NC State Extension Publications

 

North Carolina soybean growers use various planting practices to get optimum soybean stands. Planting decisions depend on a number of factors including soil texture, planting date, tillage practices, cropping rotation, equipment available, and grower preferences. When thinking about planting, growers should consider planting date, row spacing, seeding rate, and seed treatments. Also, proper seeder calibration and maintenance should not be overlooked. Use planting practices that minimize time required for soybeans to close canopy.

Planting Date

Planting date largely depends on the grower’s cropping rotation; thus, practical planting dates vary greatly from farm to farm. The optimum planting period for soybeans in North Carolina is from May 1 to June 10, but soybean planting occurs from May 1 to July 1 in the state. Seed should not be planted until soil temperatures are above 55 to 60°F.

Because soybeans are photoperiod sensitive, planting date directly impacts the number of days to flowering or the amount of time available for vegetative growth, which in turn directly affects plant yields. Planting beyond the optimum date may result in reduced yields. The goal should be to get the middles lapped and plants to a height of 3 feet before reproductive growth begins. The later the planting date, the greater the chance yields will be reduced.

The relationship between yield and planting date is shown in Figure 5-1. Notice that yields are shown as a percentage of what the high yield was for that test that year. One-hundred percent ranged from 64 bu/A (Pamlico County) to 52 bu/A (Wilson County, two years later). Planting dates are actually shown as weeks before (to the left of the dotted line) or weeks after (to the right) the last day planting could have occurred and still result in yields close to 100%. The last day that soybeans could have been planted and kept yields close to 100% turned out to agree with getting the row middles lapped (no soil showing between the rows) and with soybean plants that are about 36 inches tall.

Planting later than the 100% yield date resulted in reduced yields, and the longer planting was delayed, the greater the yield penalty. Planting earlier than the 100% yield date slightly improved yields, but not by much. The reason for this slight yield improvement is explained later in this section. All that is left to do is to determine which date the dotted line is on, but it differed between sites. At the Pamlico County site, it was July 6, but at the Wilson County site, it was May 22. Rainfall, soil water holding capacity, and relative maturity of the variety accounted for most of the difference. This optimum date will vary by location and by year.

With the row middles lapped with 36-inch tall plants, the canopy has about 4 acres of leaves in each acre of ground. This is what physiologists call a leaf area index (LAI) of 4. The top layer of leaves gets plenty of sunlight as does the second layer. The third layer gets enough to be fairly productive, but it typically doesn’t contribute as much as the top two layers. The fourth layer gets enough sunlight to produce more photosynthate (plant food) than is needed to keep those leaves alive. Soybeans can produce a fifth leaf layer, but it typically does not receive enough sunlight to produce more photosynthate than it needs to feed itself. Therefore, this layer typically translocates most of its carbohydrates out to the upper parts of the canopy and drops off. At an LAI of 4, soybeans capture about as much sunlight as soybeans know how to capture.

Farmers aren’t expected to measure LAI in their fields. They can, however, easily estimate row middles lapped with 36-inch tall plants as a viable substitute for LAI. Planting earlier than the last date you could have planted that variety and gotten an LAI of 4 doesn’t help yields much. It helps only slightly because it has a few more hours of sunlight available to capture. The yield penalty for planting after that date depends on how much later you’re considering. One week later isn’t too serious. Six weeks later is pretty serious.

Planting late enough that the LAI is only 3 means you have only the top three layers of leaves available. This scenario is not of great concern because the layer that was lost was the fourth layer, which was the layer that was contributing the least to yield. At an LAI of 3, yields will be reduced, but by less than 25%, because the three most productive layers of leaves are still intact. At an LAI of 2, yields will be reduced by a greater percentage, but still less than 50%, because the two most productive layers of leaves are still present.

