Evaluation of two soil carbon models using two Kenyan long term experimental datasets

Abstract

RothC and Century are two of the most widely used soil organic matter (SOM) models. However there are few examples of specific parameterization of these models for environmental conditions in East Africa. The aim of this study was therefore, to evaluate the ability of RothC and the Century to estimate changes in soil organic carbon (SOC) resulting from varying land use/management practices for the climate and soil conditions found in Kenya. The study used climate, soils and crop data from a long term experiment (1976-2001) carried out at The Kabete site at The Kenya National Agricultural Research Laboratories (NARL, located in a semi-humid region) and data from a 13 year experiment carried out in Machang'a (Embu District, located in a semi-arid region). The NARL experiment included various fertiliser (0,60 and 120 kg of Nand P205 ha -I), farmyard manure (FYM-5 and lOt ha -I) and plant residue treatments, in a variety of combinations. The Machang'a experiment involved a fertiliser (51 kg N ha- I ) and a FYM (0, 5 and 10 t ha- I ) treatment with both monocropping and intercropping. At Kabete both models showed a fair to good fit to measured data, although Century simulations for treatments with high levels of FYM were better than those without. At the Machang'a site with monocrops, both models showed a fair to good fit to measured data for all treatments. However, the fit of both models (especially RothC) to measured data for intercropping treatments at Machang'a was much poorer. Further model development for intercrop systems is recommended. Both models can be useful tools in soil C predictions, provided time series of measured soil C and crop production data are available for validating model performance against local or regional agricultural crops.