Seed size and shape are important for planter settings, but are not related to genetic yield potential. Information regarding planter adjustment can help improve seed delivery to the soil. Plantability and germination studies are other sources of information to help growers make decisions before planting season.

Normal conditions are not guaranteed for spring planting. Therefore, it is important to 1) understand how seed size is determined, 2) examine how seed size can affect emergence and early growth, 3) understand how proper planter settings are used to support different seed sizes, and 4) use management techniques to help improve plantability of various seed sizes with different types of planters.

Field to field differences each year result in a variety of seed sizes from hybrid production. Seed size is affected by specific hybrid characteristics, parent tendencies, and growing conditions, especially during the pollination and fill period. Seed from each ear is categorized into many size/shape categories. Typically, large rounds come from the base of the ear, flats from the center, and small flats and small rounds from the tip. Plateless seed usually comes from the base or the tip, but is outside the weight ranges set by the grading system.

Effect of Conditions on Germination

Advantages and disadvantages have been related to seed size under adverse planting conditions. Large seed can have slightly decreased emergence rates in dry soil conditions as large seed requires more moisture to initiate germination compared to small seed. Small seed can have slightly decreased emergence in cool or crusted soils, as the energy needed in these environments may be greater than the amount stored in the endosperm. After tasseling, differences in early growth related to seed size are usually not apparent.1 Regardless of seed size and shape, silking dates and grain yield are expected to be similar with similar final plant stands.

Planter Adjustment for Seed Size and Shape

Planter settings should be set for accurate seed positioning, placement, and seeding rate. When adjusted for seed size, a planter can more accurately singulate and deliver seed. Planters can deliver excessive numbers of doubles, triples, or skips when improperly adjusted for seed size. Consequently, grain yield potential can be reduced by 3 to 10 bushels per acre.2 Stand counts should verify that intended population was met to produce maximum yield potential.

Vacuum Planters

Adjustments can be made to the vacuum pressure, cell size, and seed singulation devices that can affect plantability. Planters equipped with cell or flat disks have different requirements for adjustment. Another component to examine, regardless of disk type, is the way the disk is adjusted relative to the meter housing. Having the disk rub the housing with light contact can help improve singulation, reduce seed damage, and help load the planter drives, improving their consistency.

Delivery, plantability and germination of corn seed 1

Figure 1. Celled field corn seed disk

Vacuum Planters with Cell Disks. With cell disks, seed is partially held in place by the cell and partially by the vacuum pressure (Figure 1). Plantability is aided by matching different cell sizes and vacuum pressures to fit a given seed size and shape. Disks with cells that are on the larger side of the acceptable range for a given seed size could lead to doubles, even if the vacuum pressure is adjusted to the lower side of the acceptable range. Low vacuum pressures also increase the chance of seed being shaken off of the disk when planting over rough ground, resulting in increased skips. To help reduce doubles and skips, disks with cells on the smaller side of the acceptable range can be used while running vacuum pressures on the higher side of the acceptable range.

Vacuum Planters with Flat Disks. Flat disks have become popular as they are less sensitive to different seed sizes and shapes. They can therefore provide more consistent plantability with less need to adjust vacuum pressure. Two flat disk examples are the John Deere® ProMAX 40 Flat Disk and the eSet™ system from Precision Planting. The use of flat disks generally requires an additional component or two for singulation. The ProMAX 40 Flat Disk uses a double eliminator and a knock-out wheel while the eSet system requires a non-adjustable singulator. Even with these differences, both systems reduce the need to adjust vacuum pressure to account for seed size and shape variations, thereby improving the plantability of various seed sizes and shapes. Flat seed disks may need a slightly different environment than cell disks, and users may benefit by visiting their equipment dealer for inspection and testing of their seed meters.

Finger Pick-up Planters

Planter speed is key to calibration and accurate seed placement. Planting at speeds faster than recommended could result in poor seed singulation and placement, and negative effects on yield potential. Alternatively, planting at speeds slower than the recommended range may lead to lowered populations.

Maintenance on finger pick-up planters helps minimize planting errors. The following items can be evaluated and adjusted to operator manual specifications:

  • Proper tension on the fingers
  • Meter brush condition
  • Carrier plate condition
  • Seed delivery belt pliability
  • Seed baffle cleanliness
  • Proper lubrication rate
  • Good alignment with meter drive and the lugs on the unit drive sprocket
  • Well-maintained and lubricated drive chains

Delivery, plantability and germination of corn seed 2

Figure 2. Average potential for percent singulation of vacuum planter units including Case IH ASM, John Deer® Pro-series XP with ProMax 40 Flat Disk, John Deer® MaxEmerge™ with cell disk, Kinze® EdgeVac® with cell disk, and the eSet™ flat disk from Precision Planting. Source: Monsanto Seed Technology Center in Waterman, Illinois.

