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CORN (Part 2 of 2)   Leave a comment

How Experimenters Developed Hybrid Corn

In 1905 George H. Shull and Edward M. East began developing new kinds of corn by placing pollen from one desirable strain of corn onto the silks of another strain. The process produced cross-bred strains called hybrid corn. After World War I, Henry A. Wallace (who became secretary of agriculture in 1933) and Lester Pfister began hybridizing experiments. By 1926 they had made hybrid pollinization completely workable.

The hybrid plants are remarkable growers. They commonly grow to be 18 or 20 feet tall; some have grown as high as 28 feet. A more important factor is that they have added millions of dollars to the income of corn farmers.

Before farmers had hybrid corn, an average acre of corn yielded 30 bushels. But farmers had to spend the money they received for 25 bushels to pay their costs for each acre planted, leaving only 5 bushels an acre for profit. Hybrid corn has raised the national average to more then 95 bushels an acre. Some states average more than 130 bushels an acre.

A hybridizer produces hybrid seed by first inbreeding. This fixes desirable qualities in the seed. He covers the ears of selected plants to keep airborne pollen from the silk. Later, he takes pollen from the tassels of a plant and dusts it on the silks of the same plant. After inbreeding each strain for several generations, he starts cross-breeding He takes pollen from the tassel of a plant having one desirable strain and dusts it on the silk of a plant with some other strain. The cross-bred product, or hybrid, has the qualities of each parent strain.

Next comes double-crossing. The experimenter dusts pollen from one hybrid onto a hybrid with two other strains. The seed from this cross produces a super corn with four strains bred in. This corn is sold to farmers as seed. Their crop cannot be used as seed next year because hybrid corn is not self-perpetuating. Farmers must buy new seed each year. Great use of hybrid corn threatens the supply of corn pollinated naturally. This loss would restrict improving hybrid strains and prevent developing new ones. To preserve seed of native varieties, the federal government stores seed in corn banks.

Planting and Cultivating

A strong, full crop of corn comes from fertile soil, good seed, thorough cultivation, and clean culture. The soil should be easily worked, well drained, and rich in plant food. The dark loam of the Midwestern United States is particularly well adapted for corn. The farmer chooses the seed to suit conditions on his land. In dry regions he may plant corn in deep furrows. If rainfall is plentiful he puts the seed down in hills or in drills. Once the plant starts to grow, cultivation must never be deep, or the tender, grass like roots will be injured.

Corn draws heavily on the plant food in the soil. Production is higher when corn crops are rotated on a three-year cycle. The first year a legume, such as alfalfa or sweet clover, builds up the soil with nitrogen and humus. The next year corn grows tall on these, its favourite foods. The third year a small grain is planted. Then the cycle is renewed with a legume.

Different Ways of Harvesting

If the farmer wants to store the whole plant in a silo, he cuts the corn while it is still green. If the corn is to be used for grain, it is not harvested until it is fairly dry. The ears may be picked by hand from the standing corn and husked and thrown into a wagon. On most farms mechanical corn pickers are used.

Some farmers turn cattle in to feed on the corn stalks after the ears are picked. Others cut the stalks, tie them into shocks, and let the ears get dry before husking. Many livestock raisers turn hogs into the ripe fields to feed and fatten on the corn. This method is called hogging down.

Fighting the Enemies of Corn

Corn ear worm (also called tomato fruit worm, or tobacco bud worm, or cotton boll worm), larva of a moth (Heliothis armiger); names vary depending on the various plants it infests; larvae on corn first eat the leaves, then the ears; pupation occurs in the ground; winter ploughing in North kills many pupae.

More than 350 insect pests attack the grain. The most destructive are the corn ear worm, the European corn borer, and the corn root worm Fungus growths, such as smut and various rots, are costly foes. In many cases insecticides are too expensive to be practical. Therefore the farmer uses the less expensive methods of clean culture and crop rotation. Clean culture means harvesting or destroying every part of the plant. Careful farmers either burn or plough under the stubble. This rids the cornfield of pests that live above the ground. Crop rotation suppresses root pests that live on corn by depriving them of food for one or two years.

