1 / 41

Environmental Constraints

Environmental Constraints. Text Chapter 3. Subtropical Regions. Most commercial citrus production 23.5 - 40 o NS Latitudes Minimum temperatures > -7 o C (19.6 o F Examples Rio Grande Valley ~ 26 o NL Orlando, Florida ~ 28 o NL Indio, California ~ 33 o NL.

marlow
Download Presentation

Environmental Constraints

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Environmental Constraints Text Chapter 3

  2. Subtropical Regions • Most commercial citrus production • 23.5 - 40o NS Latitudes • Minimum temperatures > -7oC (19.6oF • Examples • Rio Grande Valley ~ 26o NL • Orlando, Florida ~ 28o NL • Indio, California ~ 33o NL

  3. Tropical - Subtropical Comparison • Tropical between 23.5o NL SL • Subtropical ® 100 tonnes ha-1 • Tropical ® 15 tonnes ha-1 • Minimum 0oC (32oF) • Small fluctuations in DL 10o NL SL • Small fluctuations in temp at low to mid elevations (-3oF/1000 Ft rule)

  4. Lowland Tropical Regions • Altitude 0 - 500 m • Highest average temperatures • Highest heat units • Distinct wet-dry cycles • Wet season onset of flowering

  5. High Elevation Tropical Regions • Fog reduces light intensity (Day) • Lowers temp & CO2 assimilation • Fog (Night) decreases radiation • Increases temp • Ultraviolet radiation increased • Due to reduced particulate matter • Leaf distortion & reduced growth

  6. Limiting Factors • Flower initiation av. < 24oC • Vegetative growth > 12.5oC • Heat units > 5000 • increased respiration • < fruit solids & acids

  7. Heat Unit Calculation 12.5C + 24.5C = 18.5 2 18.5 - 12.5 = 6 6 x 30 days =180 heat units / month 180 x 12 = 2160 heat units / year

  8. Examples Site Latitude Altitude HU • Weslaco 26o05’ N 40 m 3900 • Orlando 28o40’ N 30 m 3700 • Indio, CA 33o40’N -10 m 3900 • Degania Is. 32o40’N -200 m 3600 • Lmeira, Bz 22o30’S 700 m 3000 • Colombia 4o20’N 400 m 5700

  9. Diurnal Fluctuations • Greater in subtropical regions • Mean annual temps from 15 to 18oC • But many exposed to -0oC • Minimum of -10oC (14oF) Florida • Freeze damage in US, Europe, Mexico, Australia, central China. • Rarely in Brazil

  10. Far East • Minimal damage • Large bodies of water • Satsuma mandarin / Trifoliate orange • Extended periods of cool temps • Maximum freeze hardiness • Not true in Texas and Florida

  11. The Juvenile Plant • Thorny (modified leaves) • Upright unbranched growth habit • Apical meristem abscises • lateral buds break • new shoots from lateral buds • Process repeated ® Zig-zag growth (sympodial) ® Determinate habit

  12. Duration of Juvenility • Inversely related to • tree vigor • heat unit accumulation • Example • Lemons and limes < 2 years • Others - 5 to 13 years • Air layers ‘Tahiti’ lime - fruit in 1 year

  13. Hardiness • Seedling citrus > hardy than same cultivar budded to a root stock.

  14. Influence of Climate • Lowland tropical areas with high RF • Shorter juvenile period • Arid subtropical area • Longer juvenile period • Calamondin & ‘Key’ lime - 18 months • 30oC days, 25oC nights, 16 h DL • No flushes (continuous growth)

  15. The Budded Plant (Budling) • Adult - so earlier production. • Budling - • Riverside, CA ® 30 mo. Market sz • Mannar, Sri Lanka ® 15 mo. • Difference? • Riverside 1700 heat units • Mannar 5700 heat units

  16. Net CO2 Assimilation • Linear photosynthetic photon flux (PPF) up to 700 mmol m-2 s-1 (Fig. 3.3) • PPF of 2000 m-2 s-1 represents full sunlight • Thus max CO2 assimilation at 30% full sunlight • Max growth when DL 12 h

  17. Influence of High Radiation • High light intensity may decrease CO2 assimilation • High light increase leaf temp 10oC • Optimum range 28 - 30oC • > 35oC limits RuBisCo ® inc VPD • ® Mid day stomatal closure ® poor growth

  18. Shoot and Leaf Growth • Shoot growth - 2 to 5 distinct flushes • Tropical - may be continuous • Growth begins at >12.5oC (55oF) • Spring flush • March - April NL • September - October SL • Mean temps 12 - 20oC in this period

  19. Other Flushes • Summer flushes • June - July NL • January - February SL • Fewer growing points • Longer internodes • Tropical - continuous • Same annual growth - distribution?

