Modeling nitrogen cycling in tomato-safflower and tomato-wheat rotations

The use of crop models to simulate the nitrogen (N) cycle in crop rotations is of major interest because of the complexity of processes that simultane ously interact. We studied the performance of the Erosion Productivity Impa ct Calculator (EPIC) model in simulating the N cycle in two different rotat ions under irrigation: tomato (Lycopersicon esculentum Mill.)-safflower (Ca rthamus tinctorius L.) and tomato-wheat (Triticum aestivum L.). Processing tomatoes were grown on raised beds and furrow irrigated in 1994 in the Sacr amento Valley of California, USA. Safflower and wheat were grown in 1995 an d 1994-95, respectively, after the previous tomato crop. A data set from sa fflower grown on different plots in 1994 was used to calibrate the model fo r this crop. The model accurately predicted the yield, biomass and N uptake of the crops in the rotation. Soil inorganic N was also accurately simulat ed in the two rotations. The model predicted important amounts of N leached during the winter period of 1994-95 due to the heavy rainfall. The model w as used to explore the influence of rotation type (tomato-safflower or toma to-wheat) and irrigation type (fixed amounts and dates or flexible automati c irrigation). Simulation results of the two rotations during 10 years (198 6-95) predicted average losses by leaching higher than 200 kg N ha(-1) for each rotation period, irrespective of the rotation type. Losses were more i mportant during the fall-winter and increased as rainfall increased above a threshold rainfall of 300 mm. The flexible automatic irrigation resulted i n lower N leached during the tomato crop season. Simulation results indicat ed that a fallow period during the fall-winter following processing tomatoe s should be avoided because of the high risk of N leaching losses. The intr oduction in the rotation of a deep-rooted crop, such as safflower, grown wi th low irrigation, drastically reduced the risk of N leaching during the fo llowing fall-winter period, without substantial yield reductions. (C) 1999 Elsevier Science Ltd. All rights reserved.