Think about what one single seed does for you as a farmer. A single corn seed that weighs 1/100thof an ounce has the ability to be placed in dirt, germinate, grow into a plant 7-10+ ft. tall and multiply the grain yield 500 fold. No manmade machine possesses an equivalent ability to perform a comparable feat. Seeds are living organisms. Although seed seems to be dead, it is actually in a state of quiescence. Quiescence means that the seed is at rest until desirable conditions trigger germination, but it is still alive and respiring at a low metabolic rate. Respiration rates are kept low by keeping seed in cool environments absent from moisture, which allows the seed to be kept for years without significant reduction in viability. Below outlines conditions necessary for successful germination of corn and soybean seed.
The critical soil moisture for seed germination to occur is 30% for corn and 50% for soybeans(Copeland). The following is a quick way to estimate soil moisture for clay, clay loam, silty clay loam, sandy clay loam, loam or silt loam soils. At 25-50% soil moisture, a ball of soil formed with the hand will feel slightly moist, form a weak ball when gripped in hand, but it won’t leave dirt stains on your hand like wetter soil would, and few aggregates would break off of the ball.(USDA)
Seed-to-soil contact is critical for imbibition to take place. Imbibition is uptake of water into the seed. When a seed swells with water this is not an indicator of seed viability because even dead seed will imbibe water in the same manner as live seed. Soybeans will imbibe two to five times their weight in water while corn only 1.5 to two times its weight.
Minimum and optimum temperature for germination:
- Corn: minimum 46° F; optimum 86° F
- Soybean: minimum 50° F; optimum 77° F (Isleib)
Planting should not occur before soil temperatures are near 50° F for corn and 55° F for soybeans with a positive weather outlook. At 50° F corn will take approximately 25 days to emerge. At 55-60° F corn will take 10-14 days to emerge. At 65-70° F corn only takes five to eight days to emerge (Meyer). How long a seed can last in the soil and remain viable depends on temperature, moisture, and pests.
Oxygen is necessary as respiration increases during the germination process. Lack of oxygen is rarely a concern except for flooded soil conditions, which offer a significantly lower level of oxygen to the respiring seed and can kill the seed if conditions persist.
Differences between Corn and Soybean Germination
Corn seed goes through Hypogeal germination which means the energy storage structures of the seed remain below ground when the seed germinates. A key difference of the Hypogeal germination associated with corn is the coleoptile- a temporary sheath that protects the plumule as it pushes through to the soil surface (see picture below). As the plumule expands when it senses red light, the first leaf breaks through the coleoptile and photosynthesis begins soon after.
Soybean seed goes through Epigeal germination which means that the energy storage structures (cotyledons) are pulled above the soil surface during the germination process. These cotyledons supply stored energy to the developing seedling and begin photosynthesis when they encounter light and turn green.
In conclusion, a seed is an amazing living factory that is capable of producing a plant and multiplying itself to a factor of 500+ in the case of corn. With better conditions of soil moisture and temperature seedlings will develop faster and at higher rates of survival. Storing seed at low temperature and low humidity ensures that low metabolic rates are maintained and seed viability is prolonged.
Copeland, L. O., and M. B. McDonald. Principles of Seed Science and Technology. New York, NY: Chapman & Hall, 1995. Print.
"Estimating Soil Moisture by Feel and Appearance." USDA, Apr. 1998. Web. 02 Jan. 2013. <ftp://ftp-fc.sc.egov.usda.gov/MT/www/technical/soilmoist.pdf>.
Isleib, Jim. "Michigan State University- MSU Extension." Soil Temperature, Seed Germination and the Unusual Spring of 2012. N.p., 4 May 2012. Web. 02 Jan. 2013. <http://msue.anr.msu.edu/news/soil_temperature_seed_germination_and_the_unusual_spring_of_2012>.
Meyer, Ron. "Golden Plains Area Extension - Ron Meyer - Planting Corn." Golden Plains Area Extension - Ron Meyer - Planting Corn. Golden Plains Area Extension, 13 Apr. 2011. Web. 02 Jan. 2013. <http://goldenplains.colostate.edu/agri/agri_docs/2011_planting_corn.shtml>.