Agriculture for Engineers 4 (3+1)

Lesson 34. Climatic Requirement for Fruits, Vegetables and Flowers Crops

34.1 Climate

Climate is the principal factor controlling plant growth. It refers to the average condition of the atmosphere over along period, where as the term weather is used to describe the current and temporary atmospheric conditions. For successful growing of horticultural plants, various components of climate like temperature, humidity, wind, light, rainfall, hail and frost should be carefully studied.

Man can not control these environmental factors. It is not possible to make any change in it. But the effect of these factors can be altered. For these we can take certain steps to increase or decrease its effects. i.e. effect of high or low temperature can be altered, additional moisture can be given, high wind velocity can be reduced by growing wind break around the orchard.

Climate of a region is mainly influenced by the factors viz. a) latitude b) altitude c) topography d) position related to continents and oceans e) large scale atmospheric circulation patters.

Almost all components of the climate influence horticultural crops. All are closely interrelated. The effect of each is modified by others. All crops have certain natural threshold limits of the climatic components beyond which they do not grow normally, but breeding and selection are gradually extending the threshold for many crops.

Following is a brief account on important climatic components which are affecting the production of horticultural crops.

34.1.1 Temperature

Temperature is one of the most important components of climate. It plays vital role in the production of horticultural crops. The different activities of plant like growth and development, respiration, photosynthesis, transpiration, uptake of nutrients and water and reproduction (Such as pollen viability, blossom fertilization fruit set etc.), carbohydrate and growth regulators balance, rate of maturation and senescence, and quality, yield and shelf life of the edible products. The above function of the plant should be well when the temperature at the optimum range. During high temperature plant does not perform proper functions of growth, where in low temperature physiological activities of the plant are stopped.

According to different temperature range in the tropics, the specific trees are grown in different location e.g. apple, pear, peach, almond are successfully grown in the regions of low temperature known as temperate fruits. In warm winter areas, due to insufficient chilling temperature fruit trees fail to complete their physiological rest period or meeting their chilling requirement. As a consequence, buds remain dormant, and leave and blossoms do not appear on the trees in the following spring. For this reason temperate fruit like apple, apricot, pear and plums are not considered suitable for tropical or subtropical regions. For tropical and sub tropical fruits the minimum temperature must be within the limit of tolerance of the fruit species. The fruit grown in tropical and sub tropical climate is known as tropical fruit and sub tropical fruits. Mango, chiku, papaya, banana are successfully grown in high temperature regions also known as tropical fruits.

The plant performs well in optimum temperature range. The activities of the plant are affected by very high or very low temperature. The temperature range for plant is

Minimum   4.5° to 6.5° C        (40° - 43° F)

Optimum   24° to 27° C          (75° - 85° F)

Maximum 29.5° to 45.4° C  (85° - 114° F)

Effect of low temperature

The low temperature influenced adversely on plant. There are many effects of low temperature i.e.

• Desiccation: Imbalance between absorption rate and transpiration rate.
• Chilling injury: There is a disturbance in metabolic and physiological process.
• Freezing injury: It is termed as under cooling protoplasm coagulation.

34.1.2 Humidity (moisture) and frost

The atmospheric humidity plays a vital role in deciding the amount of moisture needed to produce a fruit crops. In hot, dry weather enormous amount of water is lost through transpiration. If the atmosphere is humid, even though hot, the amount is much smaller and thus a site in humid belt needs less irrigation. High humidity combined with high temperature also promotes rapid growth. Higher yield but increase incidence of pests and diseases.

The water requirement of plant also depends on humidity but generally requirement of water is differed as per different plant species. e.g. to produce 1 kg dry matter pine tree require 25 liters. of water, apple required 250 liters, Lucern required 500 liters of water.

The plant gets water from soil, but there are many factors affecting it. i.e. (a) amount of water in the soil (b) availability of water is also depends on texture and structure of soil (c) water absorbing area of the tree.

The water is lost from the plant through transpiration by leaves. Transpiration depends on humidity, temperature, wind, light etc. is necessary to maintain the health of plant by maintaining the balance between uptake and loss of water.

34.1.3 Light

Light is an electro magnetic radiation which is a form of kinetic energy. It comes from the sun to the earth as discrete particles called quanta or photons.

Light is one of the most important affecting plant life. It is an integral part of the photosynthetic reaction in that it provides the energy for the combination of carbon dioxide (CO₂) and water (H­₂O) in the green cells having chlorophyll for the formation of carbohydrates with release of oxygen. The following equation is to explain the oxidation of water in photosynthesis.

The performance of crop of growth of plants is influenced by three aspects of light (a) quantity of light (b) intensity of light (c) duration of light.

a) Light intensity: Light intensity refers to the number of photons falling on a given area or to the total amount of light which plants receive; the intensity of light varies with the day, season, distance of equator, dust particles and water vapour in atmosphere, slope of the land and elevation. Symptoms associated with low light intensity are decrease in rate of photosynthesis with normal rates of respiration, decrease supplies of carbohydrates for growth and yield, leaf tips become discoloured, leaves and bud drop, leaves and flowers become light in colour. Due to high light intensity, the plant wilts and light coloured leaves may become gray in colour due to reduction in chlorophyll, the rate of photosynthesis is lowered down while respiration continues. All above reasons cause low yields.

b) Quality of light:Refers to the length of the waves. The visible part of spectrum of electromagnetic radiation ranges from wavelength 390 to 730 µm (nanometer).  It is also called photosynthetically active radiation.

In general, red and blue light produce a greater dry weight. Green light inhibits plant growth. Red light promotes seed germination, growth and flower bud formation in long day short night plant. Photosynthesis is more in the red region. In apple the blue violet region is more important for the development of red pigments and colour.

c) Duration of light: Refers to the period for which light is available. Duration of light required is also known as photoperiod.

 Photoperiodism: Response of plant to length daily exposure to the light is known as photoperiodism or relation of the time of flowering formation of tubers, fleshy roots etc. to the daily exposure length of period of light.

The plants are mainly grouped into three according to duration of light required.

1. Long day plant: Those plants which require 16 hours or more of daily exposure of light and short night 8-10 hours of dark period for induction of flowering e.g. radish, cauliflower, cabbage, carrot, spinach.

2. Short day plant: Those plants which require 12 hours or less of daily exposure of light and long night 10 to 14 hours dark period for induction of flowering. e.g. strawberry, potato, sweet potato, chrysanthemum, cosmos, poinsettia etc.

3. Day neutral plants: Day neutral plants are those plants in which flowering are induced irrespective of duration of light. Such plants are also known as photo insensitive plants. e.g. tomato, chilli, okra, carnation, dianthus, African violet.

4. Intermediate plants: Those plants which require definite period of daily exposure of light. e.g. wild kidney bean, Indian grass, broom grass.

34.1.4 Rainfall

This is a very important factor for horticultural crops, and if a garden or orchard is to be established in a new area it is essential that the pattern of rainfall in the region be studied before any decision is taken concerning the types of crop to be cultivated. Well-distributed and consistent rainfall is always desirable for and ideal orchard site. Rain at the time of flowering is not suitable, because most of tropical fruit crops are sensitive to rain.

34.1.5 Wind

The effect of high wind on crops can be appreciable. Complete physical destruction may result because little can stand against winds of the order of 100 km/hour, even large trees become uprooted. Some crops have quite low damage even due to high wind speed. In many regions high winds can destroy the flowers, fruits etc. Wind breaks can help reduce this problem. The wind break trees, like saru, eucalyptus, Ingadulsis are growing around the orchard for protection.