2019 was full of challenges, including what to do with purchased seed that did not get planted. If the purchased seed was not returned and was stored with intent to use it in the 2020 season, producers should consider re-testing the seed lots for germination and possibly add a seed vigor test to help make planting decisions for 2020. Most seed germination percentages on a seed tag for agricultural seeds (like corn and soybeans) are valid for 12 months from the last date of the month in which they were completed, with the exception being cool season grasses which are valid for 15 months beyond the month of testing (Ohio Revised Code, Chapter 907.07).
Seed quality is key to establishing a good crop, with major components of quality being genetic quality, physical purity (% other crops, % inert, and % weeds), and physiological quality (seed germination and vigor). Over time the physiological quality of a seed lot can change, especially as a result of its storage environment. Storing seed where the temperature (in degrees F) plus the % relative humidity are less than 100 (Harrington’s rule) helps to minimize the rate of seed deterioration (or loss in germination and vigor). However, in non-conditioned storage conditions viability may vary dramatically after 12 months with different seed lots that had similar initial germination rates (Table 1).
Seed germination is an important consideration for determining seeding rate to ensure the critical final stand for yield is achieved for crops like corn and soybeans. Check the seed tag for both the date of the test as well as the germination when planning seeding rates. This percentage is usually derived from the results of a standard warm germination test, which often assesses seed germination under optimal conditions (warm moist temperatures). To determine a seeding rate for a targeted harvest population (e.g. 32,000 plants/ac for corn), then divide your harvest population by the germination (e.g., 95%) as a decimal. In this example, 33,684 seeds/acre (32,000/0.95) would need to be planted to achieve the desired harvest population given an 95% germination rate.
A seed vigor test can provide further insight into how a seed lot may perform in the field under stressful conditions compared to other seed lots. This information could help producers plan for what lots should be planted early vs. later, as well as positioning fields that are typically more stressful for seedlings. A higher vigor score is usually more tolerant of adverse conditions than a lot with a lower vigor score. These can be used on carry over seed lots, but also can be conducted on new seed lots prior to planting.
Common seedling vigor tests include a cold test (cold moist soil) or a saturated cold test (cold moist soil conditions plus embryo is placed directly into soil). The cold test and saturated cold test provide insight into germination of a seed lot under cool conditions common to April planting dates. The cold test uses of cool moist conditions with the addition of soil, and can be conducted using rolled towels or shallow trays. The saturated cold test is a more standardized version of the cold test that uses sieved soil, the soil contains more water content (lower oxygen content as well), and places the embryo directly into the cold wet soil. The accelerated aging test helps estimate longevity of seed in storage, and has been related to field emergence and stand establishment. The seeds in this test are exposed to a short period of high heat and humidity conditions (ex: 2-3 days, 105 degrees F, 100% relative humidity) before a standard germination test is conducted. Others, such as a seedling growth rate test, can provide insight into germination as well as the amount of energy storage reserves in the seeds.
The recommendation for sampling a specific seed lot for testing is that a sample should be collected from 5 bags plus 10% of the remaining bags for that lot to ensure a representative sample. Please look to the NCR bulletin 403 - Seed Lot Sampling for more specific guidelines (https://www.ag.ndsu.edu/fss/seed-increase-program/seed-lot-sampling-ncr-bulletin-403).
J.C. Delouche and C.C. Baskin. 1973. Seed Science and Technology 1:427-452.
A.D. Knapp, T.J. Gutormson, and M.K. Misra. 1991. Seed Lot Sampling. Northcentral Region Extension Bulletin 403.
Seed Vigor Testing Handbook. 2002. Association of Official Seed Analysts.
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