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THE AVOCADO IRRIGATION CONUNDRUM

THE AVOCADO IRRIGATION CONUNDRUM. Simon Newett Dept of Agriculture, Fisheries and Forestry, Queensland. Origin of avocados - Central American highlands. Central American highlands (e.g. Michoacan State, Mexico) Deep, well drained volcanic soils Soil surface mulch of leaf litter

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THE AVOCADO IRRIGATION CONUNDRUM

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  1. THE AVOCADO IRRIGATION CONUNDRUM Simon Newett Dept of Agriculture, Fisheries and Forestry, Queensland

  2. Origin of avocados - Central American highlands • Central American highlands (e.g. Michoacan State, Mexico) • Deep, well drained volcanic soils • Soil surface mulch of leaf litter • Well structured soils, high in organic matter • Benign climate • regular rainfall (about 1500mm/yr) • absence of temperature extremes • Avocado is still a ‘young’ crop: • 1911: First release of a selected, propagated variety • 1940s: First attempt at rootstock selection

  3. The conundrum . . . . . • Avocados have a high water requirement and are sensitive to water stress but they are … • inefficient at extracting moisture from the soil • sensitive to over watering

  4. Moisture stress = excessive fruit drop

  5. Water stress = ringneck (incomplete fruit abscission)

  6. Water stress = death of seed coat = small fruit

  7. Water stress in first 11 weeks after fruitset = poor shelf life due to low calcium levels

  8. Water stress = poor quality fruitVascular browning

  9. inefficient at extracting moisture because • they don’t have root hairs • have a very shallow feeder root system (90% are in the top 15cm of soil) • can extract little water below -20 kPa

  10. No root hairs

  11. Shallow feeder root system

  12. Shallow feeder root system

  13. Shallow feeder root system

  14. sensitive to over watering because … • feeder roots have a high oxygen requirement (trees die after 48 hours inundation) and … • roots are susceptible to Phytophthora root rot (a “new encounter” disease for avocado)

  15. Drowned avocado tree

  16. Waterlogging = fruit fall & uneven ripening

  17. Healthy vs. Phytophthora infected roots

  18. Healthy vs. root rot infected tree

  19. In appreciation of these facts … • “A more focussed and responsive approach to moisture monitoring and irrigation is required. • This is emerging as a key component in achieving high yields of good quality avocados in Australia.”

  20. The solution • Plant only on well drained soil, ensure orchard drainage is near perfect • Install an irrigation system that delivers water and fertiliser evenly to every tree and does not leak when turned off • Install an accurate & reliable soil moisture monitoring system plus a back up • Follow weather forecasts to be prepared for peak demand • Monitor soil moisture several times a day in warmer months

  21. The solution (continued) • Use the concept of Readily Available Water (RAW) and aim to keep soil moisture between the Full (-8kPa) and Refill (-20kPa) points • Respond immediately to irrigation needs, but … • … don’t exceed Full Point • Irrigate several times a day if necessary • Use mulch to create a more hospitable root environment, reduce evaporation, increase soil organic matter and help combat root rot • Use overhead misters for cooling during heat waves

  22. Full point Refill point Soil moisture monitoring

  23. The concept of ‘Readily Available Water’ (RAW)

  24. The concept of ‘Readily Available Water’ (RAW) • RAW is mm of water in the soil readily available to the plants. • For avocados • = Full Point (-8kPa) - Refill Point (-20kPa)

  25. The concept of ‘Readily Available Water’ (RAW) • RAW is mm of water in the soil readily available to the plants. • For avocados • = Full Point (-8kPa) - Refill Point (-20kPa) • Example: • Sandy loam • Main root zone 15cm • 15 x 0.46 = only7mm • Literature suggests that RAW can be increased by 3 to 4mm for every 1% increase in soil organic matter.

  26. Mulching avocado trees

  27. Mulching avocado trees

  28. Overhead misters

  29. Research needed • Establish ‘Crop factors’ for different times in the annual growth cycle (thought to exceed 1.0 during flowering) • More accurately determine what water tension levels result in ring neck, excess fruit shedding, death of seed coat, and other water stress effects • Partial drying of the roots has been tried but results in crop loss • Using water stress as a management tool only has negative effects

  30. Water stress ‘memory’: induces avocado to block xylem with tyloses as a survival mechanism Un-watered Well-watered The water contained a red fluorescent dye – so red means water can flow through the vessels

  31. Typical avocado irrigation system • Tree spacing 9 x 4m • Under-tree mini sprinklers (one to two per tree) • Systems deliver 80 to 120 L/tree/hour • About 60% of orchard floor is wetted • Precipitation rates about 2mm/hour in wetted area • Systems must be capable of meeting peak demand days • Capacitance probes (e.g. Enviroscans), gypsum block and tensiometers are popular moisture monitoring tools. Capacitance probes typically measure hourly.

  32. Acknowledgements

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