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Title: APPLICATION OF EPIC MODEL TO NITROGEN CYCLING IN IRRIGATED PROCESSING TOMATOES UNDER DIFFERENT MANAGEMENT SYSTEMS

Author
item CAVERO, J - UNIV OF CALIFORNIA
item PLANT, R - UNIV OF CALIFORNIA
item SHENNAN, C - UNIV OF CALIFORNIA
item WILLIAMS, J - TAES
item Kiniry, James
item BENSON, V - NRCS

Submitted to: Agricultural Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Tomato crops are complex in terms of nitrogen dynamics because large amounts of N are taken up by the crop and the growing season is short. Nitrogen dynamics become even more complex if organic sources of N are used. A simulation model could help improve N management of tomatoes. Processing tomatoes were grown on raise beds and furrow irrigated for two years in the Sacramento Valley of California. Fertilizer N or purple vetch as green manure and composted turkey manure were used as sources for N. The EPIC model was calibrated with the first year data and validated with the second. Plant growth was accurately simulated in conventional systems that used fertilizer N and in the low input system that used fertilizer N plus vetch. EPIC accurately simulated biomass in the system with vetch and no synthetic fertilizer N, but over-predicted LAI. Nitrogen deficiency was observed in plants in this system. EPIC simulated N deficiency as a reduction in biomass production, but in the real world, the reduction of LAI was the first effect. Yields were accurately simulated except when diseases affected plant growth. A simple reduction factor for nitrate movement in the bed adequately addressed movement of nitrate. The model accurately predicted evolution of inorganic N in different soil layers. However, simulated inorganic N in the upper 15 cm. was underestimated late in the season. The model appeared to be a useful tool for N management decisions with processing tomatoes.

Technical Abstract: Vegetable crops such as tomatoes are complex in terms of nitrogen dynamics because of the large amounts of N taken up by the crop, the short growing season, and the use of irrigation. Complexity increases when N is from organic sources. A simulation model could help improve N management of this crop. Processing tomatoes were grown on raise beds and furrow irrigated for two years in the Sacramento Valley of California. Fertilizer N or purple vetch as green manure and composted turkey manure were used as sources for N. The EPIC model was calibrated with the first year data and validated with the second. Plant growth was accurately simulated in conventional systems that used fertilizer N and in the low input system that used fertilizer N plus vetch. EPIC accurately simulated biomass in the system with vetch and no synthetic fertilizer N, but over-predicted LAI. Nitrogen deficiency was observed in plants in this system. EPIC simulated N deficiency as a reduction in biomass production, but in the real world, the reduction of LAI was the first effect. Yields were accurately simulated except when diseases affected plant growth. A simple reduction factor for nitrate movement in the bed adequately addressed movement of nitrate. The model accurately predicted evolution of inorganic N in different soil layers. However, simulated inorganic N in the upper 15 cm. was underestimated late in the season. Nitrogen distribution was discussed as a cause of differences between simulated and observed values.