Seed Size Data, Seed Placed Fertilizer  03/03/15 12:36:57 PM

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Seed-Placed Fertilizer We are always looking for ways to place plant nutrients beneath the soil surface for maximum agronomic effectiveness.  Applying fertilizer directly with the seed is one option, but there is a limit to how much fertilizer can be placed there.  Seed injury from excess fertilizer near the seed can significantly reduce plant stands and crop yields when placed directly on the seed.  Urea-based fertilizers can inhibit seed germination and seedling growth due to toxic amounts of ammonia released from the hydrolysis of urea by urease.  Urease inhibitors can be used to reduce or eliminate these effects.  The salt effects of fertilizer materials, especially nitrogen (N) and potassium (K) products, reduce water availability in the soil area directly adjacent to the seed.  This can delay or inhibit seed germination. 
  Salt Index of Fertilizer Materials
Material Salt Index
Ammonium nitrate 105
Mono ammonium phosphate 30
Di ammonium phosphate 34
Urea 75
Triple superphosphate 10
Potassium chloride 116
  Source: Rader et al., 1943. Soil Sci. 55:201-218
The salt index of fertilizer has been defined as 100 times the ratio of the increase in soil-solution osmotic pressure produced by the material to the increase produced by the same weight of sodium nitrate2.  In other words, the salt index is just a relative measure of the ability of a fertilizer material to remove moisture from its surroundings.  The salt index for several fertilizer materials is shown in the table. 
Soil moisture substantially influences the impact seed-placed fertilizer has on seeds and seedlings.  Dry conditions at planting, with limited subsequent rainfall, greatly increases the potential for seedling damage.  Planting into sandy soils, or other soils with limited moisture-holding capacity, will also increase damage potential.  In addition, crops vary in their response to seed-placed fertilizer at a given soil-moisture level. Relatively large amounts of plant nutrients can be banded near the seed (such as 2 inches to the side and 2 inches below the seed) with minimal negative effects.  What are the effects of, and guidelines for, placing fertilizer directly with seed?
Corn--Only 5 lb N/a as urea was enough to cause a substantial yield reduction in a Wisconsin study.   Stand damage was not measured with ammonium nitrate until 20 lb N/a was applied.  In a Nebraska trial, application of more than 10 lb/A. of N + potassium (as K2O) delayed germination and caused uneven emergence.  In other Nebraska research, where the plots received adequate rainfall, N + K2O rates of up to 45 lb/a did not affect plant stand or yield.  This emphasizes the significance soil moisture has on the effects of seed-placed fertilizer.  Three years of Minnesota research using 5 to 15 gal/a of fluid fertilizers (4-10-10, 7-21-7, and 10-34-0) found no negative effect on corn emergence or yield.   Soil moisture levels at planting were relatively high each year.  In South Dakota, triple superphosphate (TSP) and monoammonium phosphate (MAP) were found to be less injurious than diammonium phosphate (DAP).  Free ammonia hydrolyzed from the DAP may explain this effect.  To minimize the risk of stand reduction, the South Dakota researchers suggest not using DAP, UAN or urea with corn.  They recommend not applying more than 10 lb/a of N + K2O and not more than 100 lb/a of material as 0-46-0, MAP or 10-34-0 with the seed.
Soybeans are less responsive to fertilizer applications, but, more sensitive to seed-placed fertilizer than corn.  Studies in Indiana found that soybean seed emergence was delayed and inhibited to some extent, irrespective of the kind of fertilizer used, placement with or near the seed, soil type, or moisture content of the soil.  Numerous studies have shown that soybean seed can be severely affected by seed-placed fertilizer.  Many soil-fertility specialists recommend not placing any fertilizer with soybean seed at planting.  It has been suggested that if a narrow row spacing (7.5 inch) is used, small amounts of fertilizer (half the rate used for corn) could be used due to the reduced amount of fertilizer in direct contact with the soybean seed.
Seed placement of fertilizer directly on the seed is a management option that must be carried out with caution.  Results will vary with the fertilizer source and soil-environment factors previously discussed.  Desirable properties of seed-placed fertilizers would be low salt index, high analysis and absence of NH3-liberating products such as urea and DAP.  To minimize the risk of seedling injury and stand loss with seed-applied fertilizer: don’t apply any fertilizer directly with soybean seed, and apply less than 10 lb/a of N + K2O with corn.  For placement of larger quantities of nutrients below the soil surface, the traditional starter placement (2 inches below and to the side of the seed) or a deep-band placement should be used.
