Abstract

In sweet cherry, stored nitrogen (N) accumulated the previous fall after fruit harvest supports early spring growth. To complement soil N supply, Chilean growers use foliar urea applications after harvest. So far, the information regarding the effectiveness of foliar N applications in sweet cherry trees on dwarfing rootstocks is low. To study the canopy distribution of N applied as urea foliar sprays, an experiment using a 6-yr-old 'Bing'/'Gisela(R)6' (GI6) sweet cherry orchard, located in Itahue, VII Region of Chile (35 degrees 09'53 '' S, 71 degrees 20'43 '' W), was carried out in 2007. The major goal was to investigate the N distribution and recycling in 3-yr-old fruiting branches (growth from 2004/2005, 2005/2006 and 2006/2007). A total of 60 branches were labeled using N-15-urea (2% conc.). The labeled urea was applied to the whole branch at four different dates or treatments (TR) after fruit harvest: TR1=Jan, TR2=Feb, TR3=Mar and TR4=Apr. For each TR, a group of N-15-labeled branches were destructively harvested at 3 times/stages: 15 days after the foliar application (DAA), winter (dormancy, Jul) and spring (stage I of fruit development, Oct). Individual branches were divided into different tissues/organs, dried (70 degrees C), ground and processed for GC-MS analysis. In all TR, labeled urea was absorbed by leaves and translocated to different organs of the branch. Most of the N translocation was basipetal. The highest N content was observed in the fruiting section (2004/2005 growth). The Jan application (TR1) had the highest N use efficiency (NUE%). Buds and bark showed the highest N derived from fertilizer values (NDFF%). In all TR, stored N was recovered in new organs (flowers, immature fruits and young leaves) the following spring. According to the results, urea sprays after fruit harvest constitute an effective alternative to complement soil N supply in sweet cherry trees with GI6 rootstock.