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     The geographical distribution of vegetation is determined by the climate, and the principal climatic factors that must be considered in the development of plants in any part of the country are temperature, rainfall, and sunshine.

     Temperature is the most important factor in determining the broad climatic belts within which different plants will grow and mature, as well as the more narrow belts where they will make their best development.

     Investigation has shown that every plant has its optimum temperature and moisture values during which it makes its best development, and that this varies in different periods of its growth. And not only this, but the heat and moisture must be in right proportion.

     The moisture in the soil carries plant food materials to the roots to be worked into vegetable tissue by the energy of the solar rays. If there is not enough material brought to the plant then the solar energy is wasted, and on the other hand, if the heat is not sufficient to use up all the material brought by the moisture, then the material is wasted.

     In the highest latitudes there is an excess of moisture and a deficiency of heat. These are the conditions that obtain in most of

Mean annual temperature in Nebraska

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NEBRASKA CORN IMPROVERS ASSOCIATION

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Europe, and in these countries the crop yields are determined largely by the temperature.

     In other places where the rainfall is sufficient and the temperature too low for the best growth of plants, such as in Alaska, the sunshine becomes the most important factor.

     No plant life is perfected and reaches its fullest maturity except through the influence of the short waves of solar energy which we call light. Dark rays or heat cannot replace sunlight in the growth of vegetation, but sunlight can partially replace heat. Barley and oats and similar crops can be cultivated, as they are, as far north as seventy degrees latitude only because of the quantity of light.

     A value called the "sunshine-hour degree" may he obtained by multiplying the average daily heat necessary to grow and mature a crop by the total possible number of hours of sunshine from planting to harvesting.

     If this is done for corn in the United States, the sunshine-hour degree from the date of planting to the date of harvesting corn, it is

Hours of sunshine in Nebraska

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PROCEEDINGS OF THE

found that the number of sunshine-hour degrees necessary to make a crop diminish as the latitude increases. This explains further why there is a decided difference in the quantity of heat necessary for the same crop at different latitudes due to the difference in the quantity of light.

     In the places where the temperature and sunshine are generally sufficient the development of the plant and more especially the crop yield depends most largely upon the rainfall. This is particularly true in most of the western part of the United States and to a large extent in central and eastern districts as well.

     It has been demonstrated by long experiments in most of the temperate regions that the yield of both grain and straw are greatest when the soil contains from 40 per cent to 80 per cent of its full water capacity during the most active season of growth.

     The most advantageous percentage of moisture varies with different plants, depending upon their method of using the water. In general the quantity of water necessary for a maximum crop increases with the richness of the soil, the closeness of the stand of plant, the size of the leaves, the dryness of the air, the velocity of the wind, and the temperature.

     The grain plant obtains a great part of its total weight from the soil during the early part of its growth, and a lack of moisture at this time will cause a short straw, but not ncessarily (sic) a small yield of grain. During the latter part of the growth the seed is being made chiefly from material stored in the stalk and the moisture must be present to flush the material from the stalk into the head, or the grain will be shrunken.

     A careful study of the work of others as well as personal investigation leads the writer to the conclusion that all plants have a certain critical period when favorable weather will produce a good yield, and unfavorable weather a poor one. Also that it is quite possible to determine the most critical period as well as the weather element most affecting the conditions, by a detailed study of the results in the field from the records of previous years.

     In some crops this critical period is very short. In some, temperature seems to he the most important factor, and in others it is the rainfall. In some crops, the period seems to be soon after seeding, and in others while in blossom. In apples, for example, our studies indicate that the weather during the formation of the fruit buds more than a year before the crop is harvested has a greater effect upon the yield than that of any like period between these dates,

     It seems to the writer that when the critical period for a crop has been determined together with the meteorological factor most affecting it, and the climate of a place calculated, the adaptability of that crop to that particular place can very quickly be determined. In some cases, it will be possible to vary the variety, time of seeding, fertilizing, or cultivation, so as to bring the critical period into the time when most favorable weather conditions are more apt to prevail. In other cases, it will be found best to substitute some other crop that will lend itself to these conditions. The one crop will do fairly well part of the time, while the other crop will reach its maximum most of the time.

     Further, we believe that this critical period in most instances is long enough before the date of harvest to allow for giving more attention to other crops which may perhaps be substituted. For example, there is no question but the rainfall for May is the most important factor in the hay crop in most of the northern part of the United States. If, therefore, it is found toward the latter part of this month that the rainfall has been light, other forage crops may be planted to take the place of the smaller hay crop.

