Factors Affecting Crop Production PDF

# Factors Affecting Crop Production ## Crop Growth - Internal Factors (Genetic or Hereditary) - External Factors (Environmental) - Climatic - Edaphic - Biotic - Physiographic - Socio-economic (Anthropic) ## Internal Factors - Increased yield and other desirable characters are r...

# Factors Affecting Crop Production ## Crop Growth - Internal Factors (Genetic or Hereditary) - External Factors (Environmental) - Climatic - Edaphic - Biotic - Physiographic - Socio-economic (Anthropic) ## Internal Factors - Increased yield and other desirable characters are related to the genetic makeup of the plant. - Areas to improve the potential of crop plants through genetics and plant breeding techniques: - High yields under given environmental conditions. - Early maturity (in some cases late maturity). - Resistance to lodging. - Drought, flood and salinity tolerance. - Tolerance to insects and diseases. - Chemical composition of grains (high percentage of oil, increase in protein quantity or quality, etc.). - Quality of grains (fineness, coarseness, etc.). - Quality of straw (sweetness, juiciness, etc.). ## Environmental Factors - The life of a crop is intimately related to the environmental factors of a place. - Environmental factors do not act in isolation from one another. - All these environmental factors interact with one another to influence the crop growth and production. ### A. Climatic factors - The atmospheric factors, which affect the crop plants, are called climatic factors. - They are: - Precipitation. Temperature - Atmospheric humidity. Solar radiation - Wind velocity. Atmospheric gases #### (i) Precipitation - Precipitation includes all forms of water, which falls from the atmosphere to the earth's surface, in a variety of forms such as rainfall, snow, hail, fog and dew. - Fog particles, which contact vegetation, may adhered, coalesced with other droplets and eventually form a drop large enough to fall to the ground. - Condensation of the water vapour present in the air in cool nights results in a deposit as dew. - Rainfall is one of the most important factors influencing the vegetation of a place. - Most of the crops receive their water supply from rainwater. - Rainwater is the source of soil moisture so essential for the life of a plant. - The yearly precipitation, both in total amount and seasonal distribution greatly affects the choice of cultivated crops in a place. - Low and ill-distributed rainfall are common features of dry farming wherein drought-resistant crops like sorghum, pearl millet, Italian millet and other minor millets are commonly grown. - The interaction of rainfall with temperature has a very profound effect on the vegetation and soil of a place. - Very heavy rainfall and high temperatures in the equatorial and tropical zones cause the formation of most highly developed vegetation of the world. #### (ii) Temperature - Temperature is a measure of intensity of heat energy. - The range of temperature for maximum growth of most of the agricultural plants is between 15 and 40°C. - The temperature of a place is largely determined by its distance from the equator (latitude) and the altitude. - Based on the above, the vegetations are classified as tropical, temperate, taiga, tundra and polar. - Every plant community has its own minimum, optimum and maximum temperature known as their cardinal points. - Apart from the reduction in yield many injuries on the plants and adverse effect on soil conditions occur under both extremes on temperature. | Crops | Minimum °C | Optimum °C | Maximum °C | |--------------|------------|------------|-------------| | Wheat | 4.5 | 20 | 30-32 | | Barley | 4.5 | 20 | 29-30 | | Oats | 4.5 | 20 | 29-30 | | Maize | 8-10 | 20 | 40-43 | | Sorghum | 12-13 | 25 | 40 | | Rice | 10-12 | 32 | 36-38 | | Tobacco | 12-14 | 29 | 35 | ### Effect of temperature - Air temperature is the most important weather parameter, which affects the plant life. - The growth of higher plants is restricted to a temperature between 0-60oC and the optimum 100C-40oC. - Beyond these limits, plants are damaged severely and even get killed. - The maximum production of dry matter occurs when the temperature ranges from 20 to 30°C. - Apart from yield reductions, many visible injuries on the plants are seen due to very low or very high temperatures. #### I. Low temperature effects - Plants are injured due to very low temperatures in the following ways: - Cold injury - Chilling injury - Freezing injury - Suffocation - Heaving #### High temperature effects - Cells of most plant species get killed when the temperature ranges from 50 to 60oC. - This point of temperature is called the thermal death point. But it varies with the species, the age of tissue, and the time of exposure to high temperature. - It is reported that most plant cells are killed at a temperature of 45 to 55oC. - Some plant tissues withstand a temperature of up to 1050C. - The aquatic plants and shade-loving plants are killed at a comparatively, lower temperature (40oC); whereas, for xerophytes it is 50°C. - High temperature results in the desiccation of the plants and disturbs the balance between photosynthesis and respiration. - Higher temperature increases respiration