Composition of a Corn Kernel

A kernel of corn is wrapped in a tough, fibrous outer hull (bran). Inside is the germ, or embryo, from which the new plant develops. Around the germ is a food supply called endosperm. This is chiefly starch. When the kernel germinates it draws its nourishment from the endosperm until it can put forth roots and leaves and obtain food from the soil and the air.

The moisture content of a kernel varies from 10 to 25 percent, depending upon weather and other conditions under which it was grown. Of the dry portion, about 70 percent is starch (carbohydrates). About 10 percent is gluten (protein), found in a shallow layer just under the hull. The remainder is fat or oil in the germ (4.5 percent), fibre in the hull, and minerals.

A Great Variety of Corn Products

All the parts of a corn kernel can be used to make products. From the whole kernels manufacturers make cornmeal, breakfast foods, and hominy. Some people make hominy at home by removing the hull with lye and cooking the whole grain. When the kernel is crushed it forms hominy grits. Distillers make alcohol and whiskey from whole corn kernels.

Since corn became so dominant a grain in American agriculture, it has naturally found its way to Europe and Asia. There, whether imported or grown locally, it is used mostly for animal feed, as it is in the United States. For humans, corn is less desirable nutritionally than for livestock. The protein value is of low quality, and corn is devoid of niacin one of the B-vitamins that is essential to humans. People who rely heavily on corn in their diets are subject to such niacin-deficiency diseases as pellagra. Corn cannot be used to make leavened bread, although it is much used in Latin America to make dough for such flat breads as tortillas.

The corn products refining, or wet-milling, industry makes a great variety of products from different parts of the corn kernel. Wet milling is so called because the kernels are steeped in tanks of water to soften them, and water is used in the processes that separate germ, gluten, and starch.

First to be separated from the kernel is the germ. Refined and crude corn oil have many uses as human and animal food and in industry. When oil is pressed from the germ a hard cake is left. It is ground into stock feed. One of the proteins in gluten is zein. A synthetic fibre is made from it. It is also used in lacquer, plastics, textile colours, and printing inks.

The final product of the wet-milling separation process is starch. The housewife, food manufacturers, and laundries have many uses for cornstarch. Paper manufacturers use more starch than any other industry to toughen and size (glaze) paper. Textile manufacturers are second. Cotton and synthetic yarns and fabrics are sized with starch.

Glucose (or dextrose, or grape sugar, or corn sugar), simple (monosaccharide) sugar found in fruits and other foods and in the blood of animals; fuels the energy needs for most living organisms.

A huge amount of starch is converted into corn syrups (glucose), sugars, and dextrose by cooking and chemical treatment. These too have countless uses in cooking and in various industrial processes. Even the steep water in which the kernels are soaked is important. Evaporated to a thick, soupy liquid, it is used as a food for the moulds that produce penicillin and other wonder drugs.

Corncobs are ground for a coarse livestock feed. They are used also in a polishing powder, insulation, and a form of sandblasting. Furfural, an oily liquid extracted from corncobs, goes into man-made fibres, drugs, and solvents. Some specially grown cobs are made into pipes for smoking.

Millions of tons of cornstalks are made into a rubber substitute, maizolith. A large quantity is used for making paper and wall board Even the gases from fermenting corn are used to make methyl alcohol.

American Indians had many kinds of corn, and there are now more than 1,000 named varieties. The smallest is the golden thumb popcorn plant, about 18 inches (46 centimetres) high. Some varieties have only eight rows of kernels; others, as many as 48 rows. Colours include white and shades of yellow, red, and blue.

The chief types of corn are pod, soft, sweet, pop, flint, and dent corn. Pod corn has each kernel enclosed in a pod or husk. Soft corn is used for corn flour and for roasting ears. Sweet corn has the smallest amount of starch; popcorn, the highest. Flint and dent corns lead all other varieties on the grain markets and for livestock feeding. The scientific name of corn is Zea mays.

Posted 2012/03/04 by Stelios in Education

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ECOLOGY (Part 2 of 3)   Leave a comment

Competition in Communities

Competition is a characteristic of all communities. Plant roots in dry range lands compete for water. The trees of a rain forest compete for light. Crops compete for both of these as well as for nutrients. Competition is usually keen in areas where one type of community seems to overlap another. For example, a continuum between a shrub community and a marsh contains some aspects of both communities. Animals and plants trying to establish a foothold in such an overlap must cope with difficulties often non-existent in a stable community. Shrubs moving toward the marshy area must compete with other pioneer shrubs and reeds for light and nutrients.

