Soybean seed sales by seed count

Seed corn has been sold by seed count for many years and soybean seed may soon be sold the same way. A few years ago when the topic of selling soybean seed by seed count was raised, some seed companies resisted the idea due to cost of equipment, record keeping, lack of uniform seed size, and many other excuses. Today, some seed companies are addressing the topic of seed count and are selling seed by the 160,000 seed unit.

Research at Iowa State University has shown that a 160,000 seed unit is an appropriate unit size. Table 1 includes data from a soybean seeding rate study indicating that a seeding rate of 160,000 seeds per acre is the optimum population for maximizing yield. Therefore, one unit of 160,000 seeds would be the recommended seeding rate per acre.

Table 1. Effect of row spacing and harvest stand on soybean yield in Iowa.

Narrow Rows Wide Rows
Machine

Setting
Harvest

Stand
Yield

(bu/acre)
Harvest

Stand
Yield

(bu/acre)
80,000 94,000 47.9 73,000 46.3
120,000 133,000 50.2* 110,000 49.3*
160,000 157,000 50.9* 135,000 49.8*
200,000 186,000 51.6* 165,000 50.6*
240,000 221,000 51.4* 189,000 49.8*

Narrow rows, 7.5 and 10 inches; wide rows, 30 inches.

Yields followed by an asterisk (*) are statistically similar.

The producer has advantages when buying soybean by seed count. Soybean seed will be priced per unit and the producer will know the seed costs per acre before planting. By determining the seeding rate and adjusting the planter or drill to the desired seeding rate, the producer can more precisely order the amount of seed needed for the acres to be planted at a predictable cost per acre. Price will vary by seed size, as well as variety. Some dealers say that seed count is the more equitable method of selling seed for both the producer and the seed company. Soybean seed sales by bulk and mini-bulk packaging have increased annually and bag sales are decreasing. With larger quantities of seed per container the accuracy in seed count is even more important to the producer.

Soybean seed size varies among varieties and the environment where the seed is grown. If variety A and variety B were grown in the same field and treated with the same management practices there may be as much as 500 or more seeds per pound difference between varieties at harvest, due to genetic differences. There also may be a significant difference in seed size if variety A were grown in two different fields with the same management, but one field received a 2-inch rain in early

August that the other field did not receive. Therefore, the range in seed size between varieties A and B grown on two different fields may be very different, and the number of seeds in a bag of seed sold by the pound can vary considerably. Seed sold on the seed count basis reduces excess seed or seed shortage problems.

Table 2 shows the difference in seed size for three different seeding rates and the number of pounds of seed needed per acre for each seeding rate. If the seed size of a variety seed lot is 2,400 seeds per pound, and the seeding rate is 160,000 seeds per acre, 66.7 pounds of seed is needed per acre. At the same seeding rate when the seed size is 3,400 seeds per pound, the amount of seed needed for an acre is 47.1 pounds, a difference of almost 20 pounds. By using the seed count method for seed sales, both the unit package weight and price vary, but each unit contains the same number of seeds. There would be no advantage to buying small seed of a given variety because the seed number is the same in each unit. Soybean seed should be purchased based on the expected performance of a given variety in a given field or environment, not on seed size.

Large seed companies, compared with smaller companies, may have more problems making the transition from selling seed by the pound to selling seed by seed count, but once the industry makes the move to the seed count basis it will be easier for all concerned. Numerous varieties produced in diverse environments by a given company may create a challenge due to the wide range in seed size, but the transition was made in corn years ago and will happen with soybean.

Table 2. Soybean seed size and seeding rate per sales unit.

Seeding Rate/Acre
160,000 = 1.00 unit/acre 180,000 = 1.12 units/acre 200,000 = 1.25 units/acre
Seeds/lb lb of seed/acre lb of seed/acre lb of seed/acre
2,000 80.0 90.0 100.0
2,200 72.7 81.8 90.9
2,400 66.7 75.0 83.3
2,600 61.5 69.2 76.9
2,800 57.1 64.3 71.4
3,000 53.3 60.0 66.7
3,200 50.0 56.2 62.5
3,400 47.1 52.9 58.8
3,600 44.4 50.0 55.5
3,800 42.1 47.4 52.6
4,000 40.0 45.0 50.0

Seed unit equals 160,000 seeds.

This article originally appeared on pages 22-23 of the IC-488 (3) -- March 18, 2002 issue.

Updated 03/17/2002 - 1:00pm