leading to rapid depletion of reserve food in plants resulting in growth stunted due to incipient or starvation. - Heat injury - Very high temperature often stops growth. - The plant faces incipient starvation due to high respiration rates. - The plant is stunted and if such a condition persists for a long period the plant is killed. - Direct temperature effects are noticeable in young seedlings and transplanted crops. - High temperature causes sterility in flowers. - The general effects of excessive heat are defoliation, premature dropping of fruits and in extreme cases death of plants. ### a. Effects of Temperature on Crop Production - Plants can grow only within certain limits of temperature. - For each species and variety, there are not only optimal temperature limits, but also optimal temperatures for different growth stages and functions, as well as lower and upper lethal limits. - During photosynthesis, there are certain biochemical processes preceding and following the reduction of carbon dioxide, which are affected mainly by temperature. - As long as the light is limited, temperature has little effect on the rate of photosynthesis. - When light is not limiting, it has a profound effect on the rate of photosynthesis. - In general, high temperature accelerates the growth process. - Rarely are high temperatures per se the direct cause of death of plants, provided the water supply is adequate. - Retardation of growth and difficulties in fertilization are observed even in heat-loving crops such as sorghum, at extremes of temperatures. - The harmful effects of excessive temperatures are usually aggravated by a lack of available moisture. - Hot dry winds will further increase the damage. - Increasing temperatures increase evapotranspiration. ### b. Factors Affecting Air Temperature - Latitude - The time of occurrence of maximum monthly mean temperature and minimum monthly mean temperature also depends on the latitude of a place. - For example, the coldest month is January in the northern regions of India while December is in the south. Similarly, the warmest month is May in the south while June is in the north across the country. - Altitude - The surface air temperature decreases with increasing altitude from the mean sea level as the density of air decreases. - Since the density of air is less at higher altitudes, the absorbing capacity of air is relatively less with reference to Earth's longwave radiation. - Distribution of land and water - Land and water surfaces react differently to the insolation. - Because of the great contrasts between land and water surfaces their capacity for heating the atmosphere varies. - Variations in air temperature are much greater over the land than over the water. - The differential heating process between land and sea surfaces is due to their properties. - It is one of the reasons for the Indian monsoon. - Ocean currents - The energy received over the ocean surface carried away by the ocean currents from the warm areas to cool areas. This results in temperature contrast between the equator and poles. - The occurrence of El Nino is due to changes in sea surface temperature between two oceanic regions over the globe. - Prevailing winds - Winds can moderate the surface temperature of the continents and oceans. - In the absence of winds, we feel warm in hot climates. - At the same time, the weather is pleasant if the wind blows. - Cloudiness - The amount of cloudiness affects the temperature of the earth's surface and the atmosphere. - A thick cloud reduces the amount of insolation received at a particular place and thus the daytime temperature is low. - At the same time, the lower layers of the atmosphere absorb the Earth's radiation. - This results in increasing atmospheric temperature during the night. - That is why, cloudy nights are warmer. - This is common in the humid tropical climates. - Mountain barriers - Air at the top of the mountain makes little contact with the ground and is therefore cold while in the valley at the foothills makes a great deal of contact and is therefore warm. - That is, the lower region of the earth's atmosphere is relatively warmer when compared to hillocks. ### III. Atmospheric humidity - Water is always present in the atmosphere in the form of invisible water vapour, normally known as the humidity of the air. - When the atmosphere contains the maximum possible amount of water vapour it is said to be saturated at a particular temperature and pressure. - Any increase in temperature, with water remaining constant, will make the air unsaturated. - In unsaturated conditions, the water vapour content of air is usually expressed as relative humidity, which is the ratio between the actual humidity present and the saturation humidity possible at that temperature. - The relative humidity of a place is affected by temperature and pressure. - It is also affected by wind, exposure to radiation, vegetation, and water content of the soil. - The evaporation of water from plants or a body of water is directly dependent on the relative humidity of the atmosphere. | Humidity | Definition | |--------------|------------------------------------------------------------------------| | Absolute humidity | The actual mass of water