Similarly, reeds attempting to invade the shrubby area must compete with shrubs and other reeds. This shows that competition may often be greatest among living things that have the same needs. For the same reason, competition may be extremely harsh within a species among wolves for meat or among cattle for grass, for example.

On the other hand, competition is sometimes modified through behavioural adjustments even cooperation among the members of a community. Shrubs are spaced widely on deserts. Birds nest in patterns that prevent overcrowding. Bees live together in a hive. Man can make similar adjustments, and unlike other species he can achieve cooperation by rational means. Yet human competition sometimes ends in wars, and wars frequently destroy the very things which the belligerents are striving to take away from one another.

Should it become necessary to control an undesirable species in a community, this can best be done by modifying the community. A rancher, for example, may discover that weedy annual plants are invading his native perennial pastures. His initial reaction might be to attack the weeds with chemical herbicides. This approach would be self-defeating since nature would provide the resultant bare soil with an unlimited supply of weed seed. To solve the problem ecologically, the rancher should modify the community by managing the degree and time of cattle grazing to permit normal growth of the native plant community, which would then crowd out the undesirable weeds.

Succession in Communities

A third major principle of ecology is that an orderly, predictable sequence of development takes place in any area. This sequence is called ecological succession. The successive changes produce increasingly mature communities from a barren or nearly barren start. Succession usually culminates in a climax, a fairly stable community in equilibrium with, and limited by, climate and soil.

At one time or another virtually all land surfaces have undergone basic climatic changes and been occupied by types of plants and animals which they may no longer be able to sustain. This, however, is not what is meant by ecological succession. It is known as biotic history, extends over the vast scale of geologic time, and is deduced from fossil remains. The future communities of an area cannot be predicted from its biotic history. Such prediction can be based only on a knowledge of ecological succession.

As soon as the first patches of soil are formed in barren areas, a series of events takes place that eventually terminates in the establishment of a climax community. This process is called primary succession. Because soil formation requires the slow weathering of rock, primary succession ordinarily spans hundreds of years. Once it begins, however, the sequence of events rarely alters. As soil formation proceeds, a succession of plants and animals appear. The last stage in this progression is the climax community.

Disclimax, an ecological community that occurs following a disturbance.

A disturbance at any point during primary succession or even at the climax can destroy the vegetation of a primary succession in whole or in part. The vegetation that follows a disturbance of this kind is called a disclimax. The disturbance can be caused by ploughing, logging, or overgrazing. When such a disturbance takes place, climate and soil are no longer the principal determinants of vegetation. The further natural growth of plants at the site of a disclimax, as contrasted with the raising of crops, is called secondary succession. This can be completed in a few years or, at most, in decades because soil has already been formed. After secondary succession restores a balance between eroded soil and vegetation, the further development of both again becomes dependent on primary succession. Wise landowners use secondary succession to restore overgrazed range lands, cut over timber lands, and abandoned crop lands They need only protect the land from further disturbances while secondary succession heals the scars of abuse.

Changes in the community during secondary succession are rapid, because every living thing contributes to its alteration. For instance, the weeds that grow on a vacant lot produce shade and increase the soil’s ability to absorb and store water. They also attract insects and birds and enrich the soil when they die and decay. The bare ground of the vacant lot is the best possible place for the pioneer sun-loving weeds to grow. Later the weeds are replaced by tree seedlings if the lot is in a forest climate, by native grasses if it is in a grasslands climate. Such changes occur until plants and animals that can make maximum use of the soil and climate are established.

The Ecosystem

A fourth key principle of ecology asserts that a community and its environment the living and the non-living constitute an ecological system, or ecosystem. Every natural community draws vital materials from its surroundings and transfers materials to it. Raw materials and decay products are exchanged continuously. Thus, in an undisturbed area basic resources are sustained, never exhausted.

Ecosystems exist on many kinds of lands, in lakes, in streams, and in oceans. They are found wherever soil, air, and water support communities. The combined ecosystems of the Earth constitute the biosphere.

