Simulating the soil phosphorus dynamics of four long‐term field experiments with a novel phosphorus model

Phosphorus is a nonrenewable 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 was 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 nonavailable 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, farmyard manure as organic fertilizer and control plots without fertilization. The C dynamics and 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.