Partitioning carbon (C) pools presents theoretical and practical challenges in soil modelling. In most current models, organic matter (OM) is commonly divided into a number of pools using data-fitting techniques. It is often not possible to measure the properties of each pool of soil C simulated in this way. Furthermore, there is no effective way in current soil models to properly simulate inputs of OM with variable qualities in terms of decomposability. Here, we describe a simple model, taking the OM as a whole and assuming a rate constant function changing exponentially with time, to simulate C decomposition in a multi-component OM pool. The model requires fewer parameters to be estimated than current multi-component models, and the simulated properties of OM are measurable. When changing the quantity and the quality of OM input, the model produces results similar to multi-component models, but avoids the difficulty and uncertainty of OM partitioning.