Nitrogen mineralisation in organic farming systems: a test of the NDICEA model

The validation of the carbon and nitrogen model NDICEA ( Nitrogen Dynamics in Crop rotations in Ecological Agriculture) is presented. The model allows one to estimate how crop rotations and manure applications affect the amount of mineral nitrogen in different phases of a crop rotation. The model was tested on 8 organic farms and research sites. The model's performance was tested by means of visual performance and a number of statistical measures. The results show that the model fits the observed mineral nitrogen for the top 30 cm of the soil with a modelling efficiency (ME) of 0.4 and a coefficient of determination (r) of 0.65. NDICEA is used to gain insight into the different sources of N mineralisation in the soil. Results show that the model NDICEA can be used to simulate sustainable farming systems at the field level using on-farm data and readily available climatic data. The model might therefore serve as a tool for evaluating the impact of the crop rotation and manure regime on long-term soil fertility levels and nitrogen leaching losses at the field level.