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Essay on Crops
- Essay on the Meaning of Crops
- Essay on the Classification of Crops
- Essay on the Production of Crops
- Essay on Crops and Air Temperature
- Essay on Weather and Crop Production
- Essay on the Abnormalities Affecting the Production of Crops
Essay # 1. Meaning of Crops:
A crop is the annual or season’s yield of any plant that is grown in significant quantities to be harvested as food, fodder, fuel or for any other economic purpose.
The crop plants, derived from wild progenitors through selection and breeding, have characteristics of particular agronomic value as against survival characteristics in the wild progenitors. The value of a crop is dependent on its ability to produce a larger amount of useful material than its wild progenitor.
While the wild or uncultivated plants require environmental conditions that will ensure successful regeneration, the crop plant or cultigen needs those which will allow a high probability of a satisfactory and relatively consistent yield of the harvestable parts for which it has been specifically cultivated. In the highly domesticated species, the symbiotic relationship with human-beings is such that a few would survive in the wild without his protection.
Essay # 2. Classification of Crops:
Crop plants are classified in a number of ways.
From agronomic point of view, crops are classified as:
i. Cereals or Grain Crops:
This group includes rice, wheat, barley, oats, pearl-millet, finger- millet, foxtail-millet, sorghum, maize etc.
It includes pulse crops such as gram, pigeon-pea, green-gram, black-gram, soybean, peas. cow-pea, horse-gram, lentil, etc.
iii. Oilseeds Crops:
Groundnut, mustard, sunflower, sesame, safflower, castor, rapeseed, etc. constitute this group.
iv. Fiber Crops:
This group includes cotton, flax, jute, mesta and sunhemp.
v. Forage Crops:
This group mainly includes grasses and legumes such as sorghum, elephant crass, guinea grass, berseem, lucerne and other pulse crops.
vi. Sugar Crops:
The two important crops are sugarcane and sugar beet.
vii. Root Crops:
Sweet potato and cassava are significant in this group.
viii. Tuber Crops:
Potato and elephant yam are important.
ix. Drug Crops:
Tobacco is common crop of this group in India.
x. Plantation Crops:
Tea, coffee and coconut are important.
xi. Condiments and Spices:
Important crops are cardamom, pepper, chillies, turmeric and ginger.
xii. Medicinal and Aromatic Plants:
This group is again subdivided into two—medicinal crops such as cinchona, isabgol, opium poppy, senna, belladonna, rauwolfia, lycorice and aromatic plants such as lemon grass, citronella grass, palmarosa, Japanese mint, peppermint, rose, geranium, jasmine, henna, etc.
Another simple classification could be:
i. Filed crops such as cereals, millets and pulses.
ii. Plantation crops such as tea, coffee, rubber, coconut, etc.
iii. Commercial crops includes oilseed crops, sugar crops, fiber crops and tobacco.
iv. Horticultural crops such as fruit, vegetable and ornamentals.
v. Forage and grasses like sorghum, maize, elephant grass, guinea grass and other pulse crops.
vi. Condiments and spices which includes cardamom, pepper, chillies, ginger and turmeric.
vii. Medicinal and aromatic plants as indicated under agronomic classification.
A more rationale grouping of universal applicability is that on the basis of harvested part: grain cereals, seed legumes, roots and tubers, vegetables and fruits.
Cereals derived from Ceres, the Goddess of Grain, are the most important crops in terms of area occupied and production. Cereals comprises the small grains (wheat, rice, barley, rye, oats) and large or coarse grains (maize, sorghum, millet).
Collectively, these provide over 50 per cent of world’s energy and protein needs and occupy two-thirds of the cultivated land. Importance of cereals is due to their relatively high nutritive value (10-12 per cent protein), ease of cultivation, storage and transport, wide environmental adaptability and their early maturity.
After cereals, seed legumes are the most widely cultivated crops in both temperate and tropical latitudes. They have three common features: they produce seeds in fruits (pods), that is, the legume which has given its name to the group, they produce hard and relatively large seeds (pulses) with protein as main storage compound and nearly all can fix atmospheric nitrogen in their roots.
Three most important seed legume crops producing food are soybean, field bean and groundnut. In contrast to cereals, legumes are rich in lysine, but low in sulphur containing compounds.
The third group of food crops are the roots and tubers, the bulky organs with more than 75 per cent water that limits storage. Of these, potato is a basic item of diet in all the temperate countries. Sweet potato and cassava are the most widespread of tropical tubers.
The other food crop in the top twenty is sugarcane, the harvested part being the stem for its sugar content. Sugar beet, a new crop is well adapted to environmental conditions for sugar extraction comparable to those of potato. The industrial crop that rivals the major food crops in extent is cotton, the most important fiber producing plant.
