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  • Writer's pictureWendell Koehn

What is going on inside a seed or seedling? A lot actually, a miracle!

Updated: Sep 12, 2019

“From one seed a whole handful: that was what it meant to say the bounty of the earth.” -J.M. Coetzee



On April 10, 2019 weather forecasters calculated a sharp gradient to setup near the Bates and Vernon County areas on the evening of April 13, 2019. This would result in cold wet rain to fall on newly planted corn ground. This forecast was quite different in our area than the forecasted event as that dry line pushed south and east. The difficulty they had in placing a storm with this sharp of gradient laid aside, let's look at a possible example of what could have happened had that event materialized on us. This is why your agronomist warns of seed imbibing cold water as its first drink. The pictures included here show corn seedlings not so far south of us that hit this cold wet event too soon after it went into the ground. Read on to the end of the article. Next week the forecast has high rain risks in it, and we touch a little on research done on saturated soils. It is insightful to know a little of the science behind seed germination. Truly, this is an amazing event. A corn kernel weighing about 1/100th of an ounce can multiply to 500 fold. No human invention can perform this miracle.

<Look to the bottom of this page for slides that support this article!>


-The Seed Kernel is a living organism, in a position of quiescence. It is resting, but alive. If a kernel is kept in optimum conditions (cool & dry), it will respire at a slow metabolic rate for years without much reduction in viability.

-Water level in the soil needs to be around 30% for germination to start. You can estimate this by gripping a lump of soil. If it is slightly moist, forms a weak ball that can be broken by throwing at the ground, and leaves no water stains on your hands it is between 25-50% water level.

-Temperature effects on the kernel can bring varied results even as different hybrid genetics react differently to cold weather. Also, different seed sizes can change the speed of imbibition of water. Larger seed will take longer than smaller seed, for example. This difference is minute, but when a seed is planted hours apart from another this can make a difference on a the ultimate effect of cold temperatures on the seedling. A 50 degree soil temperature or higher is important to plant into.

-Oxygen is a critical, but not often thought of component in germination. The speed of respiration increases as kernel begins the germination process. This is a concern in water saturated soils. If these conditions persist, seed mortality will occur.


Corn vs Soybean Morphology at emergence

Corn goes through hypogeal germination (seed kernel stays below ground) and soybean goes through Epigeal germination (seed kernel is pulled above the ground). Both, corn and soybean seedlings change according to light from the sun. When soybean cotyledons encounter light, they start the process of photosynthesis and turn green. When the corn coleoptile still below the soil surface senses red light from solar radiation this causes a change in one or more corn growth hormones. Since the depth at which the seedling senses red light is fairly constant, the depth of the crown is nearly the same if the seed depth is 1" or greater. Thus making it easy to mark the seed's planted depth even after kernel has wasted away.


Summary It is my opinion that cold temperatures hitting a freshly planted seed via cold air, water, or both can sicken and weaken the seedling. This problem occurs rather quickly by comparison to warm temperatures and excess water.


Reid Nodine holds mutated seedlings affected by cold injury!

Water excess and the resulting lack of oxygen is a problem that wastes away the seed's or seedling's viability over a longer period of time by contrast. Typically, an older corn plant with a healthy, robust root system will handle wet saturated soils better than a plant with roots that are trying to grow in a seed trench that was smeared, have struck a compaction layer, or is unable to intercept nutrition as soil levels are at or below critical levels inhibiting root health. The more roots the better as the corn plant will kill its own roots to convert this material to oxygen. I then ask a question: "Could drought tolerant hybrids fare better in saturated soils?" Typically, drought resistant corn products have a larger root mass. Here is a direct quote from a scientific study on saturated soils:

"High variability was observed among corn hybrids in response to prolonged soil waterlogging for 14 days or 21 days for various growth parameters. However, some corn hybrids had higher growth (Hybrids #5, #6) in optimum moisture conditions compared to other hybrids. In addition, some hybrids were more susceptible to waterlogging as indicated by the reduction in plant height and biomass production. Higher variability in hybrid responses to waterlogging and comparatively shorter duration of greenhouse experiment make it difficult to identify one or more hybrids from this experiment showing greater resistance to waterlogging stress than other hybrids."

"These results indicate that waterlogging tolerance traits may be present among commercial corn hybrids. Exact mechanisms for this tolerance were not explored in this research, but it may be important for future research to examine these mechanisms and the conditions under which optimal expression of the traits can be stimulated.

"Inclusion of more diverse genetic lines that have major differences in traits that may affect flood tolerance, such as stomatal opening and root growth, also may be necessary to identify specific flood tolerance traits as they are expressed in the field."


The complete study can be found here:

Screening Corn Hybrids for Soil Waterlogging Tolerance at an Early Growth Stage

https://www.mdpi.com/2077-0472/9/2/33/htm


As always, if you need anything feel free to reach out anytime: 417-684-5301 or wendell@topagservices.com


Works cited


Estimating soil moisture by feel and appearance

https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_051845.pdf

Seed Science: Seed Germination by Alex Johnson

https://www.farmprogress.com/seed/seed-science-seed-germination

Emergence and Seedling Characteristics of Maize Native to the Southwestern US - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Diagram-of-maize-seedling-parts_fig1_317138012 [accessed 25 Apr, 2019]

SOYBEAN ANATOMY GLYCINE MAX PLANT AT GEOCHEMBIO TAXONOMY BRIEF FACTS

http://directorioweb.me/soybean-anatomy/soybean-anatomy-glycine-max-plant-at-geochembio-taxonomy-brief-facts/


Delta Research and Extension Center, Mississippi State University, Stoneville, MS 38776, USA Plant and Soil Sciences Department, Mississippi State University, Mississippi State, MS 39762, USA Department of Soil, Atmospheric and Environmental Sciences, University of Missouri, Columbia, MO 65211, USA Division of Plant Sciences, University of Missouri, Novelty, MO 63460, USA


Professionals consulted


David Hughes, CCA Agronomist near Columbia, MO

Alex Long, CCA Agronomist for Beck's Hybrids for MO

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