ELSEVIER Agricultural Systems, 56, No. 4, pp. 391414, 1998 0 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain PII: SO308-521X(96)00100-X 0308-521X/98 $19.00 +O.OO Application of Epic Model to Nitrogen Cycling in Irrigated Processing Tomatoes Under Different Management Systems J. Cavero,a R. E. Plant,“* C. Shennaqh J. R. Williams,’ J. R. Kiniry’ & V. W. Bensonc aDepartment of Agronomy and Range Science, University of California, Davis, CA 95616, USA bDepartment of Vegetable Crops, University of California, Davis, CA 95616, USA ‘United States Department of Agriculture, Agricultural Research Service, Grassland, Soil and Water Research Laboratory, 808 E. Blackland Road, Temple, TX 76502, USA (Received 5 May 1996; revised version received 18 November 1996; accepted 20 November 1996) zyxwvutsrqponmlkjihgfedcbaZYXW ABSTRACT Vegetable crops such as processing tomatoes (Lycopersicon esculentum Mill.) are usually complex in terms of nitrogen (N) dynamics because of the large amounts absorbed by the crop, the short growing season and the use of irrigation. Complexity increases when N is supplied from an organic source. A crop simulation model could be very useful to improve N man- agement in this crop. Processing tomatoes were grown on raised beds and furrow irrigated in 1994 and 1995 in the Sacramento Valley of California. Fertilizer N and/or purple vetch (Vicia sativa L.) as green manure and composted turkey manure were used as sources of N. The Erosion Pro- ductivity Impact Calculator (EPIC) model was calibrated with 1994 data and validated with 1995 data. Plant growth was accurately simulated in the conventional systems that usedfertilizer N and in the low input system that used fertilizer N plus vetch. The model accurately simulated above-ground biomass in a system that used vetch and no synthetic fertilizer N, but it over-predicted Leaf Area Index (L.41). Nitrogen deficiency was observed in the plants in this system. The model simulated nitrogen deficiency mainly as a reduction in biomass production but in the real world the reduction of leaf area was the zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA first e#ect of nitrogen deficiency in the vegetative phase. Yields were accurately predicted except when diseases aflected plant growth. A simple reduction factor of nitrate movement in the bed *To whom correspondence should be addressed.