Saturday, 15 July 2006

Carbon Dioxide Emissions in the Atmosphere in Relation to Different Soil Managements.

Carlo Piovanelli, Stefania Simoncini, Alessandro Agnelli, Camilla Gamba, Marco Platinetti, and Marcello Pagliai. CRA-ISSDS, Piazza D'Azeglio 30, Florence, 50121, Italy

The CO2 atmospheric level has considerably increased (from 260 to 340 ppm) in the last century. The depth of soil tillage has contributed to this raising, for an estimated share between 6 and 25%, since this type of tillage determines great oxygenation and mineralization with progressive decay of the organic materials. Our investigations on the CO2 emissions in the atmosphere were developed in various agricultural and forest environments of Central Italy. The gaseous CO2 emissions from soil were made by “in situ” incubations with cover-box (40 cm diameter). The gases were analyzed by means of TCD and ECD gas-cromatography on Poropack Q column. The measures in the agricultural systems were carried out during the maize growing cycle. The forest environments (a spruce and a beech forest) were monitored from April to October. The soils under agricultural systems were located in S. Prospero and Cadriano (Emilia Romagna Region) and in Fagna (hilly environment of North Tuscany). In the former sites, soils were treated with different fertilization (pig slurry, cow slurry, fresh manure and urea), while in the Fagna site different tillage systems were investigated. The forest site (Casentino) is representative of Central Italy Apennines. The CO2 emission showed differences in relation to soil texture: the lowest CO2 emissions were found in the clay soils. The CO2 emissions increase during the maize growing season (April-September) in relation to soil temperature and seemed heavily influenced by the agricultural system. In each soil the addiction of organic fertilizers induced a significant increase of CO2 emission during the growing season. Fresh manure and high amount of pig slurry induced the highest CO2 emissions, while the mineral fertilizer seemed to increase the carbon mineralization just in the first day before the addition, after one month the CO2 emission was even less than in the control. The tillage system of the soil had strong effects on CO2 emissions too, since deep ploughing and ripper subsoiling stimulated the mineralization of the organic matter inducing the CO2 emissions, while shallow tillage is less dissipative and showed the lowest CO2 emissions. The Mediterranean forest soils did not show a significant increase of CO2 emissions, in spite of the higher carbon and biomass content than the agricultural soils. In so undisturbed ecosystem the C mineralization was low. There was a first increase of CO2 emissions in early spring due to mineralization of labile organic matter collected during the winter and a second peak of emissions in relation to the high temperature in summer. These results point out the low effect of Italian soils, in natural or low input systems, on green-house effect because of the low content of organic matter. The CO2 emissions are strongly increased both by organic fertilization and by tillage. The fresh manure induced prevailing oxidation process, with increment of CO2 emissions. The influence is generally extended for all the growing season and can produce depauperation of soil organic matter. For this reason it is absolutely necessary to adopt soil management practices suitable for protecting soil resources and for preventing their degradation. Key words: CO2 emissions, Soil tillage, Soil managements, Forest soils.

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