Purdue University
Cooperative Extension Service
West Lafayette, Indiana

Plant Populations and Seeding Rates for Soybeans

E. P. Christmas
Agronomy Extension Specialist, Purdue University

As a result of widespread adoption of highly productive management practices such as solid seeding or narrow rows, soybean growers have become more aware of the importance of optimum plant populations and seeding rates in soybean production systems. Besides following new management practices, growers also have been able to control plant populations with considerable precision because of the availability of high quality seed and improved planting equipment. New management practices and seed quality improvement indicate growers should reevaluate their current seeding practices. This publication is a guide designed to help growers determine optimum soybean population levels and seeding rates needed to reach those levels.


High soybean yields are possible with a wide range of plant populations because single plants of most varieties will utilize a 7- to 9-inch area in all directions around the main stem. Plants adjust to tow populations by producing more branches per plant and by increasing the number of pods on both the main stem and branches. There is, however, little change in seed size and in seed number per pod. While the production of more branches and pods per plant maintains the yield potential for soybeans, harvest losses may be greater in thin stands since the pods on the lateral branches will be close to the soil surface and branch lodging is apt to occur. Leaves on plants in a thin stand also take longer to produce a ground-covering canopy. This allows more weed competition and soil moisture evaporation. In contrast, a stand that is too thick may result in excessive early lodging which means reduced yields as well as increased harvest loss.

When grown under high populations, individual plants produce fewer pods, fewer branches, grow taller, and pod higher off the soil surface than when grown at low populations. Yield potential is maintained with high populations since there are more plants per acre. Soybean populations that are too high also undergo a natural thinning process due to the intense competition between plants, which reduces the stand to a more acceptable level. In other words, plants are eliminated after emergence. In summer, soybean populations can vary perhaps as much as 50 percent from recommended levels without affecting yields, as long as missing plant spaces are not too large and weeds are controlled.

There are varietal differences in soybean response to over- or under-population. Taller varieties that are lodging prone are likely to have reduced yields if populations are too high. Shorter varieties are more likely to have reduced yields if populations are too low. In general, fewer problems occur when stands are established at or near recommended levels.


Plant population refers to the number of soybean plants emerged and established in the field which can contribute to overall crop performance (yield, competition with weeds, moisture use, etc.). It is usually expressed in terms of plants per acre or plants per linear foot of row.

Soybean plant population recommendations for Indiana are shown in Table 1 (columns 3 and 4) for various row widths. At the wider row spacings (20- to 36-inch), stands that vary +/- one plant per foot will differ little in yield. However, as row width is narrowed (20-inch and below), establishing the stand to within +/- ½ plant per foot becomes more important.

The population guidelines in Table 1 are based on responses of different public soybean varieties. Most varieties grown in Indiana will produce maximum yields at these populations but there are exceptions.

For determinate varieties, you may need to increase plant populations to realize full yield potential. An extreme example is the determinate variety, Hobbit 87, which is recommended for solid seeding (6-, 7-, or 8-inch rows) at populations of 200,000 to 250,000 plants per acre, or about three plants per foot of row. You can see from the table that this is 50 percent greater than the standard recommendations. When planting semi-dwarf types, follow your seedman's population recommendations. These suggested populations have a large built-in safety factor for unusual conditions. There is no need to adjust the seeding rate for soil type or planting date. Recent studies show that soybeans can produce a normal seed yield with populations down to about 60,000 plants per acre when planted by June 7 (80,000 required for later planting) so long as the plant stands are reasonably uniform and weeds are not a serious problem.

Table 1. Suggested Per-acre Plant Populations and Seedling Rates for Soybeans Planted at Various Row Widths

                                            Col.4              Col.5           Lb. seed
                           Col. 3        Recommended          Required        needed if
Col. 1     Col.2        Suggested        total plant      seeding rate at     2500 seed/lb.
Row        Feet of     number plants      population       90% germination    (81% final
width      row/a.        /ft. of row   (Col.2 x Col.3)    and 90% emergence    emergence*)
in.          ft.         plants/ft.      plants/a.         seeds/ft.             lb./a.

