Pg. 29-31 Drought Strategies for Litchi Orchards

Litchi growers must use scarce wat efficiently. Litchi trees appear to survive dry periods quite well, but physiological functions and production are severely affected by drought. Two scenarios are discussed, namely now water available, and limited water available. In the case of no water available, mulching, no fertilizer application, and in extreme cases, severe pruning, to try to ensure tree survival, even if it means loss of production for a while, are suggested. Where water is limited, it is suggested that a portion of the best litchi orchards be managed optimally, and the rest abandoned temporarily or treated as in the case where no water is available.

Summary:

• Litchi trees can survive extended drought periods by accessing deep soil moisture, but physiological functions and production are severely affected by drought stress.
• Major drought symptoms include leaf wilting, yellowing (chlorophyll breakdown), excessive leaf drop, poor flowering, small fruit size, low fruit quality, cracked fruit skin, excessive fruit drop, and eventual tree death.
• Root die-back is the most critical effect of drought, leading to reduced water and nutrient uptake and decline in tree health.
• Photosynthesis declines significantly before visible drought symptoms appear, and recovery after re-watering can be incomplete due to root damage.
• Two drought scenarios are addressed: no water availability and limited water availability.
• No water available scenario:
  • Tree survival is prioritized over production; drastic measures are suggested such as:
    • Applying thick organic mulch (and possibly perforated plastic mulch beneath) around the root zone to minimize evaporation and soil temperature.
    • Avoiding fertilization to prevent root damage and waste.
    • Severe pruning of branches to about 2m height, sealing wounds, and painting trunks/branches white with diluted PVA paint to prevent sunburn and bark cracking.
  • Pruned branches left on the ground provide shading and mulch.
  • These interventions result in loss of production for at least one season but improve survival chances if rain returns.
• Limited water available scenario:
  • Water is allocated optimally, prioritizing the best-performing orchards, while others are temporarily abandoned or managed like in the no-water scenario.
  • Critical irrigation period is from full female flowering to two months after, as drought stress here severely impacts yield and fruit quality.
  • Winter drought might be beneficial for flower induction; minimal irrigation during winter might suffice.
  • Irrigation cycles typically start when about 90% soil moisture is depleted in winter, and about 50% in summer.
  • Efficient irrigation practices suggested include drip irrigation, irrigation at night, use of organic fertilizers to improve soil water retention, and effective weed control.
  • Mulching and small basins to minimize evaporation during irrigation are recommended.
  • Use of tensiometers or neutron probes to monitor soil moisture for precise irrigation scheduling is advised.
• Overall:
  • These strategies aim to conserve scarce water and minimize tree mortality during severe drought.
  • The recommendations require adaptation to specific orchard conditions and drought severity.
  • Young or weakened trees (due to pests, diseases) are more vulnerable to drought stress.