Research On Spatial And Temporal Evolution Of Soil Carbon Sequestration Of Oasis Farmland Ecosystem In Hexi

With the escalation of global warming, in order to explore the strategy of reducing atmospheric concentrations of greenhouse gases, the problem of terrestrial ecosystem carbon cycle and the research of carbon balance of payments has become a hot issue of current global change research. Farmland ecosystem is an important greenhouse gas sources and sinks. On the one hand, through photosynthesis of crops and man-made way to absorb a lot of carbon; on the other hand, crops and soil through respiration, as well as artificial ways indirectly the release of carbon into the process. In addition, the original cultivated land into the process so that the loss of a large number of soil organic carbon. With the increase in intensity farming, the agricultural sector is faced with an increasing number of carbon releases. Therefore, how to take measures to achieve carbon sequestration by agricultural soils sinks become one of the issues to be settled urgently.In this article, from 1949 to 2005 statistics, combined with carbon source / sink model, 4 cities and counties of the Hexi oasis Farmland ecosystem carbon sequestration of soil carbon sequestration potential of the status, the major agricultural crops, under different land use patterns of soil carbon sinks, as well as Farmland ecological carbon sink function of the system cost effectiveness analysis, a preliminary understanding on the large-scale farmland ecosystem in Hexi Oasis of the characteristics of carbon sinks and Hexi oasis farmland ecosystem in reducing the contribution to global warming. Finally, put forward in Hexi oasis farmland ecosystem increasing carbon sinks & emissions reduction strategies. Through research, received the following conclusions:(1) The conclusion of the estimate study Hexi oasis farmland ecosystem soil carbon sequestration potential is:Through the analysis the current situation and sequestration potential of oasis farmland ecosystem soil carbon of 4 cities and counties of Hexi showed that:â‘ soil carbon sequestration per unit area status and the average rate of carbon sequestration in different levels of farming is different. In the application of chemical fertilizers, organic manure, straw and no tillage or minimum tillage and other farming conditions, the soil carbon sequestration per unit area status and the average carbon sequestration rates of 6.65Tg·a-1 and 240.51kg·hm^-2·a^-1, 5.97 Tg·a-1 and 215.91 kg·hm^-2·a^-1, 3.27 Tg·a-1 and 118.26 kg·hm^-2·a^-1 and 7.86 Tg·a-1 and 284.27 kg·hm^-2·a^-1, relatively speaking, less no-tillage farming measures applicable to Hexi.â‘¡in land use patterns, farming measures the level of fertilization and climatic conditions remain unchanged, after years of farm management practices, the soil organic carbon density will reach a new steady state. According to simulation, the region west of the soil organic carbon density in 1989 by the 10.33kg·m-2 to reach a new steady state after 12.31kg·m-2.â‘¢Hexi soil carbon reserves 620Tg by 1989 to reach a new steady state at the time of 740Tg, the potential for carbon sequestration 120Tg.â‘£the density of organic carbon from the soil and its reserves, the carbon density and inter-regional changes in reserves is not very big.The second time during the soil survey, soil carbon density in Hexi District are mainly distributed in Zhangye, followed by Yongchang, Wuwei and Jiuquan; in 2005, Zhangye is still the highest density of carbon, followed by Yongchang, Jiuquan and Wuwei.(2) The conclusion of the estimate study Hexi oasis farmland ecosystem soil carbon sinks is that: Through the analysis oasis farmland ecosystem carbon sequestration, the main crop estimates, different crop changes in ecosystem carbon sinks, as well as agricultural management soil of carbon sinks of 4 cities and counties of Hexi showed that:â‘ farmland ecosystem in Hexi Oasis major contribution to carbon sequestration crop it is corn crops and vegetables, but on specific carbon sequestration, there is a big difference, which is in itself the characteristics of crops and planting of the area.â‘¡in crop-soil system of sources and sinks of CO2 on the relationship between changes, CO2 sources and sinks of the relationship between uncertainty, wheat ecological system is a medium level of carbon sinks; cotton ecosystem is a weak carbon sink; corn ecosystem is a strong carbon sinks; changes in the year, wheat ecosystem in addition to August to September is a weak carbon source, the rest of the month are carbon sinks;cotton, ecosystem in the June to September for carbon sinks, and the rest of the month as carbon source.â‘¢1949²005 years in Hexi oasis farmland ecosystem carbon sequestration was phased growth trends, the total carbon sequestration from 243,900 tons in 1949 to 2,983,700 tons in 2005, a net increase of 2,739,800 tons, an increase of 12.23 times. Carbon sequestration, the basic trend of development shows that the three stages of development: growth of fluctuations in phase (before 1960), the resumption of growth stage (1960 2000) and the rapid growth phase (after 2000).