Others of this group include flax, hemp and sisal. Plant sources of oil and foodstuff, other than those included under top twenty include safflower, castor, sunflower, linseed, sesame, mustard and rapeseed. Coconut and oil palm are large scale commercial production of oils.
Essay # 3. Production of Crops:
i. Land Resources:
For crop production the basic input is land. The continuing population increase will result in available cultivable land per capita world-wide from 0.3 ha in 1988 to 0.17 ha in 2050, with only 0.11 per capita in developing countries. The nutrient losses due to soil erosion of one tonne of good top soil in kg are 4 N, 1 P2O5, 20 K2O and 2 CaO, besides organic matter. Only 10 to 11 per cent of cultivated area is reasonably free from all constraints for crop production.
The FAO analysis of growth patterns in crop output in 93 developing countries shows that 63 per cent of the growth in production must come from higher yields and 15 per cent from higher cropping intensity. Only 22 per cent is expected from land reserve. Reported land use on global basis and in India is given in Table 1.3. Total world land area including rivers and fresh water lakes is about 13,400 M ha. Other lands include ice caps, deserts and mountains.
Of about total 6,444 M ha of rainfed agricultural potential, only 30 per cent is suitable, 10 per cent marginal and 60 per cent unsuitable in different countries. The semiarid tropics (SAT) comprise of all or part of 50 countries in five continents of the world (Central America, SW Asia, Africa, South America and South East Asia) is the home of 700 million people who are under perpetual threat of drought and occasional famine.
About 65 per cent of the arable land-carry untapped potential for cereals, pulses and oilseeds, the biggest gains to the food ladder of the globe would be from an improvement of agriculture. India has the largest SAT area (10%) of any of the developing countries.
As in 2003, about 11 per cent (1.5 billion ha) of the global land surface (13.4 billion ha) is used for crop production (arable land and land under permanent crops). This area represents about a third (36%) of the land estimated to be to some degree suitable for crop production.
The fact that there remains some 2.7 billion ha with crop production potential suggests that there is still scope for further expansion in agricultural land. However, there is also perception that there is no more or very little land to bring under cultivation economically.
Ninety per cent of the growth in crop production globally (80 per cent in developing countries) is expected to come from higher yields and increased cropping intensity, with the remainder coming from land expansion.
Recent FAO publication (FAO 2009) on “How to feed the world 2050” indicates that world arable land would expand by some 70 M ha (or less than 5 per cent), with the expansion in developing countries by about 120 M ha (or 12 per cent) being offset by a decline of some 50 M ha (or 8 per cent) in the developed countries.
Arable land expansion is mostly through deforestation. Much of the suitable land in use is concentrated in a few countries in Latin America and sub-Saharan Africa, but many countries with growing rural populations in these regions are extremely land scarce and much of the potential land is suitable for growing only a few crops that are not necessarily those for which there is the highest demand.
Also much of the land not yet in use suffers from constraints (chemical, physical, endemic diseases, lack of infrastructure etc.) that cannot easily be overcome or that it is not economically viable to do so. Part of the land is forested, protected or subject to expanding urban settlements.
Overall, however, it is fair to say that although there are many countries (in particular in the Near East/North Africa and South Asia) that have reached or are about to reach the limits of land available, on a global scale there are still sufficient land resources to feed the world population for the foreseeable future, provided that the investments required to develop these resources are made and the neglect of recent decades in the agricultural research and development effort is reversed.
Environmental degradation is increasing at a pace that is impairing the productivity of land and undermining the welfare of millions of rural people. Global assessment of soil degradation (GLASOD) defines soil degradation as a process that describes human induced phenomena which lower the current and/or future capacity of the soil to support human life.
The five causes for degradation are:
a. Removal of vegetative cover through agricultural clearing.
b. Decrease in soil cover through removal of vegetation for fuel wood, fencing etc.
c. Overgrazing by livestock leading to decrease in vegetative cover and trampling of the soil.
d. Agricultural activities like cultivation in steep slopes, farming without anti-erosion measures in arid areas, improper irrigation and use of heavy machinery.
e. Soil contamination with pollutants such as waste discharges and over use of agrochemicals.
Modern farm technologies are more productive on good soils than on poor soils. Technology may sustain yields by masking the effects of soil degradation temporarily. Yield increase through technology might have been greater if the soil has not been degraded.
ii. Water Resources:
Since statistical data on different aspects, including water and land resources and food-grain production is collected from different sources, it is likely that the readers may find differences in the data presented in the text at different contexts. Readers are requested to ignore such minor differences, if any, in the text in the statistical data presented.
World oceans cover about three fourth of earth’s surface. According to the UN estimates, the total amount of water on earth is about 1400 (1386) million cubic kilometers (M km3) which is enough to cover the earth with a layer of 3000 meters (m) depth.
