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Competency Area 5: Seeding Rates and Row Spacing

PO 21. Know factors that influence the seeding rate of major Northeast crops.
A. Compare seeding rates for corn silage and corn grain,
B. Know how soil type, planting date, and tillage systems influence corn seeding rates.

The optimum seeding rate depends on the interaction of the crop's characteristics and the environment that it is growing in. The general rule is to plant at higher populations under favorable environmental conditions (moisture and N) and to reduce seeding rates as environment becomes less favorable. For example plant corn at higher populations for grain (30000 plants/acre final stands) on soils that have good water holding capacity. Reduce populations (26,000 plants/acre final stands) on droughtier soils.

A. Compare seeding rates for corn silage and corn grain

seeding rate population rate
Generally, corn silage should be seeded at about 4,000 more kernels/acre than corn grain with final stands 3,500 plants/acre higher than corn for grain. See also PO 23.

B. Know how soil type, planting date, and tillage systems influence corn seeding rates.

Crop characteristics - compensation ability
Soybeans and wheat crops both compensate or fill in where there is a gap. Consequently, both crops have a broader optimum population than corn. Corn does not compensate as well so the seeding rate needs to be more precise.

Tillage system/planting date
Tillage systems and planting date can result in less favorable conditions for emergence. For Corn and soybean, seeding rate should be increased for early planting dates or as tillage is reduced. When Planting winter wheat and spring grains a delayed planting date results in less tillering so seeding rate needs to be increased.

Crop utilization
Dry matter yields respond to higher seeding rate.

  • Corn silage vs. grain – use a higher seeding rate for corn silage.
  • Small gains - forage vs. grain – use a higher seeding rate for forage.
  • Small grain companion crops – use a lower seeding rate for companion crops.

Row spacing
Narrow rows create more favorable environment for light utilization therefore beans and corn respond to higher seeding rates. Soybeans planted in 7" row-spacing requires 180,000 plants/acre compared to 150,000 plants/acre for 30" rows. Corn responds to higher populations in narrow rows (15-inch vs. 30-inch).

Planter
Increase seeding rate for small grains when broadcasting vs. drilling seed because of better emergence under drilled vs. broadcast conditions.

Growth habit of crop

  • Corn (fixed vs. flex ear) - Many believe flex ear types can yield well at lower populations.
  • Soybean (bush vs. narrow growth habit) - Bush type varieties are supposed to do better at wider rows and lower seeding rates.
  • Corn and soybeans bred for a vertical leaf type, especially above the ear, responds to higher populations.
  • Variety seed size - soybean and wheat varieties can have very different seed size. Plant small seeded varieties (many seeds/lb) at lower lbs/acre or bu/acre than large seeded varieties.

Other factors influencing seeding rate of forage crops in the Northeast include Seed size. Seeds per pound can vary in forage crops from 2 thousand to over 2 million. Seed size, or any seed coating, may influence the rate of seed delivery through the seeding implement.
The percentage of pure live seed (PLS) is another factor. This is a function of seed germination and seed purity. E.g. 95% germination and 97% purity = 0.95 x 0.97 = 92% PLS. Planting rate equals the recommended seeding rate divided by the PLS value. e.g. a desired seeding rate of 12 lb/acre in the above example is 12/0.92 = 13 lb/acre.
Soil type also must be considered. Lower seeding rates can be used on light, sandy soils because of more complete emergence.
Lower rates can be used on well-prepared seedbeds. Higher rates provide some insurance on less than optimum seedbeds, however high seeding rates will probably not succeed on a poor seedbed.