S13 - Session O2 - Optimizing nitrogen application for growth, productivity and quality of pomegranates

Authors: Arnon Dag *, Uri Yermiyahu , Yang Lyu, Yehuda Heler , Silit Lazare

Quantification of actual plant consumption of nitrogen (N) is necessary to optimize fertilization efficiency and minimize contamination of earth resources. We examined the performance of fruit-bearing pomegranate trees grown in soilless media and exposed to eight N-fertigation treatments, from 5 to 200 mg N L-1. Reproductive and vegetative indices were found to be optimal when 20 to 70 mg N L-1 was supplied. Nitrogen application levels over 70 mg L-1 reduced pomegranate development and reproduction. N uptake in low-level treatments was almost 100% and decreased gradually, down to 13% in 200 mg N L-1 treatment. N usage efficiency was maximized under 20 mg N L-1, in which case 80% to 90% of added N was taken up by the trees. At high N application, its efciency was reduced with less than 50% utilized by the trees. Leaf N increased to a plateau as a function of increasing irrigation solution N, maximizing at ~15 to 20 mg N g-1. Therefore, analysis of diagnostic leaves is not a valid method to identify excessive detrimental N. In respect to fruit quality, most pronounced effects were observed in trees grown under the lowest N fertilization level, which bore smaller fruit and arils, the latter with lighter color; the fruit suffered from sunburn, and the juice had lower total soluble solids, acidity and anthocyanin contents. On the other hand, Black rot incidence increased with increasing N concentration. The results should be valuable in the development of efficient , sustainable, environmentally responsible protocols for N fertilization in commercial pomegranate orchards, following adaptation and validation to real soil field conditions.