However, the fresh water constitutes a very small proportion of this enormous quantity. About 2.5 per cent (2.7%) of the total water available on the earth is fresh water of which about 68.7 per cent lies frozen in Polar Regions and another 30.1 per cent is present as groundwater. The rest is available in lakes, rivers, atmosphere, moisture, soil and vegetation.
Over 99 per cent of all water (oceans, seas, ice, most saline water and atmospheric water) is not available for our uses. Even of the remaining fraction of one per cent, much of that is out of reach. The vast majority of the fresh water available for our uses is stored in the ground.
Globally, current withdrawals of about 4,500 km3 exceeded the availability of about 4,200 km3. By 2030, the demand is expected to increase to about 6,900 km3, with a slight drop in availability to 4,100 km3. Thus, by 2030, a global deficit of 40 per cent is forecast. For India, the annual demand is expected to increase to almost 1,500 km3 against a projected availability of 744 km3, a deficit of 50 per cent.
Irrigated area in the world was about 18.5 per cent of the arable land in 1994. In 1989, 63 per cent of world’s irrigated area was in Asia, whereas in 1994 this percentage has gone up to 64 per cent. Among Asian countries, India has the largest arable land, which is close to 39 per cent of Asia’s arable land.
At the global scale, about 2,788,000 km2 (689 million acres) of agricultural land was equipped with irrigation infrastructure around the year 2000. About 68 per cent of the area equipped for irrigation is located in Asia, 17 per cent in America. 9 per cent in Europe, 5 per cent in Africa and 1 per cent in Oceania. As in 2003, the global irrigated area is 280 M ha. Largest irrigated area (57 M ha) is in India followed by China (54 M ha).
It is projected that around 20 per cent of land (40 M ha) with irrigation potential not yet equipped at preset (2003) will be brought under irrigation and about 60 per cent of all land with irrigation potential (403 M ha) would be in use by 2030.
Expansion of irrigation will be strongest in land scarce regions such as South Asia (+ 14 M ha) East Asia (+ 14 M ha) and Near East/North Africa. Only small additions will be made in the more land-abundant regions of sub-Saharan Africa and Latin America.
Most of the expansion of irrigated area is achieved by converting land in use in Tainted agriculture or land with rainfed production potential but not yet in use into irrigated land. Part of irrigation expansion takes place on arid and hyper-arid land which is not suitable for rainfed crop production. It is estimated that of the 202 M ha irrigation at present (2003), 42 M ha are on arid and hyper-arid land and of the projected increase of 40 M ha, about 2 M ha will be on such land.
Today, irrigated farming systems of the past are under serious threat of extinct due to salinity, poor drainage and weak management. Irrigated land damaged through salinisation for the top five countries, as percentage of total area irrigated by 1985 are: India 36, China 17, USSR 18, USA 44 and Pakistan 25.
India has the rare distinction of second highest dam failure in the world put at 9.2 per cent against world average of 5.9 per cent. Between 1900 and 1980, forty dams collapsed or failed in India. Irrigated area per capita for India (1989) is 0.057 ha as against 0.049 ha for the world.
Global cropping intensity of 0.93 for total land under cultivation during 1997/99 is projected to increase to 0.99 by 2030. Cropping intensity of 0.83 during 1997/99 for rainfed land is expected to approach 0.87 by 2030. For irrigated land, cropping intensity increases from 1.27 in 1997/99 to 1.41 by 2030. To maintain a diet of 2000 Cal day-1 requires 300 m3 of water per day and 420 for a diet of 3500 Cal.
Bringing one ha of new land under cultivation will produce 0.9 tonnes (t) of cereal grain, one year supply of food for about five people at FAO minimum nutritional standard of 1600 Cal day-1. If the land is irrigated, the total production increases four 3.5 t ha-1. At this level, if future irrigated area of the world reaches 1.1 billion ha, enough for 10 billion people at twice the FAO level.
In spite of the fact that irrigation can provide food for ever increasing population, experience the recent decades in expansion of irrigated area ran into several problems leading to land degradation.
Year to year changes in world irrigated area reflect the sum of the addition of the new capacity and loss of established capacity due to aquifer depletion, lowered water tables, abandonment of waterlogged area and salted land, reservoir silting and diversion of irrigation water to non-agricultural use. The future food production from irrigated areas depends more on the gains in water use efficiency than on additional new supplies.
Essay # 4. Crops and Air Temperature:
Many physical processes and chemical reactions, vital to crop growth are influenced by temperature. In general, active growth of commercial crops is confined to temperature of 5° to 40°C. However, each crop, cultivar and the growth phase has its own temperature requirements beyond which their performance is limited.
For each phase in the growth of cultivar, there is a temperature range within which growth and development is optimum. These temperature ranges are called cardinal temperatures.
