Simulation of changes in organic carbon in Flemish croplands: use in a decision support tool for farmers and in the development of a monitoring system of soil carbon stocks

On a regional scale, the most sensitive factors for monitoring of soil organic carbon stock changes have been assessed for Flanders (Belgium). On the basis of previous large scale surveys we looked at the uncertainty attributed to measurement of soil bulk density along with C concentration, depth extrapolation and number of sample points taken on a regional scale. We made recommendations on the instalment of future monitoring systems and important factors to be considered for soil C simulation models. We stress the importance of forecasting the expected statistical power (i.e. 1 - the chance of committing a type-two error β) when designing a C monitoring system. Herein β depends on the temporal correlation between future and present day C data, which is obviously unknown. Computer models could, however, provide realistic scenarios of future C evolutions from which β may be derived, e.g. in case of a paired t-test, and this in turn would affect survey design. In a farmer’s context, any simulation system for organic matter management will need to consider nutrient fluxes and legislation as well. We have developed a user-friendly online decision support tool (DST) which aims to translate insights in sustainable nutrient and soil organic matter management into practical recommendations for farmers. The DST consists of a nutrient module and an organic matter module and operates on the field scale. The organic matter module calculates the long term (30 years) evolution of organic carbon in the selected field based on the Roth-C model. The input data for this model are climate data (temperature, rainfall and evapotranspiration), soil characteristics (texture, bulk density, organic carbon content), crop rotation and input of organic materials. In the nutrient module of the DST, a mineral N balance and a P balance are calculated for the selected field. The mineral N balance consists of 7 input parameters (mineral N in the soil, mineralization of soil organic matter, catch crop, crop residues and organic materials, ploughing of permanent grassland and N deposition) and 2 output parameters (N uptake by crops and leaching). The P balance considers the application of organic materials as P input and P uptake by crops as P output. P balances are calculated over a whole crop rotation period. Validation of the DST is ongoing with 50 included farms