Contribution of soil to CO2 balance in industrial oil crops.

Cultivation of oilseed crops for energy production (methylester) leads to a positive energy balance, as found for sunflower and rapeseed in crop rotations typical of Northern Italy. In these crops, a positive CO2 balance has also been calculated, thus allowing possible mitigation of the greenhouse effect. Despite this, very little is known on the evolution of CO2 from cultivated soils, and the wide variability of data found in the literature greatly depends on the farming system. It is therefore necessary to find the most suitable type of agricultural management (input level) to optimize the CO2 balance. In this paper, some results of CO2 balances are presented, for sunflower and rapeseed used for biodiesel production, based on data derived from a survey of 400 cultivations in the Veneto Region (Po valley - North-East Italy). The dynamics of CO2 fluxes were simulated over a two-year period, and the contribution of soil in the balance was estimated with a new model (DiSOS, Dynamics of Soil Organic Matter) which takes into account the evolution of this gas from soils as a function of tillage. Analyses revealed the relative weight of tillage intensity and the amount of crop residues in maintaining the soil carbon balance. The amount of crop residues, produced by the oilseed crops considered here, turned out to be the main factor. The DiSOS model was very useful in estimating the dynamics of the soil carbon balance as a function of cropping system, and contributed towards estimating the CO2 balance of oilseed crops. Sunflower showed more stable behaviour in the various cropping systems, providing both reasonably good yields and CO2 storage even with low inputs, with associated higher energy efficiency than rapeseed. Instead, rapeseed gained more from high input levels in terms of amount of carbon storage, but was more sensitive to extensive management as regards energy efficiency.