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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, Jimmy
item Kiniry, James
item BENSON, VEREL - NRCS-TEMPLE

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

Interpretive Summary: Processing tomatoes (Lycopersicon esculentum Mill.) 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 EPIC model was calibrated with 1994 data and validated with 1995 data. Plant growth was accurately simulated in the conventional systems that used fertilizer N and in the low input system that used fertilizer N plus vetch. The model accurately simulated aboveground biomass in a system that used vetch and no synthetic fertilizer N, but it overpredicted LAI. 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 first effect of nitrogen deficiency in the vegetative phase. Yields were accurately predicted except when diseases affected plant growth. A simple reduction factor of nitrate movement in the bed adequately addressed the movement of nitrate. In general, the model accurately predicted the evolution of inorganic nitrogen in different soil layers during the crop season. However, simulated inorganic N in the upper 15 cm was underestimated in the last part of the crop season and consequently N uptake at harvest was slightly overpredicted in some cases. Nitrogen distribution and access of the roots to inorganic nitrogen are discussed as causes of this discrepancy between model simulated and observed values.

Technical Abstract: Processing tomatoes (Lycopersicon esculentum Mill.) 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 EPIC model was calibrated with 1994 data and validated with 1995 data. Plant growth was accurately simulated in the conventional systems that used fertilizer N and in the low input system that used fertilizer N plus vetch. The model accurately simulated aboveground biomass in a system that used vetch and no synthetic fertilizer N, but it overpredicted LAI. 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 first effect of nitrogen deficiency in the vegetative phase. Yields were accurately predicted except when diseases affected plant growth. A simple reduction factor of nitrate movement in the bed adequately addressed the movement of nitrate. In general, the model accurately predicted the evolution of inorganic nitrogen in different soil layers during the crop season. However, simulated inorganic N in the upper 15 cm was underestimated in the last part of the crop season and consequently N uptake at harvest was slightly overpredicted in some cases. Nitrogen distribution and access of the roots to inorganic nitrogen are discussed as causes of this discrepancy between model simulated and observed values.