Nutrient Management Research Database

As growers of processing tomato adopt Drip, plant vigor and fruit yield typically increase, suggesting a need for re-evaluation of established nitrogen fertilization practices. Trials were conducted in California in 2007-2008 to evaluate growth and nitrogen uptake dynamics of drip-irrigated processing tomatoes across nitrogen fertigation regimes ranging from deficient to excessive. Whole plants were collected at 2-week intervals for determination of biomass and nitrogen content, recently matured whole leaves for total nitrogen and petioles. Additionally, six commercial fields were sampled at 3 to 4 week intervals to document nitrogen uptake and crop nitrogen status under conditions representative of the industry. A seasonal nitrogen rate of approximated 200 kg per hectare appeared adequate to maximize fruit yields across the range of field conditions encountered. The four highest-yielding fields (143 mg per hectare mean fresh fruit mass) averaged 14 mg per hectare of above-ground biomass with fruit representing 62%; these fields averaged 296 kg per hectare biomass nitrogen, of which 71% was in the fruit. The rate of biomass development and nitrogen uptake peaked during the period between early fruit setting and early red fruit development (a period of approximately 6 weeks) during which nitrogen uptake averaged 4 to 5 kg per hectare per day. Leaf nitrogen concentration was highly correlated with whole plant nitrogen and provided a reliable indicator of plant nitrogen sufficiency throughout the season. Petiole samples did not reliably discriminate between crops with adequate or deficiency nitrogen availability.

• Three seasonal nitrogen applications rates were tested in 2007 and 2008.
• Nitrogen was applied pre-plant and then by weekly fertigations through the buried drip system.
• Low, medium, and high nitrogen regimes were tested to achieve deficient, fruit maximizing, and excessive nitrogen fertilization.
• On average, 103, 210, and 326 kg per hectare of nitrogen was applied for the three regimes.
• Tissue samples were taken to determine the effect of the nitrogen on yield, biomass development, and nitrogen uptake.

• 200 kg per hectare of nitrogen was sufficient to maximize yields across all field conditions.
• Biomass development and nitrogen uptake peaked during early fruit set and early red fruit development, an approximate 6 week period.