Nitrogen Fertilization Management in Organic Processing Tomato Production.

< style="padding-left: 52pt; text-align: left;">Nitrogen Fertilization Management in organic Processing Tomato: Making Decision by Early Nitrogen Status

Sebastian Castro Bustamante and Timothy Hartz Department of plant Sciences University of California Davis

Organic processing tomato production is a significant industry in California, yet little nitrogen fertility research is available to guide N management practices. A total of 37 Sacramento Valley organic processing tomato fields were monitored in 2012-13 with the objectives of developing information on the sufficiency of current N management practices, and determining whether early season monitoring could guide in-season N management. Between approximately 3-11 weeks after transplanting (WAT) soil mineral N, leaf N and petiole NO3-N were determined every other week. Additionally, whole plant N concentration at 11 WAT was determined in 22 of the fields. Growers were surveyed regarding N inputs and fruit yields achieved. Manure or manure-base compost was applied in 29 fields in the fall, and 2 fields in the spring. Non-composted organic fertilizers (feather meal, fish byproducts, guano, etc.) were applied to 23 fields in the fall, 14 fields pre-transplanting and 11 fields post-transplanting. An overwinter cover crop was produced in only one field prior to tomato planting. Soil mineral N in the top 60 cm 3 WAT ranged from 6-32 mg kg-1, averaging 16 mg kg-1. Apparent N limitation was common, with 30% of fields having leaf total N below the established sufficiency concentration at 11 WAT, and 36% of fields below the whole plant critical N concentration. Early season monitoring practices (3-5 WAT), such

as soil mineral N (0-12'' depth), leaf N and Petiole NO3-N, have a good performance predicting the necessity of in-season N sidedressing, when thresholds of 10-11 mg kg-1, 4.2-4.4% and 6000 mg kg-1 respectively are considered.