Soybeans will use only the top 36 inches of the canopy, if available. If the plants are 48 inches tall, yields will still be similar to what was expected from 36-inch tall plants because only the top 36 inches of the canopy received enough sunlight to be productive. At 24 inches tall, yields will be reduced by less than 33% because the leaves that are not present are the least productive leaves. Thus, the bottom axis of the planting date graph can more accurately be labelled as the LAI, with the dotted line representing an LAI of 4 (Figure 5-2). The area to the left of the dotted line represents an LAI of more than 4, and the area to the right of the dotted line represents an LAI of less than 4.

Row Spacing

A wide range of row spacings have been used successfully in soybean production. Often, row spacing decisions are made based on what equipment is already available. We typically see a yield advantage, however, for soybeans in rows 20 inches or less. Narrower row spacing allows for quicker canopy closure and greater light interception, helps block light from reaching weeds, and helps minimize moisture loss.

In a series of on-farm tests in North Carolina, soybeans in 10- and 20-inch rows yielded 3 bu/A higher when planted early, and 4 bu/A higher when planted late, than soybeans in 36 to 40 inch rows. There was little difference in yield between the 10-inch and the 20-inch rows.

The 26% of the time when there was virtually no difference (< 1 bu/A) in yield between the two row widths was mostly in droughty environments when there was little water available, so the soybeans in wide rows and the soybeans in narrow rows were both limited by lack of water. The 1 in 20 times that the narrow row advantage was more than 10 bu/A occurred mostly in high yield environments (60 bu/A or more). These data are shown in Figure 5-3. Also of interest in Figure 5-3 is how the soybeans in wide rows never yielded higher than soybeans in narrower rows. That’s not to say that soybeans in wide rows couldn’t yield higher than soybeans in narrow rows, but they didn’t in the first 1,026 times it was tried on North Carolina farms.

More recent on-farm tests showed that soybeans in 15-inch rows yielded 5 bu/A higher than soybeans in 30-inch rows. Interestingly, both sets of tests showed a greater advantage for narrow rows in higher yielding environments than in lower yielding situations. This implies that as farmers raise their yield levels, narrow rows will become more important. Also, row spacing alterations are more likely to be beneficial if canopy closure does not occur prior to bloom. Therefore, the benefits of narrow row spacing increase as the planting date becomes later.

Seeding Rate

Soybean yield is relatively insensitive to plant population. Percentage wise, the yield plateau between too many and too few is wider for soybeans than for any other crop.

Because soybeans have the unique ability to compensate, a wide range of seeding rates is acceptable. Final stands as low as 50,000 plants for May planted beans, 75,000 plants for June planted beans, and 100,000 plants for July planted beans can produce reasonable yields if plants are evenly distributed.

Figure 5-4 represents the results of 64 tests planted in 15-inch rows in May, 73 tests planted in June, and 11 tests planted in July. The tests were repeated four additional times at each location, so the lines on the graph represent the results of 256 tests planted in May, 292 tests planted in June, and 44 tests planted in July. Planted in May, 50,000 plants per acre yielded essentially as high as 175,000 plants per acre, and anything in between. Yields were lower when planted in June, as expected, but the yield pattern for the June planting date (solid line) looks a lot like the May line. Even the July line (dotted line) doesn’t look much different from the other two lines.

Figure 5-4 does a better job of helping farmers decide whether they need to replant a poor stand than to decide how many seeds per acre to plant. The graph indicates it is not necessary to replant a field that has 75,000 good plants per acre left, but farmers may be justified in absorbing the cost of replanting for peace of mind. Farmers can also use the graph to determine their minimum acceptable plant population before deciding to purchase “insurance” in the form of extra seed. There’s no reason that farmers should agree on how much of that “insurance” they want to buy.

Because soybean seed size varies among varieties and even within the same variety, planting rates should be considered in terms of plants per foot of row, not pounds per acre. Two plants per foot of row in a 7-inch row is very close to 150,000 plants per acre. That’s what the vertical line to the right side of Figure 5-4 represents. One plant per foot of 7-inch row is 75,000 plants per acre, which is what the vertical line to the left side of the graph represents. For most farmers, two plants per foot of 7-inch row looks pretty sparse, while 10 plants per foot of 35-inch row looks pretty generous, even though both are 150,000 plants per acre. Table 5-1 is useful for calculating the number of seed and plants needed per foot of row for desired populations.


