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 simultaneously interact. We studied the performance of the Erosion Productivity Impact Calculator (EPIC) model in simulating the N cycle in two different rotations under irrigation: tomato (Lycopersicon esculentum Mill.)-safflower (Carthamus tinctorius L.) and tomato-wheat (Triticum aestivum L.). Processing tomatoes were grown on raised beds and furrow irrigated in 1994 in the Sacramento Valley of California, USA. Safflower and wheat were grown in 1995 and 1994-95, respectively, after the previous tomato crop. A data set from safflower grown on different plots in 1994 was used to calibrate the model for this crop. The model accurately predicted the yield, biomass and N uptake of the crops in the rotation. Soil inorganic N was also accurately simulated 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 was used to explore the influence of rotation type (tomato-safflower or tomato-wheat) and irrigation type (fixed amounts and dates or flexible automatic irrigation). Simulation results of the two rotations during 10 years (1986-95) predicted average losses by leaching higher than 200 kg N ha(-1) for each rotation period, irrespective of the rotation type. Losses were more important during the fall-winter and increased as rainfall increased above a threshold rainfall of 300 mm. The flexible automatic irrigation resulted in lower N leached during the tomato crop season. Simulation results indicated that a fallow period during the fall-winter following processing tomatoes should be avoided because of the high risk of N leaching losses. The introduction in the rotation of a deep-rooted crop, such as safflower, grown with low irrigation, drastically reduced the risk of N leaching during the following fall-winter period, without substantial yield reductions. (C) 1999 Elsevier Science Ltd. All rights reserved.