vegetable crop productivity as influenced by light


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vegetable crop productivity as influenced by light

  2. 2. LIGHT Light is the part of the electromagnetic spectrum having wavelengths visible to the human eye (about 390-760 nm) (Moore et al. 2003).
  3. 3.    All life on earth is supported by the radiant energy of the sun. Light is one of the most important and variable components of the plant environment. The visible spectrum, a small portion of UV and infrared sections, comprise the wavelengths that are most significant for plants.
  4. 4. Phototrophic Movement of Plant  Plants sense and respond to their environments in a number of ways. Receptor molecules within plant cells perceive changes in external conditions, such as light.  Because stems grow toward a source of blue or white light they are said to have a “positive” phototropic response.  Conversely, roots are said to have a “negative” phototropic response because they grow away from a source of blue or white light.
  6. 6.  Charles Darwin, the great evolutionary biologist, investigated grass seedlings’ growth responses to blue light as early as 1881.  He already knew that growing plants would bend toward light coming from a single direction.  Darwin and his co investigator son, Francis, proposed that the seedlings were bending toward light in response to an “influence” that was transported down the stem from the growing tip.
  7. 7.  In 1926, Fritz Went, a Dutch scientist, identified the chemical messenger that causes cells on the shaded side of a shoot to elongate and grow faster than cells on the lighted side, thereby bending the stem toward the light source. He called this messenger hormone auxin.
  8. 8. Importance of Light for Plants 1. 2.   Plants use light for: Photosynthesis Photomorphogenesis both simultaneously take place in the plant and interact with each other. If photosynthesis is the “engine” providing the energy for plant growth, photomorphogenesis is the “steering wheel” to influence the direction and final plant appearance.
  9. 9. Photosynthesis
  10. 10. Photomorphogenesis  It is defined as the ability of light to regulate plant growth and development, independent of photosynthesis.  Plant processes that appear to be photomorphogenic include :  Internode elongation  Chlorophyll development  Flowering  Abscission  Lateral bud outgrowth  Root and shoot growth
  11. 11. Phytochromes (600-700nm) (710 -800 nm)
  12. 12. Three Principal Characteristics of Light Quantity (Intensity) ◦ Photosynthesis Quality (Wavelength) ◦ Photomorphogenesis Duration ◦ Photoperiodism
  13. 13. QUANTITY  Light quantity refers to the intensity or concentration of sunlight and it varies with the season of the year.  The more sunlight a plant receives (up to a point), the better capacity it has to produce plant food through photosynthesis.  Light quantity can be decreased in a garden or greenhouse by using shade-cloth.  It can be increased by surrounding plants with white or reflective material or supplemental lights.
  14. 14. Plant community can be classified into(Edmond et al.,1964) : Shade plants Partial shade and sun plants Sun plants Slight shade and direct sun tolerant plants Require low light intensity of 500-1000 foot candles. Require high light intensity of 3000-8000 ft-c. Thrive well over wide range of light intensity of 20008000 ft-c. e.g. tomato, brinjal, chilli, all cucurbits, peas and beans, sweet potato, etc. e.g. cabbage, potato, etc. Require moderately high light intensity of 1000-3000 ft-c.
  15. 15. QUALITY  Light quality refers to the colour or wavelength reaching the plant surface.  Red and blue light have the greatest effect on plant growth.  Green light is least effective to plants as most plants reflect green light and absorb very little.
  16. 16. Relative efficiency of various light colors in photosynthesis
  17. 17. RED LIGHT Red and orange light triggers hormones in plants that increase flowering and budding, but plants cannot grow with red light alone and also need blue light.  It stimulates flowering and foliage growth, but too much red light will cause a plant to become spindly.  It also induces germination and blue light promotes seed growth, but far-red light inhibits germination.  HPS (high-pressure sodium) lamp emit a red orange glow and are excellent companion lights for growing conditions. 
  18. 18. BLUE LIGHT     Blue light, referred to as cool light, encourages compact bushy growth. Blue light regulates many plant responses including stomata opening and phototropism. Metal halide grow lights emit more light in the blue spectrum and are the best source of indoor lighting to use for plant growth if there is no sunlight available. Blue light is considered an important factor in the formation of chlorophyll and chloroplast development (Akoyunoglo and Anni, 1984).