Soybean Seed Size--  This year soybean seed size is large—This is a product of the production year from 2014.  Production fields which received ample amount of moisture, produced large seed.  Much of the seed we have in the warehouse is around 2500 seeds/lb.  Does seed size impact soybean performance?
Stand Establishment
For soybean producers, one of the first goals is to get a productive stand of plants established in the spring that can attain maximum crop yield potential in the fall. Concerns about stand establishment when planting small/large seed are generally unfounded. Numerous research trials have been conducted to determine if there is an effect of seed size on soybean performance. Results indicate there is little relationship between seed size and percent emergence. While it is important to get a good stand of plants established in order to realize maximum crop yield potential, most research indicates that seed size has minimal impact on stand establishment.
Below is what we have found in recent years to work the best with a couple of popular planter settings combined with small to larger seed size.
    Ran at 5 mph---165,000 seeds/acre      
        Kinze Kinze 15" VAC 12" VAC 8" VAC
        Radial Radial JD JD JD
            Pro Series Pro Series Pro Series
    Seed Size   Meter Meter XP Meter XP Meter XP Meter
    Seeds/Lb.   48 Cell 60 Cell 108 Cell 108 Cell 108 Cell
        Plate Plate Plate Plate Plate
        Accuracy of Drop   Accuracy of Drop
  REP 1 3020   131.8 100.2 98 98.2 97.8
  REP 2 3020   123.4 100.2 99.2 97 98.2
  REP 3 3020   130.6 100.6 99.8 98 97.8
  REP 4 3020   137 100.6 99.6 97.4 98.8
  REP 5 3020   135.2 99.58 97.8 98.6 97.6
      Ave 131.6 100.236 98.88 97.84 98.04
  REP 1 2430   106 101.4 97.2 97.2 97.2
  REP 2 2430   107.4 100 97.4 98 97.2
  REP 3 2430   106.2 101.4 97.2 97.2 97.8
  REP 4 2430   109 102.6 98 97.6 98.4
  REP 5 2430   107.4 101 98.2 97.2 98
      Ave 107.2 101.28 97.6 97.44 97.72
  REP 1 2180   106.8 103.2 96.8 97.4 98
  REP 2 2180   107 103 98.4 97.8 97.8
  REP 3 2180   109.4 100.8 99.2 96.6 96.8
  REP 4 2180   103.2 101.2 98 97.2 97.4
  REP 5 2180   107.8 101.8 97.6 97.4 97
      Ave 106.84 102 98 97.28 97.4
The genetic potential of a small seed is the same as that of a large seed. Research trials suggest that seed size has little, if any, impact on yield. Because young seedlings of oilseed crops, such as soybeans, are related to the seed size, small seeds will produce slightly smaller seedlings than larger seeds. Once the plant has been established, yield potential depends on the genetic potential of the seed variety and growing conditions, regardless of seedling size.
Several multi-year studies have found no relationship between seed size and final yield. Research results indicate that seed size is not an important factor for successful soybean production.
Seed Quality vs Seed Size
Germination is an important indicator of seed quality and performance. G.E. Pepper, University of Illinois states, “When you shop for soybean seed, seed quality should be a more important consideration than seed size.” Planting a seedlot with good germination and vigor scores will provide the best chance for satisfactory stand establishment, regardless of seed size. A soybean must absorb half its weight in water before germination begins. In field situations where soil moisture might be limited, a smaller seed might actually have an advantage over a larger seed, because it takes less total water to begin the germination process.
Seeds per Desired Seeds Per Acre
pound 125,000 140,000 180,000 200,000 225,000
  Pounds Seed Per Acre
2,000 63 70 90 100 112
2,200 57 64 82 91 102
2,400 52 58 75 83 94
2,600 48 54 69 77 86
2,800 45 50 64 71 80
3,000 42 47 60 67 75
3,200 39 44 56 63 70
3,400 37 41 53 59 66
3,600 35 39 50 56 63
3,800 33 37 47 53 59
4,000 31 35 45 50 56
Corn Seed Size is influenced by several factors including genetics, the environmental conditions the seed was produced in and kernel position on the ear. Corn hybrids have unique kernel characteristics, including size and shape, based on their genetic makeup. Plant stress factors such as high temperatures and low soil moisture that occur during seed production can have significant impacts on seed size. Stress that inhibits pollination leads to fewer kernels being produced, which can result in more large rounds than normal. Stress during the grain-fill period will result in smaller, lighter-weight seed.