vapour in given volume of air. | | Specific humidity| The mass of water vapour to the mass of moist air | | Relative humidity | The percentage of water vapour present in the air | - Dew point: The temperature at which saturation occurs in a given mass of air. - The dew point temperature is often compared with the temperature of free air and is also used to predict the occurrence of fog, dew, frost or precipitation. - Vapour pressure: This is the amount of partial pressure created by water vapour in the air expressed in the units of millibar (or) inches of mercury. - Evapotranspiration of crop plants increases with temperature but decreases with high relative humidity affecting the quantity of irrigation water. - Moist air favours the growth of many fungi and bacteria and these affect seriously the crop. - The blight diseases of potatoes and tea are common examples of diseases spread under moist weather. - Similarly many kinds of insect parasites such as aphids and jassids thrive well in moist conditions. ### RH on Plant growth - Increase in RH - decreases the temperature. - This phenomenon increases the heat load of the leaves. - Since transpiration is reduced - not much heat energy is used. - Excessive heat due to closure of stomata entry of CO2 is reduced. - Reduction in transpiration reduces the rate of food translocation and uptake of nutrients. - Very high RH is beneficial to Maize, Sorghum, and Sugarcane (C4 Plants) and Harmful to – Sunflower and tobacco. - For almost all the crops it is always safe to have a moderate relative humidity of above 40%. - 60-80% conducive to growth and development of plants. - The humidity is not an independent factor. - It is closely related to rainfall, wind, and temperature. - It plays a significant role in crop production. - The humidity determines the crops grown in each region. - It affects the internal water potential of plants. - It influences certain physiological phenomena in crop plants including transpiration - The humidity is a major determinant of potential evapotranspiration. So, it determines the water requirement of crops. - High humidity reduces the irrigation water requirement of crops as the evapotranspiration losses from crops depend on atmospheric humidity. - High humidity can prolong the survival of crops under moisture stress. - However, very high or very low relative humidity is not conducive to higher yields of crops. - harmful effects of high humidity. It enhances the growth of some saprophytic and parasitic fungi, bacteria, and pests, the growth of which causes extensive damage to crop plants. - The damage caused by thrips and jassids on several crops. - High humidity at grain filling reduces crop yields. - A very high relative humidity is beneficial to maize, sorghum, sugarcane, etc., while it is harmful to crops like sunflower and tobacco. - For almost all the crops, it is always safe to have a moderate relative humidity of above 40%. ### 2. Quality of light - When white light is passed through a prism it is dispersed into wavelengths of different colors; violet 400-435 mill microns (mu); blue 435-490; green 490–574; yellow 574–595; orange 595-626 and red 626 to 750 mµ. - Visible rays 390–760 micron [, nm. ### Effect of light quality on plants - Red and blue light account for the largest proportion of the total light received by plants. - The proper combination of red and blue light can promote the growth of lettuce, tomato, and pepper. - Red light promotes the accumulation of carbohydrates in lettuce. - It is worth noting that blue light has a positive role in the synthesis and accumulation of flavonoids and polyphenols. - Blue light enhanced catalase (CAT) activity in wheat compared with white light. - Red and blue light lead to diverse morphological and physiological responses of plants, and these responses are species-specific. - The red light seems to be the most favorable light for growth followed by violet-blue. - Ultraviolet and shorter wavelengths of the visible light are scattered and infrared and longer wavelengths are absorbed by moisture of the atmosphere. - Such a light is called diffused light or skylight. - Ultraviolet and shorter wavelengths kill bacteria and many fungi. - Orange light encourages the flowering process while plants reflect a green color during the growth stage. ## IV. Solar radiation - The sun is the primary source of heat to the earth and its atmosphere. - The heat received from other celestial bodies as well as the interior of the earth is rather too insignificant to merit our attention. - The distance that separates the Earth from the sun is about 1,49,000,000 km. - The diameter of the sun measures roughly about 13,82,400 km. - The surface temperature of the sun is estimated between 5500oC and 6100oC (or 57620K). - Solar radiation provides more than 99.9% of the energy that heats the earth. - Undoubtedly, the radiant energy from the sun is the most important control of our weather and climate. - The most astonishing fact about the incoming solar radiation (insolation) that strikes the earth's surface is that it is equal to about 23 billion horsepower. - Actually, it is this amount of energy received from the sun that acts as the driving force for all the atmospheric as well as