CRISP-crayfish rice integrated system of production. 5. Simulation of nitrogen dynamics

In the lower Mondego river valley, part of the agricultural lands have been converted into rice fields during the recent years. Meanwhile, an imported and non-native species, the Louisiana Red Crayfish (Procambarus clarkii) h as invaded the fields and are hampering the establishment of especially the young rice plants. The species is lowering the potential income of the far mers and is, therefore, considered a pest. A project financed by EU was set up to define a 'best possible strategy' for the management of crayfish pop ulations in rice fields aiming to make possible the integration of the two crops in the same system. This paper presents the first outlines of a model for the nitrogen cycle in a freshwater, aquacultural farming system with c ombined growth and harvest of rice and crayfish. The fertilization of the r ice-fields is connected with high inputs of nitrogen as artificial fertiliz ers. Not all the nitrogen added as fertilizers actually ends up improving t he rice-growth. Usually, a major part enters the general biogeochemical N-c ycle of the field. The quantities added mean that this may also play a majo r role in determining the water quality of the rice field. Maintaining an a dequate water quality is important for the integration of the rice field wi th aquaculture of P. clarkii. The model has passed the phase of verificatio n and reached a state of calibration and will be integrated with other subm odels of the system. Ammonia is more abundant than the nitrate during the w et season, whereas the nitrate dominates during dry season, indicating that removal of nitrogen by denitrification will take place during this time of the year. (C) 1999 Elsevier Science B.V. All rights reserved.