The development of an ear of corn is a sequential process from the base to the tip. The range in seed maturity and filling, and the placement of a particular kernel, can result in seed from a single ear falling into several seed size categories. The question many producers ask is, “Does corn seed size impact performance?”
Here is some work we did a few years ago regarding seed grade size and accuracy of planting with various settings using a John Deere Pro Max 40 set-up with a double eliminator and various grades of seed.
40-Cell--Double Eliminator Planter Plate        
16 In. Vac Pressure        
12 Replications            
Double Eliminator settings recommended by grade size      
Eliminator Setting 1 click closed Wide Open 1 click closed 1 click closed 1 click closed Wide Open
Grade AR AR AR2 AF AF2 P22
Ave. % Accuracy 102.29 93.089 97.87 100.2 99.66 96.33
Stand Establishment
For corn growers, one of the first goals of the season is to get a productive stand of plants established that can attain maximum crop yield potential in the fall. Concerns about stand establishment when planting small seed are generally unfounded. Most research trials conducted to determine if there is an effect of seed size on corn seedling emergence have shown little correlation between the two. Corn seedling emergence results from Wisconsin research were inconsistent; results from trials in Ontario  indicated seed size had no effect on days to 50% emergence or percent final emergence. Other trials  have shown small seed to have emergence percentages equal to or better than large seed. While it is important to get a good stand of plants established in order to realize maximum crop yield potential, most research indicates that seed size has minimal impact on corn stand establishment.
The genetic potential of a small seed is the same as that of a large seed. Field research trials conducted in Illinois, Wisconsin and Ontario all demonstrated that seed size has no impact on corn yield. Data summarized across years, locations and hybrids from work done in Minnesota also found that seed size did not affect corn yields. Other research summarizing the performance of four hybrids confirms that seed size does not have a significant effect on grain yield. 

Once a plant stand has been established, corn yield potential depends on the genetics of the hybrid and the growing conditions that follow, regardless of the size of the seed used to establish the stand. Numerous studies have found no relationship between seed size and final yield. These results caused Dr. Emerson Nafziger, corn agronomist at the University of Illinois to conclude that “Seed size thus appears to be of no importance as a factor in corn production.” He summarized his work by stating “As long as corn seed is of good quality, and is planted in a manner that allows it to germinate and emerge, there appears to be no logical reason for producers to prefer one seed size over another.”
Planter Adjustments for Accurate Planting
Planter adjustment and maintenance are important with all seed sizes. With small seed, it is even more important. For finger-pickup units, be sure the dimple on the backplate does not show excess wear. Check all brushes and springs. For air planters, be sure there are no leaks in the system so proper air pressure is maintained. Check brushes for wear and replace if necessary.
Here is some work we did a few years ago to address planter speed vs. accuracy of drop.
40-Cell--Double Eliminator Planter Plate      
AR Seed Grade--16 In. Vac Pressure        
12 Replications            
MPH 3 4 4.5 5 6 7
Ave. % Accurate 99.21 98.69 102.29 97.08 95.06 89.06
Corn performance depends on the particular hybrid you are using, planted uniformly at the proper population, not on the shape or size of the seed planted. Be sure to calibrate your planter so any adjustments can be made for the seed you are using and seeding rate you desire. Seed placement factors such as seed depth, seed spacing and seed-to-soil contact are all critical for optimum performance. Check seed depth (Minimum 2”) and population after traveling at normal planting speed (5 MPH). Variable soil conditions and residue levels between fields may require adjustments. Don’t plant at speeds faster than your planter is designed to be used at, so uniform seed depth and spacing can be achieved, and maximum yield potential realized.
John W. McNamara
Wiles Bros. Inc.
606 Wiles Road
Plattsmouth NE. 68048
(402) 298-8550--Office
(402) 499-3870--Cell
(402) 298-7174--Fax
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