The cardinal or threshold temperatures are:
1. The minimum, below which there is insufficient heat for biological activity.
2. The optimum, at which the rate of metabolic processes are at their maximum.
3. The maximum, above which growth ceases.
Cardinal Temperature (°C):
Cool season cereals 0-15
Warm season cereals 15-18
Effect of Temperature on Plant Growth:
Low or high temperatures than optimum required for optimum growth and development of crops leads to decrease in final yields.
Low Temperature Injuries:
Low temperature affects several aspects of crop growth viz., survival, cell division, photosynthesis, water transport, growth and finally yield as indicated below:
1. Chilling Injury:
If the plants grown in hot temperature are exposed to low temperature, they will be killed (or) severely injured. When the night temperature is below 15°C field crops may show yellowing symptoms.
2. Freezing Injury:
When the plants are exposed to how temperature, water freezes into ice crystals in the intercellular spaces (cell dehydration) as in temperate crops (potato, tea etc.).
Formation of thick cover of ice/snow on the soil surface prevents the entry of oxygen and crop suffers. This effects respiration and lead to accumulation of harmful substances.
It is lifting of plants along with soil from actual position by ice crystals. This is a mechanical lifting.
It is due to low temperature near the canopy due to earth’s re-radiation. If the cell size is large the probability of frost damage is high.
1. Advective Frosts:
Advective frosts are due to incursion of large masses of cold air over a region from the colder areas.
2. Radiation Frost:
Occur on clear calm nights when heat is freely radiated from all exposed objects. Hoar frost (or) white frost is due to sublimation of ice crystals on objects like tree branches. Black frost freezes the vegetation because of reduction of air temperature.
Management Against Frost Damage:
Damage due to frost can be minimised through:
1. Frost free growing season.
2. Adjusting the sowing time.
3. Selection of resistant varieties.
4. Sprinkler irrigation.
High Temperature Injuries:
High temperature influence crop growth in different ways as indicated below:
1. High temperature adversely affects mineral nutrition, shoot growth and pollen development resulting in low yield.
2. The critical temperature above which plants gets killed is called ‘thermal death point’.
3. Temperature above 50°C may kill many annual crops.
4. Limit varies with plants; shade loving plants are killed at lower temperature.
High Temperature and Mineral Nutrition:
High temperature stress causes reduction in absorption and subsequent assimilation of nutrients. Absorption of calcium is reduced at temperature of 28°C in maize. Nutrient uptake is affected by both soil and air temperature in rice. Nitrate reductase activity decrease under high temperature.
High Temperature and shoot Growth:
High temperature, even for short period, affects crop growth especially in temperate crops like wheat. High air temperature reduces growth of shoots and in turn reduces root growth. High soil temperature is more crucial as damage to roots is severe resulting in substantial reduction in shoot growth. High temperature at 38°C in rice reduced plant height, root elongation and smaller roots.
High Temperature and Pollen Development:
High temperature during booting stage results in pollen abortion. In wheat, temperature higher than 27°C caused underdevelopment of anthers and loss of viability of pollen. Temperature of 30°C for two days at reduction division stage decreased grain yield by drastic reduction in grain set.
Other problems due to high temperature include dehydration and scorching of leaves, disturbance in photosynthesis and respiration, injury on exposed area of the plant (sun sclad) and stem scorches at ground level (as in cotton).
Response of living organisms to regular changes in temperature either day or night or seasonal is called thermoperiodism. Some crops are thermoperiodic in response to temperature. Some others need a degree of chilling or a minimum amount of warmth (vernalisation) before flowering and send setting can take place.
Day temperature seldom influence flower initiation, size of leaves or rate of leaf production as against pronounced effect of night temperature on these. The effect of fluctuating temperature on growth and development as opposed to constant temperature varies from species to another.
Apart from daily fluctuations in temperature, long range temperature sequences are important in plant development. Annual plants need no cold period during their development except those germinating in autumn and flowering in spring or summer after a cold winter as is the case with winter wheat.
Peaches need a period of cold weather before flower buds can open. In the absence of ideal temperature requirements during day or night at different phases of crop growth, it may not be possible to realise their yield potentials.
Essay # 5. Weather and Crop Production:
All crops and cultivars have their own optimal environmental requirements. Among the environmental factors influencing growth and development of crops, weather and climate plays dominant role.
It is the most important winter crop of northern India, both as rainfed and irrigated. Cool weather during vegetative development and warm weather for maturity is deemed ideal for wheat. When winters are moderately cold and dry or when winters are severe, but where a snow cover during winter is likely available, winter wheat is raised.
Though wheat seeds germinate from 5-35°C, the optimum range is 20-25°C. Below 4°C germination fail and above 22°C possibility of disease incidence arise. The optimum is therefore 20-22°C. Thus, the time of sowing to a great extent is determined by temperature, besides soil moisture regimes.
Any delay in sowing to take advantage of cool weather leads to poor crop stand on account of decreasing surface soil moisture with increasing time from cessation of rains. This is because wheat can adjust with the available soil moisture upto grain filling but not to temperature during early stages of growth.
