Long term effects of nitrogen fertilization on soil organic matter: applications of the DSSAT model

The conversion from natural to agricultural ecosystems and unsustainable land management and
agricultural practices have often lowered the soil organic matter (SOM) content (Doran, 2002). An
increase of SOM is required almost everywhere (Triberti et al. 2008), since it plays a key role to
maintain sustainable cropping systems. It prevents soil degradation by limiting soil cracking and
erosion, reduces pollution risks by adsorbing toxic substances, improves soil structure, plant nutrients
availability and soil microbial biodiversity. Part of SOM which has been lost can be re-sequestered
through adoption of recommended soil and crop management practices. DSSAT 4.02 (Jones et al.,
2003) has been recently integrated with the CENTURY SOM module (Gijsman et aI., 2002) and the
module for tillage effects on soil processes, to simulate the long term dynamics of SOM.The objective of this study was to analyze the long term impact of tillage and fertility management on
soil organic matter fractions in a durum wheat-corn rotation in a hilly rainfed area using field
experiments and model simulations. In this paper we report the results of the effect of the nitrogen
fertilization on SOM.