hm-2 y-1 to 1317 kg C hm-2 y-1, and the total SOC change varied from 44.89-155.11 Tg C. Taking as a whole, the order of "carbon sink" effect contribution rate under different agricultural management practices in the northern Jiangsu Province showed:type III of recommended management practices>crop residue incorporation 90%> type Ⅱ of recommended management practices>crop residue incorporation 50%>3.0 times of organic manure fertilizer>type I of recommended management practices>2.0 times of organic manure fertilizer>crop residue incorporation30%>1.0 time of organic manure fertilizer>2.0 times of nitrogen fertilized 1.5 times of nitrogen fertilizer>0.5 times of nitrogen fertilizer>no nitrogen fertilizer. Therefore, to appropriately formulate the measures, we can use reasonable nitrogen fertilizer, increase organic manure fertilizer and crop residue incorporation for carbon sequestration potential for upland soils in the northern Jiangsu Province.3.. The simulation results of different soil groups of upland in the northern Jiangsu Province from 2010 to 2039 indicated that, fluvo-aquic soil, saline soil, cinnamon soil, lime concretion black soil, purplish soil and brown soil would all exert strong "carbon sink" effect in different agricultural management practices, with average annual SOC changes between 47 kg C hm-2 y-1 to 1356 kg C hm-2 y-1, and the total SOC change varied from 0.02 Tg C to 84.09 Tg C. Relatively speaking, lithosols soil and limestone soil would exert weak "carbon source" effect at the no nitrogen fertilizer scenario, with annual emissions of organic carbon were-38 kg C hm-2 y-1 and -3 kg C hm-2 y-1, and the total carbon release were-0.008 Tg C and -0.006 Tg C, respectively; the average annual SOC changes of lithosols soil and limestone soil were varied from 83-983 kg C hm-2 y-1, and the total SOC change varied greatly from 0.02 to 1.71 Tg C. So we could see that, the agricultural management practices were conducive to accumulate soil organic carbon in addition to the lithosols soil and limestone soil at the no nitrogen fertilizer scenario, it also showed that taking the reasonable measures may have great effectively role in accumulating soil organic carbon in the region.4、The simulation results of different coutries (cities) in the northern Jiangsu Province from 2010 to 2039 showed that, the average annual SOC changes at different agricultural management practices were between 65 kg C hm-2 y-1 to 1356 kg C hm-2 y-1 in Xuzhou, Lianyungang, Suqian, Huaian and Yancheng cities, with the total SOC change varied from 4.05 Tg C to 84.09 Tg C. For the spatial distribution, the Guannan and Gunyun cities, located in the northern part, experiences the greatest carbon sequestration rate in the region at different agrictulture managements; whileas, the Xuyi, Dongtai, Jinhu and Yancheng cities, located in the north-central parts, witnesses the lowest carbon sequestration rate. Obviously, except from Xuzhou and Jinhu cities could exert "carbon source" effect at no nitrogen application scenario, while other cities all exerted "carbon sink" effect at agricultural management scenarios. Overall, the differences counties (or cities) in northern Jiangsu Province were totally different in carbon sequestration rate and potential. So it could be imperative to appropriately formulate the measures of carbon sequestration and mitigation CO2 emissions according to the priority target and administrative units in the region.5、Analysing the affected factors for the changes of soil organic carbon in the northern Jiangsu Province, the initial soil organic carbon and clay content could interpret the variation of average annual dSOC form 13.7%-44.8% and 17.4%-39.2% at the different agricultural management, which was higher affection than bulk density and pH. Climatic factors of temperature and precipitation showed significant negative correlation with the average annual SOC changes at the levels of p< 0.01. So increasing temperature and precipitation would make the negative impacts on soil organic carbon sequestration. Therefore, it was necessary for the model application to ensure the accuracy of the initial organic carbon and clay content parameters in the region and also should improve the accuracy of climate datas.