The 2009 ASHS Annual Conference

Increasing use of drip irrigation in processing tomato production worldwide, and concern over nutrient loss to the environment, makes the development of both effective and efficient fertigation management practices essential.  A total of 4 high-yield drip-irrigated processing tomato fields in California were monitored in 2007-08.  Above-ground biomass and macronutrient content was determined every 2-3 weeks, with the final sampling occurring near commercial harvest stage.  On each sampling date soil, whole leaves and petioles were also collected and analyzed for NO₃-N (soil), total N, P and K (whole leaves) and NO₃-N, PO₄-P and K (petioles).  Total fruit yield ranged among fields from 131-160 Mg ha^-1.  Mean seasonal uptake averaged 296, 43 and 388 kg ha^-1 N, P and K, respectively.  More than 70% of macronutrient uptake occurred between 5-11 weeks after transplanting, encompassing the period between early fruiting and first red fruit.  Regression analysis of nutrient uptake revealed that during the middle of that period daily nutrient uptake peaked at approximately 6, 0.6 and 7 kg ha^-1 N, P and K, respectively.  Seasonal N application averaged 216 kg ha^-1, close to the mean N removal in fruit (208 kg ha^-1).  In-season soil NO₃-N monitoring proved problematic due to stratification of NO₃-N in the wetted root zone.  Current petiole nutrient sufficiency guidelines appeared to be higher than necessary for drip-irrigated production, while whole leaf sufficiency standards were generally appropriate.