Table 5-1. Number of seed and plants needed per foot of row.

MAY PLANTING

JUNE PLANTING

JULY PLANTING

Row Spacing (in)

Row Feet/Acre

Seeds/Row Ft.

Plants/Row Ft.

Seeds/Row Ft.

Plants/Row Ft.

Seeds/Row Ft.

Plants/Row Ft.

30

17,424

7.1

6.4

9.2

8.25

11.2

10.1

20

26,146

5.4

4.9

6.5

5.9

7.7

6.9

15

34,484

4.3

3.9

4.9

4.6

5.9

5.3

7

74,674

2.2

2

2.5

2.25

2.8

2.5


The recommendations in Table 5-1 assume that half a stand will still exceed the population that would require replanting. Farmers should feel free to adjust (up or down) how much extra seed they want to buy as insurance against having to replant. To determine how many plants/row ft are needed for a given population, simply divide the desired plants/ac by the row ft/ac.

Aim for final stands of 75,000 plants for May planted beans, 90,000 plants for June planted beans, and 100,000 plants for July planted beans. Table 5-2 can be used to calculate the number of seeds needed per acre, based on expected percent germination of the seed.


Table 5-2. Seeds needed per acre based on germination percentage.

Final Stand (Plants/Acre)

% Germination

May Planting (75, 000)

June Planting (90,000)

July Planting (100,000)

Seeds/Acre

90%

83,333

100,000

111,111

85%

88,235

105,882

117,647

80%

93,750

112,500

125,000

75%

100,000

120,000

133,333

70%

107,143

128,571

142,857


Figure 5-1. Relationship between yield and planting date in soyb

Figure 5-1. Relationship between yield and planting date in soybeans.

Figure 5-2. Relationship between Leaf Area Index (LAI) and plant

Figure 5-2. Relationship between Leaf Area Index (LAI) and planting date in soybeans.

Figure 5-3. Yield difference between narrow row (< 30 inches) an

Figure 5-3. Yield difference between narrow row (< 30 inches) and wide row (36 to 42 inches) soybeans.

Figure 5-4. Relationship between soybean yield and plant populat

Figure 5-4. Relationship between soybean yield and plant populations.

Planting Depth

Soybean seeds need to be planted deep enough to get good seed-to-soil contact and shallow enough that they don’t expend more energy to get out of the ground than necessary—usually about 34 to 114 inches deep. If using a pre-emergence broadleaf herbicide (especially a metribuzin), a depth of 112 to 2 inches deep is recommended to decrease the likelihood that the soybean seedling will take up the herbicide. If planting no-till, be sure the seed are in contact with the soil, not just the residue on the soil surface.

Southern soybean varieties will emerge from deeper depths than listed in the previous paragraph, but the deeper the planting depth, the weaker the seedling will be when it does emerge. It is probably better to plant too deep (at the risk of a weaker seedling at emergence) than too shallow (at the risk of not getting good contact of the seed with the soil, so moisture can get to the seed). If planting depth is not very uniform (as with planting with a drill), make sure that most of the seeds are deep enough to get covered with some soil, even though other seeds will likely be planted deeper than recommended.

Seed Treatments

Seed treatments were originally designed to provide protection of the seedling against seedling diseases. An insecticide may be added to increase protection against soil borne insects. A biological, yield enhancer, fertilizer, growth regulator, or little-known product may be added as well. Most of these products, especially fungicides and insecticides, appear to work as advertised: they provide insurance against soil borne diseases or insects. The pests these products provide protection against, however, are seldom encountered in North Carolina, so they end up being marginally profitable at best. When the pests do appear, they often affect a few scattered plants, leaving a lower population of plants that is still sufficient for maximum yields (see discussion of seeding rates above). “Yield enhancement” products have so far been only marginally profitable.