 36        14,520           7.0          101,640              8.6                  50
 30        17,424           6.0          104,540              7.4                  52
 20        26,136           5.0          130,680              6.2                  65
 18        29,040           4.5          130,680              5.6                  65
 16        32,670           4.0          130,680              5.0                  65
 15        34,848           3.7          130,680              4.6                  65
 14        37,336           3.5          130,680              4.3                  65
 12        43,560           3.0          130,680              3.7                  65
 10        52,272           2.8          143,750              3.4                  71
  8        65,340           2.5          163,350              3.1                  81
  7        74,674           2.2          168,020              2.8                  83
  6        87,120           2.0          174,240              2.5                  86
*Final emergence =  percent warm germination x percent expected emergence


"Seeding rate" refers to the number of seeds planted and is expressed in terms of "seeds per foot of row" or "pounds of seed per acre" (Table 1, columns 5 and 6). The relationship between the number of seeds planted and the eventual plant population depends primarily on seed quality and expected emergence of live seed.

The basic formula for calculating the seeding rate necessary to establish a particular desired population is as follows:

                      Suggested plants/ft. of row
    Seeding rate  =      (Col.3 from Table 1)
      	 	          Pct.         Pct. expected
                       germination  x     emergence

Example: A farmer is planning to plant Resnik soybeans in 30-inch rows. He has purchased seed labeled "90 percent germination." Previous experience indicates that, with his soil type and equipment, he can expect to lose about 10 percent of the seedlings from crusting problems, leaving a 90 percent live seed emergence. What should be his seeding rate to establish the desired stand?

    6 plants/ft for 30-in. rows  =   6  = 7.4 seeds/ft.
    ---------------------------     ---
    .9 (germ.) x.9 (emerg.)         .81

Thus, our farmer would set his planter to drop about 74 seeds per 10 feet of row.

Information about seed drop, soybean plates, and sprocket settings is given in the owner's manual for planting equipment. Some manuals use pounds per acre when referring to seeding rates. Therefore, to select desired settings corresponding to seeds per foot, it is necessary to convert to an acre basis. This is done using Table 1 (column 2) and Table 2 in conjunction with the following formula:

                         Ft. of row/acre x Seeding rate
    Lb. seed per acre =   (from Table 1)  (from above)
                             Seeds/lb. (from Table 2)

Referring to our previous example, the farmer's seeding rate on a pounds per acre basis using Resnik soybeans would be:

17,424 ft of row/acre x 7.4 seeds/ft.of row = 128,938
-------------------------------------------   ------- = 45.6 lb. seed
    2,830 seeds/lb. for Resnik                 2,830

Regardless of the planter used, seed drop should be field-verified regularly. The number of seeds per pound also should be calculated for each lot of every variety planted because the number of seeds per pound will vary from lot-to-lot depending upon growing conditions.

The most difficult figure to accurately determine when using the above seeding rate formula is percent expected emergence. Percent warm germination is the standard measure for seed quality; every bag of commercially-processed seed in Indiana must be labeled with this information. The warm germination test is run under ideal conditions (i.e., 7 days at 70° F and high humidity) and thus is essentially a test for live seed.

Table 2. Average Number of Seeds per Pound for Various Public Soybean Varieties

Maturity group		Variety			Ave. seeds per lb.*	
Group II		Archer			2600
			Burlison		2330
			Century 84		2520
			Chapman			2170

Group III		Bass			2800
			Edison			3070
			Harper 87		2280
			Hobbit 87		2650
			Linford			2380
			Pella 86		2320
			Resnik			2830
			Williams 82		2570
			Winchester		2330

Group IV		Flyer			3170
			Corsica			2530
			Spencer			2600
			Delsoy 4210		2320
*Number of seeds per pound will vary from year-to-year,
depending on growing conditions.