  20. Leaf Area • 3 year old tree - 16,000 leaves (34 m2) • 29 yr tree - 173,000 (203 m2) • Interior PPF down to 50 mmol m-2 s-1 • What should be done?

  21. Leaf Function • Leaves C importers ~ 6 wks post bloom • Stomata on abaxial surface take time to develop - poor transpiration contr. • CO2 assimilation stabilizes in ~ 7 mo • Healthy citrus leaves may for 3 yrs.

  22. Root Growth • Temp regulates root growth, water, and nutrient uptake • Root growth begins at temp > 7oC • May - June and August - Sept. • Increases from 17 to 30oC • Water & nutrient uptake inc 10 - 30oC • Winter chlorosis

  23. Water and Root Growth • Root growth decreases significantly • When soil moisture < 45% of field capacity. • Excessive water for only a few days due to H2S produced by soil-bore bacteria caused by lack of oxygen.

  24. Flower Induction and Differentiation • Flower bud differentiation occurs during winter rest in subtropics • Or during dry season in tropics • Temperatures < 25oC ® rest • Drought > 30 days induce flower bud • Italy - water withheld from lemons - irrigated - blooms - control harvest

  25. Anthesis • Events leading to anthesis (Fig. 3.5) • Min. threshold 9.4oC (48oF) • Low to moderate temps during bloom (<20oC) ® protracted bloom • Higher temps (25-30oC) shorter bloom

  26. Factors Associated with Flowering • Carbohydrates • Girdling • Alternate bearing mandarins • Hormones - GA3 influence not clear • Nutrition -

  27. Carbohydrate / Nitrogen Ratio • I II III IV • C/NNNN CC/NNN CCC/NN CCCC/N • No fruit No Yes No • Age ® • Pruning ¬ • Irrigation ¬ • Nitrogen fertilizer ¬

  28. Pollination and Fruit Set • Bee activity minimal temp < 12.5oC • Pollen germination best at 25 - 30oC • Pollen tube growth through stylar canals - 2 days to 4 wks • Depending on cultivar & temp.

  29. Initial Fruit Set • 100,000 - 200,000 flowers / tree • Only 1 - 2 % produce fruit • 1st drop - 3 - 4 weeks post bloom • Defective flowers or no pollination • High temps (>40oC) (104oF) may cause fruit drop in Navel Oranges.

  30. Physiological Drop • 2nd drop - May - June NL • ( Nov-Dec SL) • Fruitlets 0.5 - 2.0 cm • Caused - competition for metabolites • High temps. ® H2O stress ® stomatal closure ® assim CO2¯ • Neg. C balance ® fruit abscission

  31. Longevity • Freezes primary cause of short life. • Aside from freezes: • Humid subtrop - fruit in 15-20 yrs • Med. Climates - peak 20-25 yrs • Humid subtrop - life 100 years • Mediterranean - life 200 years

  32. Fruit Yields • FL av grapefruit 41 max 120 Mg ha-1 • Oranges 31 Mg max 100 Mg ha-1 • Brazil and China 1/2 - lack irrigation • Semiarid or arid - < hu < tree size < yield. • % marketable fruit > in semiarid area • < pests, < blemishes & > peel color

  33. Fruit Growth • Sigmoid pattern (Fig. 3.7) • Phase I - Cell div. (all cells formed) • 1 - 1.5 mo - determines fruit size • Phase II - Cell differentiation • Phase III - Cell enlargement (6 mo)

  34. Maturation • Phase IV - Peel color from green to yellow or orange • Slight increase in TSS • Rapid decrease in TA • Time 6 - 16 months for ‘Valencia’ • Influenced by water and temp.

  35. External Quality • Peel color (air & soil temps < 15oC) • Chloroplasts ® Chromoplasts • Carotenoids (grapefruit) • Lycopenes (red grapefruit) • Anthocyanin (blood oranges) • Low vigor ® more color • Excessive N ® poor color

  36. Fruit Shape • High temperatures ® sheepnosed fruit • Excessive cell division in albedo near stem end.

  37. Fruit Size • Citrus 85 - 90% water by weight • Fruit size function of water • Leaves on detached fruitless twig wilt in few hrs • Leaves on detached fruited twig remain turgid for many hours • WHY?

  38. Water translocated to leaves is stored in fruit peel • Irrigation scheduling

  39. Internal Quality • Carbohydrates 75 - 80% of TSS • Regulates internal quality • TSS decrease > rapid - low tropical than in sub-tropical areas (Fig. 3.8) • TA - same relation (Fig. 3.9) • Function of heat units • Organic acids in Citric acid cycle

  40. TSS:TA Ratio • Determines edible quality • ‘Valencia’ reach 9:1 in 7 mo in tropics • Coastal subtropics - up to 16 mo • (Fig. 3.10)

  41. THE END

More Related