Ecosystems generally contain many kinds of life. A cornfield, for example, contains more than just corn. Also present are smaller plant species, insects, earthworms, and a host of soil microbes. Each of these organisms fills a specific niche each performs an essential function in the ecosystem.

The inhabitants of an ecosystem are classified as producers, consumers, and decomposers. Green plants of any kind, whether stately oaks or tiny algae, are producers because they make their own food through photosynthesis. Animals, including man, feed on plants or on other animals and are therefore classed as consumers. Organisms that cause decay bacteria and fungi are decomposers.

Food chain, sequences in which organisms within an ecosystem feed on one another.

The sequences in which the organisms within an ecosystem feed on one another are called food chains. Usually organisms of higher biological rank feed on those of lower rank. Ecologists group the members of any food chain into a pyramid of numbers. At the base of such a pyramid are the green plants, which are the most numerous organisms in the chain. The next level might contain first-order consumers, such as the sheep that eat the green plants. At the peak of the pyramid might be second-order consumers, such as the herdsmen who feed on the sheep. When the producers and consumers of an ecosystem die, their bodies are broken down by the decomposers into nutrients used by new plants for growth. In this manner, the food chain is perpetuated.

The biosphere seems capable of sustaining life even in the absence of consumers. Without consumers, the rate of plant growth would eventually strike a balance with the rate of decay caused by the decomposers. Hence, even if all herbivores, or plant-eaters, were absent from the biosphere, plant growth could be expected to stabilize at certain levels.

Through plant growth and decay, water and carbon, nitrogen, and other elements are circulated in endless cycles. The driving force behind these cycles is the sun. Solar energy becomes converted into food through the photosynthesis of green plants and into heat through the respiration of plants and animals.

APPLICATIONS OF ECOLOGY

Ecologists are often employed to solve serious environmental problems. Early in this century, for example, southern Ohio was ravaged by a terrible flood. The inhabitants of the area, determined to prevent a repetition of the disaster, constructed large earthen dams across the valleys north of Dayton to contain future flood waters Since the slopes of these dams consisted of gravel with an admixture of clay, they washed away easily. It was necessary to stabilize the steep slopes quickly with plant cover. Knowing which plants would grow best in such places, an ecologist recommended the scattering of alfalfa and clover seed, followed by brome grass and Japanese honeysuckle. His recommendations were followed, and dam slopes were soon covered with a fine cohesive turf. Many of the hills on neighbouring farms lacked such cover and were quickly eroded.

In the Dust Bowl region of Texas, sandy soil in dry areas blew into great dunes after the land was ploughed for wheat. Bulldozing these dunes was thought too expensive. However, an ecologist recommended that certain plants be raised near the shifting dunes. The plants in front of the dunes caught and held the soil, while those behind them kept the rear from blowing deeper. In a short time, wind had levelled off the high dune tops and vegetation had anchored the soil.

Ecology and Wildlife Conservation

Measures for the preservation of ducks and other migratory wild fowl are examples of ecological work with animals. When these birds grew scarce, state and federal agencies sought ways to protect them and help them reproduce. At first, laws were recommended that forbade shooting the birds in the spring when they were flying north to nest. Every female killed in the spring could mean one less brood returning in the fall. Further studies showed that many of the birds’ breeding places were being destroyed when the land was drained for other uses. Some of these sites were not well-suited for the sustained growth of crops; others, where marshes and potholes once released stored water slowly, now contributed to downstream floods. Draining thus had a doubly harmful effect. Ecologists captured the endangered birds and put aluminium bands on their legs to trace their breeding places and movements. In this way it was discovered that the problem was international. As a result, the United States began to work in close cooperation with Canada and Mexico for the protection of migratory birds.

Ecologists also investigated the food habits of birds. They recognized that if proper food was unavailable, the birds would disappear even if hunting was regulated. Experts examined the stomach contents of thousands of birds from many different areas. This work led to the finding that bird food consists mainly of plant materials that thrive under natural conditions. To ensure the availability of these materials, man had to cease altering many natural communities and to stop polluting them with his wastes.

Posted 2012/02/19 by Stelios in Education

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