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Carbon sequestration in soils
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40 2019 ND-CP 413905
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Carbon sequestration in soils An issue of great concern is the rising atmospheric concentration of greenhouse gases such as carbon dioxide and methane and their potential impact on future climate, notably accelerated global warming. Carbon dioxide and methane can be measured accurately in the atmosphere, but there is still considerable uncertainty about the storage of carbon compounds in the ocean and land ecosystems. Agro-ecosystems are believed to be the storage reservoir of up to 25 percent of the global carbon total. About one third is stored in the top 30 cm of the soil profile, one third in the subsoil and one third in the vegetation. The primary sources of agriculture-based carbon emissions are biomass burning and methane emissions from livestock and paddy rice. Together with reduction of emissions –as by the use of biomass fuels in place of fossil fuels–, carbon sequestration in soil is a valuable option to reduce the level of atmospheric carbon dioxide. Methods of sequestration include capture and storage of CO 2 from emission sources; changes in forestry, agricultural and land management practices (e.g. conservation agriculture) that will lead to net sinks for carbon or at least reduce carbon release into the atmosphere; expansion of carbon storage in wood products; and deep ocean carbon storage (Bruce et al., 1999). Agriculture that involves conventional tillage and removal of plant material mines the soil of carbon and nitrogen, and can lead to reductions in SOM of 50 percent or more after 50 years of cropping (Lal et al., 1997, Woomer et al., 2001). As soils become depleted of SOM, the water-holding capacity and nutrient availability decrease, which in turn results in reduced crop yields. Nutrient decline is closely linked to the depletion of soil organic matter in smallholder farming systems of the tropics (Parton et al., 1994; Woomer et al., 1999, 2000). Soil fertility depletion in the tropics (Smaling 1993) is recognized as the underlying cause of chronically low agricultural productivity and calls for strategies of nutrient replenishment (Sanchez et al., 1997). A number of measures related to carbon sequestration and reduction of emissions can play a role in turning soils into significant sinks for carbon. On cultivated land, these include adoption of conservation tillage (FAO 2001), use of manures, and compost as per integrated nutrient management and precision farming strategies, conversion of monoculture to complex, diverse cropping systems, meadow-based rotations, use of winter cover crops, elimination of summer fallow, establishing perennial vegetation on contours and steep slopes, and methods to increase crop productivity (Bruce et al., 1999). Also the use of nitrogen-fixing trees and crops results in improved soil organic matter content, increases the carbon sequestration capacity and thus helps reduce agriculture-induced emissions. On marginal lands, some areas could be revegetated using perennial grasses, grassed waterways, shelterbelts and trees. On grazing land, more carbon could be stored through modified grazing practices, use of improved varieties and other means such as sowing strips of legumes with phosphate fertilizer in the strips (FAO 2001). Reducing erosion on degraded soils, and reclaiming salt-affected soils could help restore soil carbon contents. In summary, there exists a confluence of interests between local land managers and society with regard to the accumulation of organic resources within farming systems, as this may increase productivity as well as the amounts of carbon in both biomass and soil. tải về 0.57 Mb. Chia sẻ với bạn bè của bạn:
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