     Since nearly 75 per cent of the world's production of corn is grown in the United States and as the economic importance of this crop is so great, it has been thought best to discuss the effect of weather upon corn.

     Corn is by far the most important crop in the United States. The acreage and also the value of the corn crop is greater than that of wheat, oats, barley, rye, buckwheat, rice, fruits and nuts combined. The relative importance of corn as compared with other cereals has remained fairly constant since the first agricultural census of 1840, but the production per capita, shows an increase after the Civil War.

     Corn (maize) was probably first brought under cultivation on the plateaus of central or South America. Under favorable conditions of soil and climate, corn is capable of relatively large yields, even with the crude cultivation of savage tribes. The best corn soils are well drained, deep, warm, black loams, with a high per cent of organic matter and available nitrogen. The geographic range of corn is limited by temperature and rainfall conditions. Varieties are known which mature in 80 days where the summer temperature is over 6 degrees. Even these requiremnts (sic) nowhere permit it to mature beyond 50 degrees North, though it may he grown for green fodder in Quebec and southern England. The great corn regions of the world are areas of continental climate. Most of the corn, except where there is supplementary irrigation, is grown in regions having an annual rainfall of at least 20 inches, with a marked summer maximum. In these regions the summer temperatures average about 75 degrees F., and both the day and

night temperatures are high. The summer rainfall should be of the thundershower type, in which periods of bright warm weather occur between rains. Corn does not thrive in regions of cool, or cloudy summers.

     The western limit of extensive corn production in the United States follows more or less closely the line of mean summer (June, July, and August) precipitation of 8 inches, extending somewhat beyond this line in Nebraska and Colorado, while in Texas where the evaporation, and the loss through torrential rains are greater, this line is scarcely reached. The hot winds of the arid portion of the southwest also dry out the pollen and silks, and interfere with pollination. The temperature requirements of different varieties of corn vary widely. Some southern varieties need an average frostless season of 180 days, and mean summer temperature of 80 degrees. Practically no corn is grown where the mean summer temperature is less than 66 degrees, or where the average night temperature during the three summer months falls below 55 degrees. Consequently, the production of corn along the northern border of the United States and at the higher elevations in the west is negligible.

     Although corn is thus grown to some extent under a wide range of climatic conditions, the most favorable environment is definitely restricted in area. The climatic boundaries of the region of greatest production in the United States are a mean summer temperature of 70 to 80 degrees, a mean night temperature exceeding 8 degrees, a frostless season of over 140 days, and an annual precipitation of from 25 to 50 inches of which seven inches occur during July and August.

     These geographic conditions which are essential to a large yield of corn are found in only a few regions in the world, and most extensively in the United States. Since corn is a highly productive crop, yielding on the average about twice as much grain and, including the fodder, over three times as much food per acre as either wheat or oats, the corn crop in the United States within its optimum georgraphic (sic) limits, reduces other crops, except cotton, to a subordinate position and especially those which require labor at the same time of year.

     Corn is preeminently the American crop, and is grown on three-fourths of all the farms in the United States. Within the United States three fourths of all the corn produced is grown in the Mississippi and Missouri Valleys. There are two centers of heavy production, one is in central Illinois, and the other in the Missouri basin of western Iowa and eastern Nebraska. In this region of concentrated production, there has developed a system of live stock farming adapted

to the utilization of corn. Nearly one half the swine of the country, and one third of the beef cattle are in the six states, Illinois, Iowa, Kansas, Nebraska, Missouri and Indiana.

     The production of corn in Europe is about one-fourth that in the United States. Hungary, Roumania (sic), Southern Russia and Italy are the leading countries in acreage. Although 5 degrees further north than the corn belt of the United States this region, with the exception of Italy, has similar conditions of soil, rainfall and temperature. The broad, fertile plains of Hungary place that country in the lead among European nations in acreage and production, but the relative importance of the crop is greater in Roumania (sic), where it occupies over 40 per cent of the cropped land, and the production is nearly four times as great per capita as in Hungary. The corn of Russia is grown mainly in Bessarabia, adjoining Roumania (sic), where the high rainfall, milder temperature and nearness to shipping points encourages its cultivation. Hungary raises something more than 200 million bushels, Roumania (sic) and Italy about half as much each, European Russia, 75 million, Bulgaria, 30 million. A little corn is raised in France, Spain and Portugal, and in Egypt and India.