  19. 19. Effect of Light Color on Vegetable Roselle (Hibiscus sabdariffa) growth Height, h(cm) and thickness, t(mm) Day 436 nm h t 470nm h 1.7 7.1 t 490nm 520nm 546nm 578nm 700nm h t h t h h t h t 1.7 8.2 1.7 t 1 8.7 1.3 6.5 2.0 6.2 1.7 7.5 1.6 5.2 2 13.2 1.8 11.0 1.3 9.0 2.0 11.0 1.6 12.5 1.6 10.0 1.6 12.0 1.7 3 16.0 1.8 15.0 1.3 11.5 2.0 12.0 1.6 13.5 1.6 11.5 1.6 16.2 1.8 4 18.2 1.7 18.0 1.3 14.0 1.8 14.5 1.6 16.5 1.5 12.0 1.5 19.0 1.8 5 22.0 1.7 21.0 1.3 17.0 1.8 15.5 1.5 20.0 1.5 13.0 1.4 22.1 1.7 6 23.0 1.7 24.0 1.3 18.3 1.8 15.7 1.5 22.5 1.5 14.0 1.4 24.9 1.7 7 23.5 1.5 27.0 1.2 19.2 1.7 15.8 1.5 23.5 1.5 14.0 1.3 28.1 1.6 8 24.0 1.4 28.0 1.2 20.0 1.7 16.8 1.5 24.0 1.5 17.0 1.3 29.2 1.6 9 25.0 1.3 29.0 1.2 22.0 1.6 23.5 1.4 25.0 1.5 20.0 1.3 30.4 1.5 10 28.0 1.3 31.0 1.3 25.0 1.6 24.8 1.4 26.0 1.5 21.0 1.3 32.4 1.4 Yerima et al., 2012
  20. 20. Response of Tomato and Pepper Transplants to Light Spectra Provided by Light Emitting Diodes Ratio Light Type White Red 3 0 2 Established Transplants(%) First Yield/ Plant (g) Blue Tomato Pepper Tomato Pepper 0 82 78 1177 156.30 1 0 90 84 1507 161.00 1 2 0 95 93 1753 155.30 0 3 0 100 98 2440 178.70 2 0 1 95 91 1603 155.30 1 0 2 95 95 1720 143.30 0 0 3 100 100 2307 104.30 0 2 1 100 100 2693 192.00 0 1 2 100 100 2530 180.00 Javanmardi et al., Shiraz university, Iran, 2013
  21. 21. DURATION Light duration or photoperiod refers to the amount of time that a plant is exposed to sunlight. Based on response to light period , plants may be classified into : Long day plants ( 12-14 hours) Short day plants (8-10 hours) Day neutral plants (photo insensitive)
  22. 22. Day neutral Long day (short night) Short day (long night) No preferential photoperiod for flowering. Require 12-14 hours of light for flowering. Require 8-10 hours of light for flowering. e.g. tomato, pepper, eggplant, cucurbitaceous vegetable crops, cowpea, okra, French bean, amaranth, etc. e.g. Potato, onion, lettuce, cabbage, cauliflower, radish, spinach, beet, turnip, carrot, etc. e.g. Sweet potato, Indian spinach, hyacinth bean, cluster bean, winged bean, etc.
  23. 23.  Day length and light intensity also influence crop water requirements. In general, the greater the intensity of light, the greater the rate of transpiration or water loss from the plant and the greater will be the need to replace the water loss.
  24. 24. Plants with tubers (%) Effect of photoperiod on tuberization in the Livingstone potato (Plectranthus esculentus) 100 90 80 70 60 50 40 30 20 10 0 10 10.5 11 11.5 12 12.5 Photoperiod (hours) 13 13.5 14 Allemann et al., 2005
  25. 25. Effect of light on vegetable crops Cucurbits  In case of cucurbits, day length and intensity of light coupled with temperature are known to influence sex expression.  In cucumber an abundance of light tends to increase the number of staminate flowers.  On the other hand , reduction of light increases the number of pistillate flowers.  Crops such as watermelon, cantaloupe and honeydew melons require high light intensity and warm temperatures to produce good growth and high sugar content in their fruit.
  26. 26. Tomato  High light intensity accompanied by high temperature is harmful to fruit set.  Reduction of light intensity by shading increases fruit set significantly at high temperature.  Mehta and Bhavamaryana, 1981 found that red light and far red light induced carotenoid synthesis, particularly lycopene in ripening fruits of tomato cv. Marglobe.
  27. 27. Capsicum  Short day conditions (9-10 hours light) stimulated plant growth and increased the productivity by 21-24% , beside improving the quality of capsicum (Egorova, 1975).  Reduction of solar radiation by 50% increased the fresh weight of whole fruit (Bigotti, 1974).  Number of days from sowing to flowering and percentage of flower drop increased as the shade increased. But capsaicin content was not affected by different shade intensities (Jeon and Chung, 1982).
