ack in February, I indicated that most soybean seed produced in Indiana in 2000 was of good quality (See article). I also indicated that soybean seed produced last year in western Illinois, Iowa and Nebraska was of very poor quality. I have since received a number of inquiries from producers that have received their soybean seed for this year with germination guarantees below 90%. Some seed companies are labeling some of their seed lots with germination guarantees of 80 and 85%. The average germination on seed lots offered for sale in Indiana is running about 89% as of this date. However, as the season progresses, expect to see the average germination of seed offered for sale in Indiana to decline as lower quality seed lots are offered for sale.
As a result of this wide range in germination of soybean seed being offered for sale for the 2001 growing season, it is very important that you check the seed tags of each seed lot that you plant to determine the germination percentage and seed size. Drills and planters should be adjusted for each seed lot to assure an adequate plant population. In 2000 I walked a number of drilled soybean fields with stands of 100,000 to 125,000 plants per acre. This same problem can occur this year if care is not taken at planting time to assure that the proper number of viable seeds are being planted.
Purdue recommends seeding rates of 200,000, 165,000, and 130,000 seeds per acre for 7.5, 15, and 30 inch rows respectively. This is equivalent to 3, 4.7, and 7.4 seeds per foot of row. These recommendations are based on seed with a minimum germination of 90%. To adjust these seeding rates for germination levels less than 90%, divide the planned seeding rate (either seeds per acre or seeds per foot of row) by the percent germination given on the tag, expressed as a decimal. For example if the planned seeding rate is 200,000 seeds per acre and the seed tag gives the germination at 80%, divide the 200,000 by .80 to give the correct seeding rate for this seed lot of 250,000 seeds per acre. This is equivalent to 3.75 seeds per foot of row with a 7.5 inch row spacing (3 divided by .80). The table below gives the adjustments in seeding rate for three levels of germination less than 90% and for the four most common row widths.
Table. Seeding rate adjustments for varying levels of germination.
Percent germination as given on the seed tag
|Row Width||90% or better||85%||80%||75%|
----------------- Seeds per acre (Seeds per foot of row)----------------
|7.5 inch||200,000 (3.0)||235,000 (3.5)||250,000 (3.75)||267,000 (4.0)|
|10 inch||165,000 (3.4)||194,000 (4.0)||206,000 (4.25)||220,000 (4.53)|
|15 inch||144,000 (4.7)||169,000 (5.53)||180,000 (5.88)||192,000 (6.27)|
|30 inch||130,000 (7.4)||153,000 (8.71)||163,000 (9.25)||173,000 (9.87)|
Usually seed lots with low germination also have reduced vigor as determined by either a cold germination test or an accelerated aging test. Every effort should be used to reduce the stresses when planting soybean seed with poor germination and possibly poor vigor. The stresses to avoid that are most important are wet and/or cold soils. Therefore, if you are planting soybeans into cold and/or wet seedbeds do not use seed lots with poor germination. Plant the good quality seed lots first leaving the poor quality seed lots for later in the planting season when soil conditions are more ideal.
One last word of caution, since the poor germination is most likely the result of hot, dry conditions at harvest last fall, these seed lots are very fragile and should be handled with care to prevent further damage. Seed treatment will not improve these poor quality seed lots, but may protect the seed from soil pathogens if the seed is planted into cold/wet soils.