biological processes on the earth. - Besides, all other sources of energy found on earth such as coal, oil wood etc., are nothing but converted forms of solar energy. - The word 'insolation' is a contraction of "incoming solar radiation". - Radiant energy from the sun that strikes the earth is called insolation. - Solar energy provides two essential needs of plants (a) light, required for photosynthesis and for many other functions plant-including seed germination, leaf expansion, growth of stem and shoot, flowering, fruiting and even dormancy, and (b) thermal conditions required for the normal physiological functions of the plant. - Solar radiation consists of a bundle of rays of radiant energy of different wavelengths. - The sum emits radiant energy in the form of electromagnetic waves. - The visible portion of the solar spectrum appears as light. - Light travels with a speed of 2,97,600 km/sec. - It takes 8 minutes and 20 seconds to reach the earth. - Light is the total effect of the combination of the seven different colours, namely red, orange, yellow, green, blue, indigo and violet. (VIBGYOR). - The waves that produce the effect of red colour are the longest and those producing the violet are the shortest. - Waves shorter than violet are called ultraviolet rays, while those longer than red are known as infrared rays. - The ultraviolet waves form only 6% of the insolation but have strong photochemical effects on some substances. - The infrared rays, even though invisible, form 43% of the insolation. - They are largely absorbed by water vapour that is concentrated in the lower atmosphere. - Solar constant is defined as the rate at which solar radiation is received outside the earth's atmosphere on a surface perpendicular to the sun's rays when the earth is at an average distance from the sun. - The Smithsonian Institute, USA has come to the conclusion that the standard value of solar constant is 1.94 gram calories per cm2/minute. - Since there is fluctuation in the amount of radiant energy emitted by the sun due to periodic disturbances on the solar surface, the amount of solar constant, therefore, registers a slight increase or decrease. However, this variation hardly exceeds 2-3%. - Light is one of the most important climatic factors for many vital processes of the plant. - It is indispensable for the synthesis of the most important pigment of the plant, i.e., the green chlorophyll. - The chlorophyll is capable of absorbing radiant energy and converting it into the potential chemical energy of carbohydrates. - The carbohydrates manufactured by plants during photosynthesis are the only link between solar energy and the living world. - It regulates the rate of transpiration by controlling the opening and closing of stomata. - Light affects the plants through its intensity, quality (wavelength), duration (photoperiod), and direction. #### 1. Light intensity - The variations in light intensity are always accompanied by changes in temperature and relative Light dity and therefore it is difficult to evaluate light effects alone. - Generally speaking, light intensity falling at a particular place is normally enough for the plants and their physiological phenomena viz., photosynthesis. - In photosynthesis about one percent of the light energy is converted into potential chemical energy. - Very low light intensity reduces the rate of photosynthesis and may even result in the closing of the stomata. - This results in reduced vegetative growth of the plants. - Very high light intensities are detrimental to plants in many ways. - It increases the rate of respiration and thus disturbs the photosynthesis-respiration balance. - It causes rapid loss of water resulting in the closure of stomata. - The most harmful effect of high light intensity is the phenomenon of "Solarization" in which all the cell contents are oxidized by atmospheric oxygen. - This oxidation is different from respiration and is termed photo oxidation. - Based on the response to light intensities, the plants are classified as follows: - Sciophytes (Shade-loving plants) - The plants that grow better under partially shaded (low light) conditions e.g., betel vines, buckwheat, etc. - Heliophytes (Sun loving plants) - Many species of plants produce maximum dry matter under high light intensities when the moisture is available at the optimum level, e.g., maize, sorghum, rice, etc. - Except under glass houses or shaded conditions, the intensity of light cannot be controlled. - Depending upon the nature of the crops, the dry matter production is affected. - Many species produce maximum dry matter under high light intensity if water is available in plenty. - However, crops like buckwheat and tobacco grown during summer produce greater dry matter if slightly shaded. ## V. Wind velocity and its effect on crop production - Air in horizontal motion is known as wind. - Vertical movement is noticed but negligibly small compared to horizontal movement as the height of the atmosphere is only for few km. - However vertical movement or uplift of air only causes significant weather changes in cloud formation and rain. - The velocity of wind at a place depends on various factors such as geographical situation, topography, altitude, distance