Emergence in the field is dependent upon a number of factors. The main ones are soil conditions, weather, date of planting, cultural practices including planting depth, and seed treatment. Emergence response to these factors often is referred to as "seedling vigor"; and all the factors must be considered in predicting percent emergence.

Soil Conditions

Soil conditions are determined by soil type, weather, and tillage practices. A cloddy, compacted, or crusted soil will generally reduce soybean emergence. Personal knowledge of and experience on individual fields is the best guide for estimating the effect of soil conditions on percent emergence.


In addition to influencing soil conditions, rainfall and temperature play a critical role in the germination and growth of soybeans. Soil and air temperatures of 55-60° F are necessary for seed germination and seedling growth; and as temperatures increase (up to about 90° F), rate of germination and growth likewise increase. Adequate soil moisture is needed to initiate seedling growth, but too much or too little can adversely affect soybean emergence.

Date of Planting

Planting date effect on emergence is related to weather and soil conditions. As soil and air temperatures increase during the planting season, the percent of emergence also should increase.

Purdue studies show that there will likely be less difference in emergence between early-and late-planted soybeans with high quality seed than with low quality seed. For instance, at 90 percent germination, we might expect a 3-8 percent emergence difference between a May 10 and a June 10 planting date; but for seed testing 80-85 percent, this difference increases to 8-13 percent.

Cultural Practices

Soybeans should be planted 1-1 1/2 inches deep. Deeper planting will reduce emergence, because the distance a soybean can grow up through the soil is limited.

Secondary tillage affects the condition of the seedbed and influences the accuracy of planting depth, crusting tendency of the soil, and moisture retention. Therefore, review your specific cultural practices, and consider if and how they might influence positively or negatively-seedling emergence when calculating your seeding rate.

Seed Treatment

The effect of a fungicide seed treatment on soybean emergence depends on two things--seed quality and weather conditions. Treating high quality seed (90 percent or greater germination) has little effect on laboratory germination or field emergence. Treatment of lower quality seed, however, may increase field emergence 5-10 percent.

The weather during germination also can affect the seed treatment-emergence relationship--i.e., as planting is delayed and conditions for germination improve, there is less emergence response to seed treatment. Remember, too, that fungicide treatment rarely increases yields, so long as adequate minimum populations are established.


The recommended plant populations shown in Table 1 are valid for double crop soybeans. However, seeding rates for soybeans following wheat may be greater, because of added difficulty in establishing desirable stands. For seeding rate and population information regarding double crop soybeans,see Purdue Extension publication ID-96, "Double Cropping Wheat and Soybeans in Indiana," available from your county Extension office.


It is not necessary to increase seeding rates for no-till soybeans if a properly weighted and adjusted drill or planter is used and soil conditions are acceptable. Special care should be taken to assure correct planting depth, good slot closure, and soil firming around the seed. Most problems occur when trying to plant when the soil is either too wet or too dry. If too wet, it is difficult to obtain good slot closure and soil firming because of "slabbing out" of soil by the no-till coulters. If too dry, it is difficult to obtain adequate coulter penetration and seed placement at the correct depth. Uniform stands and solid seeding (rows 10" or less) are important, valuable aids in providing good, early canopy closure and enhanced weed control for no-till soybean production.


Many factors affect the relationship between seeding rate and the established stand for soybeans. Fortunately, the growth characteristics of most varieties are such that establishing precise populations is not critical. Only when stands are 50 percent thinner or 50 percent thicker than the optimum populations suggested in Table 1 would serious problems be expected.

Calculating desired plant populations can be approached several ways. Table 1 goes through the exercise of determining seeding rates, expressing them on the basis of seeds per foot of row and pounds of seed per acre.

The accuracy of your seeding rate decision depends on your ability to predict percent emergence. Initially, your prediction as to emergence probably will be based on personal observation. But for future decisions, do a few field checks to confirm or improve your accuracy.

Brand names are used simply for clarity with the understanding that no discrimination is intended and no endorsement by the Indiana Cooperative Extension Service is implied.

REV 2/93
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture Cooperating. H.A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30, 1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access to our programs and facilities.