Pg. 30-31 Monitor Tree Nitrogen Status to Maintain Lychee Yields

Lychee (litchi) seedlings were grown in sand culture with different levels of applied N (nitrogen) to determine the optimum concentration of N in the plant for growth and potential yield. Differences in shoot growth above and below 1.2% N in leaves were not reflected in large differences in leaf colour. These results suggest that productivity will be affected long before leaves yellow. Growers need to monitor the levels of N in their orchards and maintain them above 1.2% for optimum production.

Summary:

• The study investigated optimal nitrogen (N) concentrations in lychee trees for growth and yield using lychee seedlings grown in sand culture and a sand-peat-soil mixture.
• Shoot growth was highly sensitive to leaf nitrogen concentration, with significant growth reductions occurring when leaf N fell below 1.2%, even before visible leaf yellowing.
• Leaf color changes lagged behind reductions in growth and yield, indicating yield loss occurs prior to noticeable deficiency symptoms.
• In sand culture, nitrogen deficiency symptoms appeared rapidly (within a month), whereas in the sand-peat-soil mixture, deficiency developed more slowly over months.
• Maximum shoot growth was associated with leaf N levels around 1.4%, while root growth peaked at slightly lower N concentrations (1.0 to 1.2%).
• Field-grown lychee trees require leaf N levels above 1.2% to maintain optimal production, with suggested optimal leaf N concentrations around 1.3 to 1.5% based on existing international studies.
• Nitrogen influences lychee yield primarily by supporting leaf growth and photosynthesis essential for fruit set.
• Nitrogen concentrations above 1.8% are unlikely to increase yield and may be uneconomical.
• The findings emphasize the importance of monitoring leaf nitrogen status as a management tool to sustain lychee yields and prevent productivity loss before visible symptoms arise.