from seashore, flat plains, vegetation etc. - Wind affects crop growth mechanically (directly) and physiologically (indirectly). ### Wind speed in different seasons - Winds represent air in motion. - The primary cause of all winds is regional differences in temperature, producing regional differences in pressure. - When these pressure differences persist for several hours, the rotation of the earth modifies the direction of motion, till the winds blow along lines of equal pressure. - Wind direction and speed are modified frequently due to seasonal variations in solar radiation and differential heating of the earth's surface. #### 1. Wind speed - The winds are generally measured over level, open terrain at 3 meters above ground. - Yet, a general idea of the distribution of the mean daily wind speed, on an annual basis as well as on a monthly basis, would be useful. - The mean daily wind speed is the value obtained by averaging the wind speed (irrespective of direction) for a whole day. - This average for all the days of a month is the mean daily wind speed for that month. - The daily values averaged for all 365 days of the year are the annual mean daily wind speed. #### 2. Wind Direction - Winds are always named after the direction they come from. - Thus, a wind from the south, blowing towards the north is called south wind. - The wind vane is an instrument used to find out the direction of the wind. - Windward refers to the direction wind comes from, and leeward refers to the direction it blows. - When a wind blows more frequently from one direction than from any other, it is called a prevailing wind. #### 3. South West Monsoon wind direction - During South West Monsoon period of June to September, the westerly winds prevail on the west of Kerala and south winds on the west of northern Circars, Orissa and Bengal. - During April and May, the region of high temperature is shifted to the north viz., upper Sind, lower Punjab and Western Rajasthan. This area becomes the minimum barometric pressure area to which monsoon winds are directed. #### 4. North East Monsoon wind direction - During North East Monsoon period of October to December, on account of the increase in barometric pressure in Northern India, there is a shift in the barometric pressure to the South East and North Easterly winds begin to flow on the eastern coast, by the end of September. - These changes bring heavy and continuous rainfall to Southern and South Eastern India. ## VI- Atmospheric gases - The atmosphere surrounding the earth contains a mixture of gases viz., carbon dioxide (0.03%), oxygen (20.95%), nitrogen (78.09%), argon (0.93) and miscellaneous gases (0.02%) in a constant proportion. #### (a) Carbon dioxide - CO2 is the main source of carbon for the various types of organic compounds in the body of the plants. - It is the main raw material for the manufacture of carbohydrates by the photosynthetic process of green plants. - Photosynthesis is approximately proportional to the concentration of CO2 in the air surrounding the foliage of the crop. - The CO2, which gets incorporated into the organic compounds of the plants, returns to the atmosphere by respiratory breakdown of these compounds and by the death, decay and combustion of plants (carbon cycle). - Increased growth and greater yield of vegetables are possible under greenhouse conditions by increasing the content. - Aquatic plants utilize the dissolved CO2, from water. #### (b) Oxygen - Life sustains because of oxygen. - The amount of O2 is normally constant in the air because plants give off O2, during photosynthesis. - Lightning, rainfall and nitrogen-fixing microorganism contributes nitrogen to the soil from the atmosphere. - Symbiotic bacteria like rhizobium, free-living bacteria like azotobacter, blue-green algae etc., fix a good amount of nitrogen in the soil. - The decomposition of dead plants and animals also adds N to the soil. - The N in the soil is made available to the crops by the activity of nitrifying bacteria. - Certain gases like SO2, CO and HF when released into the air in sufficient quantities are toxic to plants. ## B- Edaphic factors - Plants grown on land are completely dependent on the soil in which they grow for anchorage, water and mineral nutrients. - The soil factors, which affect crop growth, are: - Soil moisture; - Soil air; - Soil temperature; - Soil mineral matter; - Soil organic matter, - Soil organisms, and - Soil reaction. | Composition | Percent | |-----------------|---------| | Mineral matter | 30 | | Soil moisture | 30 | | Soil air | 30 | | Soil organic matter | 5-10 | - The available soil moisture range between the saturation point and wilting point. - The moisture with about pF 2.54 is very favourable for plant growth. - The moisture near pF 4.2 (wilting point) is absorbed by plants only with great difficulty and the plants may not be able to make vigorous growth near this moisture level. - pF: is the logarithm of height (in cm) of a water column that represents the total stress with which water is held by the soil. - Soil air - Aeration of the soil is absolutely essential for the absorption of water by roots. - O2 is required for the respiration of roots and microorganisms. - In poorly aerated soil CO2 gets