Under adequate field conditions, the planted seed absorbs water and begins growth. The radicle is first to begin elongation, figure 5, from the swollen kernel, followed by the coleoptile with the enclosed plumule (embryonic plant), and then the three to four lateral seminal roots. VE (emergence) is finally attained by rapid mesocotyl elongation which pushes the growing coleoptile to the soil surface, white line in fig. 5. Under warm, moist conditions, plant emergence will occur within 4 to 5 days after planting, but under cool or dry conditions, 2 weeks or longer may be required.

Upon emergence and exposure of the coleoptile tip to sunlight, coleoptile and mesocotyl elongation stops. At this time, the growing point (stem apex) of the plant is 2.5-3.8 cm (1-1 1/2, inches) below the soil surface and is located just above the mesocotyl. The rapidly developing embryonic leaves then grow through the coleoptilar tip and development of the above-ground plant follows.

Because the radicle and lateral seminal roots (collectively termed the seminal root system) begin growth directly from the seed, the soil depth at which they initially develop depends upon seed planting depth. Growth of these roots, however, slows soon after VE and is virtually non-existent by the V3 stage. Although the seminal root system continues to function throughout most of the corn plant's life, its most important contribution occurs before the nodal roots become well established .

The soil depth of the growing point at VE also marks the depth at which initial nodal root growth will begin. This depth (2.5-3.8 cm) is relatively constant over different planting depths due to mesocotyl elongation, see figure 6.

The nodal root system is initiated at about VE, and the first set (whorl) of nodal roots begins elongation from the first node during V1. From V1 to about R3 (after which there is very limited root growth), a set of nodal roots begins development at each progressively higher node on the stalk, up to 7 to 10 nodes total. The nodal root system becomes the major supplier of water and nutrients to the plant by the V6 stage.

All roots except the radicle, initially tend to grow at an angle of 25 to 30 degrees from horizontal. Initial radicle root growth, however, can be aimed in any direction (except up) by orienting the seed. Nodal root growth begins to turn more downward as temperatures increase and drying occurs in the upper soil layers.

Management Guides

Since longer season hybrids generally average higher yields than shorter season hybrids, choose a regionally adapted hybrid that will utilize your local growing season and particular needs. Also use planting densities (row width and plant population) high enough to efficiently utilize your land area and hybrid's potential, but not too high as to result in barren or unfilled ears.

Cool temperatures at planting generally restrict nutrient absorption from soil and cause slow growth. This can be partially eliminated by banding small amounts of fertilizer to the side and slightly below the seed. This banded fertilizer may be contacted by the seminal root system before VE.

For faster germination and emergence at early planting dates, shallow planting takes advantage of the more favorable soil temperatures near the soil surface. At late planting dates, soil temperatures are generally adequate throughout all planting depths and soil moisture content becomes the limiting factor for rapid growth. The deeper planting depths usually have better moisture content at late plantings unless recent rains have occurred.

figure 5

figure 6

Next Page - V3 Stage || Previous Page - Identifying Stages of Development || Table of Contents

Ordering information (https://www.extension.iastate.edu/store/OrderingInformation.aspx)
Permission to reprint (https://www.extension.iastate.edu/store/PermissionToReprint.aspx)