Gestione degli agroecosistemi per la ottimizzazione della dinamica della sostanza organica e per il sequestro della CO2 atmosferica

CO2 quantities released during ’90 at world level from fossil fuel use ranger from 5 to 6 Gt/anno (Rudnicki e Wawersik, 1999). Italian contribution (responsibility) represent about 3-4 % and in other word about 0.15-0.24 Gt year-1. Only 60 % of the released carbon dioxide from burning processes remain in the atmosphere (Boden et al., 1992; Berner e Berner 1996) and only 40 % refill the two main sink of the carbon cycle: ocean and terrestrial ecosystem (soil included). Both sinks are greater than atmosphere sink and the fastly exchange occurs in about ten year. Few data are actually available on CO2 fluxes from soil and CO2 fluxes from underground water. In Italy the first approach aimed to quantify carbon balance both in underground water and soils (Chiodini et al. 2000) estimate CO2 flux in 0.001-0.004 Gt C/y from 45,000 km2 equal to CO2 flux from Etna volcano the bigger CO2 producer in the world (Allard et al. 1991). Agriculture has a strategic role as far as CO2 is concerned. That opportunity, due to photosynthetic activity, characterize agriculture and forestry. In other productive areas, in fact, the only possibility is to limit greenhouse gas release. In any case possibility to have CO2 sink, removed from atmosphere thank to photosynthetic activity, must consider both crop biomass and soil organic matter. In the first case we have not enough informations to quantify the actual and future values of the contribution. Must be underlined that, in Italy, corn and sugar beet, can yearly fixed more CO2 than national forests, occupying also, soil for few months during the year. That kinds of herbaceous biomass is characterized by fast decomposition time and rate and consequently restitution of sequestered CO2 is fast. But the short period established CO2 sink is characterized by a large size and anyway induce to a more diversificated agriculture (cover crops, intercropping, crop rotation) replacing monocultural intensive cropping systems for several advantages: less soil erosion, fertilizers, herbicides etc. To improve carbon dioxide sink the most important result is the improvement of soil organic matter level. Soil organic matter is a large size sink, but the very difficult determination of it id due to the lack of knowledge of the chemical and physical characteristics of Italian soils. Considering that Italian soils, for pedological characteristics and for cropping History, are generally poor of soil organic mater, and considering, meanly, an 1.5 % of organic matter content, it is possible calculate a total amount of 826 Mt. The chances to increase that quantity is due to two integrated actions: soil incorporation of the biomass and a right management of stubble and roots. About the first task, intensive agriculture use only a little part, that correspond to the economic yield, of the produced biomass. Th other part, that represent the largest part, is always unutilized and sometimes represent a big trouble. Today Italian agricultural systems yearly produce 19 Mt of crop residues, mainly (about 56%) not harvested, and only 10.6 Mt/year are utilized for different aims (energy, industrial, agronomic). About 5.3 Mt called "potentially harvestable" are generally burned producing a large amount od CO2 (4 Mt/year ). Soil organic matter quantities can also maximized by conservative techniques: minimum tillage, crop rotation, mulching etc furnishing an increase of 0.5 % of soil organic mater of Italian soils storing about 500 Mt of carbon dioxide. These evidences stress that global CO2 contribution from diffuse out gassing, from underground water and from arable land and forest could be similar to volcanoes emission. Then in spite of human fluxes are higher than natural one, CO2 natural fluxes study seems to be important in relation to the wide area covering.