Within the season, warm temperatures shorten vegetative duration leading to decrease in life duration of crop as one proceeds from north to south in the wheat belt. By increasing the day length, late cultivars could be made to flower early with increased yield and photoperiodic delaying of flowering of early cultivars leads to poor yield.
Poor tillering is associated with earliness of the cultivars. A temperature regime with a mean maximum temperature of 25°C and a mean minimum of 12°C is considered optimal for grain development.
Optimum photothermal units are 22,000 from sowing to maturity, made up of about 10,000 from germination to flowering and about 12,000 from ear emergence to maturity. Keeping the temperature needs of wheat in view, optimum time of sowing varies from mid-October under conditions of north India to November first week in south India.
Weather in Relation of Pests and Diseases:
Climatic conditions for wheat rust in India are unsuited for the over summering of rusts. Primary inoculum for infesting wheat originates from Himalayan regions in Nepal and from Nilgiris and Palani hills in the South. Yellow, brown and black rusts show considerable variation in their incidence due to variations in their temperature requirements and tolerance.
Yellow rust is mainly restricted to northern parts of the country because of its low temperature requirements. Epidemic conditions prevail for brown rust in the entire wheat belt.
During planting time and subsequent two months period on northern India, temperatures are too low for the development of black stem rust and when favourable temperatures are reached, very little time remains for the development of fungus before the crop reaches the maturity.
Occurrence of black stem rust (Puccinia graminis tritici) can be predicted easily.
Conditions leading to out-break of the disease are:
1. Depression in Bay of Bengal or Arabian sea between 65°-85°E and 10°-15°N and ending over central India.
2. Persistent high pressure cell over south central India.
3. A deep trough extending upto south India due to movement of western disturbance.
Optimum weather conditions for yellow rust (Puccinia striiformis), in northern India are:
a. Mean temperature 9-13°C.
b. Relative humidity 70 per cent.
c. Partly cloudy conditions.
Such conditions prevail for about a week in mid-January.
For brown rust (Puccinia recondita) optimum conditions for its incidence are during February.
i. Mean temperature of 15-20°C for about a week.
ii. Relative humidity more than 70 per cent.
iii. Intermittent clouds from late January to first week of February.
Rice is a warmth loving crop requiring high temperature, ample water supply and high humidity during the growth period. Ability of rice seed to germinate under water and the capacity of plant to thrive well under flooded conditions gives rice culture a unique status.
Depending on the variety, rice requires a mean temperature above 20°C and not less than 15°C during entire growing season. Low temperatures inhibit tillering and prolong the duration. Optimum temperature for height is 25°C and that for leaf emergence 30°C. A temperature of 27° to 29°C is ideal for flower initiation.
Temperatures below 14°C and above 38°C induce sterility. Night temperature of 23°C is ideal during ripening period. On an average, critical low temperature for inducing sterility is 15-17°C for highly cold tolerant varieties and 17-19°C for cold sensitive varieties. Period of critical temperature is 10-11 days before heading.
A temperature of 27°C in mid-season (July-August) followed by 400 hours of sunshine during ripening (September-October) are optimum for high yield. Varieties with 130-140 duration give maximum yield as they receive accumulated sunshine hour of 1,000 with 220-240 hour in the last 30 days.
Since growing point remains under water in early stages, water temperature is more important during active tillering. Temperature of water should not be less than 21°C or more than 31°C at any time. Flowering is inhibited by relative humidity below 40 per cent and best at 70-80 per cent.
Weather in Relation to Pests and Diseases:
Tryporyza incertulas, known as yellow stem borer, is the most predominant species attacking rice crop. In kharif, early maturing varieties escape the infestation while late varieties are liable for infestation. Irrespective of planting, rabi crop is liable for the attack.
The meteorological limits for maximum moth emergence and abundance are: minimum temperature in the range of 14-27°C, maximum temperature in the range of 28-30°C and at 5 cm soil depth, soil temperature in the range of 19-30°C.
Pachydiplosis oryzae, causing gall midge, is most active in the latter half of the monsoon crop, particularly at tillering under conditions of land submergence. The threshold temperatures for its development are between 16° and 34°C. Years of most serious gall midge infestation are those when early rains made the flies active, but subsequent dry periods delayed planting.
If the rains in May and June are below 250 mm, its first appearance on rice will be delayed. Good pre-monsoon showers increase the humidity and help the grass to establish on which the fly multiplies. The amount of pre-monsoon rain in May and June, onset of monsoon, number of rainy days and bright sunshine hours in August and September can be used for assessing its infestation during kharif.
Dicladispa armigera (rice hispa) is not active on plants younger than three weeks or older than two months and the same is severe on late planted kharif crop. Heavy rains in July followed by abnormal low rainfall in August and September, especially from mid-August to mid-September, with lesser rainy days and more bright sunshine, steady temperature with little diurnal average relative humidity (more than 85 per cent) causes outbreak of hispa epidemics.
