The Rule Of Temporal And Spatial Distribution Of Soil Organic Carbon Of Cropland And Its Influencing Factors In China

Soil organic matter is the core of soil fertility, and it is an important component of soil, while the soil organic carbon is only part of the total weight of soil organic matter of cropland, but in terms of soil fertility, environmental protection and sustainable development of agriculture it plays a very important role and significance. Since the founding of new China, China carried out 3 large-scale soil survey work. The first soil survey work was from 1958 years, was based on the character of agricultural soil, and put forward the first national agricultural soil classification system. The second soil survey work was from 1979, was based on soil conditions, soil and soil properties for the classification, the soil type, subtype, soil, soil types, varieties and 5 grade classification. The third soil survey was carried out was from 2005, national financial subsidies to the national scope of soil testing and fertilizer projects in China. All agricultural county soil and fertilizer sector in the local field, vegetable field, orchard collected a large number of soil samples were tested, including soil organic carbon, total nitrogen, available phosphorus, available potassium, pH and so on, in order to reveal the law of soil organic carbon change, the main results and conclusions are as follows:At the regional scale, the impact of soil organic carbon dominant factor is micro regional factors, such as topography and cropping system, soil parent material, vegetation, altitude. But on the macro scale, many micro factors may not be the main factors influencing the distribution of soil organic carbon of cropland. This paper sorts out the basic data for the first time the soil survey, second soil survey and national fertilization project set on the large scale temporal and spatial distribution of soil organic carbon, discusses the natural factors(annual average temperature, annual average precipitation, longitude, latitude, altitude, climate change the nature of soil(pH), and soil clay structure, cation exchange capacity etc.) and human factors(chemical fertilizer, grain yield, total population, straw) influence of main factors on the content and distribution of organic carbon in soil, in order to provide theoretical basis for government departments to formulate relevant policies in order to reveal the soil organic carbon the evolution of the law, and the main results are as follows:1. According to the longitude in every 10 degrees of latitude, every 5 degrees, the national planning for 37 plate, on each plate in 60 years of soil organic carbon of cropland change situation were analyzed, the results showed that the, in past 60 years, North China region and the central region of soil organic carbon content of cropland showed increasing trend, and northeast China soil organic carbon content of cropland decreased significantly.2. The first soil survey, the second soil survey and test of formula fertilization by soil showed that, the macro level, the latitude and annual average temperature distribution of soil organic carbon has a important influence, soil organic carbon content and mean annual temperature reduce showed increasing trend with increasing latitude, longitude and mean annual precipitation on soil organic carbon has certain influence. In the east to Northeast China and Western China, soil organic carbon content of cropland during annual average temperature has reduced the increasing trend, in the Northern China, soil organic carbon content with the average annual precipitation decreased and showed decreasing trend; Soil organic carbon content present a decreasing trend with pH increasing, present a parabolic trend of first increased and then decreased with altitude increasing, with silt and clay content gradually increased.3. The results soil testing Formula fertilization show that, at 10℃ within the region less than for annual average temperature, soil organic carbon content and annual average temperature correlation good correlation with mean annual precipitation, at 10℃ to 20 ℃within the region, soil organic carbon content and average annual precipitation correlation good correlation with annual average temperature, in more than 20℃ area, soil organic carbon content of cropland and average annual precipitation and annual average temperature of correlation are very poor. But partial correlation results show that within the area of 10℃ to 20 ℃, soil organic carbon content although with annual mean temperature and annual mean precipitation have significant positive correlation, but soil organic carbon content and average annual precipitation correlation is greater than and annual mean temperature correlation, the average annual rainfall of only is soil organic carbon of cropland distribution in the dominant factor. In the 0-200 mm average annual precipitation in the region, soil organic carbon content and average annual precipitation have significant correlation, but the correlation with the annual mean temperature is poor, average annual precipitation played a major driving forces. In the regional range of 200-400 mm average annual precipitation, 400-600 mm, 600-800 mm, better correlation between soil organic carbon content and the annual average temperature of in correlation with mean annual precipitation, mean annual temperature major driving forces. Especially within the scope of between 400 and 800 mm area in semi humid area, soil organic carbon content and the annual average temperature of significant relationship, correlation coefficient R=0.7430. In average annual precipitation is greater than 800 mm region, soil organic carbon content and annual mean temperature and annual mean precipitation of are very poor.4. The amount of straw returned to the field of data is not comprehensive, but this study analyzed the 2004-2011 mechanical straw to field area and the amount of agricultural straw crushing and returning machine has a very significant correlation. On the macro level, using the number of China from 1990 to 2011 of mechanized straw returning machine, calculated from 1990 to 2011 straw returning area, in-depth analysis of the straw returning area and soil organic carbon content. The results showed that, in past 20 years, 31 provinces in China, there are nearly 50% of the province’s soil organic carbon content of cropland showed an increasing trend, while the northeast region of soil organic carbon content of cropland decreased more significantly. On the macro level, the change rate of straw returning to field area has significant correlation with the change of soil organic carbon in the 0.05 level. 2011 mechanization of straw mulching area of the average is 2.92 times in 1990, but compared with the national crop sown area, the proportion of the area of straw to field of our country is very low, only 16.89%.On the macro level, the climate condition is affecting the soil organic carbon of cropland distribution an important external factor, soil organic carbon pool is not an isolated ecological system, various factors influence soil organic carbon pool of natural factors and human factors in the although exist between each other closely linked, but human factors as affecting the soil carbon of cropland pool changes the dynamic factors, in a certain period of time can exceed the natural factors as the dominant factor affecting regional soil organic carbon pool change. This study will further reveal the change of farmland soil organic carbon and elucidate the natural factors and human factors on effect of soil organic carbon, for reasonable development of farmland soil management policy, promote soil carbon fixation provides scientific basis.