  28. 28. Potato  The intensity & duration of light is responsible for higher yield & quality of tuber due to increased photosynthesis but tuber must remain covered under the soil to avoid sun scalding and greening. Plains (Grown as SD In India Tuber initiation early Hills (Grown as LD Tuber initiation delayed during winters) during summers) Murti, 1975
  29. 29. Root crops  Sulgin et al., 1963 in radish reported that maximum shoot growth occurred in plants exposed to low light intensity , but fresh weight of the whole plants, leaves, stems and roots increased with increasing light intensity.  Tikhomirov et al., 1976 and Sarkar et al., 1978 noticed that root yield and quality rose with increasing light intensity in radish.
  30. 30. Bulb crop  In onion and garlic for vegetative growth lower temperature and short photoperiod are required, while relatively higher temperatures and long photoperiod are needed for bulb development.  Mann, 1952 also found that long days and high temperature encouraged bulb development in garlic.
  31. 31. Leafy vegetables  In spinach, long days and warm weather are very favorable for quick bolting of the crop.  In Amaranthus; A. caudatus, A. cruentus and A. edulis are short day species, while A. hypochondriacus is reported to be day neutral.
  32. 32. Influence of Light Induced Greening On Storage of Potato Microtubers 60 50 (%) 40 30 Control Greened 20 10 0 Biomass loss Sprout emergence MICROTUBER STORAGE CHARACTERISTICS Naik and Sarkar , CPRI, Shimla1997
  33. 33. TECHNIQUES FOR REGULATING LIGHT INTERCEPTION  The control of light is significant part of the technology of horticulture. The quality, intensity, and duration of light has manifold effects on the many physiological processes of the plant.  Light interception can be increased or decreased by many ways.
  34. 34. Increasing Light Interception It depends on: 1. Geographic location: The duration and intensity of light depend on climate and geography. Crops planted in rows oriented east and west utilize light more effectively than those planted north and south. 2. Equidistant spacing: Equidistant plant spacing is more efficient than any other because it decreases light competition. 3. Cultural practices: Weed control may be considered in part a practice to eliminate competition for light between crop and weed.
  35. 35. Reducing Light Intensity Why shade?    Low light plants don’t like high light. Reduce temperature. A shade percentage of 30 to 50% is ideal for vegetables. Shade cloth Artificial Shading methods Natural Shading compounds Tree shade
  36. 36. Natural shade
  37. 37. Effect of tree shading on production of major solanaceous crop 1600 Production per plant (in gram) 1400 1200 No shading Medium light Low light 1000 800 600 400 200 0 Egg plant Chilli Tomato Tree – scattered system Manurung et al., AVRDC Taiwan;November 2008
  38. 38. Artificial shade: 1. Shade cloth: It is a simple knit or woven fabric designed to reduce the amount of sun that reaches the vegetable bed.  Crop requiring shade cloth are lettuce, broccoli, cauliflower, peas, celery.  Size of shade cloth : 1.8mx30m, 3.6mx30m, 1.8mx50m, 3.6mx50m 2. Shading compounds: For sunburn protection at a field scale, use of film spray-on materials such as Surround, Screen Duo, and many others.
  39. 39. Different percentages of shade cloth 30% black shade cloth 70% ultra blue shade cloth 40% black shade cloth 50% black shade cloth 60% black shade cloth 65% ultra red shade cloth 60% green shade cloth 60% black white shade cloth
  40. 40. Types of Supplemental Light Sources  Incandescent lamps: It produces a continuous spectrum from blue to infrared. The greater part of overall emission is in the invisible infrared.  Fluorescent lamps: Light from ordinary fluorescent lamps is low in red and deficient in far red. Now special fluorescent lights are available that will produce light richer in red. More efficient than incandescent.  High Intensity Discharge (HID) lamps: Their use is increasing in greenhouses, despite the relatively high cost of fixtures and installation.
  41. 41. Common HID Light Fixtures Found in Greenhouses
  42. 42.  High pressure sodium lamps: It yield red visible light as well as small portions of all other visible light. They are used for the reproductive or flowering phase of the vegetable growth.  LED (Light Emitting Diode) : The newest type of grow lights use LED technology. It grow lights maximize blue and red light to provide and excellent balance for plants. High-pressure sodium lighting of greenhouse cucumber in Norway
  43. 43. Conclusion  There are many countries in which water and land are scarce. So, by using different colored lights on vegetable crops can help to get higher yield with minimum use of valuable resources.  The improvement of productivity under low light conditions can be done by using artificial sources, thus extending the production season into the winter months of the year.
  44. 44. THANK YOU