Fluency Agent

A seed lubricant in pneumatic planters is typically recommended to help reduce friction and improve uniformity of planting. Fluency Agent is a new seed lubricant that is designed to replace standard talc and graphite seed lubricants. Seed lubricants help reduce the amount of dust and seed treatment lost during planting.

Seed Placement Technology

As planter speed increases, there can be more bounce from the row unit and seed meter. This causes seeds to drop at different speeds with inconsistent spacing. A new seed conveying technology, SpeedTube™ by Precision Planting®, can be used to help control seed drop with the current planter being used by a farmer. The controlled release of seeds to minimize horizontal speed when the seed lands in the trench can help accurately and consistently place seed without bounce or rolling in the trench. SpeedTube is a seed delivery system with a slotted belt that picks up seed from the disk and controls the speed of descent to the seed trench by moving at the same speed as the planter ground speed. This technology helps place seed in the seed trench with minimal drop distances and bounce. Ground speed can be increased while maintaining good seed spacing. Monitoring actual seeding rates and making adjustments as conditions change will continue to be important with advancements in technology.

Plantability Studies

Monsanto has conducted plantability tests to provide planter setting recommendations for seed lots. Results of the tests conducted are represented in terms of percent singulation, or the percentage of single seeds released by the seed meter at the proper time. If the seed sensor detects two seeds where only one should be, then it is called a multiple. If the seed sensor detects nothing where a seed should be, then it is considered a skip. Therefore, percent singulation is determined by taking 100% properly timed single seed drops and subtracting the percent multiples and percent skips.

Figures 2 and 3 demonstrate singulation data for vacuum or finger pickup planters and various seed sizes and shapes. The finger pickup units were calibrated for larger seed, and data for smaller seed sizes and shapes are not presented. Simulated planter speed was 8.85 km (5.5 miles) per hour. Seed was harvested each fall from 2004 through 2010 and was planted the following spring from 2005 through 2011, respectively.

Germination Tests

Warm Germination Test. Warm germination testing is required by the Canada Seeds Act and Regulations. The standard method for this test is developed by the Canadian Food Inspection Agency. Hybrid seed corn certified as ‘number one grade’ needs a germination score of 90% when tested at temperatures of 25° C.3,4

Cold Germination Test. Contrastingly, Cold Germination or “Vigor” tests are not required by the Canada Seeds Act and Regulations, nor is there a standardized test across the seed industry. Many companies, universities, and independent seed testing labs have developed and implemented various forms of Cold Germination tests to help establish and differentiate the quality of their seed beyond the legal testing requirements. Monsanto has developed and deployed a proprietary, internal vigor (Cold Germination) test in an effort to better predict emergence potential across environments. The results of this test are used internally as an integral part of the quality management system to help provide only the highest quality seed to our customers. This information is not shared outside of the quality review team, because there is no way to know the actual difference between Cold Germination scores from various testing sources in the absence of an industry standard. For example, an 85% test result from the proprietary test Monsanto utilizes may be an equivalent or better indication of stress emergence compared to a 90% test result from a different, less rigorous test. Unfortunately, even if all of the variables were fully understood for each testing procedure, making a comparison of results across the tests could be misleading since it would be based on making various assumptions.

Similar to a Cold Germination test, there is not a procedure standardized across the industry for “Saturated Cold Germination” tests. Therefore, testing procedures and test results are likely to vary by lab.

Monsanto has a great deal of confidence in the Cold Germination test utilized internally. The validity of this test has been proven across millions of acres for numerous seasons. That being said, germination scores are only indicators of potential and not absolute measures of performance. They are the best indicators available to predict the experience a grower will ultimately have when seed is planted; however, they are not perfect and there will always be exceptions. Monsanto takes seed quality very seriously and strives to deliver the most consistent, highest quality seed a farmer can buy.

Delivery, plantability and germination of corn seed 3

Figure 3. Average potential for percent singulation of John Deere®, Kinze®, and Precision Planting finger pickup units are represented in the data. Source: Monsanto Seed Technology Center in Waterman, Illinois.


Overall, seed size does not affect genetic yield potential. Proper planter adjustment can help achieve an optimal stand by minimizing skips, doubles, and triples. Appropriate planter settings should be identified to improve seed plantability as it can help improve yield potential. Plantability can be optimized by adjusting planter settings, focusing on genetic yield potential, seed quality, increasing populations, and identifying planter settings that help deliver seed.