Inoculant seed treatments, however, are a different story. Since soybeans require slightly more nitrogen than corn does, a soybean crop without healthy nodules is in somewhat worse shape than a corn crop with no nitrogen fertilizer. Inoculants introduce bradyrhizobia (the bacteria that convert atmospheric nitrogen into plant useable forms of nitrogen) into the soil. Seed treatment inoculants do not seem to be as effective as inoculants put in the furrow with the seed. Apparently, it is difficult to get enough bacteria to stick to the seed, but it’s not so hard to get enough bacteria into the furrow with the seed.

Tests of inoculant materials on North Carolina fields that had not produced soybeans in the previous eight years or more resulted in a yield response in only two of the 23 locations evaluated. The yield response from the two sites, however, was enough to return double to triple the money invested in inoculating all 23 sites. Of the two sites that produced a yield response, one was in the sandhills (Moore county) and one was in the blacklands (Tyrrell county). Interestingly, the 17 inoculant materials tested ranked in almost the identical yield order at both sites. The seven inoculants that produced the highest yields, at both sites, were all soil-applied inoculants. The seven inoculants that produced the lowest yield response, at both sites, were all seed-applied inoculants.

A common recommendation, in both the South and the Midwest, is to inoculate any field that has not produced soybeans in the previous four to five years. This treatment may not be necessary, but a farmer cannot afford to not inoculate the one field out of many that needs to be inoculated. Although forage legumes can be successfully inoculated after the plants emerge and start growing, it does not seem to be possible with soybeans, which are emerging and growing in warmer temperatures.

The efficacy of some common fungicide seed treatments is listed in Table 5-3.


Table 5-3. Efficacy of fungicide seed treatments in soybeans.
Fungicide active Ingredient Pythium sp. 1 Phytophthora root rot Rhizoctonia sp. Fusarium sp. 1,3 Sudden death syndrome (SDS)
(Fusarium virguliforme)
Phomopsis sp.

Azoxystrobin

P-G

NS

VG

F-G

NR

P

Carboxin

U

U

G

U

NR

U

Chloroneb

U

P

E

P

NR

P

Ethaboxam

E

E

U

U

U

U

Fludioxonil

NR

NR

G

F-VG

NR

G

Fluopyram

NR

NR

NR

NR

VG

NR

Fluxapyroxad

U

U

E

G

NR

G

Ipconazole

P

NR

F-G

F-E

NR

G

Mefenoxam

E2

E

NR

NR

NR

NR

Metalaxyl

E2

E

NR

NR

NR

NR

PCNB

NR

NR

G

U

NR

G

Penflufen

NR

NR

G

G

NR

G

Prothioconazole

NR

NR

G

G

NR

G

Pyraclostrobin

P-G

NR

F

F

NR

G

Sedaxane

NR

NR

E

NS

NR

G

Thiabendazole

NR

NR

NS

NS

P

U

Trifloxystrobin

P

P

F-E

F-G

NR

P-F

1 Products May vary in efficacy against different Fusarium and Pythium species.
2 Areas with mefenoxam or metalasyl insensitive populations may see less efficacy with these products.
3 Listed seed treatments do not have efficacy against Fusarium virguliforme, causal agent of sudden death syndrome.
Efficacy categories: E = Excellent; VG = Very Good; G = Good; F = Fair; P = Poor; NR = Not Recommended; NS = Not Specified on product label; U = Unknown efficacy or insufficient data to rank product.
Please note: Efficacy ratings may be dependent on the rate of the fungicide product on seed. Contact your local Extension plant pathologist for recommended fungicide product rate information for your area.
Source: American Phytopathological Society. 2017. Fungicide Efficacy for Control of Soybean Seedling Diseases.

Table 5-4 lists some seed treatment product / trade names available for soybean production and their associated active ingredients.


Table 5-4. Fungicide products / trade names and active ingredients.

