Spatially explicit modelling of changes in soil organic C in agricultural soils in Italy, 2001–2100: Potential for compost amendment

The aim of this work was to perform a spatially explicit simulation of the potential increase in C storage in compost-amended agricultural soils at the national scale in Italy under a changing climate. The simulation was performed with a widely used dynamic model of soil organic C (SOC) turnover. Modelling runs were performed with the RothC model for 12 different climate scenarios and two management options: business as usual scenario and annual addition of 10 t ha−1 compost, corresponding to 1.1 t C ha−1 yr−1, to all agricultural soils. Results of the simulations for the 12 climate scenarios and business as usual management showed, on average, a loss of SOC for the whole of Italy during the period 2001–2100 period of 99 Mt (range 48–153 Mt) corresponding to 7.4% of the initial SOC content. Amendment of all agricultural land in Italy with compost resulted in a potential gain of SOC, averaged for the different climate scenarios, of 210 Mt (range 199–220 Mt) corresponding to an increase of 29.9% with respect to baseline. The annual rate of C sequestration that can be obtained in Italy, taking account of the predicted, feasible compost production for 2020, is about 0.023 Mt C yr−1. However, regional modelling identifies areas with a major potential for increasing SOC by means of adding compost and is useful for quantifying the importance of factors such as soil characteristics, land use and climate in predicting changes in SOC. In the present study, climate parameters and land use had a major impact on determining SOC accumulation.