SIMULATING TRENDS IN SOIL ORGANIC-CARBON IN LONG-TERM EXPERIMENTS USING ROTHC-26.3

As part of a model evaluation exercise, RothC-26.3, a model for the tu rnover of organic carbon in non-waterlogged soils, was fitted to measu rements of organic carbon from 18 different experimental treatments on 6 long-term experimental sites in Germany, England, the USA, the Czec h Republic and Australia. In the fitting process, the model was first run with an annual return of plant C that had been selected iterativel y to give the carbon content of the soil at the start of each experime nt. This was done for the soil and climate of each site. If the radioc arbon content of the soil organic matter was known, the inert organic carbon (IOM) content of the soil was also calculated for the start of the experiment. Using these carbon and radiocarbon contents as a start ing point, the model was then run for each of the experimental treatme nts to be fitted, using iteratively selected values for the annual ret urn of plant materials to the soil. The value used for each treatment was selected to optimise the fit between modelled and measured data ov er the whole experimental period: fitting was done by eye. Thus fitted , RothC-26.3 gave an acceptable approximation to the measurements for 14 of the treatments, hearing in mind the experimental errors in measu ring soil organic carbon on a per hectare ba is. With four of the trea tments (Highfield Bare Fellow, Park Grass plot 13d. Ruzyne farmyard ma nure plot and Tamworth rotation 5), the fit was less satisfactory. (C) 1997 Elsevier Science B.V.