Fungicide(s)

Product/Trade name

Active ingredient

Acceleron

DX-612 Fluxapyroxad

DX-309 Metalaxyl

DX-109 Pyraclostrobin

Allegiance FL

Metalaxyl

Allegiance LS

Metalaxyl

Apron XL LS

Mefenoxam

ApronMaxx RFC

Fludioxonil

Mefenoxam

ApronMaxx RTA

Fludioxonil

Mefenoxam

Catapult XL

Chloroneb

Mefenoxam

CruiserMaxx

Fludioxonil

Mefenoxam

CruiserMaxx Advanced or Cruiser Maxx Plus

Fludioxonil

Mefenoxam

CruiserMaxx Advanced Vibrance

Fludioxonil

Mefenoxam

Sedaxane

Dynasty

Azoxystrobin

EverGol Energy SB

Metalaxyl

Penflufen

Prothioconazole

ILeVO

Fluopyram

Inovate Pro

Ipconazole

Metalaxyl

Intego

Ethaboxam

Maxim 4FS

Fludioxonil

Mertect 340 F

Thiabendazole

Prevail

Carboxin

Metalaxyl

PCNB

Trilex 2000

Metalaxyl

Trifloxystrobin

Vibrance

Sedaxane

Warden CX

Fludioxonil

Mefenoxam

Sedaxane

Warden RTA

Fludioxonil

Mefenoxam

Source: American Phytopathological Society. 2017. Fungicide Efficacy for Control of Soybean Seedling Diseases.


Seed Calibration and Maintenance

It is essential to properly maintain planting equipment before going to the field. An improperly prepared planter or drill will be more difficult to calibrate, may not deposit the seed correctly in the furrow, and may be prone to breakdown in the field during planting. The best source of information on planter or seeder maintenance and preparation will be the operator’s manual that came with the implement. If you do not have a manual, contact the equipment manufacturer. Even for older implements, they can often provide an operator’s manual.

Maintenance and Preparation

Most implements have several areas in common that the owner or operator should focus on:

Seed hopper—Check the hopper for leaks and damage. Small holes in the hopper bottom or side wall will allow seed to fall through, resulting in seed loss. Check the inside of the hopper for corroded areas or blockages. Anything that impedes the flow of seed from the hopper can affect planting performance.

Seed meter—Whether it’s seed plates for drums in a row crop planter or seed wheels in a drill, the metering mechanism is responsible for measuring the seed rate and insuring correct population. Inspect the metering mechanism carefully for damage. For row crop planters, make sure you have the correct plate for the seed you have selected. A mismatch can lead to excessive skips or doubles.

Air delivery—If you are using an air planter, pressure or vacuum, check the air delivery and pressure at the seed meter. Most systems have a pressure gauge on the common air tube near the fan. Adjust the air pressure to match the recommendation for the size and type of seed you are planting. Check the air pressure and delivery at the metering unit as well. A blockage in the air tube between the metering unit and the pressure gauge at the fan will affect the air delivery.

Meter Drive—The seed meter is typically driven by one of three mechanisms:

  • Press wheel—Press wheel drives have a drive chain from the row press wheel that provides power to turn the seed meter. This is often found on older planters. Check the condition of the chain and sprockets for each unit. Check the wheel and drive bearings to make sure the press wheel turns freely.
  • Drive wheel—Many planters use a drive wheel on the planter frame to deliver power to a countershaft. Individual seed meters take power from this shaft. In this system, multiple rows are all driven at the same rate. On larger units, there may be more than one drive wheel. In this case, each wheel provides power to a section of row units or seed meters. Check the condition of the chains and sprockets to smooth performance. Check the bearings for smooth rotation. You should also check the drive wheel carefully. If the tire is the wrong size, is badly worn, or the air pressure is incorrect, there may be a significant error in seed population during planting. Air pressure in the tire can change at any time due to leaks, punctures, or other damage. Check the inflation pressure often.
  • Hydraulic drive—Hydraulic drives take the place of press wheel or drive wheel systems on some planters. The hydraulic drive is controlled by an automatic rate controller in the tractor. Drive speed is calibrated to true ground speed by the rate controller. Check the system pressure and adjust the flow delivery as recommended by the planter manual. Check for proper drive speed calibration at the start of each season. Monitor its performance as you plant as well. Be sure to keep all hydraulic connections clean. Dirt is the worst enemy of a hydraulic system. The quick connects between the tractor and the implement are an easy point of entry for dirt in the hydraulic system.

