Phosphorus is a non-renewable resource which is required for crop growth and to maintain high yields. The soil P cycle is very complex, and new model approaches can lead to a better understanding of those processes and further guide to research gaps.

The objective of this study is to present a P-submodel which has been integrated in the existing Carbon Candy Balance (CCB) model that, already comprises a C and N module. The P module is linked to the C mineralization and the associated C-pools via the C/P ratio of fresh organic material. Besides the organic P cycling the module implies a plant available P-pool (P_av), which is in a dynamic equilibrium with the non available P-pool (P_na) that comprises the strongly sorbed and occluded P fraction.

The model performance was tested and evaluated on four long-term field experiments with mineral P fertilization, farm yard manure as organic fertilizer and control plots without fertilization. The C dynamics as well as the P_av dynamics were modelled with overall good results. The relative RMSE for the C was below 10% for all treatments while the relative RMSE for P_av was below 15% for most treatments.

To accommodate for the rather small variety of available P models, the presented CNP-model is designed for agricultural field sites with a relatively low data input, namely air temperature, precipitation, soil properties, yields and management practices. The CNP-model offers a low entry threshold model approach to predict the C-N and now the P dynamics of agricultural soils.