Iowa Agricultural and Home Economics Special Report Experiment Station Publications 9-1966 How a corn plant develops John J. Hanway Iowa State University Follow this and additional works at: http://lib.dr.iastate.edu/specialreports Part of the Agricultural Education Commons Recommended Citation Hanway, John J., "How a corn plant develops" (1966). Special Report. 38. http://lib.dr.iastate.edu/specialreports/38 This Book is brought to you for free and open access by the Iowa Agricultural and Home Economics Experiment Station Publications at Iowa State University Digital Repository. It has been accepted for inclusion in Special Report by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. The Illustration^*. .«. Identifying Stages of Growth CONCLUSIONS................. How a Corn Plant Grows . Nutrient Uptake. Fertilizer Applications . JB . • Summary.« . E S i ACKNOWLEDGEMENTS Contributions by two Iowa companies helped make this publication possible. The Iowa Fertilizer and Chemical As­ sociation, Inc. provided financial support for part of the pub­ lishing costs. Parf of the cost of obtaining the color pictures was supported by the Farmers Mutual Hail Insurance Company o f Iowa. There’s more than meets the eye in a field of growing corn. One way to look behind the scene is to consider the cornfield as a complex and constantly changing community. It is a manufacturing community, with many thousands of "factor­ ies" per acre. Every corn plant is a factory that produces dry matter. The corn plant is one of the most efficient factories in the world! There's competition in this community: competition for the raw mater­ ials from the soil and atmosphere; competition coming from other dry matter producers (weeds); and competition coming from insects and dis­ eases that interfere with the factory operation. Forces of nature provide the basic plan for this community. But each of those forces can be influenced by the man who manages it. Every pro­ duction practice affects the performance of the manufacturing system. Science and experimentation have given corn producers many prac­ tices that improve total output from a field of corn. They are effective practices. Great jumps in productivity have come from them. Still, they are gross practices. They are adaptable over a wide range of situations. They will work under different levels of management. The manager who folios the general recommendation can be confident of getting a profit- amW^gjrn. He can do that without understanding why there is improve­ ment, wtoput really knowing what effect he causes. ' - Ty\, As knowledge has been gathered, a much greater precision in prac­ tices has beRge possible. Output goes up with the precision. k In the fa^tow analogy, general practice recommendations can be com­ pared to one kmd of business approach: Set up a good plant, arrange fo la supply of raw materials, hire good workmen and tell them to do therr best. By contrast, consider the factory that maintains continuous lines of information flowing on raw materials inventories, efficiency studies of the various processes, trouble-shooting crews and constant surveillance to achieve maximum performance. This publication is designed for the person who is interested in corn production precision. It centers on one part of the management: H O W A CORN PLANT DEVELOPS. Whorl FIG. 1 PARTS OF A YOUNG CORN PLANT The logic is straightforward: The manager different seasons, different dates of planting and who knows how the corn plant develops and different locations. For example: functions can do a more precise job of con­ 1. An early maturing hybrid may develop trolling the forces that affect the output. An fewer leaves or progress through the different understanding of the plant—to the extent that stages at a faster rate than indicated here. A is now possible—relates to his practice decisions late-maturing hybrid may develop more leaves on: or progress more slowly than indicated here. 2. The rate of plant development for any • Selection of most suitable varieties hybrid is directly related to temperature, so • Timing of fertilizer applications the length of time between the different stages • Timing of such cultural practices as weed, will vary as the temperature varies, both be­ insect and disease control tween and within growing seasons. 3. Increased day length early in the develop­ • Timing of harvest operations ment of the plant results in more leaves per • Production planning for total corn production plant and lengthens the time between plant emer­ operations gence and flowering or silking. Day length in­ creases from south to north in the United States at corn planting time. THE ILLUSTRATIONS 4. Deficiencies of nutrients or moisture may The pictures and discussion in this publication result in lengthening the time between different represent an adapted, midseason hybrid in central stages before silking. Iowa. Each such plant will develop 20 leaves 5. The number of kernels which develop, and will silk 66 days after plant emergence. the final size of the kernels, and the rate of in­ All normal corn plants will follow this same crease in weight of the kernels influence the general pattern of development, but the specific length of the period from silking to maturity' times between stages and numbers of leaves These vary between different hybrids and dif­ developed may vary between different hybrids, ferent environmental conditions. 2 FIG. 2 STAGES OF EAR AND GRAIN DEVELOPMENT The pictures show plants and plant parts first 3 weeks of growth—the first leaf normally at identifiable stages of morphological (form has a rounded tip, all later leaves are pointed, and structure) development. The plants were and each succeeding leaf of the first seven or grown in the field but were photographed in eight leaves is almost twice as large as the the laboratory. Scientific names of parts in a leaf below it. young plant are shown in fig. 1. However, when the stalk begins to elongate, A numbering system is used to identify the the first (lowest) five or six leaves may be torn different stages of plant development. The stage loose by stem enlargement and by development at which the plant tip emerges from the soil of the nodal roots. After this occurs, the lowest is stage 0 and the stage when the plant is mature leaf remaining on the plant may be identified is stage 10. Intermediate stages are assigned by the length of the internode below the attach­ numbers between 0 and 10. For example, stage ment of the leaf sheath. The internodes below the 5 refers to the silking stage—silks just emerging first four leaves never elongate. The internode from the husk. A decimal is used to refer to a below the attachment of the fifth leaf -elongates stage of development (intermediate) between those to about 1/2 inch in length; the internode below identified by whole digits. For example, the stage the sixth leaf elongates to about 1 inch; below halfway between stage 2 and stage 3 is identified the seventh leaf to about 2 inches; and below as stage 2.5. the eighth leaf to about 3 1/2 inches. Stages of growth after silking can be identified by the development of the kernels on the ear identifying s t a g e s o f g r o w t h (fig. 2). At stage 6, the cob is full size and the kernels are in the blister stage. At stage 7, the Stages of growth before silking can be identi­ kernels are in a soft dough (just past roasting- fied in the field by counting the number of leaves ear) stage. At stage 8, a few kernels are be­ that are fully emerged (with the collar visible) ginning to show dents. At stage 9, all kernels from the whorl. This is not difficult during the are dented, but are not dry. 3 The embryo in the seed has five leaves and ■■■■■■ the primary roots have been initiated. After planting, the seed absorbs water and the young plant begins to grow. The radicle elongates most Depth of planting influences the length of rapidly, followed by the plumule (young plant time from planting to emergence. Seedlingsfrom or shoot) and the seminal roots. The radicle deep-planted seeds have a greater depth of emerges from the end of the seed opposite the soil to penetrate. In addition, temperatures are shoot. Two to five seminal roots emerge from cooler at greater depths and growth is slower. the end of the seed near the shoot. All roots, Depth of planting determines the depth at which except the radicle, tend to grow at an angle the primary roots (radicle and seminal roots) of 25 to 30 degrees from the horizontal. The develop but does not influence the depth at radicle can be aimed any direction (except up) which the nodal (permanent) roots develop. by orienting the seed. Nutrients and food reserves in the seed gen­ The first internode elongates to raise the plant erally supply the young plant adequately prior to the soil surface. When the tip of the plant to emergence. Fertilizer placed in a band to the emerges from the soil surface into the light, side and slightly below the seed may be con­ elongation of the first internode stops and leaves tacted by the primary roots before the plant begin to emerge from the coleoptile. Under warm, emerges from the soil. Placement of too much moist conditions, the tip of the plant will emerge fertilizer too near the‘‘seed can result in salt within 4 or 5 days after planting; but, under 1 injury to the young plant. cool or dry conditions, 2 weeks or longer may be required.