Pyricularia oryzae (rice blast) is endemic in areas located in valleys or having an elevation of 600-1500 m. Blast occurs when the minimum temperature goes below 24°C with relative humidity at 90 per cent or more during seedling to tillering and ear emergence stages. More the number of such days and greater the depression of minimum temperature below 23°C, more severe the incidence.
Helmiiuhosporium oryzae responsible for helminthosporium disease, causes great damage at flowering and maturity phases.
For a crop sown in July and flowering and maturing in cool weather in November-December, outbreak of the disease is indicated by the following factors:
1. Presence of a short duration crop nearing maturity at the end of September or early October.
2. Heavy rains during flowering phase of earlier crop.
3. Prevalence of air temperature in the range of 20-30°C with higher than normal minimum temperature and lower than normal maximum temperature with reduced hours of sunshine to below 75 per cent of normal and light rain or heavy dew continuously for a week.
Sorghum requires warm weather for development and it cannot grow well or set seed at temperatures below 18-21°C. It cannot recover from freezing temperatures except at juvenile stage. It can adequately recover from drought. Minimum temperature for germination is 7° to 10°C, while the optimum is 18° to 21°C. Sorghum sown in soils with temperatures less than 20°C is liable for the attack of pathogens.
Minimum temperature for growth is 15°C, while the optimum is 27-30°C. Night temperature greater than 21°C favours ceil elongation and delays floral initiation. Sorghum is a short day plant. Panicle initiation appears to be controlled by critical dark period, which is the minimum darkness that allows flowering in sorghum. Long nights hasten flowering in tropical varieties while nights as short as 11 hours do not delay flowering of temperate varieties.
Maize in temperate regions is what sorghum is in tropics. It is rarely grown in areas where the average summer temperature is less than 19°C and mean night summer temperature is less than 13°C. Minimum temperature for germination is 10°C and the optimum is 30-35°C under adequate moisture. Optimum temperature for growth is around 34°C.
It is resistant to drought and can recover from early season drought. Temperatures above 32°C at reproductive stage reduce the yield. Soil moisture stress prior to silking, during silking and after silking reduces yield, respectively by 25, 21 and 50 per cent. Decreasing photoperiods hasten silking.
Day degree accumulations above 10°C for maize development are 120 for seedling establishment, 480 for ear formation, 630 for tip of tassel appearance, 775 for anthesis, 1070 for dough stage, 1215 for denting of kernels, 1360 for dented kernels and 1510 for maturity of long duration varieties.
Sugarcane is warmth loving crop. Restrictions in growing season can arise due to insufficient soil warmth for germination and checking cane growth by low air temperature. Minimum soil temperature for germination is in the range of 19-21°C and that of optimum in the range of 27- 38°C. No root development occurs below 12°C and it is best at 30°C.
The minimum threshold air temperature for cane growth is 16°C. Air temperature below 21°C checks vegetative growth, induce ripening and lead to better juice quality. There is close relationship between temperature for cane yield in the range of 21-30°C. Tillering is maximum at 30°C.
Temperature more than 35°C and minimum temperature less than 18°C during tillering decreases the cane yield. Night temperatures below 15°C prevent flowering and that night temperature of 22-23°C with day temperature of 27°-31°C in bright light are conducive for good flowering.
Photoperiod requirements for flower initiation are greater than 10 hours night and greater than 11 hours day length, Flower initiation occurs when the photoperiod duration is 12 hours. Weak light reduces tillering and root development. Hours of sunshine for maximum yield are 700 at tillering.
Weather in Relation to Pests and Diseases:
Scirpophaga nivella, the top borer is serious pest of sugarcane. Relatively low maximum temperatures and moderate to high relative humidity are conducive for its rapid multiplication and severity of attack.
Increase in the attack is directly correlated with an increase in maximum temperature. Under north Indian conditions, the third brood (last week of June to first week of July) attack primarily determines the severity or otherwise of top borer incidence.
Pyrilla perpusilla, the sporadic sugarcane leafhopper causes enormous loss when high humidity coupled with low maximum temperature prevails in summer and when low rainfall or long breaks occur in monsoon. Rainfall during June is most critical for the survival of the pest for attacking the crop later in the season.
It is a heat loving plant and best adapted to subtropical climates. Soil temperature is most important at germination and stand establishment. The minimum, optimum and maximum soil temperatures should be around 16°, 34° and 39°C respectively. Thus, the temperature limits for cotton germination are about 5°C higher than that for maize and about 10°C higher than that for wheat. Hence, cotton should not be sown in cold dry spells.
Cotton should be sown ahead and very much ahead of maize and wheat respectively in winter season. In summer, it should be sown later and much later than maize and wheat respectively.