accumulated and is detrimental, to the absorption of water by the roots. - Soil air is also useful in increasing the nutrient availability of the soil by, breaking down the insoluble mineral into soluble salts; • decomposing organic matter, and • bringing out nitrifying (nitrogen releasing) and nitrogen-fixing processes of bacteria - Soil temperature - It affects the physical and chemical processes going on in the soil. - It influences the rate of absorption of water and solutes, the germination of seeds and the rate of growth of the underground portions of the plant body. - The maximum absorption of water by the roots takes place generally between 20°C and 30°C. - Temperature below 20°C causes an appreciable reduction in the rate of absorption of water. - Cold soils are therefore not conducive to the rapid growth of most agricultural crops. - Soil temperature controls microbiological activity and processes involved in the availability of nutrients to plants. - Nitrification begins in the soil when the temperature reaches about 5°C. ### Soil mineral matter - The mineral content of the soil is derived from the weathering of the rocks and minerals as particles of different sizes. - These are sources of plant nutrients such as Si, Ca, Mg, Fe, K, Na and Al. - Minor elements (trace elements) like B, Mo, Zn, Cu, Co, Iodine and Fe are also present in very small quantities. ### Soil organic matter - The soil organic matter content varies from less than 1% in arid sandy soils to as much as 90% of the dry weight of well-developed soil. - It has a marked influence on the soil properties and growth of crops. - The organic matter of the soil is derived from (i) dead and decaying roots of plants and living organisms present in the soil, and (ii) dry leaves, twigs, dead plants and animals added to the soil. ### Advantages of soil organic matter - It is the source of essential plant nutrients for crop growth. It contains 95% of total N, 50-60% of the total P and 10-20% of the total S; - It increases water water-holding capacity of the soil due to its organic colloids; - It increases the cation exchange capacity (CEC) of the soil; and - It is a source of food for most of the soil organisms. ### Soil organisms - Raw organic matter in the soil is not directly used by the plants as food. - It must be broken down first into humus and then into simpler products before it can be utilized. - This work is done by different kinds of organisms as given below, which inhabit the soil in billions. | Category | Organisms | |-----------|-----------------------| | Flora | Roots of higher plants | | | Bacteria, Actinomycetes | | | Fungi, Algae | | Fauna | Earthworms | | | Burrowing vertebrates | | | Protozoa, Nematodes, Mites, Insects| ### Soil reaction - Soils may be neutral, acidic or alkaline depending upon their content of basic salts and acidic components. - Neutral soils are the best for the growth of most crops. - Soil acidity beyond a particular limit (soil with low pH) is injurious to the plant growth due to: - Aluminum toxicity under high acidity. - Interferes with the absorption of several nutrients particularly cation like K, Ca and Mg. ### Effects of high soil pH - P gets fixed in acidic soils. - Organic matter decomposition is reduced. - Activities of nitrifying and nitrogen-fixing bacteria may be checked. ### Components of Soil - Soil consists of four major components. They are (i) Mineral matter, (ii) Organic matter, (iii) water, and (iv) air. - Physically, the soil consists of stones, large pebbles, dead plant twigs, roots, leaves, and other parts of the plant, fine sand, silt, clay, and humus derived from the decomposition of organic matter. - In the organic matter portion of the soil, about half of the organic matter comprised of the dead remains of the soil life in all stages of decomposition, and the remaining half of the organic matter in the soil is alive. - The living part of the organic matter consists of plant roots, bacteria, earthworms, algae, fungi, nematodes actinomycetes, and many other living organisms - Soil contains about 50% solid space and 50% pore space. - Mineral matter and organic matter occupy the total solid space of the soil by about 45% and 5% respectively. - The total pore space of the soil is occupied and shared by air and water on a roughly equal basis. - The proportion of air and water will vary depending on the weather and environmental factors. #### (a) Soil mineral matter (SMM) - The size and composition of mineral matter in soils are variable due to the nature of the parent rock from which it has been derived. - The rock fragments are disintegrated and broken portions of the massive rocks, from which regolith through weathering, the soil has been formed. - These materials are usually very coarse and the minerals are extremely variable in size. - The primary minerals viz., quartz, biotite, muscovite (dominates coarse fractions of the soil), and the secondary minerals viz., silicate clays and hydrous oxides clays of iron and aluminium (as very fine fraction) are present. ### (b) Soil organic matter (SOM) - Soil organic matter exists as partly decayed and partially resynthesized plant and animal residues. - These are continuously being broken down as a result of