     The corn acreage of Mexico ranks next to that of the United States. The principal centers of production are located in the southern sections of the country, mostly on the high plateaus and in Yucatan. On the plateaus the summers are warm, but frosts occur occasionally in the winter months. Poor agricultural methods result in a low yield. Mexico has a great proportion of its crops in corn, however, than any other country, the acreage about equalling that of all other crops.

     In Argentina the corn acreage is 21 per cent of the land in crops, and in per capita production this country ranks next to the United States. The mean temperature during the three warmest months (December, January and February) averages 75 degrees. The annual rainfall in the corn region averages about 30 to 40 inches, but, unfortunately for corn growing the maximum comes in the late rather than the early summer.

     Considerable time has been devoted during the past ten years to the problem of ascertaining just what effect the different whether factors have on the different crops, and in trying to find the critical period. The yield in each of the eight large corn producing states in the central part of the country has been compared with the rainfall during June, July and August by means of curves. The most important fact brought out was the close relation between the rainfall for the month of July alone and the yield of corn. While the curve method of showing the relation between two factors is the most graphic, it is not the most accurate, hence a table was prepared comparing the average rainfall for the month of July for Ohio with

the average yield of corn for the whole state for a period of 60 years by the simplest form of the correlation table. This makes it plain that the rainfall for the month of July has a far greater effect upon the yield of corn in Ohio than either June or August--somewhat greater than the rainfall for June and July combined, and slightly greater than for June, July and August combined, but that the rainfall for July and August combined has a greater effect than for July alone.

Thunderheads--A welcome sight in summer

     Studying the data for ten day periods by the same correlation method, it was found that the ten days of rainfall most important were August 1st to 10th, the twenty day period most important. July 21st to August 10th, the thirty day period, July 11th to August 10th, the forty day period, July 11th to August 20th.

     The average rainfall for the state of Ohio in July for the past sixty years is 4.06 inches; the average yield of corn for Ohio for the 60 years is 34.5 bushels per acre. If the different years are grouped by July rainfall amounts, the yield figures show some very interesting results. For example, if all the rainffalls (sic) of one-fourth inch differences be grouped, and the yield figures averaged, the results will show an average increase in the yield of corn of 0.8 bushel per acre with each increase of one-fourth inch of rainfall. If the rainfall amounts are grouped for each half inch difference, the aver-

age increase in the yield with each increase in the July rainfall of one-half inch, is 1.2 bushel per acre. The average increase in the corn yield with each increase of one inch in the rainfall in July in Ohio is 2.3 bushels per acre. In the state of Ohio, a one-fourth inch rain in July would cause an average increase in the corn yield of 2,800,000 bushels with a value of $1,400,000 considering corn worth 50 cents a bushel--one-half inch will cause an average increase in yield of 4,200,000 bushels or $2,100,000, and one inch increase, 8,050,000 bushels with a money value of $4,025,000.

     It must he remembered that these figures are only averages, and it does not follow that the yield will vary as indicated every time that the rainfall for July varies one-fourth, or one-half inch, etc. Sometimes the variation will he greater, and sometimes less, but in as much as the study covers the unusually long period of 60 years the figures must he valuable.

     The practical application of this study comes in recognizing the fact that one-fourth, and even one-half inch of rain can he conserved from rapid evaporation by proper cultivation.

     After considering the relation between the corn yield and a single element, the rainfall, during certain definite periods, the question naturally arises: What is the effect of all the elments (sic), i. e., the weather during different periods of development of the corn plant? The study of a long record of data kept at Wauseon, Ohio, helps to answer this question. There seems to he little or no relation between the daily mean temperature and the yield of corn; that is, the variations in temperature did not have an important part in determining the crop yield. The variation in rainfall during the season, however, did. The investigations show the rainfall for the ten days after blossoming has the greatest effect upon the yield of corn of any period in the history of the plant. Combining temperature and rainfall facts, it seems that hot, dry weather for ten days after blossoming is very damaging to the corn yield. And dry, cool weather much less so.

     It is well known that small rainfall during a drouth may actually do more harm to a crop than good, because by merely wetting the surface of the ground an effective dust mulch may be destroyed and thus more water be lost to the crop by evaporation than has been gained by the shower.

     Or numerous light showers during the early growth of the corn, by merely wetting the surface may cause it to root near the surface where the soil will quickly dry out during later dry spells. In the investigations of accumulative effects of weather it was found that when July was quite dry the final yield was greater if the previous June was moderately dry also.

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© 2002 for the NEGenWeb Project by Pam Rietsch, Ted & Carole Miller