Pg. 41-48 Fostering strong bearing branches after harvest to increase the yield potential of litchi

The post-harvest shoot growth cycle is a period for fostering strong bearing branches for the next season, as high quality bearing branches are the basis for a productive tree. In South Africa, soil applications of fertilisers are generally carried out immediately after harvest irrespective of production area, number of post-harvest flushes and soil type. In order to determine the effect of various application times, specifically of nitrogen (N), before and after harvest, trials were conducted in both early (Malalane) and mid-season (Nelspruit) production areas on ‘Mauritius’ litchi trees between 2014 and 2016. In the early area, N applications were applied as follows: a) single application at start of harvest, b) single application after harvest, c) split application at start of harvest and at hardening of first post-harvest flush to strengthen second flush, d) no post-harvest application (all N applied before flowering; control 1) and e) farm practice (control 2). Treatments for the mid-season area were the same except that the split application (c) was applied before and after harvest (3-4 weeks apart) as there is only one post-harvest flush. The results showed that time of N application affects time of flush emergence, hardening-off time and leaf N content of the leaves. Tree starch content and leaf N at specific times were positively correlated with shoot growth, flowering and yield.

Summary:

• The post-harvest shoot growth cycle is critical for developing strong bearing branches that form the basis for productive litchi trees in the next season.
• Nitrogen (N) fertilization timing before and after harvest significantly affects flush emergence, hardening time, leaf N content, tree starch reserves, flowering, and yield.
• Trials were conducted from 2014 to 2016 in two South African production areas: early Malalane and mid-season Nelspruit, on Mauritius litchi trees.
• Different N application regimes tested included:
  • Single application at harvest start
  • Single application after harvest
  • Split application at harvest start and at hardening of first post-harvest flush
  • All N before flowering (no post-harvest)
  • Farm practice control (varied timing)
• Key findings from Malalane (early warm area):
  • N applications before harvest and split applications advanced post-harvest flush emergence and hardening.
  • Split application supported the second post-harvest flush leading to better starch accumulation.
  • Treatments with N after harvest had higher starch content during flower induction, improving flowering and yield.
  • Leaf N fluctuated with flush cycles but was generally higher with post-harvest N applications.
  • Flowering and yield were higher under split and before-harvest N applications.
• Key findings from Nelspruit (cooler mid-season area):
  • Only one proper post-harvest flush; N timing had less impact on flush emergence and hardening.
  • Flowering and yield were less affected by N timing, though “before harvest” and split treatments showed some trend for increased flowering.
  • Leaf N and starch reserves also rose with N fertilization but correlations with flowering/yield were less pronounced than in Malalane.
• The study highlights the importance of balanced N nutrition and timing to foster strong bearing branches through supporting carbohydrate (starch) reserves critical for flowering and yield.
• In warmer areas with multiple post-harvest flushes, split N applications are more beneficial than a single post-harvest application.
• In cooler areas, timing is less critical but maintaining sufficient leaf N and starch reserves remains important.
• The research supports integrating improved flush control methods (e.g., ethephon applications) with strategic N fertilization for long-term sustainable litchi production.
• The study was supported by the South African Litchi Growers Association and Agricultural Research Council.