microbial activity in soil. - Due to constant change, it must be replenished to maintain soil productivity. - The organic matter content in soil is very small and varies from only about 3-5% by weight in topsoil. - In addition to partly decayed plant and animal residues, soil organic matter contains living and dead microbial cells, microbiologically synthesized compounds and derivatives. ## C- Biotic factors - Beneficial or harmful effects caused by other plants and animals on the crop plants are the effect of biotic factors. ### Plants #### (a) Competitive and complimentary nature among field crops - Competition between plants occurs when there is demand for nutrients, moisture and sunlight, particularly when they are in short supply or the plants are closely spaced. - Optimum spacing of crops is an important agronomical practice. - When different crops such as cereals and legumes are grown together as in mixed cropping there is mutual benefit resulting in better yield. #### (b) Competition between weed and crop - Weeds reduce crop yields due to competition with crops for water, soil nutrients and light. - In dry farming conditions weeds compete with crops for water. - In irrigated tracts, the competition is severe for nutrients. - Weeds in fallow land deplete the soil of both moisture and nutrients. #### (c) Plants as Parasites - A plant parasite is dependent on its host plant for its existence. - Parasitic plants like striga, orabanche, cuscuta and loranthus live on the host plants and affect the growth of the crop plants. - Parasitic fungi, bacteria, virus etc., causes different kinds of diseases on agricultural crops. #### (d) Symbiosis - Different organisms have a mutual relationship with each other and with the environment. - This biological interrelationship among the organisms is termed as symbiosis. - For example, Legumes and rhizobia-nodule forming; Azotobacter-free living (it fixes elemental N present in the atmosphere and supplies to the plants). ### Animals #### (a) Soil animals or Soil fauna - Include protozoa, nematodes, rotifers, snails and insects. - They help organic matter decompose while using the organic matter for their living. - Harmful organisms - Insects and nematodes cause considerable damage as crop pests during the growth of plants and in the storage of grains. The average loss due to insects is about 20% throughout the world. - Beneficial organisms - Many plants are pollinated primarily by insects. Examples of beneficial organisms are: - Bees and wasps are important for pollination. - Moths, butterfly and beetles also do pollination. Beetle (Elaeis kaemeniricus) is necessary to have good pollination in oil palm crop. ## D. Physiographic factors - It can be studied under two categories such as: - Geological Strata - It accounts not only for the kind of parent material utilized in soil formation but also for the nature of crops grown in these soils for proper utilization. - Topography - The nature of the surface of the earth is known as topography. Topographic factors affect the crops indirectly by modifying climatic and edaphic factors of a place. #### 1. Altitude of the place - An increase in altitude causes a decrease in temperature and increase in precipitation and wind velocity. #### 2. Steepness of slope - It causes swift runoff of rainwater resulting in decreased moisture content of soil. - The organic matter of the soil increases resulting in high N content and acidity of the soil. #### 3. Exposure of the slope to light and wind - A mountain slope exposed to weak intensity of light and strong dry winds as the case of northern slopes of temperate regions and the Himalayas may have poor crops due to want of moisture and sunlight. - Similarly, the western slopes of Tamil Nadu hills poor crops due to damage caused by heavy winds. #### 4. Direction of the mountain chains - It governs the distribution of the rainfall during monsoon and also the type of crops in dry farming. ## D. Anthropic (socio economic) factors - Men/women produce changes in a plant environment and are responsible for scientific crop and soil management, breeding varieties for increased yield, and introduction of exotic plants. - These factors affect the management of soil and crop, which leads to higher production. - In addition to the above the socio-economic factors affecting crop production are: - the economic conditions of the farmer greatly decide the input/resource mobilizing capacity, - the educational status and technical know-how of the farmer, - the resource allocation ability and social values of the farmer, - government price policy, and - marketing and storage facilities etc. ## ATMOSPHERE - Earth is elliptical in shape and has three spheres viz., 1. Hydrosphere-the water portion, 2. Lithosphere-the solid portion, and 3. Atmosphere-the gaseous portion. - The atmosphere is the colorless, odorless and tasteless physical mixture of gasses, which surrounds the earth on all sides. - It is mobile, compressible and expandable. - The uses of the atmosphere are as follows: - Provides oxygen which is useful for crop respiration - Provides CO2 to build biomass in photosynthesis. - Provides N, which is essential for plant growth. - Acts as a medium for transportation of pollen.