Branching habit of cotton is influenced both by temperature and photoperiod. Low temperatures stimulate the development of vegetative branches. Short day cultivars develop only vegetative branches under long days; day neutral types in the absence of high temperatures behave like short day plants under long days and produce vegetative branches only.
Cardinal temperatures for cotton growth are 15-20°, 25-30° and 35-40°C. Air temperatures less than 16°C or greater than 38°C are not conducive for good vegetative development.
Cotton is unique in that its flowering cannot be forced ecologically. Temperatures above 35°C are harmful while that below 21 °C are not conducive for flower bud initiation. A mean temperature of 22-27°C is optimum for boll and fibre in relation to maturation.
A comprehensive study on arboreum cotton weather indicates:
1. Rainfall 15 days prior to sowing has significant influence on germination, which accelerates with increasing temperature upto 36°C.
2. Heavy rains during peak flowering and boll formation delay maturity and increase boll shedding.
3. High shedding occurs after heavy rains and cloudy days.
4. Excessive wet or dry weather reduces boll size.
5. About 55 per cent relative humidity and 15°C maximum temperature during boll bursting is ideal for long fibres.
6. Rainfall during flowering and boll development increase the yield.
Yield disparity between summer irrigated and rainfed crop during monsoon indicates that groundnut requires warmth and sunshine for its growth and development. Minimum temperature for germination is 10°C, while the desirable is 20°C. Relative humidity should be about 90 per cent in the first month of the growth.
Strong light of 12 hours followed by 2 hours of weak light is optimum for flower production. Flower expression can proceed satisfactorily upto a mean temperature of 33°C, but pod formation is retarded above 28°C.
An ideal rainfall for successful groundnut crop is 7.5 to 12.7 cm during summer months preceding sowing, 12.5 to 17.5 cm during 15 days after sowing, and 30 to 50 cm well distributed during the other period. It needs dry conditions at harvest.
Relative humidity of about 95 per cent and low temperatures of 15°C for more than 10 hours leads to the incidence of leaf spot. Maximum damage is in the temperature range of 22° to 25°C when the relative humidity is more than 95 per cent for 12 hours or more.
Essay # 6. Abnormalities Affecting the Production of Crops:
Major abnormalities affecting the crop production are: 1. Excessive Rains 2. Drought 3. Untimely Rains 4. Storms, Cyclones and Depressions 5. Thunderstorms, Hailstorms and Dust-Storms 6. Cold Waves and Frost 7. Heat Waves 8. Excessive or Defective Insolation 9. High Winds.
i. Excessive Rains:
When heavy rains occur particularly over catchment area of rivers, the magnitude of floods may well be imagined. For such large scale phenomena, the remedies depend on large scale planning by the government for multipurpose or hydroelectric schemes. Planned afforestation of the denuded area is one of the remedies which should receive every support from the government.
Watershed development programme, under implementation during the eighth five year plan, appears to be promising in the direction of soil erosion and runoff control leading to water flows into the rivers. For floods, individual farmer can only keep the drainage channels of his fields open and go for flood resistant cultivars, especially in the case of rice.
Frequent crop failure in dryland agriculture is due to droughts or prolonged dry spell during the crop period. Several management practices have been recommended to mitigate the adverse effect of drought.
1. Increasing the water holding capacity of soils through the application of bulky organic manures.
2. Soil and moisture conservation practices to minimise runoff.
3. Collection of runoff water during periods of heavy rains for use during drought period.
4. Minimising evaporation and transpiration losses through mulches, shelterbelts and chemicals.
5. Introduction of drought resistant and drought escaping crops and cultivars.
6. Intercropping to avoid total crop failure.
7. Farm forestry for sustainable production in dryland farming.
8. Identification of remunerative cropping systems for dryland agriculture.
iii. Untimely Rains:
Onset and withdrawal of monsoon largely determine the success of dryland agriculture. Late onset of monsoon delays sowing of crops leading to poor yields. Early withdrawal of rains affect the yield due to soil moisture stress especially when the kharif crops are at critical stages of grain development. Continuous, cyclonic rains from August lead to problem in harvesting the crops, especially groundnut in south India.
Land should be prepared for kharif crops, taking advantage of pre-monsoon showers, such that sowing could be completed, taking advantage of earliest monsoon rain. Alternately, short duration pulse crops are recommended for abnormal delay in monsoon.
As it is not possible to predict withdrawal of monsoon, it is always better to go for intercropping long and short duration crops to avoid total crop failure, especially in areas of frequent crop failures.
iv. Storms, Cyclones and Depressions:
One of the features of colossal meteorological phenomena like cyclonic storms and depressions can be predicted and forecasted. On receipt of warnings, precautionary measures can be taken for minimising the risk.