Preseason maintenance is the key to successful planting. Your preseason preparation can be made easier by practicing good maintenance when you finish planting for the season. Put the planter up ready to go or stored as recommended by the manufacturer, and your task at the beginning of the planting season will be much simpler.

Calibration

Calibration is the process of proving the planter or drill is delivering the seed at the rate intended. You should not assume the rate charts provided by the manufacturer in the manual will be exact for every application. Those charts represent what the manufacturer perceives to be average or representative conditions across a wide range of planting environments. Changes in seed properties, field condition, equipment condition and a host of other factors can influence the result. To ensure successful planting, be sure to calibrate your planting equipment.

Calibrating a Row Crop Planter

Row crop planters typically singulate individual seed. As such, calibration is often based on seed spacing in the furrow or seeds per foot of row length.

  1. Determine the seed rate. Seed rate is the number of seed to plant per acre. It takes into account the germination percentage for the seed used and the emergence percentage. Germination percentage is usually on the seed label. Emergence may be available for specific areas or conditions.

    Seed Rate, (seed ÷ acre) = Plant Population ÷ (% Germination x % Emergence)
  2. Seed spacing. Calculate the seed spacing in seeds per foot of row. To do this you will need to know the row spacing you will use as well as the seed rate calculated above.

    Seed Spacing, (seed ÷ ft) = [Seed Rate, (seed ÷ acre) x Row Spacing, inches] ÷ [43,560 sq ft per acre x 12 (inches per foot)]
    Alternatively, your manual may use a planting table with spacing quoted in inches per seed.
    Seed Spacing, (inches ÷ seed) = [43,560 sq ft per acre x 144 sq in per sq ft] ÷ [Seed Rate, (seed ÷ acre) x Row Spacing, inches]
  3. Set your planter up as indicated in the manual. If you are using a planter with a ground drive system to power the seed meter, use the chain and sprocket combinations recommended in the planter manual. If you are using a hydraulic drive, set the drive speed and pressure as indicated in your manual.
  4. Fill the hopper with enough seed to give you smooth seed feeding into the meter. If using an air planter, set the air pressure as recommended.
  5. Run the planter at the recommended speed for several feet to get the meter filled and delivering seed to the ground. Check the seed spacing in the furrow and compare it to the spacing you calculated, either seed per foot of row or seed per inch. You may want to disengage the furrow closing wheel to make measurement easier. Also, make a “dry” run with the planter positioned just low enough to engage the drive. Note that this may not accurately represent field conditions.
    1. To measure seed per foot, measure a length of row several feet long. Count the number of seed present in that space and divide the count into the distance measured. The result is seed / ft of row.
    2. To measure inches per seed, pick a section of seed in the furrow and measure from the first seed to the last seed. Divide this measurement by the number of spaces between seed in the measured distance. The result is inches / seed.
  6. Compare your spacing to the spacing necessary to achieve the population you want. If your spacing is too high or too low, make the necessary drive adjustments to correct the spacing.

Calibrating a Grain Drill

Grain drills meter seed by volume, not by singulating each seed. While not as precise as a row crop planter unit, they are very effective at establishing a uniform plant population when properly calibrated. Grain drills can be calibrated by counting the seed dropped in the calibration test or by weighing the seed.