â‘£In 4 cities and counties of the farmland ecosystem effects of carbon sinks, organic and inorganic fertilizers in which the role of a more obvious increase in SOC will enable the 0.81tCha^-1·a^-1, followed by no-tillage, SOC annual growth of 0.62 tCha^-1·a^-1. The effects of straw and organic fertilizer rather, soil organic carbon, respectively, the annual increase of 0.57 and 0.38 tCha^-1·a^-1. With single N,P,K, SOC increased almost can not even play a negative role. Combined application of nitrogen, phosphorus and potassium can only compensate for the loss of soil organic matter mineralization, can not significantly improve its content.(3) The conclusion of the patterns of different land utilization effect on soil carbon sinks is that: From changes in land use and its point of view, on the west of farmland, grassland and woodland reserves of soil organic carbon, ecosystem carbon sink functions of the impact analysis showed that,â‘ bush, Populus davidiana and (Picea crassifolia×Sabina przewalskii) to cropland or grassland, the soil surface (0 50cm) of soil organic carbon content decreased; and in the grass in the fields or to create a larch plantation, the soil surface (0 40cm) of soil organic will increase the carbon content in the soil profile of organic carbon content of the underlying land-use changes by less affected.â‘¡bush, Populus davidiana and (Sabina przewalskii×Picea crassifolia) or grassland into farmland, the decline in soil organic carbon density (35% and 14%); farmland Create a post in the larch plantation, soil organic carbon density will be increased; in the grass to create a larch plantation, the soil organic carbon density is not changed significantly. In addition, after the land-use change, soil organic carbon density than soil organic carbon content of the small magnitude of changes.â‘¢under different land use patterns of soil organic carbon accumulation is different in the 0 45cm soil, grassland soil organic carbon were significantly higher than that of soil organic carbon; in tillage, less tillage and three kinds of no-tillage farming methods, the contribution to soil carbon accumulation of the order is: Reduced tillage> no tillage> tillage.â‘£natural secondary forest ecosystems through land-use change to cropland or grassland ecosystem, the soil carbon storage sinks lower functional strength, stability, and reduced non-stability of exchange, protection and non-protective, the strength of activated carbon sinks will also be weakened. And farmland or grassland ecosystem through reforestation plantation into the ecosystem, the soil carbon storage function of the strength of these sinks will increase.⑤Carbon accumulation in vegetation productivity, the natural secondary forest and plantation ecosystems have a strong sink, and farmland and grassland ecosystem is relatively small. Reserves in the soil organic carbon change, natural secondary forest ecosystem health is strong, and farmland and grassland ecosystem as the source, plantation ecosystem health for the weak.(4) The conclusion of the assessment the function of soil carbon sinks of Hexi is that: By the mathematical model of Hexi oasis farmland ecosystem functions of soil carbon sinks analysis showed that the economic benefits,â‘ 1949 2005 years in Hexi oasis farmland ecosystem carbon sink function of changes in the trend of economic growth was phased, carbon sink function of the economic benefits from 63 million yuan in 1949 to 776 million yuan in 2005, a net increase of 713 million yuan, an increase of 11.32 times.â‘¡Hexi oasis farmland ecosystem carbon sink function of the basic economic trends showing a growth of fluctuations (before 1960), the resumption of growth (1960 to 2000) and the rapid growth of the three stages of development(since 2000).(5) Through the above analysis, the strategies of oasis farmland ecosystem carbon by sinks & emissions reduction of Hexi are that:â‘ The adaptation of farming systems: no-tillage is the least disturbance of soil tillage which can be very effective to improve soil organic carbon.â‘¡Fertilization to improve the way: long-term application of organic manure could significantly increase the activity of soil organic carbon content, inorganic fertilizer organic fertilizer can increase crop yield, and the use of Chemical fertilizers to increase the stability of soil organic carbon.â‘¢Straw: straw is to reduce the carbon emissions of farmland, increasing soil organic matter content in an important way, it can be treated straw as cattle feed, sheep, and then stool after ripening fields, not only can increase the soil organic matter content, but also the development of aquaculture, increase cost effectiveness.â‘£Other measures: such as improved crop varieties, there are plans to have to pay close attention to nurturing high temperature, drought and other extreme weather and pest resistant varieties, to ensure that the ecological environment in the new production of farmers and continuously improve and expand the absorption of carbon storage. Alternatively, you can take measures to change the surface runoff, soil improvement, expansion of artificial turf fields, such as to indirectly increase the carbon sink function.