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Corn Planting Populations: A Deeper Dive

By Sara Bauder
 
When discussing planting population with row crops, geographic location and average yearly rainfall come into play in a significant way. Corn is grown all across South Dakota, and the optimal target population varies from 15,000 to 36,000 plants per-acre depending on location.
 
Corn hybrid selection is arguably one of the most important management decisions a farmer makes each year; often, hybrid-specific information even provides optimum plant populations for each line. Of course, seed cost, soil productivity, yield potential and the price of grain as a commodity are all important factors as well.
 
With all of these variables, it can be challenging to determine what the most economically beneficial option may be when choosing a planting population.
 
Economic Optimum Corn Seeding Rate
 
According to SDSU Extension's Best Management Practices for Corn Production, determining the economic optimum corn seeding rate is a three-step process.
 
STEP 1
 
Determine the ratio between the seed cost and expected selling price (Table 1).
  • For Example: If the cost of a bag of seed is $300 or $3.75 per 1,000 kernels, and the expected selling price is $5 a-bushel, then the ratio between the purchasing price for 1,000 kernels and the selling price per bushel is 0.75.
  • This value, when combined with the yield response function and expected yield, is then used to calculate the seeding rate.
Table 1. Ratio between the cost of seed and the value of corn as a commodity.
 
 
Seed Cost ($/80,000 kernel bag)
 200.00250.00300.00350.00
 
Seed Cost ($/1000 kernels)
 2.503.133.754.38
Corn Commodity ($/bu)
Ratio of Seed Cost to Commodity Value ($/1000 kernels: $/bu)
3.000.831.041.251.46
4.000.630.780.941.10
5.000.500.630.750.88
6.000420.520.630.73
7.000.360.450.540.63
STEP 2
 
Estimate yield potential.
  • Seeding rates can be calculated for an entire field, or various parts of the field depending on producer preference and precision equipment availability.
  • Use yield history and basic field knowledge to calculate yield potential.
  • To get a generalized view of corn yield by region in South Dakota, visit the USDA National Agricultural Statistics Service website and select “South Dakota” on the map.
STEP 3
 
Determine seeding rate.
  • With steps one and two completed, the optimum planting rate can be determined based on Table 2.
  • Once the planting rate is determined, it should be adjusted for the germination rate.
  • For Example: If the optimum plant population is 29,000 plants-per-acre, then the seeding rate should be 32,000 plants-per-acre (29,000 ÷ 0.9) if the germination rate is 90%.
Table 2. Optimum planting rate based on ration between seed cost and selling price of corn and the yield estimate.
 
 
$ Cost Seed/$ per bu
 0.50.751.01.5
Yield estimates Bu/acre
Optimum planting rate (*1000)/acre1
5015.614.513.411.3
10025.824.322.819.8
15031.930.429.026.0
20035.133.932.830.5
25036.235.534.833.4
EXAMPLE
 
Use the data in Table 1 and Table 2 to calculate the economically optimum seeding rate if corn is selling for $5 per-bushel, the desired yield is 200 bushels-an-acre, and a bag of seed costs $300.
  • Answer From Table 1: The seed cost is $3.75 per 1,000 seeds (= $300 ÷ 80), and the ratio between the seed cost and corn value is 0.75.
  • Answer From Table 2: Using the 0.75 value from Table 1, if yield estimate is 200 bushels-an-acre, the optimum plant population is 33,900 plants per-acre. If the germination rate is 95%, then the germination-adjusted seeding rate should be 35,700 seeds per-acre (= 33,900 ÷ 0.95).
Additional Considerations
 
Soil characteristics should be considered as well. Typically, more highly productive soils with both adequate drainage and plant-available water can support higher populations. As you move from east to west in South Dakota, it is generally dryer, thus affecting both plant population and plant maturity selection. In addition to soil characteristics, seedbed preparation and planting equipment should also be considered.
 
In a nutshell, there is a lot more to seeding population selection than what meets the eye. If you find yourself avoiding the cold this winter, it might be wise to take some time to take a deep dive into your seed population options and fine tune your settings. 
Source : sdstate.edu

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