  1. Mark off a calibration distance in an area representative of field conditions. You can use a distance of 100 to 200 feet in one of the fields to be planted. Longer distances give more accurate calibrations but require you to handle more seed.
  2. Drive the calibration distance with the seed hopper half full and the seeding mechanism disengaged. Count the number of revolutions the drill drive wheel makes to cover this distance. You can mark the drive wheel with paint, tape, or something to make it easy to count revolutions. You should drive the test distance at least twice, once in each direction, to get the average count.
  3. Set the drill drive mechanism for the rate you want to achieve. Look at the seeding chart in the hopper or in the owner’s manual, and choose the seed type from the chart. If your seed is not listed, pick something close to its size for a first run. Make the necessary adjustments to the drive mechanism.
  4. To collect seed during calibration, you can spread a large tarp on the ground or shop floor to catch the seed. You could also place a bucket under each seed tube and catch the seed discharged.
  5. With the drill hitched to the tractor, engage the seeder drive mechanism and turn the drive wheel by hand for the number of revolutions counted in step 2 above. You may need to use a jack or some blocks to safely position the drill and still allow you to turn the drive wheel.
  6. After collecting the seed for the number of turns required, combine all seed in a container and weigh the seed. If a scale is not available, you can count the seed and compare the result to a population chart.
  7. Seed per acre is determined from the weight of the seed collected and the area used for calibration. Area is determined from the drill swath and the calibration distance used.

    Seed per Acre, (lb ÷ acre) = [Weight of Seed Collected, lb x 43,560 sq ft per acre] ÷ [Calibration Distance, ft x Drill Swath, ft]
  8. Pounds per acre of seed can be converted to number of seeds per acre if you know the number of seeds per pound for the variety planted.

    Number of Seed per Acre = Seed per Acre, (lb ÷ acre) x (Seed Count ÷ lb)
  9. Compare the seeding rate achieved by the drill to the population target you want to achieve. Adjust the drive mechanism accordingly to zero in on your population target.

Variable Rate Planting

Variable rate planting or seeding can be used effectively to optimize productivity in each field. In variable rate planting, seed populations are adjusted on the fly by a variable rate control system while planting in the field. Population changes or prescriptions can be based of soil type maps, previous yield maps, management zones, or other attribute maps.

To make variable rate planting work, you will need several pieces of precision agriculture technology:

  • GPS/GNSS receiver—The receiver will determine field position at any time you are in the field. It is necessary to determine your position when reading and planting prescription from a map.
  • Field computer—Also called a field display, the field computer is responsible for reading the position information as well as the prescription map and sending the seed rate information to the variable rate controller. Some field computers or displays have the GPS/GNSS receivers built in, others require external receivers.
  • Variable rate controller—The rate controller is often a part of the field computer or may be an added module. It takes the rate calculation from the field computer and converts it into a control signal for the variable rate drive.
  • Variable rate drive—The rate drive is a hydraulic or electric motor that turns the seed metering mechanism. Hydraulic drives typically power several row units. Electric motors are often mounted on individual row units and provide individual control.
  • Prescription map—The prescription map contains the rate information. As you move from one zone to another, the prescription map is where specific rate information, such as the seed population, and in some cases, the variety to be planted will be. This is the information read in the field to achieve variable rate.

The advantage variable rate planting offers is the ability to match seed populations or varieties to specific areas in the field. Many farmers have fields with variable soil types or some parts of a field consistently perform better than others. With variable rate planting, you can put the population or variety in each part of the field that matches its yield potential.

Double Crop Considerations

Double cropping is common practice in North Carolina. Most double crop soybeans are planted in June (or even July), making it harder to get the row middles lapped with 3-foot tall plants. Farmers can ensure the row middles lap by using narrower rows (for example, 20 inches apart of less). Later maturing varieties have more time to get tall enough (36 inches tall) than early maturing varieties do. Within a maturity group, some varieties seem to tolerate the late planting dates better than other varieties. Both the OVT and Dr. Dunphy report yield results for full-season and late-planted trails. Evaluating relative yield when planted late, rather than across all planting dates, will help determine those varieties.

Authors

Professor and Extension Soybean Specialist
Crop and Soil Sciences
Extension Specialist and Associate Professor, Machinery Systems
Biological & Agricultural Engineering

Publication date: Nov. 21, 2017
AG-835

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