| Soil organic carbon(SOC) is an essential component with key multifunctional roles in soil fertility and the biggest organic carbon pool in the terrestrial ecosystem. The balance of soil organic carbon dynamic is not only a direct impact on soil fertility and food security in cropland, but also closely related to global climate change. The factors of climate, soil properties and management measure have different functions on the balance of soil organic carbon. However, we don’t know that the functions of different factors on the balance of soil organic carbon are the same or not. Among these different factors, a fertilization measure is the important factor influencing the dynamic of soil organic carbon in cropland. Soil sequestration efficiency, unit integrated by the carbon input after a certain time turn into the amount of soil organic carbon, is a index of soil organic carbon dynamic changes. The differences of soil carbon efficiency and influence factors in Chain are still a challenge that is yet to be fully resolved.For these scientific problems, publications were searched by using Web of China Knowledge Resource Integrated Database, Wan Fang Database, Science Direct and Springer link with the three keywords “2000-2014”, “Soil organic carbon”, “China” and “Aggregate fractionation(<53 μm)”. A data set was set up with901 pairs of data from 111 published papers that reported soil organic carbon and fractionation. Long-term fertilization experiment in Chain in capacity and characteristics of mineral associated soil organic carbon, effect degree of fertilization practices and soil carbon sequestration efficiency of different particle-size fractions and bulk soil were examined using establish a corresponding database and integration of data analysis(Meta-analysis). The study not only can enrich the basic theory of soil organic carbon cycle, but also improve soil fertility; increase food production and increase carbon sink as well as control air temperature in China. The major findings obtained were as follows:1. MOC is unsaturated and can be further enhanced both in cropland and grassland soils. Therefore, the fine soil particles(<53 μm) from cropland and grassland still have a high carbon sequestration potential.. The median value of total SOC content and MOC were significantly different among the three land uses. There were significant positive correlations between total SOC and MOC in the three land uses. The proportion of MOC in cropland(74.8%) was significantly higher than those in grassland(67.8%) and forest(70.3%) soil. It was also found that the proportion of MOC varied significantly according to land use and soil classification. Regression analysis showed that the proportion of MOC decreased significantly with the increase in total SOC in black soil, paddy and brown soils, which was relatively high in SOC content. The MOC content was significantly correlated with the fine soil particles(<53 μm) in cropland, grassland and forest, indicating the MOC saturation degrees were 68.4%, 58.7% and 91.5%, according to Six(2002) estimation, respectively.2. Applying organic fertilizer including chemical fertilizers combined with organic manure has a great significance to the accumulation and sustainable management of soil organic carbon and fertility, especially for mono-copping system and sandy soil. Compared with no fertilizer treatment, fertilization practices significantly increased soil total and mineral associated organic carbon content by 39.4% and 27.7%, respectively. The increasing rate of applying organic manure(58.4% and 41.9%) was 3.4 and 5.2 times higher than that of chemical fertilizers application(13.4% and 8.0%), respectively. Generally, the effect degree of fertilization practices on the total soil and mineral associated organic carbon was significantly different among cropping systems, cropland uses, and soil textures. The effect size of organic manure application on total soil organic carbon(58.5%) and chemical fertilizers application on mineral associated organic carbon(10.7%) with mono-cropping were significantly higher than that with double cropping(55.6% and 7.3%), whereas there was no significant difference under chemical fertilizers application on total soil organic carbon(13.3% ~ 13.8%) and organic manure application on mineral associated organic carbon(42.6% ~ 43.5%) between these two cropping systems. For different cropland uses, the application of organic manure and chemical fertilizers in upland resulted in significantly higher increased rate(15.8% and 59.7%) than that in paddy fields(10.0% and 43.3%) on total and mineral associated organic carbon. However, application of chemical fertilizers did not significantly increase total or mineral associated organic carbon content in paddy field. As for soil textures, the increased rate of applying organic manure on total soil organic carbon(64.4%) and that of chemical fertilizers on mineral associated organic carbon(15.6%) in sandy soil with low content of soil organic carbon were significantly higher than that for loam and clay soil, whereas there was no significant difference for that between loam and clay soil with a mean value of 8.0%.3. Application of manure is not only an important practice for soil carbon sequestration, but also an optimal management to improve physical structure of red soil. Compared with no fertilizer treatment, fertilization practices significantly increased soil total and mineral associated organic carbon content. The increasing rate of applying organic manure(58.4% and 41.9%) was 3.4 and 5.2 times higher than that of chemical fertilizers application(13.4% and 8.0%), respectively. Generally, the effect degree of fertilization practices on the total soil and mineral associated organic carbon was significantly different among cropping systems, cropland uses, and soil textures. The effect size of organic manure application on total soil organic carbon(58.5%) and chemical fertilizers application on mineral associated organic carbon(10.7%) with mono-cropping were significantly higher than that with double cropping(55.6% and 7.3%). For different cropland uses, the application of organic manure and chemical fertilizers in upland resulted in significantly higher increased rate(15.8% and 59.7%) than that in paddy fields(10.0% and 43.3%) on total and mineral associated organic carbon. However, application of chemical fertilizers did not significantly increase total or mineral associated organic carbon content in paddy field. As for soil textures, the increased rate of applying organic manure on total soil organic carbon(64.4%) and that of chemical fertilizers on mineral associated organic carbon(15.6%) in sandy soil with low content of soil organic carbon were significantly higher than that for loam and clay soil, whereas there was no significant difference for that between loam and clay soil with a mean value of 8.0%.4. Soil organic carbon sequestration efficiency under long-term fertilization exist spatio-temporal difference of agriculture in China. It is driven by many factors. The median and variability of soil C sequestration efficiency decreased significantly with time at the experimental duration in our study. The relationships between soil C sequestration efficiency and time could be fitted by a negative exponential model. The maximum value of soil C sequestration efficiency was about 44. 6% in these studied soils. The average soil C sequestration efficiency was only 10.9% and fell about four times compared to the maximum value over 30 years. A total of 70.3% of the soil C sequestration efficiency variations could be explained by these selected variables. Interestingly, we also found that experimental duration explain about 43.4% of the variation of soil C sequestration efficiency and more than half of total explanation variables. The decreasing coefficient of soil C sequestration efficiency with time was significantly different in different climate zones, land uses and soil types in China. In different soil types, the median of soil C sequestration efficiency change rate were similar. The three most important regulating parameters of soil carbon sequestration efficiency in 20 th years were mean accumulated temperature, nitrogen input, and silt content. In addition, stepwise multiple regression analysis showed also that mean accumulate temperate were main factor that affect the change rate of soil C sequestration efficiency. Generally, there were significantly strong correlations were found between soil carbon sequestration efficiency with changes in soil C/N ratio and soil P availability for all sites at the duration of 20 years. |
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