Warning of heavy rain, especially during sowing and harvest times will be practically useful as sowings can be postponed and harvesting hastened, wherever such disturbances are expected. Weather warning on such aspects leads to efficient use of agrochemicals used for plant protection and weed control.
v. Thunderstorms, Hailstorms and Dust-Storms:
These are comparatively local in character. They usually occur before the onset and after the withdrawal of monsoon. Though short in duration, the precipitation and associated squalls are often very violent.
Hailstorms are very destructive to standing crops and even to livestock and human life. Protection against them is difficult, particularly under rural conditions. However, farmers warned before-hand can harvest their crops if they are already ripe. Shelterbelts and windbreaks can offer considerable protection to horticultural crops.
vi. Cold Waves and Frost:
Cold waves and frost are common during winter in northeast frontiers of India. There is considerable damage to grain and horticultural crops due to frost and freezing temperature. Many tropical and subtropical plants are killed even at temperatures higher than about 0°C.
Information on frequency and intensity of frosts can indicate frost-free growing season, which would help in selecting suitable crop species and varieties for areas subjected to frost.
Knowledge of critical temperatures for frost damage would be useful for planning frost prevention measures:
1. For better frost protection, the soil must be moist, compact and weed free. Frost damage is more common in sandy soil than in heavy soil under similar temperature conditions.
2. Straw mats, screens of dry grass netting, wax paper, plastic covers known as hot caps should be placed over small plants during late afternoon and removed early in the morning for frost protection.
3. Smoking and fogging by burning wood, straw, straw dust, sump oil, tar, naphthalene, etc.
4. Creation of frost smoking in which artificial fog or chemical mist with particles sufficiently large to prevent long-wave radiation.
5. Use of high speed fans for temperature inversion near ground.
6. Flooding the field for increasing the thermal capacity and conductivity for releasing latent heat when water freezes.
7. Replacing the heat lost through radiation by heat emitted from suitable heaters or small fires. Common materials for heating are wood, coal, charcoal, diesel oil. Heaters are the best for frost protection.
vii. Heat Waves:
Just as cold waves are injurious to crops in winter, heat waves are injurious in summer. Deccan and central parts of the country experience hot waves during March, April and May. During this period, temperatures go beyond 43°C. Blowing of hot winds leads to pollen and premature fruit drop. Most of the water bodies dry up in a short time leading to water shortage.
Heat evasion by shading of plants appears to be effective to minimise the adverse effect of heat wave. A number of shade structures from wood or fibre are used, especially to protect vegetable crops grown on sandy soils during summer. Windbreaks also can reduce the heat wave effect by decreasing the velocity of hot winds.
viii. Excessive or Defective Insolation:
During clear day in summer, soil temperatures reach as high as 70°C over black soils. High soil temperature affect seed germination and functional activity of roots. Irrigation can depress the soil temperature, but the effect lasts only as long as there is enough moisture on the surface layers. A layer of chalk or surface mulch of straw or any other organic waste helps not only to keep the soil layers cool, but also to conserve soil moisture.
When the insolation is weak, soil temperature decrease to the extent of affecting plant growth. A black cover (charcoal powder) is useful for absorbing insulation and heating up the soil.
ix. High Winds:
Wind affects the crops directly by increasing the evapotranspiration and causing several types of mechanical damage including lodging. When the wind is hot, it accelerates the plant desiccation. Use of shelterbelts is the only practical remedy for protecting the crops from high winds. Shelterbelts are primarily meant for altering wind speed and its direction. They also aid in soil conservation and efficient use of soil moisture by reducing evapotranspiration rate of crops.
In practice, there are three main types of shelterbelts:
(1) Dense shelterbelts with little permeability.
(2) Shelterbelts with medium and even permeability from soil surface to top of the belt.
(3) Alley type shelterbelts which may be rows of tall trees without shrubs as an understorey and which are open in the lower parts.
Dense shelterbelts are impermeable to air flow and hence exhibit sharp peaks of stream lines at distances of about 1 to 2 times the height of the belt. The stream lines, however, descend steeply and become horizontal at about 15 to 25 times the height of the belt.
Thus, as compared to permeable belt, larger wind reduction is achieved immediately behind the dense belt. However, the original wind velocity is restored at much shorter distance in the case of dense belt than permeable belt. Thus, the wind reduction zone is much greater in the permeable belt.
In alley type belts, as there are gaps between the trees, many steam-lines pass through the lower part of the belt. The wind reduction in immediate neighbourhood, in the beside will be lower than in other types. However, the zone of wind reduction would be wide in this case also.
For the best wind speed reduction and greatest downward influence, the shelter should be more porous on lower heights. In fact, the density can increase with height in proportion to the logarithmic nature of the wind profile.
The optimal degree of permeability of a shelterbelt is about 30-35 per cent, if large cultivated fields are to be protected. This would mean that there should be many small gaps in the belt such that their total area works out to be 30-50 per cent of the total area of the belt.