The factors affecting horticultural crops

A. Temperature:

• Temperature affects important physiological functions like respiration, photosynthesis, transpiration etc
• The activity of enzyme is doubled with every 10 °C rise in temperature up to certain limit
• The maximum and minimum temperature to support plant growth lies between 5-36 °C
• Temperature affects growth and development of horticultural crops during different phase of growth such as seed germination, flowering, pollination, fruit set, seed production, seed dormancy, quality of seed, occurrence of disease and pest
• Some horticultural plants such as temperate fruits need chilling hours (250-1500) with temperature below 7°C for breaking dormancy and better flowering
• So, the fruits like apple, pear, peach, strawberry, apricot, etc. can’t be grown in tropics
• Vegetables specially biennial crops like onion, carrot, cabbage require chilling temperature (0- 10°C) to produce flower and seed (vernalization effect)
• On the other hand, tropical fruits like mango, banana, pineapple, jackfruit, etc require a long growing season and high temperature without any frost and snow
• Heat budget (heat unit) is the total hour of temperature required for the maturity of particular crop
• Heat budget is very much useful for the detection of right time for harvesting
• The source of heat is sun for all plants
• Finally, one heat budget must be balanced i.e. what amount it comes to earth, what amount is utilized by plants and what amount is reflected out, etc.

B. Rainfall

• Water is the most important compound in the biological world
• Most living thing contain high water that is about 70-90%
• Terrestrial animal contains 60-85% water by weight of their body, aquatic animals contain 95% water by weight of their body whereas blood plasma or blood contain 95% water
• Water plays vital role in photosynthesis
• It is the solvent system of the cell and provides medium for transfer within the plants
• The amount of rainfall in a given region determines the type of horticultural crops to be grown successfully there.
• Horticultural plants need ensured supply of water
• If rainfall is disturbed throughout the year, most fruits need to be irrigated
• Rainfall effects on various phases of plant growth such as germination, vegetative growth, flowering, fruit set maturity and harvesting, fruit quality, disease and pest occurrence and seed viability in storage

C. Light

• Sun is the primary source of energy available to the earth and its atmosphere
• Plant response to a broader light of wavelength 300-800 nm
• Light particles are called photons or quanta
• Light influences several aspects of plant development and physiology
• It is the integral part of photosynthesis
• Photosynthesis increases with intensity of light to some extent provided other conditions are favorable
• U.V wavelength (100-400 nm) tends the plant to be dwarf

Based on duration of light response (i.e. photo periodism), plants are divided into:

I. short day plants (SDP)

• Require short light duration( maximum of 12 hr) or longer night (12-14 hr) for initiation of reproductive phase
• Example: onion, sweet potato, etc

II. long day plants (LDP)

• Require long light duration( minimum 13 hr) or 8-10 hr night
• Example: bean, cowpea, radish, spinach, lettuce, etc

III. Day neutral plants (DNP)

• Photo insensitive plants
• Example: most of perennial fruit crops
• Light also affects the quality of fruits
• Light is generally beyond the control of grower
• However, manipulation of light can be done by altering planting season
• In green house condition, all the aspects of light i.e. intensity, quality, duration may be controlled but the cost will be very high (expensive)

D. Wind

• Wind helps in pollination and dispersal of seeds
• Too high and too low velocity is harmful for fruit set
• High wind can interfere with pollination and may cause premature dropping of flowers and fruits
• High wind velocity also enhances soil erosion
• Severe winds are harmful at the time of flowering and fruit set
• Planting one or more rows of wind breaks (i.e. trees) at right angle to the prevailing wind reduce the wind velocity
• Trees used for wind breaks are eucalyptus, sisoo, mulberry, gulmohar, etc. the effectiveness of wind breaks depends upon weight and thickness of trees.

E. Humidity

• The influence of humidity depends upon the type of plant as well as on the availability of soil moisture
• Example: xerophytes tolerate reduced humidity whereas plants of tropical origin like banana, mango, jack fruit require high humidity
• The primary effect of humidity is on transpiration rate
• Increased transpiration and too low humidity cause wilting and desiccation in plant
• Water loss can be minimized by maintaining high relative humidity around the nursery to establish the newly propagated plant
• High relative humidity around the cutting is necessary to prevent desiccation
• Dry weather an low humidity are favorable for seed maturity and harvesting in most of the crops, most of the seeds store well under low humidity

F. Hailstone

• When the air containing high humidity reaches low temperature in high atmospheric region, water vapor turns into small, solid ball shaped pallets and fall to the earth as hail
• It causes several damages to plants, breaks branches of trees, kills small plants
• Hail is especially dangerous for fruit crops